GB2521218A

GB2521218A - Methods and apparatuses for use in handling of lined pipe

Info

Publication number: GB2521218A
Application number: GB1322152.8A
Authority: GB
Inventors: Vibor Paravic
Original assignee: CEONA SERVICES UK Ltd
Current assignee: CEONA SERVICES UK Ltd
Priority date: 2013-12-16
Filing date: 2013-12-16
Publication date: 2015-06-17
Also published as: WO2015092383A1; GB201322152D0

Abstract

The application discloses a method for laying a pipeline of joined sections of steel pipe having a corrosion resistant metallic or other liner. The method comprises: laying the pipeline from a pipelaying vessel by joining together sections of pipe; sealing a length of the pipeline using first and second seals; flooding the length of the pipeline between first and second seals with a fluid and pressurising the fluid; and causing the first and second seals to move relative to the pipe as the pipeline is laid to maintain a locally increased internal pressure in a section of the pipeline in which the liner is at risk of wrinkling due to bending of the pipe. The locally increased internal pressure may be maintained in a section of the pipe that is subject to elastic deformation and/or plastic deformation. The locally increased internal pressure may be only applied in sections of the pipeline in which the metallic liner is at risk of wrinkling due to bending of the pipe. Sections of the pipeline other than the section subject to the locally increased internal pressure are preferably laid in the substantial absence of internal pressure. The first and second seals may be caused to move relative to the pipe by operation of independently driven mechanical conveying means provided inside the pipe. Alternatively, the first and second seals may be caused to move relative to the pipe by tethering the seals to a fixture unmovable relative to the pipe as it is being laid.

Description

METHODS AND APPARATUSES FOR USE IN HANDLING OF LINED PIPE

The present invention relates generally to methods and apparatuses for use in handling pipe having an internal liner, and in particular for use in averting the wrinkling of the internal liner of the pipe due to bending. The invention finds particular utility in the production and laying of mechanically lined rigid steel pipe (MLP) from a pipelaying vessel, and in the production of lengths of pipe for storage at a spoolbase.

Pipelines for use in the subsea conveying of fluids such as gas or crude oil are often exposed to the corrosive effects of these fluids which, unless the pipeline is protected by some material resistant to their effect or corrosion, can cause damage to the pipeline and even pipeline failure, which is difficult and expensive to remedy.

Corrosion resistant alloys (CRA), such as lnconelTM 625, available from the Special Metals Corporation of New Hartford, New York, USA, are known to provide resistance to corrosion in extreme environments such as in oil and gas pipelines. To avoid having to unnecessarily provide the entirety of the pipeline pipe as relatively high cost corrosion resistant alloy, it is known to provide bimetallic pipe in which an outer, typically carbon steel pipe is provided as a host pipe, the inner surface of which is protected by a layer of a corrosion resistant alloy.

It is known to provide bimetallic pipe by cladding the inner surface of the carbon still pipe with metallurgically bonded CRA layer, or even a weld overlay. However an alternative method which has, in some cases a cost benefit, of producing bimetallic pipe is to provide a liner to the inner surface of the carbon steel pipe made from CRA or other material. The lining process involves the creation of a mechanical bond between the liner and the pipe by inserting the liner into a length of the pipe and hydraulically or mechanically expanding the pipe and liner together such that the inner liner undergoes a plastic deformation while the outer pipe undergoes an elastic or plastic deformation. Upon relaxation of the expansion force or pressure, an interference contact stress or interference fit is produced at the interface between the liner in the pipe, causing the liner to become mechanically bonded to the internal surface of the pipe.

While MLP may be preferable from a pipe manufacturing and cost-effectiveness perspective, a known problem is that, in pipeline construction methodologies that involve reeling the pipeline onto and off of a storage spool during production and laying, forces imparted on the pipe during the reeling process by bending of the pipe can cause the internal liner to wrinkle.

In reeling MLF, significant bending strain is imparted to the pipe as it is wound onto and unwound from a storage reel which can result in a significant amount of wrinkling in the CRA liner. The wrinkling mechanism may be as a result of, among other things, the bending stress itself, ovalisation of the pipe cross section, or differential longitudinal compression and strains on the liner along the curvature of the bend due to the periodic circumferential fixation of the liner in the region of the joining welds.

This wrinkling is an undesirable result as the wrinkles can cause mechanical and material issues with the liner (such as embrittlement) as well as significant problems within the pipe during and after the pipeline is commissioned and is in use, which can lead to the failure of the pipeline before the end of its serviceable term.

To avoid this wrinkling for reeled MLP, it is known, for example from international patent application publication numbers WO 2008/072970 Al and WO 2011/124919 Al, to pressurise the entire length of the pipeline as it is reeled onto a storage reel and later to pressurise the entire length of the pipeline and it is unwound from the storage reel, straightened and laid, after which it is depressurised. The pressurisation appears to help prevent the liner from wrinkling due to bending stresses in the pipe on reeling and unreeling.

Two common pipeline laying methods are shown in Figure 1. Each method is named by the geometry of the pipe after it is dispensed from the vessel and is laid on the seafloor.

