NO344320B1

NO344320B1 - Pipe system for connecting subsea infrastructure

Info

Publication number: NO344320B1
Application number: NO20181109A
Authority: NO
Inventors: Jan-Allan Kristiansen
Original assignee: Kristiansen Jan Allan
Priority date: 2018-08-24
Filing date: 2018-08-24
Publication date: 2019-11-04
Also published as: WO2020040645A1

Description

PIPE SYSTEM FOR CONNECTING SUBSEA INFRASTRUCTURE

This invention relates to a pipe system for connecting installations on the seabed, wherein the pipe system comprises a pipe having two end sections and a plurality of intermediate pipe sections being arranged substantially parallel in a first position, and a pipe connector arranged on each end section for connecting the pipe to the installations.

Background of the invention

The maturing of the subsea technology industry and the constant implementation of more cost-efficient solutions is a driver to invent, develop, test and bring about new costefficient systems and solutions to the market. This to reduce the dependency on high-cost factors such as specialised manpower, large fabrication facilities, large vessels and extensive seabed preparations prior to installation. Another incentive being to reduce the cost related to future de-commissioning and removal of the systems once the field is shut down. Furthermore, a general reduction in dimensions, cost, vessels size etc. leave the industry with a less resource-intensive system and hence a system that may be considered much more environmentally friendly.

One of the substantial cost drivers that has been an incentive for developing the invention, is to be able to reduce the requirement for seabed stabilisation on the location were an inline tee tie-in point is to be located. Conventional technology requires stabilisation of the pipeline at the tee itself, as well as stabilisation of the tee protection system. The stability requirement is normally solved by constructing a rock blanket on the seabed that is acting as a foundation for pipelines laid onto it. This blanket is constructed on location prior to installing the pipeline with the intention to act as a foundation for the in-line tee units and its local protection to provide stability against any overturning forces and moments acting on the tee protection from other industrial activity such as fishing and trawling.

Furthermore, today’s technology encourages the final pipe fabrication to be performed onshore after installing the subsea production facilities and after processing the metrology data defining distances and angles for the so-called tie-in spool. It is a cost reducing driver to come up with a system that is versatile enough to allow such final post metrology fabrication to be performed offshore, preferably immediately after the production structure is installed, and from the same vessel, to avoid a separate spool installation and tie-in campaign. The invention allows this to be performed within a fully enclosed, covered-up and controlled environment on a vessel deck when at sea. The reduced number of variable parameters to be defined with regards to the metrology weld locations may allow such work to be completed within minutes and on-board the vessel shortly after metrology is performed.

Field joint preparations and fabrication of the field joint that needs be performed after welding can also be performed in a controlled manner, even in cases were a mould is to be used. It is fully feasible to maintain a controlled environment for the most complex field joint operations as well.

Known prior art

Today, there are different systems on the market to connect for example a pipeline end to a platform riser, as well as to connect subsea production facilities to a pipeline end and to in-line connection points along the pipeline.

In harsh environments and in areas were fishing activities are predominant, such subsea structures are all covered up, in most cases with a retrofit protection structures in the form of individual GRP covers, but also in the form of covers applied to an integrated spool lifting and installation system.

A description of a typical spool and spool protection system and how it is prepared, installed and protected is outlined below:

- The pipeline with its connection point, either at the pipeline end or at the in-line tee connection point, is laid onto the seabed by a dedicated lay vessel;

- A subsea production unit, template or satellite with its manifold piping and valves, is installed close to the pipeline connection point;

- A detailed metrology is performed to fully define the two ends relative each other in three dimensions. The two ends being the connection points on the pipeline and the subsea unit;

- The metrology data is processed to determine the final geometry of the spool and the spool metrology welds are performed onshore. Today the spool sizes dictate this process to be performed onshore close to a load out site to facilitate a direct lift to the installation vessel after completion of the metrology welds, coating and testing;

- The spool is often test lifted using dedicated lift spreaders adjusted to suit the spool; - The spool is loaded onto the vessel together with the lift spreader and sea fastened.

Such vessels will normally also carry dedicated tie-in tooling and protection covers if deck space allows;

- The vessel arrives in the field, set up on location and install the spools onto the seabed. Dedicated tie-in tooling is deployed to complete the last stages of the pull in to mate the hubs and to connect the spool to the manifold interface and the pipeline interface;

- The site is inspected, and the GRP covers are installed over the spool between the two connecting interfaces;

- The final stabilisation of the GRP covers is performed by a separate rock dump operation of a dedicated vessel after the tie-in vessel has performed its work and left the premises.

An alternative method is disclosed in document GB 2520717, describing a method for integrating a tie-in spool with its protection system such that it can be installed as one unitised system.

Document WO 2012/004665 discloses a method for how to arrange a three-dimensional spool to minimize tie-in loads and its main dimensions within a framed system ready for installation and tie-in to the subsea pipeline end and the template manifold end.

