GB2438473A

GB2438473A - A subsea gas transmission pipeline

Info

Publication number: GB2438473A
Application number: GB0700251A
Authority: GB
Inventors: Kasra Zarisfi
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-01-10
Filing date: 2007-01-05
Publication date: 2007-11-28
Also published as: GB0600388D0; GB0700251D0

Abstract

A subsea gas transmission system uses a submersible pipeline 3 and stations to transport gas through marine distances, the pipeline 3 being submerged and suspended from the seabed 1. The pipeline 3 is able to balance the external hydrostatic pressure with its internal variable operating gas pressure in order to maintain its buoyancy. The pipeline 3 preferably has a mooring system comprising cables 6 with ballast. The ballast may have a buoyant ballast element 7, chain ballast 8 and fixed ballast 9. This arrangement allows the pipeline to equalize the internal and external pressures by varying its underwater depth (see figures 8 to 12). The pipeline 3 preferably comprises a plurality of rigid (concrete) pipe sections 4 joined by flexible connections 5.

Description

1 2438473 Gas, Sub Sea, Transmission System And Submersible,

Suspension, Flexible Pipeline

Table of contents Page

Introduction 3

Chapter 1 4 Submersible, Suspension, Flexible Pipelines

1-1 Introduction 4

1-2 SSFP Gas Transmission 5 1-3 SSFP Components 9 1-4 SSFP Stability 13 1-5 SSF General Notifications 31 Chapter II 34 GSSTS Components

2-1 Introduction 34

2-2 GSSTS Offshore Stations 34 2-3 GSSTS Mini Stations 48 2-4 GSSTS Branches and Costal Stations 52 Chapter III 55 SSFP Installation, Construction and Operation

3-1 Introduction 55

3-1 SSFP Installation 55 3-2 SSFP Construction 59 3-3 SSFP Operation 63

Drawings Description 66 ) 3

Introduction

The methods of energy supplying are important issues which people are thinking about them.

The most world's required energy is formed from fossil fuels now and it predict that in the year 2025 still fossil fuels will provide 50% of the words energy but they have destructive influence on our environment so we are trying to avoid of using them. In this challenge using of natural gas the cleanest fossil fuel as a source of energy is the best feasible solution for our near future.

Due to above explanation consuming natural gas is developing more and more how in the close future it will passes coil and will be the second world sours of energy after oil.

Nowadays gas is transferred through the pipe lines in thousands of miles on the lands but sea and oceans are boundaries which the gas transmission is limited by them.

The only solution that has been founded yet to break these boundaries is that transferring gas with tankers in form of LNG in marine distances and this technology is developing now due to the increase in demand of natural gas.

Our experiences in the oil and gas industries show that pipelines are the most easy, efficient and safe way for fuels (especially gas) transmission.

Gas Sub Sea Transmission System (GSSTS) is a system which is introduced here to transfer the gas between marine destinations by a special pipeline.

It is quit different from the usual gas pipelines however it can have the pipeline's transferring advantages.

GSSTS include a long Submersible Suspension Flexible Pipeline (SSFP) which is its main part and other component such as: Costal stations, Offshore stations, Mini stations and branch lines.

Gas is transferred between supplying and consuming costal stations by along SSFP which is operated from offshore stations.

The essay has been written in three chapters. In first chapter SSFP's components, characteristics and feasibility are explained. The second chapter is describing the other GSSTS's components and finally in chapter Three, SSFP construction and installation feasibility are explained. ) 4

Chapter I Submersible, Suspension, Flexible Pipelines

1-1 Introduction

Gas pipeline's internal pressure is the first basic parameter which applies forces on the pipe and creates stresses in the pipe structure therefore the most pipes materials must made from steels which have high toughness and strength.

If we don't have internal pressure we don't need tough and high strength materials so we can change our pipe's material. It is the first basic reason for thinking about a pipe with different pressure condition.

Submersible Suspension Flexible Pipeline (SSFP) is a pipe which is continued through the oceans and is kept submersible therefore against all other pipes it can cancel out its internal pressure with its surround external pressure.

If the pipe wants to be stable in this condition first it must cancel its buoyant force and also must be kept suspension in a specific depth of water and second it must be flexible to be able to release deep sea improper forces from its structure.

Gas Pipeline diameter is an important basic issue. The larger diameter the higher gas transmission and the more efficient pipeline but increase in gas pipeline's diameter is limited due to safety, construction and cost however SSFP surrounds allows us to raise its diameter more than usual pipes and have high efficient pipe.

In this chapter first the transmission -efficiency of SSFP has been considered then in second part the pipe component are introduced after that in third part feasibility of the pipe is explained by basic calculations and at the end some general points about SSFP are explained.

SSFP can have various specifications in different conditions but in here we assumed a specific SSFP as an example and we calculated its parameters for clarification.

All calculations here have not been done to find the final results for designing. They are done to give us a better understanding and feeling about SSFP and also show the SSFP feasibility.

The assumed SSFP's specifications are as follow. So future data and numbers which are mentioned for clarification (specially the numbers in the parentheses) are all base on the bellow table. Most of these specifications are explained in this chapter and the remains are illustrated in other chapters.

Both SI and Imperial units are used for calculation therefore to avoid unit changing the specifications are given here in both unit systems.

____________ 5

Description SI Unit Imperial Unit

Max Gas Flow Rate 200 Million 7 Billion Cubic Meter per Cubic Feet per ____________________________ Day Day Mm Gas Flow Rate 100 Million 3.5 Billion Cubic Meter per Cubic Feet per ____________________________ Day Day SSFP Internal Diameter 2.5m (2500mm) 100 Inches SSFP External Diameter 3.144m ( 3.2 m) 125 Inches ____________________________ (3144mm) ______________________ SSFP Wall Thickness 322 mm 12.5 Inches Max/Mm Internal Pressure 25/20 M Pascal 3700/3000 psig (Gas Pressure) (250/200 Barg) ___________________________ Average Internal Pressure 22.5 M Pascal 3350 psig (Gas Pressure) (225 barg) _________________________ Max/Mm External Pressure 25/20 M Pascal 3700/3000 psig (Water Hydrostatic ptessure) (250/200 Barg) ________________________ Average External Pressure 22.5 M Pascal 3350 psig (Water Hydrostatic pressure) (25 barg) _________________________________ SSFP Max/Mm Depth 2500/2000 m 7625 /6100 ft SSFP Average Depth 2250 in 6860 ft Seafloor Average Depth 2800 m 8540 ft SSFP Whole Length 8000 km 5000 Mile (Between Supplying and Consuming points) _______________________ _________________________________ SSFP Segment Length 100'OOOm 60 Mile (Distance between Iwo offshore statIons) (100 km) _________________________________ SSFP Primary Segment Length 5000 in 3 Mile (Distance between two mini stations) ________________________ ___________________________________ SSFP Element length 12 m 37 ft (Concrete Cylinder length + Flexible Joint) (II 700+300)nun _________________________________ SSFP Element weight 80000 Kg 176000 Ibm SSFP Bars Quantity/Diameter 8/20 mm 8/ 1 Inch Mooring Cable Average Length -800 m 2440 ft --Moormg Cable Diameter 8 mm 1/3 Inch Mooring Cable Unit weight 0.4 kg/rn 0.3 Ibm/ft ____________________________ (3.9 N/rn) ______________________ Internal and External Temperature 2 C 36 F Sea water Density 1024 kg/rn3 80 Ibm! ft3 Deep Water Velocity 0.3 mIs 0.9 ft/s 1-2 SSFP Gas Transmission SSFP gas transmission efficiency is one of the issues which must be considered for the pipe feasibility.

SSFP would connect long marine destinations and it must transfer the gas without compressor stations because in practice it is not available to build compressor stations on seas or oceans therefore it should be more efficient than normal pipelines and transfer the gas with a low pressure drop however SSFPs can have some special small compressors to increase their gas transmission capacity.

Gas flow rate depends on many parameters the general flow equation of natural gas in a pipe is 2 P2 58GMIJ- = /g.R < 11 -2 -RTave*Zave x f'x D25 Vl.856 I y Zavei.G.L 1f Therefore: JPP X/TXD25 The above proportion shows that if the transmission factor assume constant the flow rate is a direct function of diameter and difference pressure (AP), but it is an inverse function of length.

Fortunately Length, P and Diameter are not in a same proportion with flow rate therefore if we increase the pipe diameter and running it in higher pressure (the thing that we can do for SSFP) we are able to transfer high flow rate gas through a long pipe.

The supposed SSFP has a length of 5000 miles. This length is chosen because the most gas supplying and consuming points are not more far from than 5000 miles.

In no compressor station case we want to find the maximum length of SSFP which can transfer the minimum gas flow rate and compare it with the required length. For doing this we checked all common gas transferring equations in pipelines as follow.

Find the flow regime Re=" ---p Where in this case for Natural Gas actual Re could be find by.

Re 45Qb.G = 45x 3.5x109 x-= 42'OOO'OOO D 24 100 Nikuradse (Fully Turbulent) 1f1 4loio[3.7__] Where -K= 0.084 Inch (Rough concrete) Ke 0.00156 Inch (Smoothed concrete) = 41og10(3.7 100J = 14.575 (Rough concrete) = 4logio(3.7 0 56J - 21.5 (Smoothed concrete) Prandtl -Von Karman (Partly Turbulent) IT Re l-=4log,0-1-0.6 Vf 14.575 = 41og10x 14575 -0.6 -+ Re = 90'648 (Rough concrete) 21.5 = 4log10x-.--0.6 -* Re = 7'20l'756 (Smoothed concrete) The calculation shows that the actual Re number is larger than transition Re number so the flow regime is fully turbulent Length estimation The most frequently recommended equations high flow rate, high pressure systems with fully turbulent regime are as follow. Where

Qi= 3.5 x 1O ft3/day (mm gas flow rate) Tave 493 R G= 0.64 Tb=520R Pb= 14.7 psia Zave= 1.0 P= 3700 psig (max pressure in up stream) P2= 3000 psig (mm pressure in down stream) E0 (horizontal pipe) Panhandle B 102 0.510 Qb 737.02(') p2 _p2 -E 1.D253 F) [G 961.L.7;p.ZapJ 3.5 x I 9 = 732.02(--) 3700 3000 1 x 100253 I4.7J L0.64 9 xLx493j L = 12200 Mile Weymouth Qb =432.7._1' p2 _E1.D2667 L Llzye.Zove J 3.5xlO9=432.7--I3700 _30002105X1002667 14.7[0.ó4xLx 493] L = 13200 Mile AGA Fully Turbulent T'P2 P2 E' 37D Qb38.774b_l I -2 4Iog.D25 L G.L.Tave *Zave J K Where -Ke 0.084 Inch (Rough concrete) Ke 0.00156 Inch (Smoothed concrete) a-Rough concrete 14.7 L0.64xLx493] L 0.084 J L4850Mile b-Smoothed concrete 3310 =&774x x{3700 30002 i 5[4ioj37100110O25 -- 14.7 [0.64xLx493] [ 0.00156J L 10500 Mile Since all above fully turbulent equations are experimental equations, it can be predicted that the answers can have error because diameter and pressures of SSFP are higher than usual pipelines and it can put SSFP out of these equations using ranges and also in AGA formula the roughness of SSFP flexible joints (explained later) was not mentioned in calculation but the aim of doing these calculations is not to find the exact answer, it is to show SSFP with a long length can be used for gas transmission.

It can be noted that the most found results are longer than the required length (5000 miles) and we still can increase the pipe diameter and also it is possible that we have smooth internal surface so these points can cover the probable error which we have in our answers.

If the GSSTS has small compressor stations in its offshore stations not only the gas transmission feasibility of the system can be proved strongly but also GSSTS can transfer the gas between longer destinations (no limitation in theory) and it also can have a few supplying and many consuming points.

If we assumed the offshore stations distance is 60 miles with the same calculation but for the maximum gas flow rate (7 billion cubic feet per day), we will find that the pressure drop between two stations is about 40psi (less than 3bars) and we need 2M Watts (2000 kilo watt) compressors in our offshore stations to cancel out this pressure drop and transfer the gas with almost constant pressure. A 2M Watts compressor is a small compressor which can be used in offshore stations.

1-3 SSFP Components SSFP has two major parts; they are its body and its mooring system. The body is a flexible pipe and the mooring system is the part which keeps the pipe submersible. These parts are introduced here basically but in the stability section we are going to design some of them and they can be clarified better by designing examples.

SSFP Body Body structure is formed by thousands of cylindrical rigid parts which are connected flexibly as a chain. Between any two rigid elements there is a flexible ring, which seals the connections so generally the body is made from two different elements, rigid and flexible elements. It will look like a flexible pipe but its structure is totally different from the usual flexible pipes. Fig I

Rigid Element gidpartsareconcrete cylinders. Theirdutyisto cancel out the bouncyforce ofthe pipe -and also to resist against compressible stresses so they are heavy and have a thick wall. They also can be made from the other materials such as composites, ceramics, metals or polymers but concrete is the first suggested material for them.

Concrete cylinder has longitudinal steel bars which are passing through the concrete wall thickness like rods in reinforced concrete. They situated in the wall with an equal distances.

The connection between concrete cylinders to other parts is done by these internal wall bars so all longitudinal forces (tensile force) which are applied to the pipe are cancelled out by the bars.

Concrete cylinder has bevel ends which covered by steel end caps. The caps have special form (they have some steps) to make the concrete cylinder ends suitable for connecting to flexible Joint and also protect the end's edges from breaking during construction and installation phase.

Fig 2-Fig 3 Water penetrates into the pipe due to external pressure because concrete is a semi permeable material therefore the outside surface of the concrete cylinders is covered and sealed by a polymer layer which resists to the sea water. )

If the pipe internal concrete surface is not smooth we can cover it with a thin layer of polymer or glass to reach better transmission efficiency.

We prefer internal gas penetrates to the concrete than sea water because we can protect the bars from corrosion so if the pipe has an internal cover we prepared a small open area to let the gas penetrates in the concrete but the problem is that if the internal gas pressure became higher than the external pressure the gas will gathered behind the pipe's external sealing layer and will damage it so we need an open area on external layer (something like a small check valves) to release the gas.

Flexible Element Flexible joints are special parts in piping systems. They are rarely used for large diameter pipes and they usually have a complex structure in high pressure usage.

SSFP includes millions of flexible joints so it seems that they are weakness for the pipe but there is a big difference between these and the usual ones and it is that usual flexible joints are designed to be suitable for high internal pressure but there is no or little internal and external difference pressure in SSFP flexible joint and it helps them to be sealed easier than normal flexible joint. Fig 4

SSFP flexible joint has a complex shape too. It includes a few thin sealing rings which are fixed between two concrete cylinders.

Sealing ring is look like a short thin piece of pipe. It has two parts, structure and body.

The structure made from steel rings which have channel cross section. The rings channels are matched upward and downward alternately how their edges lock together. The structure should resist to the probable internal or external pressure.

The body is an elastomer which covers the structure completely (it fills the hallow space between the channels) and it makes the joint seal. The elastomer should be chosen careflully.

It must have a long life under cyclic loads in seawater condition because the seal failing can ontinue to the pipefailure. ------Fig 6 The concrete cylinder has bevelled ends which have a few steps so when two concrete cylinders sit face to face the cross section between their walls is a trapezium-trapezoid (base on the external surface) which has stairs on its left and right side.

Different sealing ring with different length and diameters sits on theses steps and fixed to the concrete cylinder by clamps and they are sealed like hose connections sealing.

The trapezoid left and right side cross each other on the pipe centre and it helps the pipe to bends at flexible joint symmetrically.

Fig 2-Fig 4 There are very small lines between the flexible joint layers (sealing rings). These lines distribute the pipe internal and external difference pressure between the layers. Therefore each layer should be resist to small pressure. For example if we have four layers and the pipe max difference pressure is 5 bar then the difference pressure between the layers will be I 25 bar. Due to distributed lines diameter are very small the flow rate which passes through them is very low so in practice we can neglect this amount of leakage however we can have a small pressure valve on the first and the last layer distributed lines. The valves can stop the flow when the pipe is in the normal operation (Little difference between Internal and external pressure) and they can open only when there is a high difference pressure.

It is obvious if sealing ring can resist to the maximum predicted difference pressure we don't need many sealing rings and just an external and an internal ring will be fine for flexible joint. Fig3

Due to the sealing rings are thin they will buckle very soon under external pressure so small beams come out from the concrete cylinder ends and are sitting under the sealing rings to protect them from buckling. These beams are stopper too. It means when the pipe is bending after the joint is compressed enough the two beams touch each other and stop the joint deformation.

Generally flexible joint can be design in various shapes but we should notice that the joint should be able to be installed easily and fast between concrete cylinders because the pipe has thousands of these joints and a difficult installation can make problems in pipe construction.

Flexible joint has middle chains which connect the bars flexibly between two concrete cylinders. They are the joint's parts which resist to tensile force.

The middle chains are short chains which have higher tensile strength than concrete cylinder's bars Middle chain includes two eye-nuts which are connected together by a few close-link (chain segment). Eye- nuts have right-hand and left-hand thread and the bars ends have been threaded right-hand and left-hand too so the middle chains can be fastened between bars while the bars are fixed.

The chains in normal condition are relax but if the pipe is pulled or bend they will be stretched and do not let the flexible joint (sealing rings) to expand more than their specific expansion allowance. Fig4

SSFP Mooring System The term "mooring system" reminds us of huge complicated systems which make massive offshore floating platforms stable. Mooring system in SSFP will do the same thing but there are differences between these two systems, first is that the offshore platform mooring is a pointed system but SSFP mooring is a linear system (one tries to fix a point but the other tries to fix a line), second is that forces which apply to a platform are much stronger than the forces which apply to SSFP because the marine waves and currents are much stronger on surface than in deep water. The third difference is that a mooring system is design to fix platforms how it can moved a few meters but SSFP mooring system allows the pipe to move more than a hundred meters.

Due to above explanations a unit of SSFP mooring system is very smaller and more simple than platform mooring although a long SSFP whole mooring system weight can be much heavier than the biggest offshore platform's mooring system.

A unit of the mooring system include Cable, Fixed Ballast, Chain Ballast, and Buoyant Ballast. Cable arranging can be varied, depending on sea floor depth and lateral current, which is explained later but the most important one is separated cable arranging which can be used in the most SSFP. In separated cable arranging each concrete cylinder is kept submerged from two points with two cables. The points are located on the bottom and close to both ends of a concrete cylinder. The cables merge together and make one stronger cable.

The end point of this cable connects to the Fixed Ballast which is settled on the sea floor. The Ballast is designed to remain fixed against highest forces which are applied by the cable. It can made form reinforced concrete or other materials. Chain Ballast is made from small weights which are connected along the cable. They are started from at the end of cable (connection point to the Fixed Ballast) and due to the pipe requirement are continued along the cable (500 meter from the cable end point) till the Buoyant Ballast. Chain Ballast can be made from lead or other substance. Its parts can have a continuous shape like chain, or can be separated weights which connected to the cable at small regular intervals of around one meter. Buoyant Ballast is the last weight (the highest) which hangs from the cable, It can be made from lead or other material. During the normal operation it always is submersible. Fig 7

SSFP's mooring system has two major duties: First is to keep the pipe submersible and stable in a specified corridor against the loads which apply to the pipe. The corridor has width, height, and length. Three dimensional corridors compared to two dimensional conventional pipes. Width and height of the corridor can reach up to 300-500 meters.