Figure 1A shows an S-lay method which involves the pipe being passed from a reel or welding station (not shown) on board a pipelaying vessel 110 (also known as a lay barge) over a stinger 111 at the rear of the vessel 110 to control the path of the pipe 115 and maintain it in an essentially straight orientation for as long as possible. The pipe experiences two bends, namely the first as the pipe 115 is formed along and exits the stinger 111 and the second sag bend' as it reaches the sea bed 116.

Figure lB shows a J-lay method which uses a vertical or almost vertical tower 112 to control the laying of the pipe 115. The pipe 115 either passes from a reel or an onboard welding station (not shown) on the vessel 110 up and through the tower 112. It then leaves the tower 112 in a substantially vertical direction so that the pipe 115 only experiences one bend, namely the sag bend' as it reaches the seabed 116.

The present inventors have realised that, while the bending stresses experienced by the pipe 115 due to S laying and J laying are less than that experienced than when being wound around a reel, the pipe liner may still be at risk of wrinkling due to bending. For example, as the discovery and development of subsea oilfields and reserves moves into deeper water the problem of liner wrinkling due to the sag bend may become an issue. Of course, for a pipeline that is laid from a pressurised reel of MLP, the liner is protected and so the problem of wrinkling due to the lay geometry does not arise. However, for pipelines not laid from pressurised reels, wrinkling due to the lay geometry can be a problem. Further, other recently proposed pipe handling and laying methods such as a G lay' method such as shown in Figure 2 and to be explained in greater detail in the embodiments, also impart bending strains on the pipe as the pipe is laid. Thus wrinkling of CRA or other pipe liner due to bending stresses imparted due to the handling of the pipe on a pipelaying vessel and the lay geometry after the pipeline leaves the vessel, not from reeling, can also lead to undesirable wrinkling, which should ideally be avoided or at least limited.

It is known that having a sufficiently thick CRA or other liner can reduce the likelihood or magnitude of wrinkling, or avoid wrinkling completely, when the pipe is bent or deformed during laying. Indeed, due to this phenomenon, CRA or lined pipe is generally chosen for a specific project having a liner thickness sufficient to avoid wrinkling due to the laying process. In the case of a corrosion resistant liners, the fundamental thickness of the CRA liner that is required is that which is sufficient to protect against corrosion over the serviceable life of the pipeline and is dependent on the conditions in which the pipe is to operate. In many cases the liner thickness that is used is greater than that needed to withstand chemical attack over the serviceable life of the pipeline, or that needed to successfully perform the function of the liner. For example, in the context of reeling MLP onto and off of a spool, International patent application publication number WO 2011/048430 Al discloses two methodologies for calculating a minimum liner thickness necessary to avert wrinkling during reeling of MLP.

Given that the cost per unit weight of corrosion resistant alloys and other liner materials can be very high, the cost of the liner material can become a significant component of the fixed material costs of the pipeline. Thus while using a sufficiently thick liner can reduce wrinkling, it can also lead to result in the use of a large amount of an expensive liner material. Where a thicker liner than is necessary, e.g. to avoid corrosion, is used to reduce wrinkling, the amount of liner material used can be far in excess of that needed for the pipeline to function properly and, e.g. to protect against chemical attack during use.

Therefore, viewed from one aspect, the present invention provides a method for reducing wrinkling of an internal liner of a pipe for use in a subsea pipeline while the pipe is being produced, the method comprising: sealing a length of the pipe using first and second seals; flooding the length of the pipe between first and second seals with a fluid and pressurising the fluid; and causing the first and second seals to move relative to the pipe as the pipe is lengthened by joining sections of pipe to maintain a locally increased internal pressure in a section of the pipe in which the liner is at risk of wrinkling or deforming due to handling or bending of the pipe.

The method may be used in a pipeline production and laying vessel. In this context, the method may be used to maintain a locally increased internal pressure in a section of the pipe as the pipe passes through a bend in the pipeline as it is handled by apparatus on the deck of a pipeline laying vessel before it is laid and through a bend in the lay geometry as the pipe is laid from a pipeline laying vessel.

The method may also be used in the production and handling of lined pipe for storage (and for later reeling onto a spool) at a spool base. In this context, the method may be used to maintain a locally increased internal pressure in a section of the pipe as the pipe passes through a bend in the storage geometry of the pipe in the spoolbase.

By these aspects of the present invention, in a pipe having an internal liner formed by joining pipe sections together, for example on a pipelaying vessel or at a spool base, sections of the pipe in which the liner is at risk of wrinkling due to bending or handling of the pipe can be protected from wrinkling or deformation by the localised application of an internal pressure by a pressurised fluid. In this way, the liner can be protected from wrinkling and deformation due to handling and bending of the pipe during production and handling or laying (such as due to a sag bend when laid from a pipeline production and laying vessel). This is achievable without having to pressurise an entire length of a pipeline from a leading end to a trailing end, which is difficult and hazardous, particularly for pipelines formed by joining pipe sections together on a pipelaying vessel. This is also achieved without the need to increase the thickness and weight of the pipeline or the liner.