Problems and disadvantages with the known prior art

The known issues and problem areas associated with known prior art are pointed out and discussed below:

- The spool and its routing from the pipeline connection to the template manifold interface normally require a large footprint on the seabed, especially to cater for a large pipeline end expansion, a large distance between the two connecting hubs and to allow a large enough margin to either side of the movement envelope of the spool to allow setting of individual GRP covers just sufficiently stringent to ensure the spool is free to move underneath when it is stabilised by external means of rock dump.

- The individual spools are normally of substantial height and length that require a lifting beam system to follow its shape, making the system cumbersome to design, fabricate, test and use.

- Individual spools often require a large amount of deck space. The total lifted weight, including the raised pipe connectors, is normally high.

- Normally, the limited flexibility in the spool systems used to day, impose relatively large forces and moments from expansions of steel flow lines and pipelines reacting into the connection points.

- A large amount of rock dump is both required and used for stabilisation of the required spool protection structures. This also applies for the cases where a caged protection structure has been included instead of a GRP-system.

- A general disadvantage related to the use of conventional systems is the congestion of the seabed over a larger area and at an increased number of locations to allow flowlines and other lines to be laid in pre-tie-in configurations prior to a separate tie-in campaign to take place. This is particularly relevant if drilling is performed on the actual location.

- At locations where spools are tied into pipeline in-line tees the tee structure includes a take-off bend, some piping, an isolation valve, a tie-in porch with a second barrier seal off hub. Such tee arrangement is positioned at the top of the pipe, and since the structure is rather high, easily up to 2-3 meters or more, its protection structure needs to be of substantial length and width to withstand fishing loads without causing local damage and or lateral motion to the pipeline. The required initial seabed stability is in most cases provided by a blanket of rock being applied onto the soft seabed often up to 20 meters wide, 25 meters or longer and at some locations 1,5-2 meters thick. In other words, a substantial amount of rock is required to ensure the tee protection structure is stable. The inherent problem is that the structure is relatively high relative to its width and length, and these relative proportions require stabilisation firstly by the stabilisation layer of rock installed onto the seabed, then by the protection cover itself and lastly by additional rock around the structure to increase its stability against transverse movement and overturning movement.

Other known problems are related to the use of large vessels, use of specially designed intervention equipment, the requirement for separate installation trips, and a distinct number of trips dictated by the number of spools and the chosen protection systems.

The invention and its use

The invention is a versatile system that may be used for integration of any spool and spool specific components or tie-in component that either ties in to a pipeline in-line tee hub, a template or satellite hub, a pipeline end manifold, Pig Launcher & Receiver (PLR), Wye piece or valve, such as an Emergency Shut down Valve (ESV) close to a platform or alike. The invention may include the control for integrated units, e.g. for valves pertinent to an ESV / riser base. It may contain the systems and the operation of systems used for connections to a rigid riser connection or a flexible riser as well as connecting the spool pipe to an expanding pipeline end, a stationary pipeline point, or a template / satellite manifold end.

In particular when the invention is used close to a platform, the following advantages are envisaged:

- It may provide a direct connection to an expanding pipeline end manifold at one end and providing a fully stable connection at the other end for connection to the riser end without any spool sweeping movement along the seabed outwit the system boundaries;

- It may provide an unrivalled pipeline expansion take up capacity while maintaining a smaller footprint compared to any comparable steel spool. A narrower approach route is highly regarded close to a platform approach route and the reduced seabed footprint of the invention allow an increased number of approaches to be allowed as direct approaches to a platform and thereby saving significant cost in that it in general is allowing a shorter approach route for other adjacent sea lines;

- It may allow for the inclusion of an emergency shut down system with its valves (ESV) and controls to be integrated in the spool system without adding required seabed footprint;

- It may allow for the inclusion of valves and wye-piece take-off in the integrated unit to save valuable seabed space;

- It may allow for a direct connection to a flexible riser to allow the integrated system to act as a fully stable riser base;

- It may allow for an integrated storage and protection to an umbilical distribution assembly if found applicable to the field development and/or to control any integrated controls and or valve systems, and

- It may provide a system for a common installation with inbuilt protection of the integrated units.