Fixed ballast makes a final upper boundary limit above the pipe against upward force and lateral force (current forces) so the pipe can not go upper than it. The boundary is a sector of a circle which the fixed ballast is the centre and its radius is the cable length in full tension mood (chain ballast is completely submersible). Fig8

In practice the pipe will rarely reach to this boundary since as result of upward arid Lateral forces the pipe will move in direction of the force and pull the cable and also make some part of chain ballast submersible so cable tensile force will increase and this can continue till the cable tensile force can cancel out the current applied force.

If a downward current applies a force to sink the pipe while the pipe is sinking the chain ballast will sit on the sea floor so the buoyancy force of the pipe will increase and it will continue till the buoyancy force can cancel out the sinking force. The final lower boundary for the pipe sinking is the depth which the buoyant ballast sits on the sea floor. In this case the buoyancy force will increase gradually against sinking force and keep the pipe in its corridors. Buoyant ballast should be designed to cancel out any unpredicted force because after it nothing will raise the buoyancy against the sinking force. However after this happen the pipe will not completely sink because the pipe will bends and it influences on next buoyant ballasts to sit and cancel the sinking force.

Fig 10 The same story can happen for an upward force and the fixed ballast but in both of these cases it is better the influence of beside ballasts is not assumed in design of fixed and buoyant ballasts.

While the pipe moves vertically in its corridors the external pressure will change so the pipe structures will absorb the extra force. )

The second duty is to control the internal and external pressures difference how they are always equal. It means if the internal pressure of the pipe due to operating conditions is changed, the mooring system should change the pipe depth to reach a proper external pressure. This act is done by the chain ballast. The weight of chain ballast unit length is a function of gas density. When the internal pressure drops, the gas density decreases and the pipe becomes lighter so it rises until further units of chain ballast are lifted, thus increasing the weight and cancelling the upward pull. At this new position again the pipe external and internal pressures is maintained equal. This system helps the pipe to be in the best situation (equal internal and external pressure) and also it makes the pipe compatible for using in wide operation range due to different conditions. Fig 9 1-4 SSFP Stability SSFP would be submersible in oceans deep water. They should remain stable in a distinct route during their operating life.

Deep water behaviour is not known as well as other surrounds so it is difficult to contemplate all elements and predict their influence on SSFP.

Marine currents, wave, biology and human activity are main factors for SSFP stability however deep water current is the most important factor for SSFP stability and it can limit using of SSFP. In the other word if the deep water currant has high velocity (more than lm/s) in practice we can not use SSFP.

In this section we are going to show SSFP stability by doing basic calculation for the mentioned SSFP as an example.

Marine currents Marine currents are generated by the thrust of the wind, the spine of earth, moon's and sun's gravity (tides) and changing in water density as a result of temperature or salinity.

There are many type of ocean currents such as Surface Currents, Deep Water Currents, Thermohaline, Gyres, Upwelling, Downwelling, Spirals etc but only their physical characteristics in depth of about 2000 meter (6700 feet) influence on SSFP stability.

Major ocean currents like Golf Stream, Labrador Current, and Equatorial Currents are surface currents. Golf Stream as fastest currant has velocity of about 2.5mJs but it is not extending to the depth of 2000 meter so surface currents should be considered in the pipe installation phase and they do not influent on the pipe during its normal operation..

Deep currants source are Antarctica and Arctic Oceans the water becomes cool and dense and also its salinity is increased in these areas so it sinks to the bottom of the oceans gently in some cases it can moves with speed of 0.2 rn/s but generally deep water currents have a velocity of few millimetres in second.

The deep water velocity is assumed as 0.3 rn/s in here and it is predicted that this speed can cover the most areas in the oceans however SSFP can be specially designed to be stable in water velocity of about 0. 5 rn/s.

Fixed and Buoyant Ballasts' weight: Upper critical point is the case where the pipe is operated in the lowest pressure (Chain Ballast is fully lifted and the pipe is in its greatest height from the sea bed) and an upward current applies a force to the pipe. In this case the Fixed Ballast weight should cancel out the current's force. Fig 8

For the lower critical point; the pipe is operated in the highest pressure, the Chain Ballast is completely sat on the sea floor whilst the Buoyant Ballast is floating by the last link, when a downward current exerts force on the pipe. In this case, the increased buoyancy as the Buoyant Ballast lands on the sea bed should be enough to cancel the down force.

Fig 10 WFBw = WBB = = Pea Water.1)0.C.U L Where WFBW = Fixed Ballast Weight in Water (Wet Weight) = Buoyant Ballast Weight in Water (Wet Weight) = Current's Vertical Force D0 Pipe Outside Diameter (3.2 m) C =Drag Coefficient =L2 = Currant's Vertical Velocity (0.3 mIs) L = Length of the pipe element which connect to one mooring system (concrete cylinder + flexible joint =12 m) PseaWaser = Sea Water Density (1030 Kg /m3) Note:-When 0.3 m/s water flow ispassingaround the pipe theReynolds umbéris x. 5 R = -= 6 = 8.5 x 10 and in this Reynolds number range the drag coefficient V 1.12x10 decreases but in here to be more confident we use max drag coefficient in our calculation) WFBW!xIo3ox3.2x1.2xo.32x12_ w8 =WBBW -F =2136 N or WWBW -WBBw =218 kg Its dry weight is WFBD = WaRD = x W,.8 Where Pa -P Sea Water = Fixed Ballast Dry Weight ) WBBD Buoyant Ballast Dry Weight = Density of Ballast Material For a concrete Ballast WFBD = WBBD 2400 x 2136=3742 N = 382 Kg 2400-1030 For a lead Ballast WFBD = WBBD = 11300 x 2136 = 2350N 240 Kg 11300-1030 If the pipe is laid parallel with deep water it can assume that the lateral (Horizontal) current is weaker than the vertical assumed current (0.3 mIs). If the lateral current velocity is less than half of vertical currants (about 0.15 mIs) and the sea depth is about 2800m as the follow calculation shows the founded result for fixed ballast's weight will be enough for pipe stability against lateral current too but for higher vertical velocity fixed ballast's weight should increase or it should have some small pile into the seafloor, the other option is to change the pipe's cable arranging.

When the pipe is in upper critical point and a lateral currant applies a force on the pipe the friction force between Fixed Ballast and seafloor should be greater than the currant force.

FFrIC,j,, = Fc4Ij FFflOfl p W,.8,, = PSeoWogerj)oC1H1' And from equation we know WFBW = P&o Water *jo.C.U, L Where FFrIcljOn = Friction Force --Fe,, = Current's Force Horizontal p = Coefficient of static friction between Fixed Ballast and seafloor = Currant's Horizontal Velocity (can be assumed 0.15 mIs) FFr:Ct, = Ff11 P P5eaatero = PSeoWa:erJ)oC.UHL - p = And if =0.3 then UCH = 0.55U In this situation if the pipe cable has 800 m length (500m as chain ballast and 300m remain), the final cable angle and lateral diversion will be as follow. In following calculation the current horizontal velocity is assumed the same as vertical currant (0.3 m/s) ) Fig 11 F. Tana= (H WBBW + WchBw + WCabIeWr d = (LCafrje + LchR) x Sina Where

N

a = Cable Angle with vertical Axis WA9w = Chain Ballast's wet weight (18718 N See the calculations in the Chain Ballast section) WCabIeWeI = Wet Cable Weight between the pipe and buoyant ballast d = Lateral Displacement = Cable Length between the pipe and buoyant ballast (300m) LchB = Chain Ballast's Length (SOOm) Fch, =-2-x1030x3.2x1.2x0.32x12_3FcH =2136 WCabIeWel = (0.4 x 7850-1030) x 300 x 9.8 = 1022 Tana= 2136+ 20367 + 1022 d = 800 x Sin5.2 -* d = 72.5m When the pipe is in the lower critical point and there is a lateral currant, friction force is not a significant factor for pipe stability because in that position the Chain Ballast is sitting on the seafloor and it increases the friction force gradually but the factor which should be noticed is the pipe lateral displacement. It is important for the pipe structure internal forces. Currants width is big but they don't move the whole pipe and some part of the pipe will stay as they where are. So between these two areas the pipe will tensile. The bigger displacement will make the bigger tensile stresses in pipe's bars.

For the same pipe in its lower critical point we have Fig 12

F

Tana = W88 + WCbIWeI d1 = LCable x Sin a

A CV "2

UXAVeWChBW d = d1 + d2 Where d1 = Lateral Displacement due to the cable's angle d2 Lateral Displacement due to chain ballast sliding on seafloor d = Total Lateral Displacement AveWChBW = Average Chain Ballast Weight per meter (20367N/500m = 41N/m) Tana= -+a=34 2136+ 1022 d1 =300xSin34=-*d1 =168 m 2136 -d =174m 0.3x41 2 d=168+l74=342 Meters Weight calculations for the Chain Ballast Chain ballast weight is equal to the difference between highest and lowest gas weight in a pipe element which is connected to one mooring system.

WChBW = (Wa5Max -WGMfl) x L WchBW = Chain Ballast Weight in Water (wet weight) WGaSM = Max Gas weight in the pipe per meter WGaSM,fl = Mm Gas weight in the pipe per meter L = Length of the pipe element which connect to one mooring system (12 m) So the Chain ballast wet weight is: WchBw =(p2GpIG)x_L_xL Where -PGsM, = Gas density in PMIfl Mm internal pressure PGM Gas density in GaM Max internal pressure Internal pressure difference should be the same as external pressure difference so Mnternai = Mexrernai (as,.iar -GasM,n) = (25MP -2OMP) = Where &z is the pipe displacement and it is equal with chain ballast length.

If natural gas behaves like an ideal gas then density of gas was a linear function of pressure so the chain ballast could have a constant weight per unit length but the Equation of State for natural gas can be in a form of P = RT -a therefore chain ballast weight will v-b v2+cbv+db2 increase from top to bottom. )

With using Peng-Robinsori model for Equation of State, natural gas with 0.95% mole Methane and 0.5% mole Ethane composition has the following properties.

Gas Pressure (Barg) Gas Densjy (kg/rn3) Temperature (C ) 202.64 2 200.1 (200+0.1) 202.73 2 210 210.49 2 220 217.9 2 230 224.92 2 240 231.56 2 249.90 (250 -0.1) 237.81 2 250 237.87 2 For example if the max internal pressure is 250 Barg (250x i05 Pascal) and the mm internal pressure is 200 barg and also the pipe segments have a I 2m length and the cable diameter is 8mm then: = AP p01gAh + 5xl0 1030x9.8x A/i -* A/i = 495rn 500rn And =(P2G -p1)x-xL -p (237.9-202.6)x,tx2.5 x12-+ WChBW = 2080kg = 20367N But as it said before this weight (2080kg) is not distributed constantly on the whole length (500m) so each meter of chain ballast has different weight. For example to find the first and the last meter of chain ballast weightin here first the external pressure changes due o one ---meter move is found and then the gas density after the same internal pressure change is calculated. New density can gives us the proper weight for chain ballast unit length. Barg

For the first meter (top of chain ballast) 1 =2SObar - p =237.87kg/rn3 And F =249.9bar-+p2 =237.81kg/rn3 (237.87-237.81)x if x2.5 xl2-+WChBW =3.53 Kg/rn (top) This weight is the wet weight of chain ballast first meter (top of chain ballast) and it includes the weight of one meter cable plus added weight.

Added weight is a concrete or lead weight which is fixed to the cable to provide the suitable weight for chain ballast.

-WCabIe Wet 7850-1030 WAdded Wet = WTO,,, -WCabIeWel Wet = *3-(0.4x) -3 18 Kg/rn (top) 7850 -Its dry weight For concrete Ballast is WAddCdD'7, x3.18=5.57 Kg/rn (top) 2400-1030 And for lead Ballast is WAedD,) = x 3.18 = 3.50 Kg/rn (top) 11300-1030 For the last meter (bottom of chain ballast) = 200bar -* = 202.64kg/rn3 And P = 200. ibar -p2 = 202.73kg/rn3 rx2.52 Wc,,BW (202.73-202.64)x x12- W8 = 5.30 Kg/rn (bottom) 7850-1030 WAdded Wet = 5.30 -(0.4 x) = 4.95 Kg/rn (bottom) Its dry weight For concrete Ballast is TAddedD = x 4.95 = 8.67 Kg/rn (bottom) 3 2400- 1030 And for lead Ballast is WAddedD = x 4.95 5.45 Kg/rn (bottom) 7 11300-1030 The pipe wall thickness: SSFP wall thickness is designed due to the gas buoyant force instead of the wall stresses.

Because the required thickness to reach the appropriate weight to cancel out the pipe buoyancy is much thicker than the thickness which the pipe needs to with stand against compressible stresses.

The pipe wall thickness can calculate with below equations.

Wconretewet + + + + WBBW + WCJblewe, = F80700, Where WConeW Wet = The concrete cylinders pure wet weight W8ars wet = Concrete cylinder's internal bars wet weight = Flexible Joint Wet Weight (assumed 400kg) Max Gas weight in the pipe = Buoyant Ballast weight in water (wet weight) = 218 Kg WC4b!eWeI = Cable wet weight (The part of cable which is above the Buoyant Ballast) WCab!eWet =(0.4x 7858 1030)x300=104 Kg F8oyac The Pipe Buoyancy Force All above factors should be calculated for a complete pipe element (a concrete cylinder with a flexible joint which has 1 2m length) And (,z j2' = -x (Pconcrere -Peaarer) x L WConcreteWel J 1.7 = l2589D -78682 W,rs = n x -i-x -( PCOflCrCIC -x L = 133 kg = _L. < PGOSMW x L =14005 Kg F8001,, = x Pea Water x L = 60641 Kg So (l2589D-78682)+133+4OO+14OO5+2l8+W4=-6O641-,.D=3.144m = 3144mm So the pipe wall thickness will be: t = 322 mm We found the required pipe thickness due to the pipe buoyant force so we can now calculate the pipe internal stresses.

In normal operation (same internal and external pressure) both tangential and radial stresses in the pipe are the same and equal to the pressure so if our maximum operating pressure is 2SObar or 25 Mp the stress in concrete will be the same (-25 Mp, compressible). It is less than a middle range concrete max ultimate compressible stress (-30 Mp) so the pipe is Ok.

in the case which a vertical currant applies a force on pipe we know: -Ff11 = Current's Force Horizontal =2 136 N (for max currant velocity 0.3 m/s) Ave = Average Chain Ballast Weight per meter (41 N / m) So due to the currant force the pipe will change its depth about 50 meters (2136/41=52) and this change makes a different pressure about 5 bars on the pipe so we can calculate the pipe stresses in this condition as follow.

Pr2 -r,2 r02 (p0 -p,) 2 2 r -r 0r = Pr2 Pr2 r2r2(p -p,) r0 -r, Where = SSFP Tangential Stress o, =SSFP Radial Stress = Average Inside pressure (25 Mp) = Average Outside Pressure (24.5 Mp) r = Inside Radius (1.250 m) Outside Radius (1.572 m) *fonCrete = Max Concrete Ultimate Compressible Stress (300 kg/cm2 =300bar=30 Mp for middle range straight concrete) -(25x 1.252) -(24.5 x 1.5722) (1.25 x 1.5722x (24.5_25)) -1. 5722 _1.252 1.9 -2l.48+(---) -0.9 r -+r=1.572--+a,=-23.OMp ---1.9 -21.48+(--) 0.9 -r=I.25-.+otmm=22.5Mp -2l.48-(-) 0r = 09 r -+ r = 1.572 -* 0r1nax = -24.7 Mp -25.8-(--) = 0.9 r -r=1.25-a,min =-30 Mp And the answers can be acceptable.

The above equations show the pipe stresses when it is completely seal like steel pipes but if the gas penetrates in to the concrete it can releases the stress from the concrete structure. It is can be considered as a new theory and we need experimental examinations to find the real stresses.

The above unknown theory is mentioned here just to explain a probable problem. If we assume concrete as 100% permeable material then the gas saturate it completely and there will be no stresses between the concert grains and the problem in this case is that if the internal pressure of the pipe become higher than external pressure then the pipe (concrete) will be under the tensile stresses and due to concrete poor tensile strength the pipe will be ruptured. In this case to solve the problem we should operate the pipe in the higher external pressure than internal pressure in normal operation how if the pipe has upward movement its internal pressure never exceeds the external pressure so the pipe always has compressible stress.

in reality we need to find the influence of the gas penetration on stresses and then choose the relation between the pipe external and internal pressure to operate the pipe in its best stress conditions.

The external pressure on thin pipes can buckle them but SSFP is not a thin pipe and it can resist to buckling.

The flowing calculations can show it.

2E(---) D) 1e1 2 1-v Where Pei = Elastic Critical Pressure E = The modulus of Elasticity (15-40 Gp for Concrete) v = Poisson's Ratio (0.1-0.3 for Concrete) t = Pipe Wall Thickness (3.144 m) D = Pipe External Diameter (0.322 m) 2x25x io (O.322 -*J,=56Mp And it is higher than max concrete ultimate compressible stress (30 Mp).

Cable Design: Seafloor under the pipe's corridor has different depths but the pipe should be submersible in a constant depth so the cable length will be variables along the pipe and it requires perfect seafloor topography to find what the suitable cable length is for any of the pipe's segment (any concrete cylinder).

Longer cables are heavier too and it makes the pipe unbalance therefore buoyant ballasts' weight should be reduced for longer cables. It means in general the wet weight of buoyant ballast plus the wet weight of its above cable should be the same along the whole pipe The Cable should resist against the sum of ballasts' wet weight plus its wet weights So TCCb!e = WCb!W + W,.8 + W88, + WchBw Where TCab!e Cable tensile force = Cable wet weight (The part of cable which is above the Buoyant Ballast) WFRw = Fixed Ballast weight in water (wet weight) = 2136 N WBBW = Buoyant Ballast weight in water (wet weight) = 20367 N WchBW = Chain Ballast weight in water (wet weight) = 2136 N For example if sea floor average depth is 2800m and the pipe operating lowest depth is 2200m and cable dry weight per meter is 0.4 kg/rn then we have: (0.4x 7850-1030) 300x 9.8 1022 N ab!e=22+2136+20367+2136_*7Qb,e=25661 N=26lSkgf And the cable diameter will be -Cable YCable -7tD61 Where YCablc = The Cable Material Yield Strength (600 Mp) TCCb!e = Cable tensile force DCabk = Cable Diameter So 600x 106 _25661 -+ D =0.0074m =7.4mm n/)Cable And we choose it 8 mm The SSFP cables should made from a very high strength material to decrease the cable weight.