Similarly in the case of a liner being designed and introduced for a purpose other than corrosion resistance, such as insulation or ensuring flow properties, these methods can be used to optimized the liner design and address the issue of liner wrinkling.

Once a length of pipe is pressurised and sealed, further sections of the pipe are joined together to lengthen the pipe and the pressurised length is moved forward to encompass the section of the handling geometry (which may be the geometry of the pipe as it is handled on the deck of and laid from a pipeline production and laying vessel, or the geometry of the pipe as it is to be produced and stored at a spoolbase) in which the liner is at risk of wrinkling due to bending of the pipe during handling and laying. At this point the seals are caused to move backwards, along the inside of the pipe, at a rate substantially corresponding to the production rate of the pipe. In this way, as the pipe passes through the section of the handling geometry subject to bending and where there is a risk of wrinkling or liner deformation, the pipe is internally pressurised and wrinkling is averted. Once the pipe has been extended even further, the pipe passes into a section of the pipe handling geometry that is not subject to critical levels of bending and past the leading seal, where the internal pressure is dropped. Alternatively the motion of the pipe during handling and the relative motion of the pressure seals is decoupled, therefore the pipeline is pressurized for a section of pipe that slightly extends beyond the region of the critical bending, thus when the pipe is moved to join further sections the seals remain stationary in the pipe. Once the pipeline motion has stopped the seals are reposition to maintain pressure in the critical bending zone as well as prepare the pipe for the joining moving of the next section.

Importantly, the present invention provides a mechanism by which ever thinner liners can be reliably deployed without risk of wrinkling due to bending during the pipe handling and laying processes. In this way, a liner thickness that is only as thick as that which is needed to, for example, protect against chemical attack over the serviceable life of the pipeline, is achievable. This allows the thickness of the liner to be chosen as thin as possible, which can lead to significant savings of unnecessary use of valuable corrosion resistant alloy material or other liner material, which leads to significant cost savings compared to pipelines laid without using the claimed method.

Preferably, the pipe is rigid pipe. Alternatively, the pipe may be a flexible hose or umbilical.

Preferably the pipe has been lined by a mechanical lining process, providing mechanically lined pipe (MLP), preferably rigid MLP. Even more preferably the liner is made of a corrosion resistant alloy (CRA). Other liner materials may be provided in rigid/non-rigid lined pipe which may be metallic or non-metallic and which may be provided to perform a function or functions other than/as well as corrosion resistance, such as ensuring the flow properties of the pipe, insulating the pipe, or other protective functions, etc. The locally increased internal pressure may be maintained in a section of the pipe that is subject to elastic deformation and/or plastic deformation. The locally increased internal pressure is preferably only applied in sections of the pipeline in which the liner is at risk of wrinkling or deformation due to bending or handling of the pipe. Sections of the pipeline other than the section subject to the locally increased internal pressure preferably have a substantial absence of increased internal pressure.

The first and second seals may be caused to move relative to the pipe as the pipe is lengthened by operation of independently driven mechanical conveying means provided inside the pipe. The independently driven mechanical conveying means may be configured to move along inside the pipe at a rate substantially corresponding to the lay rate, optionally over the period of one or more pipe joins. The mechanical conveying means may be a crawling robot. The crawling robot may move in the pipe by one or more of: a reciprocating crawling mechanism; a helical drive mechanism; a brush drive mechanism; a magnetic engaging mechanism; and a wheeled drive mechanism. The independently driven mechanical conveying means may be powered and/or controlled from the pipelaying vessel via either an control umbilical or by non-contact remote control methods or and automatic system. The power source may be provided local to the robot, such as a local battery power source, or may be located remote from the robot and transferred via an umbilical. The control system that causes the robot to move may be operated manual or automatically under program control or a mixture of both. The control signals may be generated locally (e.g. for automated program control) and/or remotely and transmitted to the robot via an umbilical or a non-contact remote-control method In this way, one or more powered robots may be placed into the pipeline to move the seals along the inside of the pipeline to maintain the position of the seals relative to the lay geometry. The robots can move at a constant rate or can crawl in a reciprocating motion inside the pipeline, ideally the robots can move in the time required to join the next section of pipe.

Alternatively, the first and second seals may be caused to move relative to the pipe by tethering the seals to a fixture unmovable relative to the pipe as it is being produced.

The pressure in the pressurised section of the pipeline is preferably sufficient to avert wrinkling in the liner due to the bending or handling. This may be greater than 5 bar, preferably greater than 10 bar, more preferably greater than 15 bar, even more preferably greater than 20 bar, more preferably still greater than 25 bar. The pressure may be adjusted for ambient pressure, for example, at a bend on or near the sea bed, taking into account hydrostatic pressure due to depth below sea level.

The thickness of the liner used in the pipe is preferably less than that which would be necessary to avoid wrinkling of the liner were the section of the pipeline in which the liner is at risk of wrinkling due to bending not pressurised during handling and/or laying.