If the invention is used for tie-in of templates / satellites to e.g. pipeline in-line tees and alike it will maintain similar advantages as described above, with some additional advantages, as described in the following:

- It may allow for a direct connection to any part of a pipeline either susceptible to expansion or anchored to the ground via an in-line tee or a pipeline end manifold or similar, even after start-up of the pipeline if the barriers for the pipeline connection points are in place;

- It may allow for the inclusion of a Wye Piece branch for a direct spool to adjacent pipeline take-off. Such branch will normally include a shut-in valve and a blind hub. Such arrangement will also allow inclusion of a Pig Launcher and Receiver (PLR) connection unit into the integrated system if found advantageous;

- It may be designed to compensate for large pipeline expansions due to its in one embodiment spatial configuration. This embodiment is especially useful if the connection point is at the end of a pipeline transporting an internal medium of high pressure and temperature close to subsea producers;

- It may e.g. allow for the inclusion of a valve system positioned in line with the spool pipe and parallel to the pipeline and supported by the structure. This may enable moving the isolation valve and the tie-in hub at the in-line tee away from its conventional location atop of the pipeline to be integrated with the invention, giving the advantage that the passage of tees through tensioners on the pipeline lay barge is removed as a severe installation hassle and a potential hazard;

- It may allow for an internal umbilical routing in the integrated structure to potentially benefit future step outs and /or being used as landing space and protection for an Umbilical Termination Assembly (UTA) if the field control lines distribution requirements finds this as beneficial;

- It may be configured as an integrated spool installation frame;

- It may be configured as an integrated spool protection system, and

- It may allow for simplified ROV / AUV access compared to existing state of the art technology.

More specifically, the invention also has the following unique advantages in that it:

- Provides production and assembly support during the system fabrication process; - Simplifies site transportation and load-out since it can be temporarily moved from one location to another by adding several individual wheels directly to its structural members;

- Allows direct sea-fastening support utilising strong points directly in its structural

members;

- Is its own strong-beam with direct connection of lift rigging without use of an external lift beam. This reduces required lift height and crane head room significantly and thereby reduces related lifting hazards;

- Provides long-term protection and structural stabilitty against industrial activity and dropped objects without having to utilise additional overlaying glass-reinforced polymer (GRP) structures or concrete mattresses or alike when placed on the seabed. In particular the invention may maintain an open frame structure and still include the required resistance against trawling and falling objects from surface activities;

- Allows for a direct integration of concrete mattresses or alike to avoid rock dumping for stability purposes if the system design show this as beneficial for the area it is used within;

- May be integrated with skirts to the underside of its structural frame in contact with the seabed to act as stability means agains seabed motion caused by external loading, and

- May be integrated with gravity based fall down units, flat foundations or similar structures pivoted off the main frame to allow additional seabed stabilisation means allowing additional weight to be applied. Integrated skirts that penetrates into the seabed soil may be also included on the pivoting units as well for added stability. One may even easily integrate local guide funnels onto the main structure of the invention that allows mini piles or similar to be hammered into the seabed soil for a set length. All the above may be integrated at the same time if found advantageous.

Further the invention is a versatile system for inclusion of lifecycle operations in that it may:

- Allow for a simpler retrievability at end-of-fieldlife due to its inherent strong-backed functionality for lifting and the fact that it does not require deburial from rock coverage to the degree that todays state of the art systems do;

- Provide inclusion for permanent and / or temporary parking for, as well as being highly accessible for, ROV / AUV systems used for monitoring of components and/or systems, and

- Allow for incorporation of movable hatches for direct access to included equipment.

The invention may be used in harsh environments where fishing activities are expected and where production equipment and units located on the seabed need to cater for repeated impacts and interfaces with fishing gear.

The invention and its various embodiments are sufficiently versatile to be used as a structural link for connections between two opposite expanding pipelines, and on pipeline ends where one or both lines are having its integration to the unit as a mid-line connection point.

The invention is envisaged to co-operate seamlessly with existing spool and tie-in components and technologies used in today’s offshore oil and gas market, and will therefore complement and improve existing technology to achieve the following;

- Be a low-cost alternative to existing systems;

- Have an overall low weight compared to existing systems;

- Provide a reduced on-the-seabed footprint compared to existing systems;

- Allow equally good or better protection to sensitive equipment compared to existing systems;

- Allow enough see-through when inspection units are positioned for such tasks (inspection maintenance and repair) while maintaining all its functionalities as described herein;

- Be significantly smaller in size as compared to conventional systems to allow lighter vessels to perform transportation and installation;

- To allow for implementation of AUV- and ROV-complementary equipment;

- Allow easy change-out of valves, PLRs etc. that may be included in the system, and - Allow for alternative types of additional foundation systems implemented as dictated by external industrial activities at the relevant seabed location.

The invention is intended to remedy or to reduce at least one of the disadvantages of the prior art, or at least provide a useful alternative to prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

Main objectives of the invention

The main objectives of the invention are described in the following:

- Ensure that a spool system in a looped and spatial configuration can be ascertained within a frame system that ensures full protection of all spool legs;

- Allowing both transverse and longitudinal adjustments of the spool housing structural frame to take place on the vessel after metrology to ensure that the leg connecting to the relevant template lock down point suit the existing template interface;

- To achieve weight reduction, dimensional reduction, reduced material consumption, to allow for the use of smaller installation vessels and to allow for a reduction in site preparations;