The cable tensile force is limited to above value (25661 N) because after the fixed ballast is lifted there is noting to increase the tensile force so the cables are designed to be a little stronger than the maximum tensile force to protect from failing.

In design of cables (Wire Ropes) usually high safety factors (Can be between 3 to 12) are used but in here since the cables are one of the most expensive part of the pipe and any little increase in cable diameter will cost millions, a little safety factor suggest for the cable, however some safety factors which are mentioned in ballasts designing can be a safety factor for the cable too.

Corrosion should be fully considered for cables. In practice cables repair is too difficult to do and the disaster is that a few millimetres corroded area can make a hundreds meters of cable useless.

All the protection ways such as Cathodic protection, Use a water proof protection cover, change in cable material (using stainless steel or polymers), Hot deep galvanizing, etc are possible depends on each method's cost. In here we don't go further to the corrosion system details because it's a big subject but as corrosion is a well-known subject nowadays we can be shore that it will be solved for SSFPs' cables.

If the sea floor depth is very deep the cable arranging can be different from Separated Cable Arranging. Fig 7 In other cable arranging many concrete cylinders can be kept by one cable or they can connect to mooring system form their both lateral sides.

Some of new suggested cable arranging is Bundle Arranging, Bridge Arranging and Centipede Arranging. In Bundle Arranging a few cables which are connected to the concrete cylinders will merge together and then will continue with a thick strong cable to the sea floor.

Fig 14 Bridge Arranging is exactly the mirror of the cable arranging for suspension bridge. The cables which are connected to the concrete cylinders comes done vertically and connect to a main parabolic cable which is kept from its both ends with the mooring system. Fig 13 If the pipe is passing throw deep oceans which the lateral currants velocity are higher than predicted speed the Centipede cable arranging can introduce to the pipe. In this arranging the pipe can be kept from the top or bottom and from the both lateral sides. It means concrete cylinders are connected with two mooring system which are on the pipe both sides. There is a pair of ballast for any pipe segment. Figl5 The new option for chain and the buoyant ballast is that the ballasts' weights can be replaced by sphere floats. Fig 16 In cross section cables made a triangle with seafloor and this arranging is very strength against lateral forces. This cable arranging can also include bundle arranging or bridge arranging in this case the pipe is look like a huge centipede which is standing on the seafloor.

It is obvious that in these arranging when 10 or 20 pipe elements are kept by one cable the mooring system which connected to this cable is 10 or 20 times heaver than the mooring system of Separated Cable Arranging. --For a specific length of the pipe (for example 250m) the total tensile stress which applies to the cables is approximately the same. So the sum of cables' cross section area for all cable arranging is the same and it means they also have same weight.

So theses new cable arranging not only are more complicated but also can be heaver and more expensive than Separated Cable Arranging. The reason for using this arranging for deep water is that while the cable becomes longer the corrosion will be a bigger problem for it.

The corrosion is a function of lateral surface.

A thick cable which has an equal strength with 25 smaller cables has a same weight with them but its circumference area is less than them (a fifth of them) and the less lateral surface the less corrosion and the less corrosion protection need.

Therefore these new cable arranging can be chosen for passing very deep oceans areas (more than 4000 meter depth).

There are thousands of cables which are hanging from the pipe so it seams they can easily become knotty butt when the pipe is settled in the sea all the cables will move to gather so no knotting will happen. )

Bar design Internal bars make continues pipe from concrete cylinders and they give the meaning of pipe to SSFP indeed. They are connected together flexibly so tensile forces just apply to them.

The bars must resist to different forces such as tensile force due to bending, installation, seismic activities (especially earthquake) and pipe rupturing.

The bars designing is based on bending and installations forces and the other two case are secondary issue because they are not directly depends on bars strength and many other subject can influence on them.

Pipe rupturing is a situation which the pipe is broken by unpredicted loud under the sea and water has come into it. In this case the required bar strength can be evaluate to keep the other parts safe it depend on the pipe failure protection systems (sea mini stations) and we are not going to the its detail designing in here.

Bars are to long so it is better they made from steels with a high tensile strength (60000- 90000psi or 400-600 MPa) to make them more economical. They do not have welding problems so they can be made from high carbon steel with acceptable toughness.

Tensile force due to bending (Operating Tensile force) When the pipe bends as a reason (ex. a cusrant force) a tensile force is applied to the pipe. So the pipe's bar shall be able to cancel out this force to avoid pipe breaking.

Flexible systems behaviour is complicated therefore in here a simplified model is used to assume the pipe tensile force but the simplification hypothesises increase the force hence the actual tensile force should be less than the founded force.

The assumed model is a flexible cable which is connected to many springs along its length vertically how a long distributed force is applied to part of it.

The cable is assumed as the pipe, springs are Chain ballast and the distributed force is the currant's force. Spring of constant is assumed to be equal to the highest chain ballast weight per meter. -In reality when a currant moves in oceans there is a velocity profile between the currants' boundaries which starts form zero to the max velocity but in here we supposed that a sudden distributed force starts in a specific point with a constant value and it means a sudden current cross the pipe on that specific point so the founded tensile force will be greater than the force in practice.

In assumed model the cable has two curves with different equations one before the distributed force and the other after it. The maximum tensile force is accrued in the point which this two curve connected to each other (distributed force starting point). At this point the two curves' tangent line should be the same and it can happen in 0= r/4.

If the whole vertical displacement of cable is assumed 2C then the connection point vertical displacement will be equal to C (y=C) With specifying these boundary limits we can consider one of the curves for finding the tensile force.

Cables equilibrium equation is as follow Where (fr2T Co Load per unit of honzontal length 7; = TCosO Horizontal component of tensile force In this case o. = Icy Where k = Spring of constant So = --= dr2T 7; The answer of above equation is in form of y = Ae + BeA2X Therefore y = Ae'1 + Ber When x - -then y=O so B should be zero (B0) and the equation changes to If fA7=K then y=Ae When y=C then 0= r/4 ln(C/A) y=Ae -+C=Ae -+x=

K dy

tan0=--.tan9=AKxe-tan-=AKxe K ->l=AKxe A dx 4 K=!_T =kC2

C

The cable's exponential curve equations can be written as follow ---y=Aec In here for finding the value of arbitrary Constant A, first the length of cable's exponential curve is calculated and then it is compared with the cable mechanical characteristic (amount of changes in_length due to tensile force).

s = 1 11+ (d2.dx And also dr) s = f(x) The function which is come from cable mechanical characteristic ! dy A!r. A y=AeC so if -=a then s = i +(aeJ2 s = [l/2[sin ae + ae(ae)2 + I]]: ) 1 1 1 I ___ s = f(x)=1/2 (sinhae +ae(ae)2 +l)-(sinh'a +aa2 +1) With finding the arbitrary constant A the cable's exponential curve equation will be specified so we can find tangent line's angle and the tensile force in any point of the cable as follow: T-T0/cosO Or I In((/A) ! 1 / T=L kt (AC)dxj sinO For example for SSFP vertical movement about 50 m (displacement due to 0.3mis vertical flow) and horizontal movement about 342 m (displacement due to 0.3m/s horizontal flow) the maximum tensile force will be as follow.

k Ave WchBW Vertical -kHorjonlal = Ave W118 tan LX (For simplification it is assumed that the chain ballast is floating between the pipe and fixed ballast and it is not sits on the sea floor) Where k = Spring of constant L = Length of the pipe element (1 2m) Ave WchBw = Average Chain Ballast Weight per meter(20367N/500m 41N/m) a Mooring Cable Angle with Vertical Axis tana = Horizontal displacement / distance between pipe and seafloor (342/300) = -+ k = 3.42 N/rn2 2C=50m and C=25m T0=kC2 -TJ, 3.42x252 - .7= 2137.5 N So T = 7/cosO -* Tpfj = 63281/cos(,r/4) Ty.,jcj1 = 3023 N 41 x 342/300 = 12 = 2C=342m and C=171m 1=kC2-*7=3.9x1712-*7=114O4O N T 7/cosG - TMarHoriZOntl =1 14040/cos(r/4) =161280 N Tensile force due to installation process SSFP construction process should be done on the onshore costal area because it is too difficult and expensive to do this process on the oceans so after construction there is a very long pipe which must carrying to middle of oceans for erection.

The pipe bars should resist the tensile force due to the pipe installation process. It means the pipe should not go to pieces when carrier ships pull it from the costal factory.

A pipe segment too long (100 km) to carry with just one carrier ship therefore any primary segment (5 km) shall be carry by a carrier ship. However if many vessels are used in shipping phase the carrying process will be complicated.

It is supposed that a SSFP will be carried with 20 vessels. The vessels speed can be variable but due to the time which is taken to construct a new SSFP segment the Carrier ships do not need to carry the pipe fast so 3m/s (l 0 km/h or 6Knots) can be suitable.

In here calculation is done for a separate 5000m primary segment.

A Flat-Plate which has a same surface area as the pipe's external area is replaced to find the drag force. The pipe outside diameter is 3.2 m (See wall thickness calculations) so the replaced plate width is I0.05m.

ReL = P5ecr,.oger" -4 Re 1024 x 3 x 5000 -+ ReL =1.536 x 1010 p ix103 So we should use Flat-Plate boundary layer theory in turbulent flow. Theory of rough flat plate flow can not cover this case because roughness parameter (- = 106) is too small.

Drag force is D = --CDPSeCwOIeTU2bL Where D = Drag force (it is equal with the pipe's tensile force) CD = Drag Coefficient U= Vessels or the pipe speed L = Length of the pipe segment (5000m) b = Flat-Plate width (10.05) Psenwager = Sea Water Density (can be assumed 1024Kg/rn3) -Drag coefficient can evaluate from below equation 0.031 0.031 C0--C= I -+C0=l.O87xIO ReL (l.536xI0' ) Therefore

N

But in real pipe transportation, the Drag force will be much bigger than the founded result because the ballast package are hanging from the pipe while it is pulled and they will increase the pipe drag coefficient.

The above calculation shows the installation tensile force is grater than operating tensile force so why we don't pull the pipe in a shorter segment to have a smaller bars. The answer is that the safety factor which should considered for bars designing will increase the operating tensile force so the final calculated force not only can cover the installation force but also can cover the fatigue issue of operating force.

If we compared the unpredicted forces which can be applied to the main three parts of the pipe (concrete cylinder, cable and Bar) we find that, Concrete cylinders just influence in difference between internal and external pressure which is not an unpredictable subject. The cable never sea the over loads because if the tensile force in the cable passes its limit the only thing that will happen is that cables will lift up fixed ballasts and after that cable force will remain constant and equal to whole ballast's weight.

But many unpredicted and uncertainties forces (sticking a big octopus to the pipe in installation process) can apply to the bars. Bars failure means no pipe or loosing a big segment of pipe. If the bars fail the water comes in and makes it heavy and the pipe sinks to seafloor so considering a safety factor is necessary.

Choosing a safety factor for bars designing needs experimental records and statistic information and also it is depended on the availability of protection mechanism which are used in the pipe so it is difficult to find a correct number for it but especially in first designing it must have a great value. The bars' weight compare to cables' weight is small therefore exercising a high safety factor is possible and this safety factor can guarantee the pipe stability in water.

In here we choose 8 bars with 20mm diameter for our SSFP So 0YBar,rDx 8 Where CTYBGr = The Bars' Material Yield Strength (600 Mp) = Bars Total Tensile Force DCabIe Bars Diameter Thus 600x1Q6 2---6 *+T ar=2355 KN ---r25 xlO x8 (It is about 9 times bigger than the required founded tensile force) Earthquake and seismic activity: When we think about massive Tsunamis evidence it seams that oceans seismic and volcanic activity will destroy the pipe. In this part the pipe behaviour is considered briefly for these problems.

If an earthquake makes a fault in sea floor, displacement waves will come up vertically through the water to release in sea surface. In other word the waves choose the shortest way to reach the sea surface and don't distribute in whole water, after they come up they create surface waves which move very quickly but these surface waves does not influence on deep water. They are broad and gentle swell in open seas but as they approach the shore they will change and can damage the costal area.

If the pipe has a proper distance with earthquake's epicentre it willnot sea the waves therefore the pipe root selecting is an important designing point which can predict the pipe from seismic activity.

Earthquakes are usually happened in tectonic plate boundaries and nowadays distribution of major earthquake and volcanoes are well known in the world so the pipe root selection can be chosen simply far from these hazardous areas to protect the pipe.

Due to above explanation we do not design the pipe for earthquake but we like to consider what the pipe behaviour is while an earthquake is happening.

Earthquake itself is a complex so its effect on such submersible pipe in ocean is a complicated subject too. Therefore in here is tried to simplify the subject as much as possible.

If a single rigid body like submarine is submersible in water it has full degree of freedom (no isolated) and due to an earthquake waves it will move so no internal force applies to it and it is safe with earthquake. Apply a couple also can turn the rigid body but it dose not seam the earthquake can make a couple in sea water so it is not considered in here.

If we look at SSFP from the same point of view it just isolated in its longitudinal direction but not completely isolated because it can expand longitudinally thus we should looking for the some earthquake's effect which tries to pull the pipe and make a longitudinally force on It.

With a brief review of earth quick we know that there are two type of body waves (P and S) and also two type of surface waves ( Rayleigh and Love). When a P wave passes over the pipe the pipe will moves and deforms a little in a very short time. The model that can explain this case is a long spring witch has a rigid or a stronger spring at the middle. Passing P wave over the pipe makes a compressible force in the pipe in a very short time so it will not damage the pipe. S wave can not touch the pipe because it dose not pass through liquids.

If earthquake epicentre is located under the pipe surface waves will shake seafloor love wave makes shear between water and seafloor so with same reason of S wave they never reach to the pipe. Rayleigh wave can displace the water which is above seafloor vertically and this displacement will go to the sea surface and it will shake the pipe but the pipe movement will be in its free axes so it will move and there is no internal force in it.

Above basic explanation shows the pipe is safe against ocean's earthquake but the problem will recognize when the seafloor is fractured and there is a fault on it. In this case if SSFP is above fault and it is perpendicular with-the fault direction. When the-fracture-happens, a-huge column of water which is above the fault moves vertically and take some part of the pipe while the other part is remain in state water. The pipe will bend above the fault and stretch the pipe.

The tensile force in the pipe can be a function of the fault displacement and velocity and acceleration of fracture and also it is a function of the pipe's longitudinal flexibility, weight and diameter.

The pipe behaviour in this condition is to difficult to investigate in here but the point is that this case is a vary special case for SSFP and it can never happen for a pipe so we can accept the pipe feasibility while we keep this part hold for further researches.

1-5 SSFP General Notifications SSFP description has many points which are hardly related together. They are different subjects and it's difficult to arrange them how they follow a specific subject therefore in here these points are mentioned together as some notes.

Gas Composition The gas composition is an important issue in SSFP. The pipe will be designed for the most common gas composition. If the gas which is being transferred has a big different composition it will change the pipe setting point (different internal and external pressure in normal operating).

We like that our gas has a high percentage of Ethane because the gas is running in very high pressure (250 bars) and temperature about 2C . th this condition if heavier component (C2+) mole fraction is more than 10%, then the gas can changes to liquid form.

For above reason it is better that the pipe operating pressure is limited to 250 bars and depth of about 2500 m and also the gas composition has more than 90% mole Ethane.

Gas pressure in the pipe Gas Density in many cases is neglect able but in SSFP gas has high pressure and it is dense so gas hydrostatic pressure should be mentioned for pressure calculation.

For example if we notice to a specific SSFP between two offshore stations when there is no flow in the pipe it is horizontal but when gas transfers throw it will have a very slight slope because due to gas transfer, pressure will drop and also gas density will decrease so the pipe down stream will go up. The point is that the internal pressure at pipe downstream will be less than the predicted pressure. The reason is that the pressure drop will change the pipe level and the level change, will change the gas hydrostatic pressure and again this new --pressure change will change the pipe level, until the pipe will be in equilibrium therefore if the upstream pressure be assumed constant, then downstream pressure will be equal to upstream pressure minus predicted pressure drop and hydrostatic pressure.

<p≥ - + It is difficult to say which level can be assumed as a base level for calculating the hydrostatic pressure. If the upstream pressure has a constant value (like a branch connection at down stream) the most level changes will accrue at the downstream and the pipe downstream will goes up when the gas consumed and it will goes down when the gas feed to the pipe.

However in the other cases depends on gas volume in pipe's upstream and downstream some part of the pipe will going down and some of it will going up.

Pipe failure The third party damage and corrosion which are the most important cause for usual pipes failure are not big issues in SSFP. Because the pipe environment is far from the human activities and also the pipe dose not carry corrosive materials and also cracks will not grow in SSFP walls because it is under the compressible stresses. But the pipe may fails anyway so we have a failure system in the pipe to protect the pipe as much as possible (it is explained in mini station section) and also we can store spare pipe segments (100 km) in oceans. The spare segment must have been ready to install and it should have all the installation tools and have been filled by gas.

If a pipe segment failed the spare segment will be carried and will be installed instead of the failed segment.

The spare segments are stored under the water (depth of installation, 100 m) while they connects to the installation balloons (Sea the installation section) so they must be stored in the area which the ocean have a general calm condition Leakage in the pipe It is predicted that SSFP will not have any leakage during in its operating parts but a small leakage or small amount of liquids can make the pipe un stable so we must protect the pipe from them.

Leakage system is explained in mini stations parts.

Vibration Sub sea pipelines must be checked for vortex induced vibration but for SSFP it can be different.

In one hand the currant flow velocity can be variable between 0 and 0.3mIs so the Reynolds number can be change from 0 to 8.5 x iO thus we will have all type of flow patterns (Steady separation, Karman vortex, wide turbulent, narrow turbulent) after the pipe therefore the vortexes' frequency will have a wide range.

In the other hand SSFP has 6 degrees of vibration and it is difficult to find its natural frequency modes and if the pipe depth is changed, its natural frequency modes will be changed too so SSFP has a wide range of natural frequency.

If we want to classified SSFP base on DNV code its LID ratio is more than 250 (it is infinity indeed) so it will behave like cables but the problem is that the distance between fixed point in this cable is to big so its dynamic behaviour is complicated.

From above explanation it is difficult to say the resonance can accrue or not but the point is ihaISSFP-is flexible and it can move freely so when-the pipe bratesthereisno fixed point along the pipe that high stresses concentrate in it thus the pipe will oscillates when a flow passes over it but this vibration does not make a problem in the pipe.

Fatigue Fatigue design and fracture mechanics do not mention in SSFP concrete cylinder design because all stresses are compressible stress in the cylinders however SSFP's cables and bars must design for cyclic loads.

SSFP connection to offshore stations The offshore stations are assumed as fixed point so it is predicted that the pipe need to be more flexible and strength when it wants to connect with stations. So we can increase the pipe mechanical characteristics when it reaches to a station.

SSFP has two end Y branches which connect the pipe to the stations. The Y branches are sited on the stations and are fixed with them so they are not free to move with the pipe therefore they have a flexible part (they are explained in mini stations section) which can bend with a shaip angle to mach the pipe with the station.