The method preferably further comprises: inserting first and second seals in the pipe as it is being produced and pressurising the pipe therebetween; welding sections of pipe together to form the pipe; and when the pressurised length of the pipe reaches a position in which the liner is at risk of wrinkling or deformation due to bending or handling of the pipe, causing the seals to move in the pipe to substantially maintain their position with respect to the section of the pipe at risk of wrinkling or deformation as the pipe is lengthened. In this way, seals can be inserted into the pipe, for example, when pipeline production commences on a pipelaying vessel, the length of pipe therebetween can be pressurised and the seals spaced the necessary distance apart, and then allowed to travel with the pipeline, for example, down the lay geometry, until the correct position is reached, whereupon the seals are caused to move in the pipeline to maintain their position. Where two or more sections of the pipe need to be protected in this way, this process can be repeated in-line to create two separate, locally pressurised sections of the pipe. The method preferably further comprises: arranging the first and second seals such that the pressurised length of the pipe is greater than the length of the section of the pipe in which the liner is at risk of wrinkling or deformation due to handling or bending of the pipe. In this way a section of the pipe can be pressurised at the leading edge of the pipe and moved into position where there is a risk of wrinkles occurring, before the seals are caused to move in the pipeline to maintain their position relative to the section of the pipe at risk of wrinkling or deformation as the pipe is lengthened. As a result, the entire length of the pipeline can be protected from wrinkling due to, for example, the lay geometry.

The methods preferably further comprise laying the pipe from a pipelaying vessel as the pipe is produced by joining together sections of pipe The pipelaying method may be S-lay, J-lay or G-lay. The invention may also find utility in other lay geometries, such as that used in the GSP Falcon (formerly known as the Seaway Falcon). The pipeline may be formed by joining together sections of pipe at an on-board station. The method optionally actually further comprises forming the pipe by joining together sections of pipe at an on-board station.

Preferably, the pipeline is not unwound from a reel on the pipelaying vessel. The methods of aspects of the invention find particular utility where the pipeline is being formed on board the vessel, rather than unwound from a reel.

Alternatively, the methods may further comprise handling the pipe for storage at a spool base as the pipe is produced by joining together sections of pipe, where the pipe is stored in a bent configuration ready for later winding on to a reel. In this way, lengths of pipe can be formed at a spool base and stored in a bent configuration, such as a U shape, an S shape or an enlarged 0 shape, for example, with localised bends, where they can later be wound onto a spool of a reel barge for reel laying in the field. This allows the space that the spool base needs to occupy to be significantly less than for straight lengths of stored pipe. Further, the length of pipe that can be stored in a spoolbase of a given size can be made longer. Thus in the context of producing pipe at a spoolbase for storage, the present invention conserves space and increases capacity and reeling efficiency.

The method preferably further comprises causing the first and second seals to move so as to substantially maintain their position with respect to the section of the pipe at risk of wrinkling or deformation due to bending or handling of the pipe as the pipe is lengthened. For example, in a pipelaying vessel context, the first and second seals may be caused to maintain their position relative to the deck of the pipelaying vessel and/or the lay geometry.

In a spoolbase context, the first and second seals may be caused to maintain their position relative to the spoolbase. The position of the seals relative to the pipeline may vary slightly if that lay rate and the movement rate of the seals are not matched. This may occur, for example, if the locomotion of the seals within the pipeline is achieved using a crawling or reciprocating mechanism, and or if the lay rate is non-linear.

Viewed from another aspect, the present invention provides apparatus for maintaining a pressurised section within a pipe as it is being produced, comprising: means for maintaining a seal in the pipe; and independently driven mechanical conveying means for moving the seals along inside the pipe, wherein the independently driven mechanical conveying means is configured to be operable to move along inside the pipe at a rate substantially corresponding to the production rate. Apparatus according to this aspect of the present invention provides a robot capable of protecting pipelines lined with, e.g., CRA liners from experiencing wrinkling in accordance with the methods as set out above. Viewed from yet another aspect, the present invention provides use of the above described apparatus.

Certain preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1A shows an S lay method of laying a pipeline in which embodiments of aspects of the present invention are usable; Figure 1 B shows a J lay method of laying a pipeline in which embodiments of aspects of the present invention are usable; Figure 2 shows a detail of a G lay method of laying a pipeline in which embodiments of aspects of the present invention are usable; Figure 3A illustrates an embodiment of a crawling robot apparatus usable in accordance with methods of the present invention to move seals in the pipeline; Figure 38 illustrates an alternative apparatus usable in accordance with methods of the present invention to move seals in the pipeline; Figure 4 show a method of an embodiment of aspects of the present invention; and Figure 5 illustrates how methods of aspects of the invention may be utilised at an example spoolbase.

Referring to Figure 2, there is shown a vessel 1 which includes a deck area 2 and an inclined alignment area 3 on which are positioned on-board welding means 4, tensioner means 5 and coating means 6. The alignment area 3 is inclined at an angle a with respect to the 10 horizontal plane of the deck of the vessel.

To form and lay the pipeline, the pipe 20 passes from suitable storage means (not shown) which may be any standard storage means such as reels of pipe or straight lengths of pipe section to the welding means 4 where they are welded together to form a single pipeline.