- To allow for system flexibility to a point where it is not the spool structural relations and or stress relations that dictates the spool size between connection hubs, but the field architecture in the sense that structures need to be installed with a distance apart from its connection point on the pipeline to the template manifold. The minimum required separation distance would still not be dictated by the spool system. The invention being able to reduce the theoretical minimum distance between its connection points so that the length of the pipe can be predominantly determined by a field architectural assessment;

- To integrate the spool, the spool protection and the spool lifting device into one common assembled unit that is both handleable, installable, and that provide seabed stability as well as protection;

- To be installable through the water surface at a higher sea state than what is possible for any of the individual objects being installed separately using the known prior art; - Allow inclusions of valves in the system so that the valves can be removed from e.g.

the pipeline in-line tee system and onto the invention itself. Further, to allow the valve assembly to be retrievable from the spool itself for repair or replacement. Such operations being fully reversible in the sense that a new valve assembly may be installed onto the system;

- Allow inclusion of pipe manipulating features to allow spool end sections to be movable in all major axes of freedom to simplify and ease end connections with use of low capacity tie-in tools. And so that the tie-in tools may be designed to fully favour the clamp closing force required to obtain a fully tight sealing;

- Allow inclusion of local protection systems to individual and moving spool legs inside the system. This allows for rock ingress into the mid part of the piping system without compromising the functionality of the spool. It shall be noted that this is a totally new and fundamental change to any presently known subsea spool system requiring protection structures;

- Allow spool branching / off takes to be included directly to spool legs;

- Allow inclusion of Wye pieces if needed for a branch off-take to another subsea satellite or template location;

- Allow inclusion of umbilical lines (electrical, optical, hydraulic and alike) and umbilical termination assembly (UTA) parking locations in the structure. Allow for integration of umbilical line jumpers to other units and manifolds;

- Allow for inclusion of or possibility for connecting a PLR if required. A PLR will require a so-called wye piece to be present for pig running to the receiving PLR;

- Reduce the system overall weight and reduce overall complexity in that a reduced number of individual units are required to fulfil the operational functionality;

- To reduce the requirement for pre-installation of equipment, seabed intervention and pre-installation preparations in the form of rock dump;

- To reduce the requirement for use of post installation seabed stabilisation means such as rock dump by dedicated vessels;

- Allow for recovery at end of field life without other operations than internal pipe cleaning prior to disconnecting and direct lift off to surface vessels using the existing structures, and

- Enable load out and installation with a lower total lifted weight and lower lifting height.

Secondary objectives of the invention

The secondary objectives of the invention are described in the following:

- Initiate pre-tensioning or compression into the spool to allow a reduction in spool dimensions when combining such tension or contraction relative to the required tie-in motions and the later occurring pipeline expansion;

- Reduce the required number of operational steps required in all phases from start fabrication until end of field life to reduce the overall project cost;

- Ensure direct installation of a complete system in one operation that is fully assembled instead of being built up in stages in several offshore operations, and

- Reduce the overall spool dimensional limitation set by vessel size, vessel lift capacity and so on.

The main advantages related to the use of the invention:

- It is applicable for single bore, multi-bore and a combination of spools within one system;

- It offers significant cost saving potential in all phases of a project (design, fabrication, installation and operation);

- It may accommodate existing tie-in systems;

- It offers easy and fast recovery at end of field life;

- It offers considerable reduction in overall dimensions compared to a single Z- or U-shaped spool. Spool size reduction may be more than 60% compared to a similar Z-shaped spool;

- Longitudinal flexibility for ease of axial movements in the spool. The transverse stiffness is still significant, but lower than compared to a Z-shaped spool;

- The frame may act as an artificial seabed with a controllable friction coefficient against the spool legs;

- Simple inspection by for example ROV;

- The frame may act as a supporting structural unit with no requirement for a conventional spreader during transport, load-out, installation and end of field life retrievals; - It may be stacked on the vessel deck and sea fastened for direct lift off.

- No specific sea fastening units for support of termination heads are required.

- It may include an improved axial stroking capacity within a maintained frame footprint as well as possibilities for inclusion of spool pipe supports and vibration damping devices to cater for operational induced vibrations, slugging, water hammering effects and alike.

- Integration into a subsea structure having connection points with limited height removes the requirement for a tie-in porch to be implemented in the template / satellite structure, and

- The high flexibility inherent in the spatial configuration re-distributes forces, moments and deflections to a degree where metrology data may be significantly reduced, even omitted - This in combination with allowance of induction bending of the major spool bends presents the possibility of significant cost reduction.

The invention is defined by the independent patent claim. The dependent claims define advantageous embodiments of the invention.

In a first aspect, the invention relates to a pipe system for connecting installations on a seabed, the pipe system comprising:

- a pipe comprising two end sections and a plurality of intermediate pipe sections being arranged substantially parallel in a first position;

- a pipe connector arranged on each end section for connecting the pipe to the installations;

- a frame for carrying the pipe,

wherein a first intermediate pipe section, in a second position, is configured to cross, by means of a guide, a second intermediate pipe section as a result of a horizontal displacement of the first intermediate pipe section.