Passing over Sea Ridges and Trenches The world oceans' topography shows that in the most marine distances we can find a suitable root with depth of 2000-3000 meters between or around continents for our SSFP.

In special cases we may need to pass seafloor ridges or trenches and we don't like to change the whole pipe level just for passing theses areas so the follow recommendation could be used if the pipe crossing area with ridge or trench has a narrow width.

If we reach a ridges and want to pass over it the pipe internal pressure will became higher than the hydrostatic pressure so the best choice is that use normal steel pipes and laid them on the ridges. The problem is that usual steel pipes have smaller diameter than SSFP so if we want to use them we should have a few connecting pipes. For example we need 4x56" or 8x26" pipes. To avoid using many pipes we can put a compressors at the beginning the connecting pipe to increase its capacity.

If SSFP reaches a deep trench and wants to pass over it, its cables will becomes very long so for this particular short length we can keep the pipe submersible from sea surface with floater spheres. It is the same system as the pipe ballasts but in this case the cables are hanging from floater spheres on sea surface. Due to sea surface condition it can not recommended for a long SSFP.

Life in deep water Life in deep water should be considered completely. Life in depth about 2000 meter is very limited and no big animals live in this depth so the pipe will not heat by the animals directly ----but if animals, plants otbacteria stick to-the-pipe they can-change-the-pipe density and make it unstable however the sea creatures have close density with water so small colony of them around the pipe can be neglect able.

The animals usually have tails in this depth and it means the want to move so they will not stick to the pipe but the Chemosynthetic Communities (plant and bacteria) like mussels and tube worms may be seen on the pipe especially if there is a gas leakage somewhere because they can use Methane as source of energy for living.

It can be predicted that we will sea them in downer section because we have gas leaking in this the area during the operating and maintenance.

SSFP other parts SSFP has some secondary parts such as internal and external Railways, electricity cables, internal pipes which are explained in the other chapters Chapter II GSSTS Components

2-1 Introduction

The Sub Sea Transmission System (GSSTS) is made from different parts with different abilities that are matched together. In chapter one, we introduced the Submersible Suspension Flexible Pipe (SSFP) as a main part of GSSTS but our system needs more components to be able to transfer the gas through the oceans.

In this chapter we describe what the GSSTS's secondary components are and how they function and emphasise on their special ability and their new systems and devices.

GSSTS's components are: Offshore stations, Mini stations, Costal stations and Branch lines which are explained in this chapter in order.

These components may be completely new devices or may be exactly the same as the equipment that we have used before in the industry but generally they are feasible and the methods of design, construction, installation and operation of them are well known in the industry; therefore in this chapter we are not going to explain the details of this issue.

2-2 GSSTS Offshore Stations --Stations are important parts of pipeline systems. They are access ways for operating, getting information and inspection of pipelines, therefore GSSTS like any other pipeline system needs stations to separate the pipe in smailer segments and have a complete control on these segments.

GSSTS stations are similar to onshore stations in their work, but they should be able to function in the middle of oceans and in deep waters. GSSTS stations are also used for the pipe installation so in contrast to onshore pipelines first we need to install the stations to be able to install SSFP's segments.

It is a difficult problem to find what the right distance between GSSTS stations is. It needs a risk analysis and the risk analysis needs experimental data and there is no experiment for GSSTS. Obvious parameters such as maximum load for pipe segment length or economical balance between loss of pipe segment and having more stations are not clear now; therefore we just follow the onshore pipelines standards to choose the distance but we will increase it and choose 100 lan for stations distance.

There is no specific reason for increasing the stations distances. It is just chosen to show it is believed that SSFP will be more reliable than onshore pipes. It is obvious that the stations distance can be reduced due to any specific requirement.

It can be useful if we have the brief following comparison between GSSTS stations and common offshore platforms; although they seem to be similar but they are indeed different.

a. GSSTS stations are much smaller in dimension and weight than offshore platforms.

b. GSSTS stations have a same duty as onshore pipeline stations so their activities are much simpler than offshore platforms. For this reason people are staying in these stations temporally and the station is controlled from the shore in the normal operation.

c. GSSTS stations should submerge to protect themselves from adverse conditions on the surface. In these stations the facilities are not concentrated at the top like offshore platfonns; they are distributed in deep water shallow water and on the sea surface.

GSSTS Offshore Stations are new type of stations but designs, construction, installation etc of them are not new subjects. They are well known issues in offshore (platform), marine (submarine), oil and gas (sphere vessel), dam (hydro mechanical equipment) and other industries. Therefore physical feasibility of GSSTS Offshore Stations can be proven by studying the same evidence in the other industries. Thus in here we try to explain new points and the part's general shape, availability, duty and we are not going to discuss about details of designs, construction, installation etc. GSSTS Offshore Station has four main parts. They are Upper Section, Downer Section, Floated Section and Mooring Systems which are described one by one. Mooring system with some other systems which are not specific to any section are explained together as GSSTS Station Systems Fig 17-Fig 18 SSTS Offshore Station Upper Section ---The offshore station upper sëiion liThe only part which peojléhave access All the installation, operating, maintenance activities are leading from this section.

Upper section is designed as submersible. This feature protects it from the ocean's strong hydrodynamic forces and also helps achieve lighter structure and mooring system for upper section. Upper section must be accessible when it is submersible so it can not submerge so deep for protection and its depth (about 100 meters) should be suitable for diving.

Upper section is able to float on the calm sea surface for accessing, installation or maintenance progress and can be submersible under the water while the pipe is in normal operation.

The station's upper section parts from down to up are: two pontoons, external open workshop, central sphere, helipad and a strong structure which connects these parts together.

They are explained after the following lines. Upper section geometry is pyramidal. Central sphere located at the apex of the pyramid, the main columns are lateral edges and pontoons form the sides of the square base.

Fig 19-Fig 20-Fig 21 Pontoons: Station's pontoons are two cylindrical vessels which are parallel with the pipe because pipe must be able to come up between them for the installation process. The station's submarine system uses them as water tanks. When they are full of water, most of the station's buoyant force will cancel out with their weight and the upper section will be ready to submerge by pulling the mooring cable. In both floating and submersible upper section position filling air in pontoons will increase the station's buoyant force thus the mooring system cable will stretch more and make the upper Section stable.

While upper section is floating, pontoons are submersible to decrease the wave attacked area and have less tremor in station however pontoons can be floating due to any requirements.

Pontoons are also tanks for fuel and chemicals (inhibitors, anti foam, etc). These tanks have a mobile sealed wall (like an engine piston and cylinder) to keep the buoyant force almost constant. While fuel and chemicals are consuming the wall moves and water is filling in the other side of thank without mixing with the consumed liquids and when fuel or chemical tank are charging movable sealed wall goes back and discharges the water in to the sea.

Fig 19-Fig 20-Fig 21 External open workshop: Some GSSTS installation and maintenance process needs a specific area which must be accessible. Upper section has an open external workshop to do these activities. It is a rectangular area between central sphere and pontoons. Workshop floor has structure which is covered by grated plates (using grated plates will decrease wave and currant forces). It has a longitudinal gate which opens for take the equipment in or sends it out. The gate is opened and closed by powerful hydraulic jacks. Overhead cranes can lift or move things any where on the workshop area so the ship which takes station's necessities puts the shipments on work shop and the cranes carry them to the right place. There are strong winches and big wheels for pipe installation. Winches pull the pipe's head (Y branch) and take it over the wheels and in to the workshop.

After finishing the connecting process the floor gate opens and the pipe is sent to the water. Workshop distance to sea surface is adjustable but usually it is close to the water while station is floating.

Fig 19-Fig 20-Fig 21 Structure: Station's upper section main parts are connected by a strong structure. It is a support for external equipment such as, pipes, winches, cranes, hydraulic jacks, lights, cameras, etc to install on it.

The structure columns are a pyramid's lateral edges and they are not vertical. Therefore due to station's weight and the other forces they want to keep distance together. In the pipe direction pontoons fix columns bottom but in pipe perpendicular direction there is no connection between column's ends because it should be open for pipe access. In this direction trusses are designed to increase the colunin straight against lateral displacement.

All structure elements (beams and columns) have circular cross section to drop the oceans wave and currant forces.

Stations structure has ladders, platforms, stairs and hand rails to make the whole upper section accessible safely.

Station's structure holds two lifeboats above pontoons to be used in emergency case.

Fig 19-Fig 20-Fig 21 Helipad: Helicopter can be good vehicle for fast access to station. There is a small helipad above the central sphere. Due to station movements the helipad must have a locking system to keep the Helicopter fixed on its surface.

Central sphere: Central sphere is GSSTS's brain It is a hallow sphere like LPG sphere tanks but it is under the external pressure the same as submarines.

The pipe crew can stay in to do their commissions while it is submerged.

Central sphere must be designed to resist the hydrostatic external pressure in depth about 100 meters properly and safely for this reason it has also an internal structure to increase its strength against external pressure.

It predicts that central sphere has a diameter between JO to 15 meters but due to special requirement its diameter can increases.

Generally inside central sphere can separate to these areas: entrances, control room, engine room, accommodation area and workshop / lab which are explained as follows.

Fig 19-Fig 20-Fig 21 Entrances Central sphere can have two main entrance one on the top and the other at its bottom.

The top one is for human access it is small and can open and close manually, it has two doors and an entrance room at the middle and people can go inside in both wet and dry conditions.

It can be similar to submarine entrances. In normal operation the Offshore Station Upper Section comes up and floats on sea surface (dry condition) then people simply open the first door go to entrance room and open the second door and finally get in to central sphere. In special case which the upper part can not come up (wet condition) a diver will do this instruction: opening the first door, going to the entrance room, closing the first door, gently depressurising the room, sending the water into central sphere, opening the second door and finally going to central sphere.

The bottom entrance is an access to the external work shop and also a way for taking the instruments and facilities in or out central sphere. It is one big flange shape door and can use only in dry conditions. Because The opening and closingof itcouldbe difficultand- takes time, it can has a manhole which is used for human access and passing small instrument.

Control room and controlling system GSSTS Offshore Stations control room is the same as others control rooms in industries it has required area for controlling systems and people who work with them. Main part of electronic devices will be installed in this area and it is possible to control the system from inside or outside (for example from a coastal station) the station. SCADA is a good candidate for the controlling system; it can send the information stations to stations or using satellite to make a controlling network. Detail specification of the controlling system is not mentioned in this report however its availability and duties can be explained as follows.

The controlling system must sense, transfer, receive, record, dispatch, and analyze data, such as outside and inside pressure, flow rate, temperature, elevation, gas composition and then perform suitable commands.

It should be able to find the pipe profile and movement and also mooring system reaction with help of a powerful radar system which sends waves between two stations. This radar system can also report any ship transporting or other activity in the pipe surrounding area and send them a notice that they are in hazardous area.

It must be also responsible with weather, sea surface, under water conditions and also currants velocity, wave impact, pipe's tensile forces, leakage, failure.

The controlling system will order to all GSSTS instrument and equipment so all systems and package, control valves, power generators, pumps, compressors, winches and cranes, internal and external pigs, inside outside lights and cameras, etc will be managed by GSSTS controlling system in central sphere's control room.

Engine room Power Generator, air condition system, nitrogen maker package, water treatment package, parts of flaring system and the other mechanical devices such as pumps, compressors, electro motors, valves, control valves, etc which are used for operation or belong to the other systems will be installed in engine room.

In here we illustrate some above facilities which the most part of them are in the engine room and the others are explained in the other sections.

Power Generator The GSSTS requirement power will be supplied by the station's power generator.

Each station has a generator which can drive by an internal combustion engine or turbine.

The runner must be able to work with both gas and petrol. In installation phase and emergency cases it will use petrol but the gas which comes from the pipe will be the main source of fuel during normal operation.

The generator must supply the station's two mega watts compressor so its capacity should be higher than the compressor.

The generators electricity will be connected and matched together (voltage, frequency etc) by the pipe to provide a unit source of electricity. If one station's generator shuts down, it will be supported by its neighbour stations.

Air conditioning system Central sphere must be well ventilated. Air conditioning system prepares suitable fresh air for personnel in central sphere. It has some pipes which connected to floated section and can take fresh air from sea surface these pipe are flexible pipes which can resist the water external -pressure. It also can send stale air and gases (exhaust gas) from central sphere to the atmosphere by another pipe.

Nitrogen extractor package GSSTS like other oil and gas plant needs nitrogen for purging gas to avoid fire or exploration. Nitrogen extractor package is a small system which prepares required nitrogen in the pipe's installation phase and also for its operating and maintenance.

Water treatment package The water which is pumped from the pipe is polluted and is mixed with hydrocarbons condensate and chemicals (inhibitors etc) so it is not possible to send it to seawater and also inhibitors are expensive therefore main duty of this system is to separate chemicals to renew them and treat the water for sending it to the environment. Its other optional duty can be preparing consumption water for station's crew from seawater.

This system can also help to care properly external facilities such as cranes, winches, lifeboat, etc. In practice it is not possible to separate these parts from the water but if we keep them in seal bag which is full of pure water and anti corrosion chemicals we can save them from sea water destruction (corrosion and sea creations). The bag doesn't need any special mechanical specification because no force will apply on it. Covering bags just needs to be sealed and made from the materials which are resistant in sea water.

Submarine system and Shared Pumps and Compressors In GSSTS operation we submerge or lift up upper section and some other parts by changing the buoyancy force. We call this system, submarine system because it is the same as the way which submarines submerge (filling water in their tanks) or coming up (filling air or vacuuming their tanks). Submarine system haspumps, compressors, valves, etc which are all in engine room. Submarine system tanks are located on the part which wants to move and they are filled from engine room by connection pipes.

The station's systems usually are not working together so due to limitation area in engine room, the predicted pumps or compressors will be used to run different systems at separate times.

Accommodation area All necessities for housing a few people in the station should be considered in this area. The crew commissioning in the stations can be present for long durations in the installation phase and it probably will be shorter in operating arid maintenance periods.

In some cases the station may remain submerged for weeks without any access to surface.

The accommodation area must have enough amenities and supplies to maintain the crew in this period of time.

Workshop and lab There is an area in the central sphere to do overhaul and maintenance activity, store some primary tools and spare parts and also it can include a lab for tools calibration, inspection etc. Overhead cranes will cover all the engine room and workshop area and they are available to move things any where inside central sphere and also send them out or take them in to the station's sphere.

GSSTS Offshore Station Downer Section The pipe physical operation is done by station's downer section indeed. It is the only section which has connection with the pipe so we can run the pipe with downer section equipments and facilities which are able to be controlled from the upper section. A pair of operating facility is considered for this section. When on set is out of order the spare one runs the pipe while the repairing is in progress.

Downer section is located between two SSFP segments and it connects the end Y branches together.

It has three main parts: a casing which is a house in deep water for the other parts to sit and settled in it, a pair of middle cylinders which are short pipes that include the most upper section equipments and two pairs of control able block valves which are located in each middle cylinder both ends.

The pipes' end Y branches sit on the casing how their branches are face to face. A middle cylinder and block valves connect each branch to its opposite branch.

Fig 23-Fig 24-Fig 25 Downer section parts must be able to go up for probable maintenance so they have separable connection joints. These jomts can be the points for leakage therefore the downer section is working and is kept in the depth which the water hydrostatic pressure is exactly the same as the gas pressure.

In practice it is difficult to control the external and internal pressure to be exactly the same therefore we set the gas pressure a little higher because if there is a probable leak we will prefer the gas goes out than the water comes in.

Downer section is designed to have no weight in its normal operating. In the other word its weight is cancel out by its buoyant force.

Downer section will goes up and down the same as pipe due to the changes in the gas pressure but it is resist to move against upward and downward currants to keep itself in a same internal and external pressure so in this case it is a fix point of the pipe. Downer section can moves laterally with the pipe but its flexibility is much less than the pipe therefore we can assume it as a fix point for the pipe horizontal movement too.

Middle Cylinder Downer section has a pair of middle cylinder. They are short length pipes (about 12 meter) with the same diameter as SSFP (lOO"or 2.5 meter). These parts can move between station's upper and downer section easily therefore the most equipments and instruments are insulted on theses part to be easy accessible for checking and repairmen.

Middle cylinder is the main connection point in the system. It fixes the SSFP segments together; it connects SSFP to the shore gas supplying and consuming areas and it is joints upper and downer sections so it is people's only way to accesses the pipe.

In here middle cylinder introduced by describing its main parts which are lines and cables, equipments and Branches Middle cylinder lines and cables Middle cylinder has many lines (feeding, liquid and gas lines) and cables (instrument and power cables) which connect it to control and engine rooms. These lines and cables are flexible and can move with middle cylinder. They join together and make unit flexible rope.

Since we have a pair of middle cylinder we will have a pair of rope too which are located in both sides of the pipe. They can be supported by mooring system's cables. The rope has a U -shape which is hanged frOm its bóTh diiIEóinciiiral sphere and middle cylinder. When middle cylinder is in upper section the U legs have the same length but when it is in downer section the external U leg is much longer than the other.

Fig 18 Feeding line Feeding line is the biggest line (Diameter around 4"-6") between central sphere and middle cylinder. It transfers high pressure gas between these points. Its first duty is to fill a new SSFP segment with gas for installation. In this case one of the middle cylinders is in downer section and is connected to an installed SSFP; the other one is in upper section and is connected to a new SSFP segment. Gas comes to engine room throw the downer middle cylinder's feeding line, is controlled there and then goes to the new pipe throw the upper middle cylinder's feeding line. While a new SSFP segment is filling with gas it sinks and takes the middle cylinder and the feeding line.

In normal operation feeding line sends the gas to engine room for consumption. It also can used to fill the pipe or middle cylinder with nitrogen or air.

Usual flexible pipes are the best suggestion to choose for the feeding line.

Liquid and gas line Theses lines are between central sphere and middle cylinder too. They used to transfer liquids and low pressure gas between theses points. Due to they are also parts of flaring system they are explained in GSSTS station systems section.

Power and instrument cable Power cable prepares all required electricity for running downer section equipments from engines room's generator. This electricity is also distributed between other offshore stations from the middle cylinder and through the SSFP.

Instrument cable transfers all commands and reports between control room and instruments and equipments Middle cylinder equipments Middle cylinder equipments can be categorised as follow.

Gas Compressor The gas pressure drops while it is transferring throw the pipe. If we want a constant pressure along the pipe we need gas compressors to raise the gas pressure.

Middle cylinder's rotary compressor is much simpler than the onshore pipeline's compressors because it just compresses the gas for about few bars (about 40 PSI). This compressor has just one stage and it has not any particular cooling system.

A strong electromotor (2 Mwatts) which gets its power from engine room tems the compressor. Generally we have just one compressor in each station because if it fails the neighbour stations can be covering the pressure drop during the repairmen therefore one middle cylinder is bigger than the other one and has a compressor and the other one is used as a bypass.

Fig 23-Fig 25 High Pressure Pump It is a reciprocating pump with a low flow rate and very high head out put. Actually it is part flaring system. it can use tofihlinor4rain -liquids-from the middle-cylinder or used to spray the inhibitor into the pipe at middle cylinder or to pump it through the inhibitor pipe.