The pipeline passes through a tensioner to help control the feed of the pipeline to guidance means 7 via the coating means 6 (if present). The guidance means may, for example, be a freely mounted rotatable wheel which is not powered.

The vessel may be a standard length vessel such that the deck area is up to 80m long, for example in the range 25-80m, or 50-75m long. The welding means are any suitable means for joining adjacent sections of rigid pipe which are arranged to be transferred from a storage area to the deck. The sections of pipe are joined to form a pipeline 20 which may be coated as necessary, taking into account the environment where the pipeline is being laid. Suitable coatings may include fbe (fusion bonded epoxy) resins, polymers, etc. The pipeline is fed over, around or through the guidance means 7 up to discharge means 8.

This may also, for example, be a free mounted rotatable wheel with a suitably textured and contoured surface to grip the pipeline 20 as it passes over the top of or around the wheel 8.

The wheel 7 and wheel 8 carry the pipeline 20 for less than a full turn and are used only for guidance and tensioning of the pipeline, not for storage. In this regard, wheels 7 and 8 are not to be considered reels which are used for loading, storing, spooling and paying out lengths of pipeline stored thereon.

The pipeline 20 then passes through straightening means 9, and further tensioning means after which it leaves the pipeline handling apparatus provided on the deck of the vessel 1 to be laid by passing through a moonpool 11 in the bottom of the vessel 1 and down to the sea floor 12. Once a sufficient length of pipeline 20 has dropped to the seafloor 12, some or all of the tensioning means 10 may be switched off and the discharge of the pipeline 20 may be controlled solely by the tensioning means 5, friction on the discharge means 8 and gravity on the pipeline 20.

The tensioning means 5, may be conventional tensioners of a suitable size for the pipelines being laid. For example, they may be tensioners for holding up to 2000 metric tonnes (mt), for example in the range 200-2000mt, or 300-l000mt, or 300-700mt, or 350-SSOmt.

Alternatively, the first tensioning means 5 could be a set of two or more tensioners of smaller size arranged in series such that one or more could be used in a particular project depending on the size and weight of the pipeline being laid.

These tensioners may be of a size such as 200mt, or 300mt, or 400mt or SOOmt. The tensioners not being used could be moved to one side so as not to get in the way of the pipeline as it is being fed to the guidance means 7.

Similarly, the second tensioning means 10 could be a set of two or more tensioners of smaller size arranged in series such that one or more could be used in a particular project depending on the size and weight of the pipeline being laid. These tensioners may be of a size such as 200mt, or 300mt, or 400mt or 500mt. The tensioners not being used could be moved to one side so as not to get in the way of the pipeline as it is being discharged from the discharge means 8.

Alternatively, the second tensioner 10 may be of a much smaller size as the principle role of this could simply be to assist in the initial pulling of the pipeline 20 over, around or through the guidance means 7 and on to the discharge means 8. This could be done by means of a wire attached to the front end of the pipeline which is then passed over, around or through the guidance means 7 and discharge means 8 and through straightening means 9 to the tensioning means 10. This can then be fed through the tensioning means 10, pulling the assembled pipeline behind it until the pipeline reaches the tensioner 10. The tensioning means 10 may also take some of the weight of the pipeline 20 until a sufficient length has been laid for gravity to help control the speed of movement of the pipeline through the process.

The straightening means 9 are preferably arranged between the discharge means 8 and the tensioning means 10 to straighten out the pipeline 20 before it passes through the moonpool 11. This may not be needed if the diameter of the discharge means 8 is sufficiently large that the bending of the pipeline 20 is within the elastic limits of the pipeline so it will resume a substantially straight orientation after discharge from the discharge means 8. Where the discharge means are a wheel, the diameter may be of the order of 20 to 30 m, for example 25 to 28 m. On larger vessels the wheel could be even larger, for example 30-35m in diameter, which may be useful for the laying of deepwater pipelines.

After the pipeline 20 is formed by joining sections of MLP together, and before it is laid on the seabed, in "G" laying, the pipeline undergoes a number of bends due to the handling apparatus on the deck of the vessel 1. In the C laying, the pipeline 20 is first bent around the wheel guidance means 7 and then fed under tension up to and bent around the wheel discharge means 8. The effects of the bending stresses due to being fed around wheel 7 and wheel 8 are then undone by straightener 9 which effectively performs a reverse bend on the pipeline 20. These three bends each involve a plastic deformation of the pipe 20. As a result, the pipe handling on the deck of the vessel 1 gives rise to a first section of the pipeline in which the metallic liner is at risk of wrinkling due to bending of the pipe 20, indicated by the broken line marked R1 in Figure 2.

Thereafter, the pipeline 20 passes in a straight line through moonpool 11 and down towards the seabed 12. As the pipeline approaches the seabed 12, it undergoes another, more gradual "sag" bend due to its own weight, as it flattens out to rest on the seabed 12. This elastic deformation of the pipe 20 gives rise to a second section of the pipeline in which the metallic liner is at risk of wrinkling due to bending of the pipe 20, indicated by the broken line marked R2 in Figure 2.