An intermediate pipe section should be understood as a section of the pipe arranged between the two end sections.

The invention has the effect that it may significantly reduce the footprint of a pipe, such as a spool, connecting subsea structures and thus reduce cost related to design, fabrication, installation and/or operation. The geometry of the pipe provides a longitudinal flexibility for ease of lateral movements without requiring a large footprint.

The pipe may comprise several hairpin curves arranging the plurality of intermediate pipe sections substantially parallel in a horizontal plane, in the first position. The phrase substantially parallel does not restrict the intermediate pipe sections to be parallel, however, they may deviate from being parallel. In one embodiment, the intermediate pipe sections may be arranged with an angle of up to ten degrees relative to each other.

The first intermediate pipe section may be sloped upwards, in an operable position, such that the end portion of the first intermediate pipe section is arranged at a higher elevation than an end portion of the second intermediate pipe section, and thus the first intermediate pipe section may not contact the second intermediate pipe section in the second position.

The frame may stiffen the pipe system to reduce the risk of damaging the pipe during installation. The frame may further provide a stable foundation for the pipe on the seabed. The frame may even further provide protection against external influences such as dropped objects or trawls. In one embodiment, the frame may carry several pipes.

The frame may embrace the pipe and/or the pipe connectors. In one embodiment, the pipe may be loosely arranged inside the frame to allow the pipe to displace.

A pipe system according to the invention allows for control of where in the pipe the greatest flexibility is to occur and where in the pipe a stationary section or leg should be located when the end sections of the pipe moves. The flexibility of the pipe may be used to preload the pipe from its natural zero load position to allow an intermediate locked position that allows interaction with a long-term creep of a pipeline system, as well as utilising a tie-in tool to connect the pipe under pre-tensioning to later allow a pipeline expansion. This feature allows the footprint of the pipe to be minimised. Further, the pipe may be integrated with a device that allows the pipe connectors to be locked in any axial position to aid connection and disconnection of the pipe to access a tie-in hub.

In one embodiment, a third intermediate pipe section is arranged at a higher elevation than the remaining intermediate pipe sections, wherein the first intermediate pipe section is configured to cross between the second intermediate pipe section and the third inter mediate pipe section in the second position. This embodiment of the invention has the effect that it may further reduce the footprint of the pipe as the intermediate pipe sections are arranged in different planes overlying each other. This spatial configured may reduce a planar extension of the intermediate pipe sections.

In one embodiment, the guide is arranged with a slope such that the first intermediate pipe section is elevated above the second intermediate pipe section in the second position. This embodiment of the invention has the effect that the end portion of the first intermediate pipe section do not contact the second intermediate pipe section in the second position even though the intermediate pipe sections are planar relative to each other in the first position.

In one embodiment, the guide is hinged to the frame and comprising an actuator for rotating the guide about a hinge whereby the slope of the guide is adjusted. This embodiment of the invention has the effect that vertical position of the end portion of the first intermediate pipe section relative to the second intermediate pipe section may be actively and controllably adjusted to avoid contact between the intermediate pipe sections. This may in turn allow for larger deflections in the pipe without the intermediate pipe sections contacting each other.

The actuator may for example be a hydraulic cylinder, an articulated jack or a screw. The actuator may be connected to a driving means, such as a hydraulic pump or a ROV torque tool configured to drive the actuator.

In one embodiment, the frame comprises an end frame slideably connected to an intermediate frame section such that a frame configuration is adaptable to various sizes of pipe. This embodiment of the invention has the effect that the frame may be used for different pipe lengths. Adjusting a position of the end frame may alter a length of the intermediate frame section, thus a length of the intermediate pipe sections may vary while still being complementary to the same frame. This is particularly advantageous where the premetrology data is inaccurate, hence the planned length of the pipe is unsure.

In one embodiment, the pipe system may further comprise a positioning tool configured to adjust a vertical position and lateral position of the pipe end section, wherein the positioning tool comprises an actuator connected to a displacement element coupled with said end section. This embodiment of the invention has the effect that the position of the pipe connector may be manipulated such that it may be aligned with its tie-in point after the pipe system is landed on the seabed. This in turn has the effect that smaller tie-in tools may be employed as only minor alignment is required prior to the tie-in.

In one embodiment, the system may further comprise a protective element over a portion of the pipe. This embodiment of the invention has the effect that it may protect the pipe and/or pipe connectors against dropped objects and/or trawling. In one embodiment, the protective element may be a stiff material such as glass reinforced polymer (GRP) or grating. In one embodiment, the protective element may be a flexible material such as polyurethane jacket and/or rubber jacket. It should be noted that a portion of the pipe may refer to the entire pipe. In another embodiment, the portion of the pipe may be one of the intermediate pipe sections.