Fig 26 Control Valves and Connections All flow lines are connected to middle cylinder by control valves therefore all the inputs and outputs will be controllable. Middle cylinder with its control valves and connections is able to send out or take in gases (natural gas, nitrogen, air) or liquids (water, condensates, inhibitors) to the other parts (the pipe, upper section, flaring system, etc) and its surrounded environment.

Fig 26 Controlling and electrical devises -Middle cylinder has many sensors and controlling devices. It can sense internal and external pressure, gas flow rate, internal and external temperature, elevation, and also gas composition, out side currants velocity, wave impact, the pipe tensile and lateral forces and leakage.

All downer contactors and controlling switches and devices which are running downer section equipment are installed in middle cylinder.

The power should be distributed from middle cylinders to the whole system so middle cylinders have transformers which raise the voltage to transfer electricity through the pipe with less energy loss.

Pigging Equipments Middle cylinder can introduce SSFP pig (special pig) in to the pipe and also sends common types of pigs into the branch lines.

SSFP pigs are explained in the SSFP operating section.

Middle Cylinder Branches All branches such as consuming, feeding or bypasses are connected to the pipe from middle cylinder. These connections are similar to the connection between the pipe and middle cylinder. It means they have block valves and specific area in the casing to sit.

The branches connections usually are blocked by blind flanges but it is simply possible to take the flange out and install a new branch.

All middle cylinders have an equal tee for bypass connection and some of them due to their location have consuming or feeding connections Casing: Middle cylinders, Y branches and block valves must be settled in a specific place to be able to connect together. It should be notice that It is difficult to send a part in right place form its 2000 meter above.

Downer section's casing is a steel structure which is a hose for all downer parts. It leads them to sit on their right place properly and joint to gather.

It is predicted that the structure has dimensions about 20x 15 x 15 meter.

The casing has four columns which are guides for mooring system's lift (the lift which moves between upper and downer section). These guides trap the lift and lead it to the right place.

The downer equipments are fixed to the lift when they are going down so if the lift be leaded and goes into the right place, the carried equipment will automatically go to the right place.

However the equipment sitting areas have some guides which can lead them to sit in their xact ghfIacë --------Casing can go up or down on central mooring system cables (it is explained later) or can stick to them. As it mentioned before the casing must keep downer section in the depth which has the same internal and external pressure. So it has a moving system to change its depth with the gas pressure changes and also has a breaking system to keep it fix against vertical currents.

It has four sets of moving-breaking systems one in each cable, moving part is run by an electromotor gearbox and the breaking part has an electrical magnet to stick it to the cable.

Moving-breaking systems are able to separate and take up for repairing, for this reason the break is designed to be free in failure mode and the electromotor gearbox can rotate free when it is out of order.

Downer section parts are designed to have total zero weight in normal operating so they can move easily.

Casing almost never comes up to the sea surface but it is possible to do this.

Casing has lights and cameras to give us a view of downer section. They are installed on a frame which is able to carry up.

Fig 23-Fig 24-Fig 25 Control able Block Valves Downer Section has four valves (two in each line) which are located between Y branches and middle cylinders. They are big and must be full bore so the best type of valve which can be chosen for them is gate valve. These valves have not been used in oil and gas industry but we can see them in water industry especially in dams' body or in hydroelectric power stations.

These valves are on-off valves and they rarely be used to control gas flow in the pipe.

Fig 27 These valves are different with the whole other valves because first they are not under the pressure and second their environment has not atmospheric pressure. These important characteristics make them feasible to be used in offshore stations.

Same external and internal pressure makes their body lighter and simpler and also helps them to be seal properly and easily. Their surround pressure let them to have a specific connecting mechanism which can not be used in the other valves. We call this mechanism Magnetic-Vacuum connection.

Due to maintenance requirement, stations valves must be able to connect and disconnect to middle cylinder and Y branches frequently and easily.

Block valves, middle cylinders and Y branches have flanges at their ends for connection.

Flanges have a big circular groove on their surface which sunounded by 0 ring's (large rubbery rings for sealing).

Block valves have powerful electrical magnets which can magnetize their flanges, they also have a suction system (pump, control valves, etc) which is connected to the flange's groove.

When valves and middle cylinders or Y branches sit on their right position their flanges are located face to face. Valve flange will be magnetized and will absorb middle cylinder's or Y branch's flange and will stick to them (there are some guides on flanges to lead them to mach together properly). Then valve's pump sucks and puts out the water which remains in the groove therefore the hydrostatic external pressure pushes the flanges together and make them seal. After that the flange magnetizing will stop till another connecting process.

Fig27-Fig 28 If the vacuuming system fails valves flange will be magnetized temporarily to be keeping the --------flanges in connect while-the maintenance is in progress. ------Sealing 0 rings may need to change after separation so the 0 rings always are installed on the part which wants to come up for repairing. It means between valve and middle cylinder, 0 rings are installed on middle cylinder flange and between valve and Y branches they are sited on valve flange.

Vacuuming system is an elegant system so it is suggested that the valve has a pair of it to save one as a spare.

To separate the flanges, the vacuumed area must be filled with water. It is possible that vacuuming system control valve fails and it can not release the vacuumed area so flanges will be sticking together. There is a sealed needle on the top of valve's flange which is crammed in the hole that connects to flange's groove. The above problem will be solved by pulling this needle out.

Fig 29 A block valve has a hydraulic jack which opens and closes the gate. The valve hydraulic servomotor system include pump, valves, hydraulic connections, electric panel, etc are water resist and installed on the valve but they are controlled from stations control room.

Valves segments specially the ones that touch the seawater (flanges surface, etc) are made from high corrosion resistance stainless steel.

Ef the pipe has some small internal lines for example vacuum absorber and inhibitor injector lines (they are explained in mini stations), the valve must connect them to the middle cylinder. For these reason the valve's gate and casing have some holes which pass the lines through the valve. When the gate is close it also closes these lines and when it is open its holes situate face to face with the casing holes and let the flows pass through the valves how there is no connection between them and the pipe therefore the valve must have a good sealing around these points because the lines are run in different pressure. These line may need to be closed in normal operation so the valves can move the gate to close the lines while it is open (main gas line is open).

Fig 27 Gas leakage from flanges during the connection process can create hydrates. The hydrate crystals on flanges surface make a problem for sealing so the valve has a heating system to remove the probable hydrate around the flanges.

Middle cylinder can have its own valves to protect it from seawater when it goes up or comes down it means there are eight valves in downer Section (four in each line) These valves are the same as station's control able valves but they arc wedded to middle cylinder and they don't have connecting systems and using them is optional.

GSSTS Offshore Station Floated Section Offshore station must get in touch with sea surface and atmosphere so floated section is introduced to cover this necessity. It is a small sphere (diameter around one or two meter) with a little derrick on its top and a little weight at its bottom and the upper section keeps it by a rope.

The weight which is connected to the sphere bottom makes the floated section balance and keeps the derrick vertically on its top.

Floated section is almost always floated and it is designed to resist against stormy conditions however it can submerge for short time in unpredicted conditions (upper section can pull it iinch) Théis iupported ring beside the helipad which floated section can sits on it while upper section is floating.

Floated section has instruments to sense the sea surface and atmospheric conditions and report it to central sphere (a camera can add for viewing) and an alarming light is on its highest point to show the hazardous area.

Since the dispatching (telecom) information is much easier through air than water a transmitter and receiver is installed in flouted section which controlling and information exchange are done by these systems.

Ventilation lines' head and flaring system's tips are located close together in a small area on floated Section therefore they should design how the unlike gases don't come in to the fresh air line.

Fig 22 GSSTS Offshore Station Systems ) There are many systems and mechanisms in GSSTS station. In here some independent station's systems is explained.

Mooring System: GSSTS Offshore Stations are not massive like offshore platforms so they will fluctuate and displace simply due to sea waves and currants. They need strong mooring system to make them stable in oceans. The mooring system has two pats Lateral mooring and central moonn.

Lateral Mooring The station's mooring system is look like a square pyramid. The upper section is on the pyramid's apex. The square base's sides are parallel or perpendicular with the pipe and four weights are sited on its apex. The weighs are connected to the upper section by strong cables.

The cables made the pyramid's lateral edge.

The cables are connected to the bottom of upper section's columns and have the same angle as columns. It helps to reduce bending stresses in the upper section structure.

Lateral mooring system prepares both lateral and vertical stability for upper section. It especially gives lateral stability to the upper section while it is floating and some activity (Pipe installation or repair some equipments on external work shop, landing a helicopter, etc) is doing on it.

Central Mooring There is another weight on the centre of the pyramid's square base which is connected to the upper Section with four cables. These cables are the pyramid's height and made the central mooring.

Central mooring makes the station's downer section stable under the water (as it explained before the case locks to this cable to keep the downer section in suitable depth). It is the connective way between upper and downer sections.

These cables are like rails for a special lift which moves between two sections. When the central mooring system's lift is coming down it can stick to any part of downer section and takes the part up. The lift can move with a Submarine system (the system which is used in -submarinesfor submerging or lifting) or can have a long cable and is pulled by a winch from the upper section or has both of them.

Central mooring system can give vertical stability to the station's upper section.

The following process for upper section submerging is suggested to have simple puling system.

First the upper section submarine system cancels out the most buoyant force. Then the winches pull down the station to the proper depth after that the winches are locked and fmally the submarine system increases the buoyant force therefore the cable will be stretched and the required tensile force for station stability is prepared. It is the same process when the station wants to go up.

Due to above explanation the winches must have strong locking or braking systems however they do not need strong rotary systems for pulling the cable.

The winches can work hydraulically how their driver pump is installed in the engine room.

Due to the station's conditions, total tensile force can be divided between Central and Lateral cables by winches locking system for example when the stations is floating in wavy water the Lateral cables must have greater tensile force and while the lift is moving, central cables should have greater tensile force.

Fig 17-FIg 18 Monitoring System Most activities in GSSTS installation, operating, etc will be done in dark deep water without any human presence so monitoring system will be our eyes to know about what exactly happens in GSSTS.

Cameras and lights are any where in the stations (all of them can be carried to surface for maintenance) and also pigs can have cameras for seeing inside and out side the pipe.

Today technology has introduced us deep water cameras and lights which can work in high pressure deep water however they are expensive devices.

Movable Block Valve Systems Sometimes we need to block the pipe temporarily for example if a control valves in the station downer section is out of order, we must first block the pipe and then take it out.

Movable Block Valve Systems is a machine which can move inside the pipe and be controlled from the control room. It has itself source of energy independent of the pipe. This machine main part includes a compressor and two balloons. When it introduce to the pipe from middle cylinder it moves and passes control valve and inters to Y branch then it inflates the balloon with gas by the compressor and blocks the branch temporarily so the control valve can be released for repairing. If the valve break down how it is close the machine is introduced from the other middle cylinder goes in to the Y branch, turns and comes behind of the damaged valve and blocks the pipe. After the valve is repaired it will release the gas from the balloon and comes up to be used for the same other cases.

Fig 30 Flaring System Almost all the oil and gas plants has a flaring system for safety or burning the useless gases.

In some small onshore gas pipeline stations there is no flaring system and gas blows to the atmosphere directly. But methane is a strong green house gas and sending it to the atmosphere can increase global warningtherefore weprefer to-be able-to -burn all the useless --gas in our GSSTS stations.

GSSTS flaring system are distributed in the whole offshore station. Its upper part (between floated and upper section) includes one set but its lower parts (between upper and downer section) made from a pair of set.

Flaring system downer parts are installed on middle cylinder and move with it.

The flaring system components from down to up are: pair of two phase separators, a pair of high pressure pumps, a pair of downer gas lines, a pair of liquid lines, gas vessel, liquid tank, pilot, upper gas line and tip.

Fig 26 Two Phase Separator It is a vessel beside middle cylinder which all useless liquids and gases go there to separate. It has low internal pressure but it is a high pressure vessel indeed because a high external pressure wants to crumple it. )

The vessel is connected to downer gas line, middle cylinder and leakage system suction line from the top and is connected to the high pressure pump and middle cylinder from the bottom. Pumping system controls the liquid level in the separator.

High pressure pump Gas goes up from the separator due to difference of pressure but the liquid should be pumped to the station's upper sections. Flare's high pressure pump must have 2000 meter outlet head so it will be a special reciprocating pump. Actually it is not a very powerful pump because liquid flow rate is low.

Downer gas Line Downer gas line is a flexible pipe which connects two phase separators (in downer section) and gas vessel (in upper section) together. This line should resist against high external pressure (specially buckling) and also should be flexible to move with middle cylinder.

Today's flexible pipes are suitable for it; however these pipes' layers can be changed for this particular usage (stronger inner carcass, weaker cross wound tensile armours and no zeta interlocked spiral).

This line is an exception in flaring line design because it has valves (check, control valves) at its both ends. If the line fails, check valve and control valve will close to protect the vessels from sea water.

Liquid line Liquid lines connects high pressure pump (in downer section) to the liquid tank (in upper section). It must be flexible but does not need a strong structure because in this pipe internal and external pressures are in equilibrium.

Liquid hose is a good suggestion for the liquid line.

Gas vessel The Gas which comes from two phase separators passes through downer gas line and reaches gas vessel in engine room. In this vessel useless gas (exhaust gas) are added, any probable liquid separates and then the whole gas is sent to the burner. ----Liquid tank The pumped liquid gathers in engine room's liquid tank. The probable gas send to gas vessel and liquid send to water treatment package. Pilot

Flaring system's pilot is in engine room. Due to sea surface variable conditions it sends fire to flare tip thought a pipe from engine room.

Upper gas line Upper gas line takes a place between gas vessel and flare tip. It is a flexible pipe like downer gas line and it has two valves at its both ends but the difference is that its diameter is bigger than downer line (due to gas flow rate and velocity) and its external pressure is much lower than downer line. Tip

Flare tip is installed on floated section. It has a special design to be able to work on sea surface.

2-3 Mini Stations It is hard to name these parts "station" but in some cases they are look like stations so we call them "Mini Stations" in here.

Mini stations are tube shape steel parts which separate a pipe segment to shorter parts (primary segment). Their interval distances are about 5000 meter (to find the reason see Mini station's Installation Usage) and the most parts of them are not accessible.

Generally using mini stations increases the pipe reliability because they can be useful for running the pipe in the following subjects.

* They can give us better information about the pipe.

* They can help us to control the pipe leakage if it is necessary.

* They can help us to have predicted pipe failure if it is required.

* They are used for the pipe installation * They are used for the pipe operation and safety Mini stations have a specific system or mechanism for any of above usages. Theses mechanisms are not related together so theyare explained one by one in here.

Fig 31 Mini Station Instruments Mini station's instruments are a package in a seal box which slicks to it. These parts can be very helpful however using them is optional.

Mini station's internal and external areas have different type of instrument packages which --- -___reQQmpletelyseparate._----------The packages are able to work in high pressure. They send the information wireless by radio waves throw the gas and seawater or electrical waves (codes) throw the pipe's bars.

Instrument packages are moved and installed by internal and external pigs the pigs catch them by their electrical magnets.

Instrument packages can connect to the pipe's high voltage circle and prepare their consuming power. They also have their own battery as temporary source of energy.

The external package has spherical shape. It can measure external (seawater) pressure, temperature and also speed of currants around the pipe. It can send signals to the control rooms to clarify its exact situation in the ocean. External package is trapped in its casing which connects to the top of the station. It is lighter than water so if it is detached the pipe or pig, it will comes to sea surface and can be caught there. -The internal package has an area in the bottom of the station to sit there how it does not make any outgrowth in the pipe. It can measure internal (gas) pressure and temperature. It also can include the transformer which prepares low voltage currant for cables cathodic protection from pipe's high voltage circle (if sacrificing anodes are not used) and a mechanism to close inhibitor injection valves if the pipe has a leakage system (see leakage system).

Mini Station Leakage System Generally no water leakage predicted in SSFP because in normal operation the internal gas pressure is a little higher than external water pressure so we don't need a system to control the leakage but in a special case if there is a leak in the pipe it will be a disaster because it will make the pipe unbalance and can be a cause of failure.

Water in the pipe condition (pressure and temperature) will be crystallize and change to hydrates. It can be good and also bad news. It is good because if we have a small leakage, the water hydration may block the leak stream and stops the leakage. But it is bad because, if there is a middle range leakage in the pipe water comes into the pipe and crystallizes and will block the pipe. The pipe mass will increase in the leak point so the pipe sinks and it can be a reason for the pipe failure.

We need practical tests to find what the hydrate behaviour in the pipe is in different rate of leakage. If water hydrates concentrate in a small area and block the pipe and also stop the leaking we may prefer to repair it (not easy job) but if it distributed to the pipe and continue to pipe failure then we should think about having a leakage system.

Due to above explanation the leakage system is an optional system but we introduce it here to show in a pesstmistic point of view if we have a leakage there is a solution for it.

Mini station leakage system has two systems first is vacuum absorber and second is inhibitor injector. These parts have lines which are laid in a specific small trench at the pipe bottom.

We call theses lines "SSFP internal lines". The lines pressure is different to internal (gas) pipe pressure so they are pressurised lines. These line are continuing through the pipe till connect to the offshore station (controllable block valves and flaring system). Due to the lines have small diameters (1"-2") they do not need any flexible joint and their flexibility is enough to deform easily with SSFP.

The lines have a Tee before SSFP's end Y branches which make them two lines To go inside the both branches and connect to the both controllable block valves.

There are special check valves on the lines before they connect to the controllable block valves. Check valves will close the internal lines if controllable block valve is sent to the --- -upper section-for-repairmen. -The point abourthesespecial checkvalves is that they are not accessible and can never be repaired so it is better we have two valves for each junction to be more confidant.

If we want to use leakage system, our SSFP must have slope to be able to gather the liquid (can be gas condensate or water) in the mini stations so the pipe's cables should be arranged how the mini stations become the lowest points. If we arrange the mooring system how the difference height between the SSFP highest points and mini stations is about 25 meters, the pipe slop will be about %1 and it can be enough for liquid movement at bottom of the pipe but the point is that the highest point is not at the middle of two mini stations. It is closer to the station which the gas comes through it because the gas flow can helps the liquids to move at the bottom of the pipe.

If SSFP does not have an internal cover to make its surface smooth we can cover just the bottom of pipe to help the liquids movement.

Fig35 -Vacuum Absorber System ) Vacuum absorber's line is connected to flaring system so it is low pressure line. The vacuum absorber has a simple suction mechanism. It has a pit at the mini station bottom and there is a floater which can control a small suction valve. If some liquids gather in the pit the floater comes up and opens the valve so the low pressure line is sucking the liquids and sends them to flaring system till the floater falls and closes the valve.

It is predict that the suction valves will have a small amount of gas leaking so we always have a gas flow between these valves and flare tips which is burned in sea surface.

Inhibitor Injector System Inhibitor injector's line carries inhibitor inside the whole pipe. Inhibitor is pumped from offshore stations through this line so it has a higher pressure than SSFP internal pressure.

