EP-4532966-B1 - A SAG BEND SUPPORT DEVICE FOR AN UNDERWATER PIPE, AND A PIPE LAYING SYSTEM COMPRISING THE SAME

Inventors

• ROBERTS, PETER

Dates

Publication Date

20260506

Application Date

20230525

Claims (12)

1. A sag bend support device (1) for attachment to an underwater pipe (3) being laid, the sag bend support device (1) comprising at least two supports (9) for slidable attachment to the pipe (3) and at least two buoyancy elements (7), and being configured to support the sag bend to reduce the radius of curvature of the sag bend and thereby limit bending stresses in the pipe (3), wherein each of the supports (9) is associated with at least one of the buoyancy elements (7) for imposing a buoyant force (U 1 , U 2 ) thereon, characterised in that the supports (9) are joined to one another via a tether (8), and wherein the tether (8) is attached to a leading one of the supports (9), in a direction of sliding travel along the pipe (3), and extends to and slidably engages with a trailing one of the supports (9) before terminating at the at least one buoyancy element (7) that imposes a buoyant force (U 1 ) on the trailing one of the supports (9).
2. A sag bend support device as claimed in Claim 1 further comprising a braking mechanism for controlling the sliding of at least one of the supports along the pipe.
3. A sag bend support device as claimed in Claim 2, wherein the braking mechanism is arranged to apply a constant or variable braking force.
4. A sag bend support device as claimed in any preceding claim, wherein one or more of the supports comprises one or more wheels, rollers or tracks for engaging the pipe to assist sliding movement of the support along the pipe.
5. A sag bend support device as claimed in any preceding claim, wherein at least one of the buoyancy elements comprises a gas filled bag.
6. A sag bend support device as claimed in any preceding claim, wherein the tether comprises a cord, cable or strap.
7. A sag bend support device as claimed in any preceding claim, wherein the buoyancy elements are configured such that the buoyant force imposed on the two supports is different.
8. A sag bend support device as claimed in any preceding claim, wherein the trailing one of the supports comprises a pulley (16) or capstan (17) for slidably engaging with the tether.
9. A sag bend support device as claimed in any preceding claim, wherein the leading one of the supports comprises at least one of the buoyancy elements attached thereto, preferably wherein the arrangement of the buoyancy elements is such that a greater buoyant force is imposed on the leading one of the supports than on the trailing one of the supports.
10. A sag bend support device as claimed in any preceding claim, wherein at least one of the supports comprises a frame (14), which is pivotally mounted to a trolley that slides along the pipe.
11. A pipe laying system comprising a lay vessel (5), a pipe (3), and a sag bend support device (1) as defined in any of the preceding claims for supporting a sag bend of the pipe (3).
12. A pipe laying system as claimed in Claim 11, which is configured to maintain at least one of the supports at a constant distance along the pipe from the lay vessel.

Description

The present disclosure relates to a sag bend support device for supporting the sag bend of an underwater pipe during installation. It further relates to a pipe installation system comprising the sag bend support device, and a method for installing an underwater pipe using the sag bend support device. Marine pipelines are generally installed onto the seabed in a manner analogous to the installation of marine telephone or power cables, wherein the top of the cable is paid out under tension by an installation cable laying ship as it moves ahead. The cable thereby hangs in a catenary shape under a horizontal force sufficient to prevent a sharp bend forming in the most vulnerable section of the cable known as the "sag bend", which lies just above the seabed. The same principle applies to marine pipelines but the major distinction between cables and pipelines is that a pipeline is generally significantly heavier and less flexible than a cable, necessitating a significantly larger and more robust installation vessel. Pipe lay vessels are typically built in one of three generic configurations: 1) S-Lay configuration.2) J-Lay configuration.3) Reel-Lay configuration. An S-Lay configured vessel has the pipe departing over the stern of the vessel substantially horizontally such that the pipe bends twice into a double catenary with a convex bend downwards through the sea surface and a concave bend back towards the horizontal in the sag bend just above the seabed. This was the original technique employed on thin-walled pipe in shallow water where the vessel could be a dumb barge laying the pipe whilst pulling itself forwards on multiple anchors, reset sequentially by anchor-handling tugs in a manner analogous to a spider or crab walking. Such shallow-water pipelines are usually covered in concrete to protect them but more significantly, to give them sufficient negative buoyancy to sink onto the seabed and remain in place in the presence of the high currents often associated with shallow water. Such S-Lay vessels may also have a curved framework, or "Stinger", projecting beyond the stern of the vessel to help control the convex bend of the pipe downwards as it passes beyond the stern of the vessel. J-Lay configuration vessels are employed in deeper water where continuously anchoring and re-anchoring the vessel is impractical. The horizontal force on the pipe is provided by steerable thrusters on the vessel. The pipe hangs more nearly vertical off the vessel in a single catenary to minimise the necessary horizontal force being induced by the thrusters. Such pipe is generally not weight coated but has sufficient negative buoyancy to remain in place once laid because of the thick steel pipe wall needed to resist hydrostatic pressure at such depths. The speed at which any pipe laying vessel can move forwards is affected by multiple issues including how quickly new pipe inventory can be re-stocked onto the pipe lay vessel out in the open sea and in particular by how quickly each weld between pipe sections can be made and inspected to be proven sound. The J-Lay technique usually necessitates making repeated vertical pipe welds on sequential sections of heavy pipe with very high wall thickness. Reel-Lay configuration vessels mimic cable-laying practice by bending the pipe around a large vertical drum or into a large horizontal carousel. The pipe is deformed plastically twice as it is reeled and unreeled once again. Reel-installed pipe is generally of low diameter and cannot be concrete weight coated as such coating would break off when reeled. Prior art arrangements are known from WO 2015/185951, US 4065822 and CN 114044096. Several generations of marine pipeline installation vessels (hereinafter referred to as lay vessels) have now been commissioned over many decades with increasing axial tension and horizontal force capability at each generation to match the increasing water depth of oil and gas reservoirs under exploitation. The largest current generation of lay vessels, however, has now reached its limiting pipe lay depth capability as calculated using the code of recommended practice. The depth beyond which code compliance cannot be met by any particular pipeline is influenced by two code requirements. Firstly, the code specifies a minimum recommended wall thickness limited by the risk of hydrostatic external pressure collapse at the proposed depth of installation. Secondly, the code specifies a maximum recommended combined bending and compressive stress that is acceptable in the Sag Bend region at that depth. Increasing the water depth into which the current large vessels can lay pipe would increase the net weight of the pipe being supported in a catenary. Firstly, it would not be possible to avoid exceeding the maximum code-recommended combined bending and compressive stress that is acceptable in the Sag Bend region. Secondly, there would be the risk of overloading the mechanical handling gear on the lay vessel, which mig