In one embodiment, the protective element is clamped to the pipe, the protective element com-prising a void arranged between a lower structural element and a flexible upper structural element such that energy from an object impacting the flexible upper structural element is absorbed by a medium inside the void. The void may be open towards the surrounding sea such that the void is filled with seawater. The protective element may be compact in size such that it fits inside the frame for protecting a portion of the pipe such as one of the intermediate pipe sections. Due to the incompressibility of water it may act as a damping medium when the upper structural element is moved towards the pipe.

In one embodiment, the protective element is buoyant in water, the protective element being slideably connected to the clamp for allowing restricted vertical displacement of the protective element to create a second void between the lower structural element and the pipe when submerged. This embodiment of the invention has the effect that it further reduces the risk of damaging the pipe upon an impact from a dropped object.

In one embodiment, the pipe system may comprise a support member configured to support the third intermediate pipe section, thereby reducing a free span of the third intermediate pipe section. This embodiment of the invention has the effect that it may increase the expected operating lifetime of the pipe as the support member may reduce vibrations in the pipe and thus reduce the risk of a fatigue fracture in the pipe. This is especially advantageous if the third intermediate pipe section is long, for example more than five meters. Free span should be understood as a suspended distance between two pipe supports.

In one embodiment, the pipe system may further comprise a stabilizing unit hinged to the frame, wherein the stabilizing unit, in a flipped down position, is configured to increase the stability of the pipe system when positioned on the seabed. This embodiment of the invention has the effect that it may reduce the need for seabed intervention such as rock dumping to create a stable foundation for the pipe system. The stabilizing unit may provide enough additional support for the pipe system to rest stable on the seabed. As the stabilizing unit is hinged it may be in a folded-up position during deployed from a vessel such that the footprint of the pipe system through the splash zone, i.e. the water surface, is not increased. In one embodiment, the pipe system may comprise several stabilizing units.

In one embodiment, the frame is provided with grating covering openings in the frame. This embodiment of the invention has the effect that the frame provides a shelter for the pipe against external influences. The pipe system may not require additional protection, e.g. GRP covers, to be installed after installation of the pipe system as the protection is integrated in the frame.

In one embodiment, the frame is provided with protruding elements configured to penetrate a foundation such as the seabed. This embodiment of the invention has the effect that it may further increase the stability of the pipe system on the seabed. The protruding elements may restrict sideways movement of the frame. The protruding elements may be a pipe, a skirt and/or a rod.

In one embodiment, the pipe system may comprise a ROV panel operated system using hydraulics or direct holding devices that may move a pipe section in all 6 degrees of freedom to aid connection operations and reduce associated connection loads and moments.

In the following is described an example of a preferred embodiment, illustrated in the accompanying drawings, wherein:

Fig. 1 Shows a perspective view of a pipe system according to the invention;

Fig. 2 Shows a perspective view of a pipe according to one embodiment of the invention;

Fig. 3a Shows a top view of the pipe in a first position;

Fig. 3b Shows a top view of the pipe in a second position;

Fig. 4a Shows a cross section of the pipe system comprising a

guide;

Fig. 4b Shows a cross section of the pipe system comprising a positioning tool;

Fig. 5 Shows a portion of a cross section of the pipe system comprising a stabilizing unit;

Fig. 6 Shows a portion of a side view of the pipe system with the pipe in the second

position, and

Fig. 7 Shows an end frame slideably connected to an intermediate frame section in three different positions; nominal, left and right.

Figure 1 shows the pipe system 1 comprising a pipe 3, also known as a spool, arranged inside a frame 4. The pipe system 1 is shown in a as-installed configuration on a seabed (not shown). The pipe 3 comprises an pipe connector 34a, 34b in each of two pipe end sections 30, see also figure 2. The pipe 3 is shown to comprise three intermediate pipe sections 31, 32, 33. The pipe 3 is shown in a first position wherein the three intermediate pipe sections 31, 32, 33 is arranged substantially parallel to each other, see also figure 3a.

A first pipe connector 34a is shown to be connected to an inline tee 20 on a pipeline 2. A second pipe connector 34b is shown to be free. The frame 4 has multiple purposes, e.g. protect the pipe 3 when installed, provide a stable foundation for the pipe during operation, carry the pipe 3 during installation and simplify the installation of the pipe, i.e. connection to subsea installations.

The pipe 3 is designed to take up displacements in a subsea system, e.g. a pipeline 2. Displacements may arise from for example expansion in the pipeline 2 due to temperature changes inside the pipeline 2. In the event of longitudinal displacement of the pipeline 2, the displacement will be transferred to the pipe 3. The displacement will cause a second intermediate pipe section 32 to move relative to a first and third intermediate pipe section 31, 33, see figure 3b. A guide 5 deflects the second intermediate pipe section 32 such that it crosses between the first and third intermediate pipe section 31.