If the inhibitor which is sprayed to the gas from the offshore stations (middle cylinder) can not prevent the leakage hydration we can use this system to send inhibitor and spry it to the gas from a closer area to the leakage point for better prevention. Inhibitor internal line also can connect offshore stations inhibitor tanks and make a bigger source of inhibitor.

The inhibitor injector system sprays inhibitors in mini stations. The spray nuzzle has a valve which normally is open but it can be closed by internal instrument package.

If we have a leakage, the pipe will deforms at that point so we can find the leakage by considering on the pipe profile. In this case all the nuzzles' valves are closed by the instrument packages except the one which is near to the leak point then inhibitor is pumped from offshore stations and it is sprayed to the gas.

Leakage system can reduce the risk of using GSSTS and also can gather the gas condensate therefore it is suggested to use specially in first experiment.

Mini Station Failure System Mini station failure system is used to release the damaged part of SSFP and protect the other parts from failure.

As it mentioned before due to SSFP flexibility all conditions of failures will terminate to increase the tensile force in the pipe. We now that if an unpredicted lateral force applies to the pipe for example due to a sheep anchor, the pipes tensile force will grow till the pipe goes to pieces.

If there is a big leakage in the pipe or if the pipe rupture, water will comes into the pipe and -will make it heaver and heaver so inihis conditidli lsô the tensile force will increase. As a reason of above description we need a system which reactions with increase in the pipe tensile force.

The failure system is the mini station body indeed. Its parts are: two block valves, two lateral pipes, one middle ring, and one weigh ring. The middle ring is welded between the two block valves. The ring weigh is inside the middle ring and it is trapped between the valves. The two lateral pipes are welded to the valves and connect the system to SSFP.

Fig 31 Block valve is a gate valve with a simple structure. It has a gate which can slide in its casing and a compressible spring always bushes the gate to be closed. There are no control devices in this valve.

Fig 33 The SSFP's internal lines (vacuum and inhibitor) must pass through theses valve so if they are steel lines they should change to polyethylene (brittle polymers) lines where they pass the block valves. When the valve's gate is closing it breaks the polyethylene lines and while it blocks the main line it closes the internal lines too.

Fig 34 The valves casings are located at the bottom of mini stations body to keep it in balance.

Lateral pipes has two section, one is flexible part which is connected to SSFP and has a same wet weight per length as SSFP and the other is rigid part which is welded to the valves and it is lighter than SSFP so its buoyant force is much bigger than its weight.

Middle ring is the failure system's sensitive part. It has a specific failure area (a groove with a sealing cover) which its resistant due to tensile force is less than SSFP so if the pipe wants to be torn it will goes to pieces from this area.

Weight ring is a heavy ring which its weight is chosen to cancel out the buoyant force of the two lateral pipes (rigid part) so when all failure system's parts are jointed to gather the whole system wet weight per length will be the same as SSFP. Weight ring sits free inside the middle ring without any connection.

Weight ring has pins which comes out from the middle ring and sit on the top of valves' gates and lock them and don't let them close. There are compressible springs between the weight ring and the valves. These springs are always pushing the valves to separate from the weight ring.

Fig 32 We explain about the parts but how the system works.

If the pipe tensile force increases then the middle ring will fail sooner than the other parts.

When the middle ring is torn its sealing cover keep the joint seal for a short time. In this time the springs push the weigh ring to separate from the valves so the pins come out and make the gates free to close. Thus the valves close before the water comes in to the pipe.

After it the pipe will goes to pieces and the weight ring will release and sink to the sea. When it happens, the pipe pieces ends will go up because the rigid lateral pipe is lighter than the water.

Mini station block valves may never close in whole SSFP life so they should be simple and cheap and also they are never checked or repair during the operating therefore we can predict leakage when they are closed.

--The above system take..These valves in the level which the water pressure is lower than the ---gas pressure so if there is a leak in the valve it will be gas that is leaking out not water is coming in.

Fig 32 Mini station failure system will increase the pipe reliability so by using them we can decrease the number of offshore station however using them can be an optional issue due to our future experiment of using GSSTS.

Mini Station's Installation Usage SSFP will be transferred by carrier ships from its costal mill to the installation point. The ships pull the pipe with long strong cables which are connected to mini stations so SSFP is pulled from its mini stations indeed. Due to the pulling force the pipe is bended after the pulling points so mini stations must be more flexible than the other parts of the SSFP and bend in theses points properly.

Fig 35 Mini station's lateral pipes have flexible parts which makes the mini station more flexible than the pipe. These parts are made from many flexible joints and short steel rings, these flexible joints are exactly the same as SSFP's flexible.

The mini station has three mooring cable one for the middle rigid part and two for the lateral flexible parts. These mooring cables keep the station parallel with the pipe in normal operating.

Mini Station's Operating and Safety Usage Mini stations have safety valves. If the pipe internal (gas) pressure increase how it makes tensile stress in concrete cylinder, safety valves will be open and release the gas to the water to protect the pipe from rupture but this can never happens in the pipe's life and these valves are not accessible and also can be leakage sources so use of them can be optional.

However as it mentioned before in operating phase if we need to take the pipe to the sea surface (for maintenance, etc), we will need these safety valves to release the internal air or gas and protect the pipe from probable rupture while it goes up.

2-4 Branches and Costal Stations GSSTS is a link between onshore gas industries indeed. Therefore it must have branch lines to transfer gas between SSFP and the cost and also should have costal stations to connect it Some of these stations and branches are used to send the gas from the pipe to the shore for consumption and some of them are used to feed the pipe from gas sources so in here we separate them in consuming and feeding groups.

GSSTS's sections are completely well known subjects in the oil and gas industry. They are important sections and request a high rang of technology but there is no specific new point of using (design, construction, operation, etc) them so in here we describe them briefly and don't go to clarify any details of these sections.

Feeding Costa1 Stations ---Feeding station is a compressor station which takes the gas from the producer's pipeline or network (the gas resource) and then pressurises it about 250-300 bars and sends it through the feeding line.

In feeding stations the gas hydrostatic pressure is positive (SSFP is lower than feeding stations) and it will helps for gas transferring from stations to the pipe.

For example if we assume the gas density has an average value of 100 kg/ m3 in depth of 2000 meters the positive gas hydrostatic pressure will be = 1cgh -tP = 100 x 9.8 x 2000=1.96Mpa +2Obar Feeding stations are able to cool the pressurised gas below the seawater temperature (2 C ) and separate the gas condensate to send dry pure gas to the pipe.

Feeding stations can have the same facelifts which are used in the usual onshore gas compressor stations.

Consuming Costal Stations Consuming stations are look like onshore valve stations. They take gas form the pipe and give it to the consumer's pipelines or networks.

They break the gas pressure to the demanded consuming pressure.

The pressure drop in branch line and also the negative gas hydrostatic pressure about -20 bars (consuming stations are higher than SSFP) will decrease the gas pressure but if still there is a big difference between the station gas input and out put pressure we can have a turbo expander there to use the released pressure energy.

Consuming stations have valves system, metering system and pig receiver.

Feeding and Consuming Branch lines Feeding and consuming lines' are steel offshore lines which are buried or sited on the seafloor. They length is depends on the distance between the costal station and deep water (width of continent plateau). They can lay on seafloor for about 200-300 km but the pipe and costal stations situation are chosen how to make theses lines as short as possible. These pipes are pig able. They are laying on seafloor from the costal station to a fixed anchoring point which is sited beside the offshore station. In the fixed anchoring point the lines are connected to the risers to reach the station.

Fig 38 There is no valve or valve station suggested for feeding and consuming lines between offshore stations and costal stations.

SSFP has a big capacity of gas transferring therefore we need a large diameter feeding pipes (30"-48") to be able to reach the proper gas flow rates in our feeding lines.

These lines are under a high external pressure in deep water and have a high internal pressure in sallow water so they should have thick wall and also external stiffener rings to be prevented from buckling in deep water.

Due to installation problems it can be suggested to use a few smaller feeding lines instead of a big one for example four 24" lines instead of one 48" line.

Consuming lines are much smaller than feeding lines (8"-20") and do not have above problems. We try to run the gas in consuming lines with maximum possible velocity (less than the erosion velocity) to have a better flow rate with a smaller pipe.

Feeding and _onsunziing Branch Risers --.----Risers are flexible pipes which are taking a place between the station's middle cylinder and the berried offshore lines (fixed anchorage point).

Offshore stations should be located in the area which seafloor is not much deeper than SSFP operating depth to decrease the riser length as much as possible. For example if our SSFP works between 2000 and 2500 meter depth, the seafloor which has depth of about 2700 meter can be a good area for the offshore stations.

The riser is designed to have no weight in the average operating gas pressure but it can be lighter or heavier than water due to changes in the gas pressure.

The riser can have a hanger which keeps its waist (middle) at the pipe average working depth (for above example it is 2250m). The hanger includes a weight which is sitting on the seafloor and a submersible balloon they are connected together by a cable. The riser is hanged from the cable below the balloon. Using the hanger is optional but it can provide a better curve for the riser submersible part and also it dose not let the riser to sit in the sea floor.

Usual flexible pipes can be the best choice for using as the risers.

Fig 38 Riser is connected to the station how SSFP is connected. It has a Y branch at its hcad with block valves which are sitting on offshore station's downer section. There are joining segments (lines) which sit under the middle cylinder and connect them to the branch block valves.

The branch equipment in the stations (Y branch, block valves, joining lines) have bigger diameter than the risers to be able to be controlled from the station and their size is fixed and does not depend on the branch line size.

Fig 37 Chapter III SSFP Installation, Construction and Operation

introduction

In first chapter we always supposed that we have our SSFP ready at the middle of oceans in deep water and tried to explain how it can work or how it is stable in the water.

But having something some where is not enough to prove the feasibility of that thing we must prove how we can make it and how we can put it in the right place.

If we have a similar experiment of making or installing of something (like GSSTS secondary component) we can refer those methods for our new system and suppose that the system is ready and it is in the right place.

But we have not had any similar mechanism like SSFP in industiy so we must explain how we can construct SSFP and also how we can install it in its right place to show and prove that SSFP is feasible.

SSFP operating in general can be look like the other pipelines operating but since it is under the water its operating has some specific issues which must be clarify.

In this chapter first we illustrate the specific methods of SSFP installation and then we are going to explain what we suggest for constructing of SSFP and finally we describe some new issues in SSFP operation.

-1SSfJnsta11ation SSFP installation means all process which must be done that a SSFP segment which is ready in costa! mill is settled in deep water between two offshore stations.

We separate the installation processes in two phases.

First phase is transportation phase. In this phase a pipe segment is taken from the costal mill and fixed between two offshore stations.

The second phase is submerging phase, in this phase the fixed segment is submerged into deep water to reach the proper depth and settled under the water.

SSFP density is less than the seawater density while it has atinosphenc air so it will floats on the water therefore we need specific tools to submerge it during both transportation and submerging phase. These tools are added to the pipe in the factory (construction phase). They are big in quantity (about 8300 Sets for one segment installation), weight (each set is about 12000kg) and length ( each set has about 2000 meter length) but they are renewable so after that one segment is installed they collect from the water and send back to the factory to be fixed on another pipe segment. )

An installation tool set include a pair of chain weights (similar to chain ballast), a saddle bag, a floating balloon (predicted diameter is about 3 meters), and a cable which connects the chains and balloon. Each concrete cylinder has a set of installation tools.

Chains are gathered into a big saddle bag which is sited on the back of the pipe.

Installation balloons are connected to gather with a strong cable and can be pulled by a carrier ship on sea surface.

The balloon buoyant force is bigger than the chains wet weight so if the tool is released in the sea its balloon floats and its chains sink and hang from it like a tail.

Fig 39-Fig 40-Fig 41 Transportation Phase This phase starts from the point which SSFP segment has been delivered from its costal mill to shallow water. SSFP is submersible and carrier ships are ready to pull it.

SSFP must be carried under the water (depth of about 100 meter) to be protected from surface waves.

SSFP depth is fixed by installation tool's cable. When the cable is stretched completely the balloons keep the pipe submerging in the cables length so the pipe can be kept submersible temporarily while it is transported.

The cable is jointed to the pipe by a ribbon which is wrapped around the pipe. This ribbon can be cut in other installation phase to separate the cable from the pipe and release the installation chains.

Fig 43 SSFP is pulled from mini stations. These points are more flexible and have higher tensile strength than the pipe. A 100 km SSFP segment can has 19 mini stations with 5km (primary segment length) interval distance.

Carrier ships (20 ships for above example) are not moving back to back. They move in two close parallel lines this make the pipe to a slight zigzag shape and this shape helps that the ship not to collide the balloons and also helps to mach the ship's speed.

Carrier ships go forward (300-500 meter) than the mini stations that they pull. The distance between ship and mini station makes the cable more horizontal so it reduces the upward force which cable applies to the pipe and also drops the cable tensile force. For example if the pipe -----is pulled in depth of 100 meters and ships are300 nitërs iiiforward andthe required puling force for a 5000 meter primary segment is 400 KN then the cable tensile force will be 420 KN and the pipe upward force will be 130 KN.

The installation tools that are added to mini stations have one more weight which cancels out the cable upward force. The added weight is a little heavier than the upward force (for above example can be 14 tons) and sits on the mini station. Mini station's installation tools have a stronger cables and bigger balloons (4 meters diameter) to be able to cancel out the wet weight of both chain weight and added weight.

Balloons are connected together by strong cables and are pulled by the same ship which is pulling the pipe so balloons always are at the top the segment which they are support. The drag force of pulling balloons on sea surface will be much grater than the pipe drag force so we should use very strong cables between the balloons to carry them but the distribution of forces are definite in these cables and the cables tensile force decreases as we goes along the segment so we can use weaker cables to connect farther and last balloons.

Fig 39 We will try to do transportation phase in a calm sea conditions but the pipe may need to be carried more than thousands miles and it can takes more than a month therefore we must predict stormy condition during the pipe transportation. The pipe can be safe under the water but the stability of balloons and their cables must be mentioned due to oceans wavy condition.

Submerging Phase In this phase SSFP have been carried by ships and it is between two offshore stations. The offshore stations pull the segment's ends (Y branches) and take them in to the station to connect the segment with the system. For doing this the pipe Y branches are taken to the sea surface and then are bulled by the stations winches. When the Y branch is coming close to the station it sits on the stations big wheels and is slid and pulled into the work shop.

In the workshop the Y branch is opened (it was blocked for carrying) and it is connected to block valves and middle cylinders.

When the connections become complete two pigs with a batch of nitrogen at the middle pass through the pipe and send the air out and fill the pipe with gas.

Afler the pipe segment is fully filled by gas the work shop floor gate will open and send the pipe in to the water and the pipe settle between two stations while it is submersible in sallow (100 meter) water.

In the factory, SSFP's ballasts (fixed, chain and buoyant) and cables are gathered and put in order in a box which is fixed at the bottom of the pipe (ballast package). In practice it is not possible to carry the pipe while its ballasts are hanging from it. The box is the fixed ballast indeed which find box shape to contain the other parts.

Fig 40, Fig 41 The ballasts packages are fixed to the pipe by wide thin ribbons which are wrapped around the pipe.

The ribbon is made from longitudinal polymeric fibbers. It has high strength against tensile force but it is week against shear forces so it can be cut easily (the ribbon behaves like a piece of paper) and A thin sharp cable is laid between the pipe and the ribbon along the pipe segment After the pipe settle between two stations the sharp cable is pulled by speedboat.

The cable cuts the ribbons while it is being pulled by the boat and releases the ballasts. The boat can do it in a few minutes so the pipe movement due to ballast releasing will be -- -coordinated. --We can have two sharp cables which are pulled by two speedboats in the same time from each of two offshore stations. It can reduce the releasing time and also increase the method's certainty.

Other ways can be suggested for ballast releasing but the above method is simple and it seams practical.

When the ballasts are released they are sinking into the water. While they are sinking the pipe loose some weight and it will comes up and floats on sea surface for a short time and it is the last time that we can see it. The ballasts sink very soon and hang completely from the pipe segment so the pipe reaches to its previous weight again and it is submerging to the water till it reaches the former depth (100 meters).

The pipe settles in shallow water again while its ballasts are hanging from it and they are not sitting on the seafloor.

Fig 44 After the above section we release the installation tool's cables from the pipe exactly with the same method that we released the ballasts. When the cables are released the pipe sinks because it is heaverthan water but while it is sinking the installation tool's chains come out from the saddle bags and decrease the pipe weight so the pipe is submerging till its weight (density) becomes the same as seawater. Thus the pipe will settle in shallow water one more time but this time a little dipper (for example in depth of 150 meters).

Fig 45 Now the pipe is ready to be filled by gas but we need a big source of gas for feeding so the installation should start from feeding costal station. while we goes further we can feed the new segments from the pipe section which has been installed. It is possible to use a LNG tanker as a source of gas for feeding the pipe during the installation but it can be difficult process.

In feeding stage one of the middle cylinders is connecting to the feeding branch or installed pipe and sends the gas thought the feeding lines (One of offshore station lines) to the other middle cylinder which is connecting to the new pipe segment. While the new segment is being filled by gas its weight (density) increase and it is sinking into the water at the same time the installation tool's chains are going out from the saddle bags and decrease the pipe weight (density). Therefore the pipe always is in equilibrium (has a same density as seawater) and submerges gently to deeper water. The chains wet weight per length is a function of gas density and they always keep the Segment in low difference of external and internal pressure while it is submerging. The chain weight details are exactly the same as chain ballast so we are not going explain it again.

Fig 45 The pipe submerging will have four stages. They are as follow First: pipe installation submerging This happens from the shallow water till the depth which is installation tool's release the pipe. It means in this stage the chains are with the pipe during the submerging so the difference of external and internal pressure low and constant.

Second: pipe free sinking ---Free sinking will happen between the depth which the chains-release the pipe and the lepth which the fixed ballast sits to the seafloor. After the chain goes out completely there will be nothing to cancel out the increase in pipe weight due to gas filling so the segment sinks till its fixed ballasts sit on the sea floor and drop the pipe weight. In this stage the pipe external pressure is increasing while the internal pressure is almost constant.

Third: pipe's fixed ballast sitting When the pipe fixed ballasts sit on the seafloor the pipe weight (density) will reduce rapidly so the pipe will stay at this level while we are filling the pipe with gas. In this stage the pipe internal pressure is increasing while the external pressure is constant.

Fourth: the pipe normal submerging After the fixed ballast weight cancel out by the added gas weight the pipe will submerge in its normal mood. In this stage the pipe chain ballast is sitting on the seafloor while there is no difference between external and internal pressure.

When the new pipe segment reaches to the proper depth its both Y branches are trapped in the station's downer section and sit on their specific area then the block valves and middle cylinder are matched between new segment and the installed pipe and connect them together.

3-2 SSFP Construction SSFP can have a very long length (8000km) but it will be constructed and installed in a shorter segments. The SSFP segments has the same length as offshore stations interval distances (It can be variable but we chose it 100 km in here).