In order to reduce or completely avert wrinkling of the liner in the pipe 20 as it passes through the sections R1 and R2 of the G lay process, in accordance with aspects of the present invention first and second seals are provided at the leading and trailing ends of these sections and the pipeline 20 is pressurised therebetween by a fluid. The seals may be any suitable apparatus for sealing the pipeline at pressure and being moveable while maintaining the seach, such as an inflatable bladder or moveable pig.

To seal the section R1, seal SIL is provided at the leading end of section Ri, and seal SIT is provided at the trailing end of section R1. Likewise, to seal the section R2, seal S2L is provided at the leading end of section R2, and seal 52T is provided at the trailing end of section R2.

Between the pairs of seals SIL, SIT and S2L, S2T, the pipeline 20 contains a fluid retained under pressure in the sections R1 and R2 sufficiently greater than the ambient pressure, for example greater than 25 bar, in order to reduce or completely avert wrinkling of the liner.

As the pipeline 20 is lengthened by joining sections of pipe together and then discharged around the handling apparatus provided on-board vessel 1, the pipe 20 progresses along the lay geometry and through the sections R1 and R2 in which the metallic liner is at risk of wrinkling due to bending of the pipe.

However, as the pipeline 20 moves along lay geometry, the pairs of seals SIL, SIT and S2L, S2T are caused to move in the pipe 20 relative to the pipe. The moving is such that the pressurised sections of the pipe are maintained in position in the lay geometry to correspond to the sections of the pipeline R1 and R2 in which the metallic liner is at risk of wrinkling due to bending of the pipe.

As a result, as the pipe is bent in sections R1 and R2, wrinkling of the liner is reduced or completely avoided by virtue of the locally increased internal pressure. In this way, the thickness of the liner is less than that which would be necessary to avoid wrinkling of the liner were the sections R1 and R2 of the pipeline not pressurised during pipelaying. In this case, the liner thickness corresponds to the thickness needed to protect the carbon steel pipe from corrosion during the serviceable lifetime of the pipeline 20.

Any suitable mechanism for causing the seals to move within the pipe 20 at a rate sufficient to maintain their position (i.e. faster than the slowest welding or other processing stage of the pipeline forming and laying process) in the lay geometry which does not otherwise harm the pipe can be used.

Referring now to Figure 3A, this Figure illustrates one preferred mechanism in accordance with aspects of the invention is to use independently driven crawling electro-mechanical devices or robots' 25 coupled to the leading and trailing seals SL, ST disposed inside pipeline 20 (bending not shown) sealing pressurised liquid P therebetween. Each crawling robot 25 is powered from the vessel 1 by a umbilical (not shown) passing along inside the pipe and is caused to move in the pipe in the direction shown by the adjoining arrows against the direction of travel of the pipe 20, by an appropriate means for locomotion.

Operation and control signals may also be sent remotely to the robots via the umbilical or, alternatively, the robots can be operated by a non-contact remote control method while being powered by a contained power source. Instead of being manually operated by operator-generated control signals, the robots may be partially or entirely automatically operated by program control.

The leading seal SL is pushed backwards in pipe 20 by its associated robot 25, whereas the trailing seal ST is pulled backwards in pipe 20 by its associated robot 25. The crawling robots may move in the pipe by one or more of: a reciprocating crawling mechanism; a helical drive mechanism; a brush drive mechanism; a magnetic engaging mechanism; and a wheeled drive mechanism. Instead of individual robots being provided coupled to each seal, a single robot may be provided inside the pipe to move each pair of seals, or even all seals provided in the pipe, which may be tethered together by appropriate tethering means. The movement and other functioning of the robots 25 may be controlled remotely from an automated controller or a human controller provided on-board vessel 1, or the robots may control themselves using control means provided locally to robots 25.

Referring now to Figure 3B, this shows an alternative mechanism for moving the seals in the pipe to maintain their position relative to the lay profile. Here, no robots are provided but instead a tether 30 is used to couple the leading and trailing seals SL, S1 inside pipeline 22 to a tethering point 31 such as a bulkhead or anchoring loop on vessel 1 (not shown) that remains stationary relative to the pipeline 20 as it is laid.

A preferred method for inserting the seals into the pipeline and maintaining their position to prevent or reduce wrinkling will now be described with reference to figure 4.

In step 401, the leading and trailing seals are inserted in the pipeline as it is being laid. The seals may initially be inserted proximate to each other in the first section of pipe making up the pipeline. However, ultimately the first and second seals are to be arranged such that the pressurised length of the pipeline is greater than the length of the section of the lay profile in which the liner is at risk of wrinkling due to bending of the pipe.

In step 402, the space in the pipeline between the leading and trailing seals is flooded and pressurised to a pressure sufficient to reduce or avert wrinkling in the desired risk section of the lay profile. This may be achieved by pumping water into the pipeline between the seals under pressure. Preferably this flooding and pressurising is performed while the pipeline is being lengthened by joining sections of pipe together and while the first pipe section is progressing out into the lay geometry. Preferably, simultaneously with the flooding and pressurising, the trailing seal is being moved until the distance between the leading and trailing seals corresponds to the length of the section of the pipeline to be protected from wrinkling.