The third intermediate pipe section 33 is raised relative to the first and second intermediate pipe section 31, 32, see also figure 4a, which reduces the overall footprint of the pipe 3. The frame 3 is provided with support members 8 to reduce the free span of the third intermediate pipe section 33. A long free span may cause fatigue in the pipe 3 as a result of vibrations.

Figure 4a further shows the guide 5 comprising an actuator 50 depicted as a winding system operable by ROV. The winding system 50 is configured to adjust a slope of the guide 5. The guide 5 is connected to the frame 4 by means of a hinge 51.

Figure 4a also shows a protective element 7 connected to the second intermediate pipe section 32 by means of a clamp 70. The protective element 7 comprises a lower structural element 72 disposed partly around said pipe section 32. A first void 71 separates the lower structural element 72 from an upper structural element 73. The first void 71 is open towards the surroundings such that it fills with water when submerged. In case of an impact, for example from a dropped object (not shown), the energy from said object will be absorbed and transferred through the water in the first void 71, thus reducing the risk of damage to the underlying pipe 32.

The lower structural element 72 is raised from second intermediate pipe section 32 to create a second void 74 between said pipe section 32 and the protective element 7. In this particular embodiment, the protective element 7 is buoyant and the clamp 70 is configured to allow the protective element 7 to restrictively travel vertically. Thus, creating said void 74 when submerged. The second void 74 increases the damping effect upon an impact from a dropped object in that the whole protective element 7 will move towards said pipe section 32 and force water to flow around the upper protective element 73. The underlying pipe section 32 will not move until the lower structural element 72 is in contact with said pipe section 32. Thus, the first void 71 and the second void 74 creates a double damping effect.

Figure 4b shows a positioning tool 6 having two actuators 60 for adjusting a lateral position and a vertical position of the pipe end section 30. The actuators 60 are operable by ROV via a torque tool interface 600. The torque tool interface 600 is connected to a length adjustable rod 601. The length adjustable rod 601 is configured to manipulate a displacement element 61a, 61b. A first displacement element 61a is shown as a strop running between the length adjustable rod 601, under the pipe end section 30 and to a fixed point. Stroking the length adjustable rod 601 adjusts the height of the pipe end section 30. A second displacement element 61b is shown as a carriage, wherein the pipe end section 30 is placed in the carriage 61b. Stroking the length adjustable rod 601 connected to the carriage 61b displaces the pipe end section 30 laterally, i.e. sideways.

Figure 5 shows a stabilising unit 9 for increasing a footprint of the pipe system 1 when installed on the seabed. In figure 1 it is shown that the pipe system 1 comprises several stabilizing units 9. Increasing the footprint spreads the load of the pipe system 1 over a larger area, thus increasing its stability. During installation the stabilizing units 9 may be folded up, as can be seen in figure 4a. This reduces the load on a lift rigging from waves during lowering of the pipe system 1 through a water surface, so called splash zone. It also reduces drag through a water column. The stabilizing units 9 are depicted as plates hinged to the frame 4. An underside of the stabilizing units 9 may include a skirt foundation to improve a ground resistance.

Figure 6 shows the pipe 3 in the second position, wherein the first pipe connector 34a has been displaced such that the second intermediate pipe section 32 is rotated and crossing over the first intermediate pipe section 31 and under the third intermediate pipe section 33. The guide 5 (not shown in this figure) ensures that there is no contact between the first and the second intermediate pipe sections 31, 32 by raising the second intermediate pipe section 32 as it is displaced.

Figure 7 shows an end frame 40 slideably connected to an intermediate frame section 41. The end frame 40 carries one of the pipe end sections 30. A lateral position of the end frame 40 relative to the intermediate frame section 41 may be adjusted by sliding the end frame 40 along the slideable connection 301. Thus, a frame configuration may be adapted to suit various sizes, i.e. length, of pipe 3. The pipe end section 30 has a nominal position 300 as shown in detail A. The nominal position 300 is typically set in accordance with field measurements. Detail B shows the frame configuration for a shorter pipe 3, i.e. shorter than nominal 300. Detail C shows the frame configuration for a longer pipe 3, i.e. longer than nominal 300.

Description of mode of operation and use

The invention may be used for several applications. However, it is mainly intended to be used to connect a subsea producing facility (not shown) via its pipe connectors 34a, 34b to the pipeline 2 using a conventional spool 3 that can accommodate the fact that the pipeline 2 is moving relatively the production facility when the internal of the spool 3 is carrying well stream that is under pressure and at an elevated temperature versus the seawater.

The pipe system 1 may be used on all pipelines and interconnected pipelines, with fixed or movable connection points 20.

A typical use of the pipe system is described in the following;

- Various parts of the pipeline 2 are manufactured and assembled on land according to predefined route layouts, required functionalities and dimensions determined by the field lay out and detailed design.

- The required pre-installation seabed preparations are performed prior to start-up of the installation operations.