Our pipe will made in two phase first is manufacturing the pipe elements like concrete cylinder, flexible joint, ballast, etc and second is constructing the pipe with connecting this elements together. The manufacturing phase is a big challenge (for 8000 km pipe we need about 640'OOO sets of concrete cylinder, flexible joint, ballast, etc) but it is not a new issue.

The pipe's elements manufacturing technologies are well know subjects in the industry so we do not explain further detail's of this phase in here. But if we suppose that we have the pipe's all elements entire and ready in our warehouse, then we should explain that how we can construct a long (100km) pipe segment from them.

We can not send the pipe to the sea while we are constructing it. Because constructing a 100 km pipe will take time so the constructed part shall remain in the costal water for a long time and it will derange the area's shipping and transportations and also it is possible that the pipe will be damaged by costal waves or shipping activities (anchor, etc). Therefore we need to construct a complete segment in the factory to be able to send it out in a short time for installation.

The SSFP mill will be a huge factory. It may not be the largest mill but the mill which is suggested here will be definitely the longest mill in the world.

For explaining SSFP constructing first we specify SSFP mill and its parts and then we illustrate the construction process in the mill.

The SSFP mill is a costal factory which is look like a big train station that has two exiting way from its ends one to the sea and one to shore and many platforms but Instead of the train grooves between platforms it has longer dipper and wider cannels which can be filled, and -emptied with water. -SSFP mill sections from sea to shore direction are: offshore sending platform, sending cannel, leading lake, constructing cannels, test leading lake, and testing pipe. They are described as follow Fig 46 All the mill dimensions that we specified here are just for examples and can be variable.

The other type of constructing methods can be suggested instead of this method but it can be a good option too and the other things is that the aim of introducing this method is to prove SSFP constructing feasibility not to find the exact method for constructing it.

Offshore Sending Platform Offshore platform is a fixed platform which is installed in the sea how it is in elongation of the mill. The sea depth should be suitable for the pipe submerging (depth around 150 meters).

It is a double deck platform The platform has a sending machine to send the pipe into the sea.

Sending machine is the machine which can move the pipe between cannels which have different elevation or can pass it to the sea from offshore platform while the installation tools and balloons are fixed to it.

The machine is made from lots of wheels which the pipe can slide on them gently. The wheels longitudinally create a curve which the pipe can bend and matches to it when it passes on the machine.

The machine has two decks the lower one for passing the pipe and the upper for passing the installation balloons.

Fig 47-Fig 48 The platform distance to the shore must not be more than the pipe primary segment length because the pipe may fail due to the tensile force. In the case that the required sea depth (150 meter) area is far from than this length we need more than one platform.

The platform obviously has all facilities that people needs to work on it that they are secondary issues and we don't explain them in here.

Sending Cannel Sending cannel is the cannel which connects the mill to the sea. Its length depends on where we can find a proper area to construct the mill and how far that area is from the sea so it is completely variable. En one area it can be 500 meter and in the other area it may reach to 10000 meters. The cannel has a trapezoid cross section which its minimum width is bigger than the pipe or the installation balloons diameter (about 5 meters) and its depth is deeper than sum of the pipe diameter, balloon diameter and the mini station valves length (about 18 meters). Its downstream part which connects to the sea is dipper than the other parts because the tide height should add to its depth. For example if the tide height is 10 meters then the downstream cannel required depth will be 28 meters.

Sending cannel usually is empty and it just is full when a SSFP segment is complete and should be transferred. It has a connection to the mill pump station which can make the cannel full or empty of water.

The area that we choose for the mill may have higher level than seawater level for example meters above the sea level. We can not dig the sending cannel that much (50 meters) therefore we must made the cannel like a stairs. It means we separate the cannel to the shorter sections how the sections have different levels but each section has constant level. ---- ---Sending cannel has some-sending machines alorigit they are the same as the platform's sending machine. They pull out the pipe from the cannel (out of the water) on their rails and send it to the other cannel section.

The required tensile force to pull the pipe in cannels is higher than the pulling force on the sea so the sending machines interval distances are shorter than the pipe primary segment (it can be about 1000 meters).

If we have a short sending cannel with no change in its level it will have a minimum of two sending machines at the cannels both ends but if the cannel is separated to different section due to the levelling change or maximum allowable pulling length (1000 meters) the cannel should have more than two sending machines.

First Leading Lake First leading lake is an area with almost triangle shape how the constructing cannels are connected to its base and the sending cannel is connected to its apex.

The lake depth is deeper than sum of the pipe diameter and balloon diameter and ballast package height (about 15 meters) so the pipe can passes the lake while its balloons and blasts are installed on it.

The lake has a connection to the mill pump station which can make it full or empty but it is usually empty.

Constructing Cannels Constructing Cannels are the largest section of the mill and the construction activists is done in this area.

In here we suggest that the cannels have the same length as SSFP primary segments therefore we will have 20 caimels with a length of 5000 meters which can store a 100 km segment of SSFP completely.

Constructing cannels generally have the same width (5 meters) and depth (15 meters) as sending cannel but they have a rectangular cross section and they have some supports that concrete cylinders and installation tools balloons and the ballast package can sit on them safely after they are connected to gather.

A constructing cannel has some gantry cranes which can move along it.

The cannels have a railway at their bottom so wagons can carry the pipe elements from the warehouses or factories to theses cannels.

The mill has a programmed and automatic transportation system. This system has electrical wagons which controlled automatically and they are moving between the cannels and warehouses and factories and prepare the cannels procurements.

Constructing cannels have gates at their both ends and they have connection with the mill pump station so the can be full or empty of water independently of their both ends lakes conditions. Close to the cannels gates there is a strong support and a winch which can pull the pipe.

Second Leading Lake Second leading lake is located between constructing cannels and testing pipe. It is exactly the same as the first leading lake but it is shallower (depth of about 4 meters). Second leading lake has a railways network at its bottom which connects the constructing cannels' railways to the other factories and warehouses so It is usually dry.

Second leading lake must be full and emptied very fast because while it is full of water its railways network is not working. For this reason it is connected to the first leading lake by a line pipe and can be filed from or drained to the first lake from this way. -----Testing Pipe Testing pipe is a long pipe (500-1000 meters) with a large diameter (about 4 meters) that located at the end of the mill. Testing pipe has a same level with the second lake and its internal diameter is bigger than the SSFP so the pipe can goes inside the test pipe. Test pipe can be pressurised with water to apply an external pressure on the pipe.

The mill has winches which can pull the pipe segments between different sections.

SSFP Constructing Process This phase starts in constructing cannels. The wagons take the pipe elements (concrete cylinders and the flexible joints, etc) to the cannels and gantry cranes lift them and put the segments on their supports and people joint them together. Since we have 20 cannels we have construction line and it helps to raise the construction speed and save the time.

When the pipe length reach to the test pipe length for example 1000 meter, two special steel joints are fixed on the piece of pipe both ends.

These joints are short steel pipes which have an end cap (like concrete cylinder's end cap) on their one side so a flexible joint can be installed on them as usual.

All mechanical characteristics of these short steel pipes are stronger than SSFP.

After the especial joints are installed to caps (the caps have manhole on them) are welded to the short pipes and make the pipe seal. Now the pipe is ready for test so the constructing cannel and the second lake are filled with water. The pipe is floating because it is lighter than the water. The cannel's gate is opened and the piece of pipe is pulled by a winch to pass through the lake and go inside the test pipe.

The test pipe cap is closed and the lake is drained. The test pipe is filled by water completely and pressunsed so the piece of pipe can be tested under the suitable external pressure. After the test the lake and cannel are filled with water and the piece of pipe re pulled to its cannel.

Above procedure continues till a SSFP primary segment is completed in a constructing cannel so we will have five 1000 meters piece of pipe ready which is laid back to back on a cannel.

We cut out the ends cap from the piece of pipes and instead of them we weld a short pipe to connect the pieces together. Since the welded joints are completely seal and also the short pipes has a higher mechanical property we don't need an external pressure test for these parts. The first and the last cap will remain on the pipe to keep the primary segment seal.

After the above step the primary segment must pass a tensile test so the constructing cannel will fill with the water and the pipe segment is floating and then it is pulled from its both ends by a strong winch. With this test all the bars and joints are tested to have a required tensile strength. After the test the cannel is drained and the pipe is sitting on its supports The pipe tests are finished and the pipe added parts (ballasts package, installation package and balloons) must be installed on it now.

The added parts have been taken to the constructing cannels by wagons while the piece of pipe was going to the pipe test. Ballast package are on the cannel's floor and installation saddlebag and balloons are on the canne'sj&&platforms. ----- -intliis phase ballasts package are fixed to the pipe bottom with ribbons and the saddle bags is sited on the pipe pack. After that the balloons bottom are jointed to the top of the pipe by a pin type junction while the balloons cables are coiled around free spools and finally the cables are fixed to the pipe by ribbons.

After the adding parts are completely installed on all 20 pipe primary segments then the pipe can be ready to be sent out the mill. It predicted that this step takes about few days so we can waiting for a suitable weather condition and send our pipe in a calm sea.

For sending the pipe all constructing cannels, first leading lake and sending cannels are filled with water.

A primary segment with its ballast and installation packages is heavier than water but because it is jointed with balloons it will lifted up from the cannels supports by balloons while the cannel is being filled with water.

The primary segments are pulled one by one by winches and pass the lake and sit on the first sending machine and then go to the sending cannel. When two segments ends are come out from the water by the first sending machine their end caps are cut and a mini station set between them and it continues till all primary segments are connected together.

The first primary segment cap remains till it reaches the offshore platforms. In the platform the cap is cut and a Y branch is jointed to the pipe.

While the pipe is passing through the platform the joints between balloons and concrete cylinders are released so balloons keep floating but the pipe is sinking till the coiled cables open and the cables are stretched completely and the pipe is hanging from the balloons.

When the last segment end comes up to the platform its cap is cut too and the other Y branch is jointed to the pipe.

The pipe's carrier ships berth to the platform and when a mini station comes into the platform people connect the carrier ship cable to the pipe and then the ship moves and pulls the pipe in to the sea.

3-3 SSFP Operation Generally operating a pipeline is much simpler than the other oil and gas industry sections.

SSFP like other pipelines has a simple operating. It usually is operated and controlled from some shore offices which are close to the pipe. Operating, dispatch, maintenance, inspections, etc are done by a small group of people who can service a long section of the pipe.

In here we explain three different subjects which can relate to the operating phase. First is about pipe ability for variable demands of gas, second one is how we can take out the pipe and release it from deep water and third one is about SSFP pigs.

SSFP Ability The gas consuming rate is variable in different months of years sowe ied to changeThepipe -- -transmission capacity clue to the Therefore we will operate the pipe in deeper level and higher pressure to increase the pipe capacity when there is a high demand of gas for example in winter and also in low demands time like summer we will operate the pipe in shallower level and lower pressure to save more energy in the feeding compressor station (onshore station).

We can also increase or decrease the pipe transmission capacity by running more or less compressors in our offshore stations.

One of the advantages off SSFP is that it is not only can use as a gas transmission system but also it can be used as a small gas reservoir. We can feed the gas to the line constantly how our consumption capacity is variable.

For example if we have 8000 km of SSFP with the capacity of 200 Million cubic meters per day and the pipe is working between 2000m and 2500m depth. We can save about one and a half billion cubic meter gas in the pipe between its highest and lowest operating pressure.

It means the pipe can prepare 8 days of the consumption gas without any input. This advantage can give us more time to mach the gas production with its consumption.

SSFP as a reservoir can cover the different rate of gas consumption between days and nights.

For above example if we consume gas in three different rates of 100, 200 and 300 mcm3/d in a day in three 8 hours periods while we have constant feeding rate of 200 mcm3/d the pipe can mach its input and out put simply.

When the gas consumption is higher than the feeding rate the gas will depressurise and the pipe is coming up and when the gas consumption is lower than the feeding rate. The gas will pressurise and the pipe is going down.

In this example the pipe will changes its depth about 30 meters during the higher and the lower rate of consumption.

SSFP Releasing The pipe normally will have never come up to the sea surface during its life time but in a special case if a pipe segment is damaged, we can take it out by doing the following process.

We must carry a spare segment and install it between the damaged pipe offshore stations as a bypass and send the gas through the new pipe. After that we should release the gas and fill the damaged pipe with air by using pigs. We should send two pigs with a patch of nitrogen between them through the pipe to avoid mixing of gas and air.

When the segment has been filled by air completely we depressurise the air so the pipe segment becomes lighter and it is coming up till it reach to its upper limit border (it is kept by the fixed ballast). With continuing the pipe depressurising the air density drops and buoyant force lifts the fixed ballasts from the sea bed.

After the ballasts are lifted there is nothing to keep the pipe submersible so the pipe will come up to the surface without any controlling. While the pipe is coming up the external pressure will decrease and tensile stresses can appear in the concrete cylinder so the safety valves in mini stations will be opened and send the air to the water and keep the external and internal pressure almost equal to protect the pipe from rupture.

When the pipe segment is floating we can do the repairmen but we need to add installation tools on the pipe to send it back and it will be a quit difficult work on the sea surface. The problem is that we must do this in a short critical time because surface waves can damage the pipe simply.

SSFPjgs --*---SSFP pigs are much different with usual pigs. They can not move due to difference pressure so they have an electrical runner. Internal and external rails are installed along the pipe to guide the pigs and prepared the electricity for them to move inside and out side the pipe.

The SSFP pigs usually are used for batching, viewing (inspection), and may be used for cleaning, installing and measurement.

A batching pig has a same shape as usual pigs. It has two seals at its ends but it does not sits on the seals it has some wheels which keep it at the centre of pipe and electro motor gearbox which move it through the pipe. It can be used to remove hydrates if we have any hydrate in the pipe! For this purpose the pig has an electrical heating system at its head to vaporise the hydrates crystals.

Batching, cleaning pigs are rarely used during the operation time.

The pigs which are mostly used in operating are viewer pigs. They are cameras with a strong light which are able to work in high pressure conditions. Viewer pigs are small devices which can moves on the pipe inside or outside rails fast and give us useful information about the pipe inside and out side conditions. These pigs can also install the mini stations instrument packages (if we have them). The other option for using viewer pigs is that we add measurement instrument to them and use them instead of mini stations instrument packages. s)

In this case we do not have continues reports from the pipe external and internal conditions but if we run the pigs regularly we can get competent information.

All pigs are controlled by a wire less system from offshore stations their sender and receiver devices can be in the middle cylinder (for internal pigs) or be in the central sphere (for external pigs).

Drawings Description

Fig 1: It shows the elements which are connected together and made SSFP i-Concrete Cylinder 2-Flexible Joint 3-Internal Steel Bars Fig 2: It is cross section of two concrete cylinders which sit face to face while the flexible joint has not been installed between them. The bevelled ends sides cross each other at the pipe centre 1-Concrete Cylinder 2- Steel End Cap 3-Internal Steel Bars Fig 3: It shows cross section of two concrete cylinders' walls which sit face to face. The steel end cap has some steps which sealing rings will be installed on them 1-Concrete Cylinder 2-Steel End Cap 3-Internal Steel Bars Fig 4: It is flexible joint cross section.

In here it shows buckling arrestor beam just for first ring but all sealing rings can have it. The beam is a sector of circle with a centre on the pipe central axis so when it moves there is no change in its shape 1-Concrete Cylinder 2-Sealing Ring 3-Internal Steel Bars 4-Eye-Nut 5-Chain Close-Link 6-Buckling Arrestor Beam 7-Empty Space Fig 5: It is flexible joint cross section which shows sealing rings and distributed lines I-Sealing Ring 2-Empty Space 3-Small Distributed Line 4-Small Pressure Valve 5-Clamp Fig 6: It shows a section of sealing ring I- Sealing Ring Body (Elastomer) 2-Sealing Ring Structure (Steel Ring with Channel cross section) Fig7:.

This fig shows an installed SSFP which is in its highest operating level. All pipe's elements (concrete cylinder) have their separate mooring system.

1-Seafloor 2-Sea Surface 3-SSFP 4-Concrete Cylinder 5-Flexible Joint 6-Mooring Cable 7-Bouyant Ballast 8-Chain Ballast 9-Fixed Ballast Fig 8: It is SSFP in its highest operating level (gas lowest operating pressure) and chain ballast is completely stretched.

1-SSFP 2-Mooring Cable 3-Bouyant Ballast 4-Chain Ballast 5-Fixed Ballast 6-Seafloor Fig 9: It is SSFP in its normal operating level (gas normal operating pressure) and some part of chain ballast sits on seafloor and the remain part is submersible.

1-SSFP 2-Mooring Cable 3-Bouyant Ballast 4-Chain Ballast 5-Fixed Ballast 6-Seafloor Fig 10: It is SSFP in its lowest operating level (gas highest operating pressure) and chain ballast is completely sits on seafloor.

1-SSFP 2-Mooring Cable 3-Bouyant Ballast 4-Chain Ballast 5-Fixed Ballast 6-Seafloor Fig 11: It is SSFP in its highest operating level while a horizontal currant applies a force on SSFP I -SSFP 2-Mooring Cable 3-Bouyant Ballast 4-Chain Ballast 5-Fixed Ballast 6-Seafloor Fig 12: It is SSFP in its lowest operating level while a horizontal currant applies a force on SSFP I -SSFP 2-Mooring Cable 3-Bouyant Ballast 4-Chain Ballast 5-Fixed Ballast 6-Seafloor Fig 13: Bundle cable arranging, can be used when the seafloor is very deep.

I -SSFP 2-Mooring Cable 3-King Cable 4-Bouyant Ballast 5-Chain Ballast 6-Fixed Ballast 7-Seafloor Fig 14: Bridge cable arranging, can be used when the seafloor is very deep.

I -SSFP 2-Mooring Cable 3-King Cable 4-Bouyant Ballast 5-Chain Ballast 6-Fixed Ballast 7-Seafloor Fig 15: Centipede cable arranging, can be used when the seafloor is very deep and there is a lateral currant with high velocity (more than 0.5 m/s) around SSFP.

1-SSFP 2-Lateral Mooring Cable 3-Lateral King Cable 4-Bouyant Ballast 5-Chain Ballast 6-Fixed Ballast 7-Seafloor Fig 16: Centipede cable arranging, can be used the same as fig 15. In this case mooring system has some floating sphere (balloons) instead of chain and buoyant ballasts' weights but its function is the same base as normal mooring system.