In step 403, the pipeline is extended preferably by welding sections of pipe together on the pipelaying vessel to form the pipeline. By extending the pipeline, the pressurised section of the pipe is progress through the lay geometry.

In step 404, when the pressurised length of the pipeline reaches a position along the lay profile in which the liner is at risk of wrinkling due to bending of the pipe, the process moves on to step 405 in which the seals are caused to move in the pipe to substantially maintain their position with respect to the lay profile as the pipeline is laid.

Where there is more than one section of the pipeline at risk of wrinkling during laying, the pairs of seals may be inserted one after the other in-line and moved in the pipeline appropriate place such that the entire length of the pipeline is protected from wrinkling during laying.

While the method of aspects of the present invention has been described in detail above in the exemplary embodiment in the context of a G lay geometry method, the present invention is not limited to any specific lay geometry and can be used to reduce or avoid wrinkling in any laying method in which the liner of the pipeline is at risk of wrinkling to bending. For example, the method can be readily used in S lay and J lay methods and also in other geometries such as that used in the GSP Falcon.

The present invention finds particular utility in laying methodologies where sections of mechanically lined pipe are joined together on board a pipelaying vessel or lay barge in order to form a pipeline. However, the present invention may also be used to prevent wrinkling in an internal liner of pipe due to bending during the handling or laying of the pipeline while the pipeline is being formed in contexts other than on a pipelaying vessel.

For example, the present invention may be used in the context of a spoolbase. Referring to Figure 5, it can be seen that a spoolbase 500 is laid out adjacent a shoreline 501 to produce and store long lengths of pipe, i.e. "pipestalks" 502, such as rigid MLP, for later collection by a reel laying vessel 503 by winding the lengths of pipe onto the reel 504 provided thereon.

Although illustrated in Figure 5 side-by-side, the pipestalks 502 may be stored in a rack (not shown) arranged around the spool base.

To produce the pipestalks 502, sections of pipe 505 are fed to pipe welding and firing line 506 where the pipe sections are joined, for example by one or more welds, tested and processed according to any other necessary steps, and from there the pipestalks 502 progress along the storage racks towards bending means 507 as additional sections of pipe 502 are joined to lengthen the pipestalk 502.

To conserve space, for example where geographical or topographical circumstances limit the available space, or to maximise the capacity and reeling efficiency of the spoolbase 500, bending means 507 is provided to bend the pipestalks so that they double-back on themselves, doubling the length of the pipestalks 502 that can be stored at spoolbase 500, or halving the space needed for spoolbase 500. While a single 180 degree bend is shown in spoolbase 500, more bends, of a higher or lower angle, may be provided to bend pipestalks 502 in tighter spaces, or around available space due to local topography.

The bend 507 however provides a section S3 of the pipe in which, where lined pipe, such as CRA-lined MLP, is being produced, the liner is at risk of wrinkling or deforming due to bending of the pipe. To reduce wrinkling or avoid wrinkling entirely, the above-described methods can be utilised. For example, leading and trailing seals SL, S are inserted into pipestalks during production spaced a length greater than R3 apart, and the length of pipe therebetween is flooded and pressurised. When the pipestalk has passed through 53, the seals SL, ST are caused to move to protect pipe in 53 from wrinkling of the liner. As the pipestalks 502 are reeled onto vessel 503, the seals SL, ST are similarly caused to move to protect the pipe liner in 53. After pipestalk production has finished and the pipestalks are to be spooled onto a reel 504, a suitable additional method to protect the pipe during winding/spooling onto the reel may be used, but that is not part of this invention.