- The pipeline 2 is laid and its in-line tee 20 location and orientation are defined as part of the lay operation. I.e. the pipeline in-line tee 20 metrology vs. the pipeline 2 parameters is known.

- The subsea production structure (not shown) is installed and its orientation is defined 100% relative its manifold hub (not shown) location vs. the pipeline in line tee 20 hub. - The pipe end section 30 opposite the pipeline 2 is adjusted both transverse and laterally. The pipe end sections 30 are cut and prepared for weld-in to suit metrology results. The pipe 3 is subject to 100% NDE and the exposed pipe 3 segments are field joint coated.

- The pipe 3 is water filled if required and the installation lift is prepared.

- The pipe system 1 is landed on the seabed with the pipe connectors 34a, 34b guided onto the corresponding landing position on the pipeline 2 and on the manifold. These landing / guiding systems are preinstalled at the pipe connectors 34a, 34b.

- Pull-in and connection tooling (not shown) is docked at the pipe connectors 34a, 34b as dictated by the actual tie-in system used. The final mating, connection and testing is carried out and the tooling is moved to the opposite end for a repeat of the operations.

- Finally, the pipe system 1 is stabilised as required by its location requirements, either being sat directly on the seabed or rock dump stabilised to the degree required for by the stabilizing units 9.

Alternative embodiments

- The pipe 3 may be employed to follow a number of layouts ranging from the so called Z configuration, L configuration and U configuration. Even when longer pipe 3 spans are needed, the intermediate pipe sections 31, 32, 33 required to create a high expansion capability may only be along a limited part of the total length of the pipe 3. Other sections may be reduced in structural height and thereby reduce the overall cost. - The intermediate pipe sections 31, 32, 33 may be made in all steel grades according to specific requirements for strength and corrosion resistance requirements.

- Umbilical functions and servicing lines may be integrated into the pipe system 1. - Using an integrated installation and protection frame 4 has the advantage that several pipes 3 may be installed simultaneously within the frame 4.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

C l a i m s

1. A pipe system (1) for connecting installations (2) on a seabed, the pipe system (1) comprising:

- a pipe (3) comprising two end sections (30) and a plurality of intermediate pipe sections (31, 32, 33) being arranged substantially parallel in a first position;

- a pipe connector (34a, 34b) arranged on each end section (30) for connecting the pipe (3) to the installations (2);

- a frame (4) for carrying the pipe (3),

c h a r a c t e r i z e d i n that a first intermediate pipe section (32), in a second position, is configured to cross, by means of a guide (5), a second intermediate pipe section (31) as a result of a horizontal displacement of the first intermediate pipe section (32).

2. The pipe system (1) according to claim 1, wherein a third intermediate pipe section (33) is arranged at a higher elevation than the remaining intermediate pipe sections (31, 32), wherein the first intermediate pipe section (32) is configured to cross between the second intermediate pipe section (31) and the third intermediate pipe section (33) in the second position.

3. The pipe system (1) according to claim 1 or 2, wherein the guide (5) is arranged with a slope such that the first intermediate pipe section (32) is elevated above the second intermediate pipe section (31) in the second position.

4. The pipe system (1) according to claim 3, wherein the guide (5) is hinged to the frame (4) and comprising an actuator (50) for rotating the guide (5) about a hinge (51) whereby the slope of the guide (5) is adjusted.

5. The pipe system (1) according to any of the preceding claims, wherein the frame (4) comprises an end frame (40) slideably connected to an intermediate frame section (41) such that a frame configuration is adaptable to various sizes of pipe (3).

6. The pipe system (1) according to any of the preceding claims, further comprising a positioning tool (6) configured to adjust a vertical position and lateral position of the pipe end section (30), wherein the positioning tool (6) comprises an actuator (60) connected to a displacement element (61a, 61b) coupled with said end section (30).

7. The pipe system (1) according to any of the preceding claims, further comprising a protective element (7) over a portion of the pipe (3).

8. The pipe system (1) according to claim 7, wherein the protective element (7) is clamped (70) to the pipe (3), the protective element (7) comprising a first void (71) arranged between a lower structural element (72) and a flexible upper structural element (73) such that energy from an object impacting the flexible upper structural element (73) is absorbed by a medium inside the first void (72).

9. The pipe system (1) according to claim 8, wherein the protective element (7) is buoyant in water, the protective element (7) being slideably connected to the clamp (70) for allowing restricted vertical displacement of the protective element (7) to create a second void (74) between the lower structural element (72) and the pipe (3) when submerged.

10. The pipe system (1) according to any of the preceding claims, further comprising a support member (8) configured to support the third intermediate pipe section (33), thereby reducing a free span of the third intermediate pipe section (33).

11. The pipe system (1) according to any of the preceding claims, further comprising a stabilizing unit (9) hinged to the frame (4), wherein the stabilizing unit (9), in a flipped down position, is configured to increase the stability of the pipe system (1) when positioned on the seabed.