1-SSFP 2-Lateral Mooring Cable 3-Lateral King Cable 4-Bouyant Balloon 5-Chain Balloon 6-Fixed Ballast.7-Seafloor --------Fig 17: It shows side view of offshore station. The view plate is parallel to SSFP 1-Floating Section 2-Upper Section 3-Downer Section 4-Lateral Mooring Cable (Mooring Pyramid's Lateral Edge) 5-Centeral Mooring Cable (Mooring Pyramid's Height) 6-Mooring Weight 7-Spesial Lift 8-SSFP 9-Sea surface 10-Seafloor Il-Downer section Equipments (Middle Cylinder, Compressor, Block valve) 12-Flexible Rope (Include lines) between Floating Section and Upper Section Fig 18: It shows side view of offshore station. The view plate is perpendicular to SSFP 1-Floating Section 2-Upper Section 3- Downer Section 4-Lateral Mooring Cable (Mooring Pyramid's Lateral Edge) 5-Centeral Mooring Cable (Mooring Pyramid's Height) 6-Mooring Weight 7-Spesial Lift 8-SSFP 9-Sea surface 10-Seafloor 11-Middle Cylinder (while it is going up)12-Flexible Rope (Include lines) between Upper Section and Downer Section Fig 19: It is a simple shape of offshore station's Upper Section from its side. The view plate is parallel to SSFP I -Centeral Sphere 2-Structure (Main Column) 3-External Open Workshop 4-Pontoon 5-Helipad 6-Structure (Helipad Supports) 7-Top Entrance 8-Bottom Entrance Fig 20: It is a simple shape of offshore station's Upper Section from its side. The view plate is perpendicular to SSFP 1-Centeral Sphere 2-Structure (Main Column) 3-External Open Workshop 4-Pontoon 5-Helipad 6-Structure (Trusses) 7-External Workshop's Gate Fig 21: It shows top view of offshore station's Upper Section.

1-Pontoon 2-Structure (Main Column) .3-External Open Workshop 4-Centeral Sphere 5-Helipad Fig 22: It shows offshore station's Floating Section 1-Derrick 2-Flaoting Sphere 3-Connecting Beam 4-Weight 5-Flexible Rope (Include lines) between Floating Section and Upper Section Fig 23: It shows side view of offshore station's Downer Section. The view plate is parallel to SSFP 1-Downer Section Floor (The Equipment Sitting Area) 2-Column 3-Middel Cylinder (Which Has Compressor) 4-Middle Cylinder 5-Block Valves 6-Y Branch 7-Centeral Mooring Cable 8-Y Branch Flexible Part 9-SSFP Fig 24: It is a cross section of offshore station's Downer Section. The crossing plate is perpendicular to SSFP 1-Downer Section Floor (The Equipment Sitting Area) 2-Column 3-Middel Cylinder (Which Has Compressor) 4-Middle Cylinder (Which Has Branch) 5-Block Valves 6-Y Branch 7-Centeral Mooring Cable 8-Column Leading Edge Fig 25: It shows top view of offshore station's Downer Section.

---1-Downer Section Floor (The Equipment Sitting Area) 2-Column -3Middel Cylinder -- (Which Has Compressor) 4-Middle Cylinder 5-Branch 6-Block Valves 7-Y Branch 8-Centeral Mooring Cable 9-Column Leading Edge Fig 26: It is a simple diagram which shows Middle Cylinder and Flaring system lines and connections 1-Middle Cylinder 2-Two Phase Separator 3-High Pressure Pump (Reciprocating Pump) 4-Control Valves 5-Feeding line 6-Downer Low Pressure Gas Line 7-Liquid Line 8-SSFP Internal Line (Vacuum Absorber Line) 9-SSFP Internal Line (Inhibitor Injector) 10-Gas Line between Middle Cylinder and Two Phase Separator 11-Liquid Line between Middle Cylinder and Two Phase Separator 12-Middle Cylinder Gas Line to the Environment (Sea Water) 13-Middle Cylinder Liquid Line to the Environment (Sea Water) 14-Liquid Level in Two Phase Separator Fig 27: It is a cross section of Controllable Block Valve while it is fixed between middle cylinder and V branch.

When the valve's flange wants to mach to the other flange, the hollow space between them is full of water so the suction line and bump should be at the bottom of valve to send out the water properly.

The needle should be at the top of valve and has a big tail to be accessible.

1-Block Valve Casing 2-Gate 3-Hydrolic Jack (Servo Motor) 4-Block Valve Flange 5-Electrical Magnet 6-Other Equipment (Middle Cylinder or Y branch) 7-Middle Cylinder's or Y branch's Flange 8-Suction Pump 9-Suction line 10-Flange Top Needle 11-SSFP Internal Line (Vacuum or Injector line) Fig 28: It is a cross section of block valve's Connecting Flange at the bottom of flange 1-Block Valve Flange 2-Middle Cylinder's or Y branch's Flange 3-Sealing Ring (0 Ring) 4-Hollow Space between Flanges 5-Electrical Magnet 6-Suction Line Fig 29: It is a cross section of block valve's Connecting Flange at the top of flange.

1-Block Valve Flange 2-Middle Cylinder's or Y branch's Flange 3-Sealing Ring (0 Ring) 4-Hollow Space between Flanges 5-Electrical Magnet 6-Flange Top Needle 7-Needle's Seal 8-SSFP Internal Line (Vacuum or Injector line) 9-Vacuum Releasing Line Fig 30: This figure shows a schematic Movable Block Valve. It is a vehicle which can move on middle cylinder and Y branch railway.

If a block valve is broken down while it is close the vehicle can introduce from the other middle cylinder, turns in Y branch, goes behind the broken valve and finally blocked the way.

1-Middle Cylinder 2-Block Valve 3-Y Branch 4-Movable Block Valve (In Middle Cylinder) 5-Movable Block Valve (While it is passing through Y branch) 6-Movable Valve's Vehicle 7-Movable Valve's Balloon (When it is not pressurised) 8-Middle Cylinder's and Y branch's Railway 9-Movable Valve's Balloon (When it is pressurised) Fig 31: It is a view of Mini Station.

Some parts of Mini Station such as leakage system, instrumentatiojLpackage, safety valves are not shown in this figure.

1-Lateral Pipe Flexible Part 2-Lateral Pipe Rigid Part 3-Block Valve 4-Middle Ring 5-SSFP 6-Rigid Jointing Segment 7-Flexible joint 8-Stiffener 9-Buckling Arrestor 1 0-Weekest Point in Middle Ring 11-Stiffener and Buckling Arrestor Fig 32: It is a cross section of block valves and middle ring and it shows how the gates are locked by ring weigh pins.

1-Block Valve Casing 2-Gate 3-Compressed Spring (Top) 4-Ring Weigh 5-Ring Weight's Spring 6-Locking Pin Fig 33: It is a cross section from bottom of block valve's casing and show how the spring can be compressed and fixed between gate and casing. -Gate's structure has an internal space which the spring can go through it.

1-Block Valve Casing's Bottom 2-Block Valve Casing 3-Gate 4-Compressed Spring (Bottom) Fig 34: It is a cross section from top of block valve's casing. Internal lines in this area (crossing the valve) are made from brittle polymers so the gate will break these lines when the valve is closing.

1-Block Valve Casing's Top 2-Lateral Pipe Rigid Part 3-Middle Ring 4-Ring Weigh 5-Ring Weight's Spring 6-SSFP Internal Line (Plastic Part which Should be Broken When the Valve is Closing) Fig 35: It illustrates the usage of Mini Station in installation. When the carrier ships pull SSFP, the pipe will be bended after the pulling point therefore mini stations should be enough flexible to bend at these points.

I -SSFP 2-Mini Station 3-Bend after Pulling 4-Sea Surface 5-Carrier Ship 6-Cable Fig 36: This figure shows the required slop of SSFP for gathering liquids in mini stations.

Second slop is lower than the first one because the gas flow helps the liquids to move.

l-SSFP 2-Mini Station 3-SSFP First Slop 4-SSFP Second Slop Fig 37: It is a top view of a downer section which has a Branch Branch joint lines are sitting under the middle cylinders.

I-Downer Section 2-Middle Cylinder 3-Branch's Joining Segment (line) 4-Branch's Block Valve 5-Branch's Y Branch 6-Branch's line Fig 38: This fig shows a branch while it is connecting to downer section. Branch's submersiblepart is designed how it has a same density as seawater when the gas in its normal operating pressure is passing through it.

1-Downer Section (In its Highest Operating Level) 2-Downer Section (In its Lowest Operating Level) 3-Branch's line Submersible Part (Transferring Low Pressure Gas and lighter than Water) 4-Branch's line Submersible Part (Transferring High Pressure Gas and Heavier than Water) 5-Station Mooring's Weight 6-Balloon 7-Cable 8-Weight 9-Branch's Riser 10-Branch's Anchoring point 1 1-Branch's line Buried Part Fig 39: This fig shows a part of SSFP which is being earned by a carrier ship while all installation tools are fixed to it.

1-SSFP 2-Mini Station 3-Ballast Package 4-Instalation Tool Package 5-Installation Balloon 6-Mini Station Installation Balloon (Bigger than the Others) 7-Strong Chain or Cable between Balloons 8-Sea Surface 9-SSFP Pulling Cable 10-Balloons Pulling Cable 11-Carrier Ship Fig 40: It is a cross section of a SSFP in the factory while all installation tools are fixed to it.

1-Conceret Cylinder 2-Ballast Package 3-Installation tool Package (Sack and chain) 4-Installation Balloon 5-Balloon's Joint Fig 41: It is a side view of a SSFP element (one concrete cylinder) in the factory while all installation tools are fixed to it.

1-Conceret Cylinder 2-Ballast Package 3-Installation tool Package 4-Installation Balloon 5-Balloon's Joint 6-Flexible Joint 7- Ribbon Which Fixes the Ballast Package 8-Ribbon Which Fixes Balloons Cable Fig 42: It is SSFP with its installation tools when it is moving in the factory. The installation balloons are fixed to the pipe 1-Installation Balloon 2-SSFP Element (Concrete Cylinder) 3-Instalation tool Package 4-Ballast Package Fig 43: It is SSFP with its installation tools when it is being carried in sea or oceans (after the factory's offshore platform). The installation balloons are separated from the pipe and the cables between balloons and the pipe are stretched completely.

i-Installation Balloon 2-SSFP Element (Concrete Cylinder) 3-Instalation tool Package 4-Ballast Package 5-Balloon's Cable Fig 44: In here SSFP segment has been installed between two offshore stations and its mooring system package has been released to the water.

1-Installation Balloon 2-SSFP Element (Concrete Cylinder) 3-instalation tool Package 4-Fixed Ballast 5-Balloon's Cable 6-Chain Ballast 7-Bouyant Ballast 8-SSFP Mooring's Cable Fig 45: In here SSFP's installation package has been released and the pipe is being filled by gas.

1-Installation Balloon 2-SSFP Element (Concrete Cylinder) 3-instalation tool's Chain 4-Fixed Ballast 5-Balloon's Cable 6-Chain Ballast 7-Bouyant Ballast 8-SSFP Mooring's Cable Fig 46: This fig shows a top view of suggested factory for SSFP construction.

1-Constructing Area 2-Constructing Cannels 3-Constructing Platforms 4-First leading Lake 5-Sending Machine 6-Sending Cannel 7-Offshore Sending Platform 8-Secound Leading Lake 9-Testing Pipe 10- Piece of SSFP in Test 11-Piece of SSFP carrying for test 12-Ready Piece of SSFP 13-SSFP Passing Through Leading Lake 14-SSFP Passing Through Sending Cannel 1 5-SSFP Sinking to the Sea Fig 47: It is a side view of sending machine. This machine can pass the pipe between two cannels or ---between leading lake, caime1 and sea whickhave different elevation so we do-not-need -gates between leading lake, cannels and sea.

There is the same machine on offshore platform which is not shown in here.

I -SSFP 2-Installation Balloons 3-Cable between Balloons 4-Sending Machine Wheels (First Floor) 5-Sending Machine Wheels (Second Floor) 6-Sending Cannel or First Leading Lake (In Higher Elevation) 7-Sending Cannel or Sea (In Lower Elevation) Fig 48: It is a cross section of sending machine. It has two deck (floor) one for passing the pipe and the other for passing the installation balloons.

1-Sending Machine's Structure 2-Sending Machine Wheels (First Floor) 3-Sending Machine Wheels (Second Floor) 4-SSFP 5-Ballast Package 6-Installation Package 7-Installation Balloon

Claims

Claims I-A gas subsea transmission system, which uses a submersible

pipeline and stations to transport gas through marine distances the pipeline is submerged and suspended and able to equalize its internal and external pressure it means the pipe can equalize its external hydrostatic pressure with its internal variable operating gas pressure.

2-A submersible pipeline in claim I has a mooring system that makes the pipe stable and equalizes its pressures by changing the pipe depth the mooring system connects the pipeline to seafloor by cables the cables end have chain shape parts which partly sit on the seafloor these parts have specific weight per length which match the changes in the pipe depth with changes in gas density and pressure this specific weight per length is a function of internal gas density changes due to the changes in the gas pressure Suppose a submersible rigid ball which includes air and has fixed buoyancy is hung from a chain in a deep pool in a specilic depth while some part of the chain is sitting on the floor in this equilibrium level the ball lift force is canceled out by the chain weight if some more air is fed to the ball, the air pressure increases, the ball becomes heaver and its lift force decreases and its submerged weight increases so the ball sinks and allows the chain to sit on the floor until the new lift force becomes equal to the new chain weight The new equilibrium level is deeper than the old one so the hydrostatic pressure around the ball in the new level is higher than the first equilibrium level this example shows that an increase in the ball air (internal) pressure produces an increase in the hydrostatic (external) pressure around it therefore if the chain weight per length is a suitable function of gas pressure and density changes, the changes in hydrostatic (external) pressure can be the same as the changes in gas (internal) pressure so the external and internal pressures can be kept equal.

3-Gas subsea transmission systems in claim I include subsea stations that control and operate the pipeline they are stabled and connected to the seafloor by mooring system these stations are submerged during the operation and can be floated for maintenance requirement.

4-A submersible pipeline in claim I is installed by special tools which can keep the pipe's external and internal pressure equal while it is submerged theses tools have a special chain shape parts with a specific weight per length the same specification as the mooring system chain shape parts in claim 2 --;-Amendments to the claims have been filed as follows Claims I-A gas subsea transmission system which uses a submersible suspension pressure-equaliser pipeline and submergible offshore stations to transport gas through marine distances The pipeline is submerged and suspended in deep water and able to equalize its internal and external pressure along its whole length This means the pipeline can equalize its external hydrostatic pressure with its internal variable operating gas pressure by changing its depth Obviously by chance the internal content pressure and external hydrostatic pressure can be equal in some areas along any offshore pipelines depending on the operating condition The claimed pipe is unique because it can equalise the gas internal and hydrostatic external pressure along its whole length It should be noted that all offshore pipeline's external pressure partially cancels out the internal pressure due to operating conditions but this phenomenon is not controllable and cannot have a specific value The claimed pipeline can be designed such that it can cancel any required amount of internal gas pressure with the hydrostatic external pressure along its length while the internal pressure is varying In other words the pipe can be designed to keep the internal and external pressure difference constant to any required value along its whole length.

2-A submersible suspension pressure-equaliser pipeline in claim 1 has a mooring system that makes the pipe stable and equalizes the pipe internal and external pressures The mooring system does this by adjusting the pipe depth depending upon the gas internal pressure The mooring system connects the pipeline to seafloor by cables The cables have chain shape parts (weights) which are called as chain ballast Some parts of chain ballast arc sitting on the seafloor The function of mooring system can be clarified by example 1 Example 1 Suppose that a rigid ball (steel ball) is hung from a chain in a deep pool and it is submersible in a specific depth while some part of the chain is sitting on the floor If some more air is fed to the ball buoyant force of ball is S....' not changed because it is rigid and there is no change in its volume However as the air pressure increases the ball becomes heavier and it's submerge weight (dry weight minus buoyancy) increases so the ball sinks and allows the chain to sit on the floor until the new lifting force (negative submerge weight *:w: or buoyancy minus dry weight) becomes equal to the new chain weight The new equilibrium point is deeper than the old one so the hydrostatic pressure around the ball in this point is higher than the first equilibrium point The above : example shows that an increase in the ball air (internal) pressure produces an * * increase in the hydrostatic (external) pressure around it Therefore if the chain weight per unit length is a suitable function of air density base on pressure changes, the increase in hydrostatic (external) pressure can be the same as the increase in gas (internal) pressure End of example I_____________________ The mooring system chain ballast weight per unit length can be selected such that it can accommodate the changes in the pipe depth with changes in gas density or pressure This specific weight per length is a function of internal gas density changes due to the changes in the gas pressure The mooring system chain ballast is novel and different from other identical available systems because it has a unique weight per length for any specific depth This unique specification can be clarify by example 2 This example is just for explanation and valid for a specific operating case where gas and environmental temperature is constant and the pipe is designed to have an exact equal external and internal pressure The present calculation can be modified to accommodate any other operating conditions____________ Example 2 If it is assumed that the chain ballast is hung vertically and A and B are two points one unit length apart on the chain ballast and A is above B Following physical characteristic are considered_________________________ = Depth of Pipe Centre Line below Sea Surface while Point A is touching the see bed ______________________________________________________ D3 = Depth of Pipe Centre Line below Sea Surface while Point B is touching the see bed ________________________________________________________ = Hydrostatic Pressure at Depth DA = Hydrostatic Pressure at Depth D8 PA = Gas Density at Pressure PA (Note that the gas temperature is assumed constant and equal to the environment temperature)_______________________ p8 = Gas Density at Pressure P8 (Note that the gas temperature is assumed constant and equal to the environment temperature)______________________ V, = Gas volume per unit length of pipe___________________________ = Weight of AB Segment of Chain Ballast per Unit Length of the Pipe_ W, can be calculated as follow___________________________________ = (PA -p9)x VGOS end of example 2 3-A gas subsea transmission system in claim I includes submergible offshore stations that control and operate the pipeline These stations are special * w because they can be submerged during the operation and can be floated for access They are stabilized in sea by their mooring system The mooring system cable are also providing a means of connection between offshore station and the pipe. S...

4-An offshore station in claim 6 has some valves which are connected to the pipe S.....

* Theses valves have a unique connection mechanism They have a groove in their connecting surface which traps some water Valves are connected to the : ... pipe first by a magnetic system then the trapped water is pumped out and high *....: external hydrostatic force provide a tight joint and connect the valve to the * pipe.

5-An offshore station in claim 6 has a mechanism which is able to collect the liquids from the pipe and send them to the environment For this reason the pipe in claim 1 has few small diameter internal pipes though which the collected liquids are transferred.

6-A submersible suspension pressure-equaliser pipeline in claim 1 has fail safe mechanisms along its length The mechanism includes two block valves The joint strength between these valves is weaker than the pipe strength therefore failure due to tensile forces happens at this joint These valves are automatically closed before the pipe goes to pieces and block the pipe.

7-A gas subsea transmission system in claim 1 has some special mechanism which can block the pipe These tools can be introduce into the pipe from offshore stations in claim 6 They are special vehicles which can moves inside the pipe They can inflate a balloon shape devices in the pipe to block the pipe.

8-A submersible suspension pressure-equaliser pipeline in claim I is installed and submerged by special tools These tools keep the pipe's external and internal pressure equal while it is submerged They have a special chain shape parts with a specific weight per length Their function is the same as pipe's mooring system function in claim
2.

9-A submersible suspension pressure-equaliser pipeline in claim i is constructed in a special coastal factory The factory includes many canals trough which that a specific length of pipe is constructed and transferred The canals are filled with water and the pipe floats to be carried. * * * *** **** * * **** **.. * * S... * S S. * . * S..

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