Claims

Claims: 1. A method for reducing or completely averting the wrinkling of an internal liner of a pipe for use in a subsea pipeline while the pipe is being produced, the method comprising: sealing a length of the pipe using first and second seals; flooding the length of the pipe between first and second seals with a fluid and pressurising the fluid; and causing the first and second seals to move relative to the pipe as the pipe is lengthened by joining sections of pipe to maintain a locally increased internal pressure in a section of the pipe in which the liner is at risk of wrinkling or deforming due to handling or bending of the pipe.
2. A method as claimed in claim 1, wherein the pipe is rigid pipe, preferably mechanically lined pipe (MLP), wherein even more preferably the liner is made of a corrosion resistant alloy.
3. A method as claimed in claim 1 or 2, wherein the locally increased internal pressure is maintained in a section of the pipe that is subject to elastic deformation and/or plastic deformation.
4. A method as claimed in claim 1, 2 or 3, wherein the locally increased internal pressure is only applied in sections of the pipe in which the liner is at risk of wrinkling or deformation due to bending or handling of the pipe.
5. A method as claimed in any preceding claim, wherein sections of the pipe other than the section subject to the locally increased internal pressure have a substantial absence of increased internal pressure.
6. A method as claimed in any preceding claim, wherein the first and second seals are caused to move relative to the pipe as the pipe is lengthened by operation of independently driven mechanical conveying means provided inside the pipe.
7. A method as claimed in claim 6, wherein the independently driven mechanical conveying means is configured to move along inside the pipe at a rate substantially corresponding to the production rate, optionally over the period of one or more pipe joins.
8. A method as claimed in claim 6 or 7, wherein the mechanical conveying means is a crawling robot.
9. A method as claimed in claim 8, wherein the crawling robot moves in the pipe by one or more of: a reciprocating crawling mechanism; a helical drive mechanism; a brush drive mechanism; a magnetic engaging mechanism; a tracked mechanism; and a wheeled drive mechanism.
10. A method as claimed in any of claims 6 to 9, wherein the independently driven mechanical conveying means is powered and/or controlled from the pipelaying vessel via an umbilical and/or via a remote non-contact system.
11. A method as claimed in any of claims 1 to 5, wherein the first and second seals are caused to move relative to the pipe by tethering the seals to a fixture unmovable relative to the pipe as it is being produced.
12. A method as claimed in any preceding claim, wherein the pressure in the pressurised section of the pipe is sufficient to avert wrinkling in the liner due to the bending or handling.
13. A method as claimed in any preceding claim, wherein the thickness of the liner is less than that which would be necessary to avoid wrinkling of the liner were the section of the pipe in which the liner is at risk of wrinkling due to bending not pressurised during handling and/or laying.
14. A method as claimed in any preceding claim, further comprising: inserting first and second seals in the pipe as it is being produced and pressurising the pipe therebetween; welding sections of pipe together to form the pipe; and when the pressurised length of the pipe reaches a position in which the liner is at risk of wrinkling or deformation due to bending or handling of the pipe, causing the seals to move in the pipe to substantially maintain their position with respect to the section of the pipe at risk of wrinkling or deformation as the pipe is lengthened.
15. A method as claimed in any preceding claim, further comprising arranging the first and second seals such that the pressurised length of the pipe is greater than the length of the section of the pipe in which the liner is at risk of wrinkling or deformation due to handling or bending of the pipe.
16. A method as claimed in any preceding claim, further comprising laying the pipe from a pipelaying vessel as the pipe is produced by joining together sections of pipe.
17. A method as claimed in claim 16, wherein the pipelaying method is S-lay, J-lay or G-lay.
18. A method as claimed in claim 16 or 17, wherein the pipe is formed by joining together sections of pipe at an on-board station, the method optionally further comprising forming the pipe by joining together sections of pipe at an on-board station, and optionally the pipeline is not unwound from a reel on the pipelaying vessel.
19. A method as claimed in any of claims ito 15, further comprising handling the pipe for storage at a spool base as the pipe is produced by joining together sections of pipe, where the pipe is stored in a bent configuration ready for later winding on to a reel.
20. A method as claimed in any preceding claim, comprising causing the first and second seals to move so as to substantially maintain their position with respect to the section of the pipe at risk of wrinkling or deformation due to bending or handling of the pipe as the pipe is lengthened.
21. A method as claimed in any of claims i to 15, wherein the method is used to maintain a locally increased internal pressure in a section of the pipe as the pipe passes through a bend: in the pipeline as it is handled by apparatus on the deck of a pipeline laying vessel before it is laid; in the lay geometry as the pipe is laid from a pipeline laying vessel; or in the storage geometry of the pipe in a spoolbase.
22. A method for use in laying a pipeline of joined sections of pipe having an internal liner, the method comprising: laying the pipeline from a pipelaying vessel as the pipeline is formed by joining together sections of pipe; sealing a length of the pipeline using first and second seals; flooding the length of the pipeline between first and second seals with a fluid and pressurising the fluid; and causing the first and second seals to move relative to the pipe as the pipeline is lengthened to maintain a locally increased internal pressure in a section of the pipeline in which the liner is at risk of wrinkling or deforming due to handling or bending of the pipe.
23. Apparatus for maintaining a pressurised section within a pipe as it is being produced 25, comprising: means for maintaining a seal in the pipe; and independently driven mechanical conveying means for moving the seals along inside the pipe, wherein the independently driven mechanical conveying means is configured to be operable to move along inside the pipe at a rate substantially corresponding to the production rate.
24. Use of apparatus as claimed in claim 23 in accordance with any of the methods of claims ito 22.
25. A method for use in handling and laying a pipeline of joined pipe sections having an internal liner, comprising: maintaining a locally increased internal pressure in a length of the pipeline over a section of the pipeline in which the liner is at risk of wrinkling or deformation due to handling or bending of the pipe while the pipe is lengthened due to production.
26. A method as claimed in claim 25, wherein the bending is due to the lay profile of the pipeline caused by the geometry of the pipeline laying method.
27. A method for reducing wrinkling of an internal liner of a pipe for use in a subsea pipeline while the pipe is being produced substantially as hereinbefore described, with reference to the accompanying drawings.
28. Apparatus for maintaining a pressurised section within a pipe as it is being produced substantially as hereinbefore described, with reference to Figures 1A, 1B, 2 and 3A or Figures 1A, 1 B, 2 and 3B or Figures 3A and 5 or Figures 3B and 5.