WO2010049667A1

WO2010049667A1 - Apparatus and method for reducing stress across subsea pipe joints

Info

Publication number: WO2010049667A1
Application number: PCT/GB2009/002477
Authority: WO
Inventors: Alan David Foxton
Original assignee: Subsea7 Limited
Priority date: 2008-10-27
Filing date: 2009-10-20
Publication date: 2010-05-06
Also published as: GB0819688D0

Abstract

An apparatus and method is provided for reducing the stress across welded joints of insulated subsea pipes, wherein the insulating material covering the pipe is reinforcing at least in the region covering the pipe joint. The invention is useful for, inter alia, prolonging the fatigue life of a welded joint, and allowing the use of existing welding and NDT techniques to current pipeline build standards. Otherwise the latter would have to be up-graded, and the performance of the NDT equipment significantly improved.

Description

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Apparatus and Method for Reducing Stress across Subsea Pipe Joints

The present invention relates to a method and apparatus for reducing stress across welded pipe joints, in particular, of joints of pipelines for subsea use.

Pipelines are often used to transport hydrocarbon fluids (oil and natural gas) on land and in marine environments. In the present invention, the term "pipeline" is intended to refer to all types of pipeline or other means for handling such fluids, including risers and catenary risers, tubing strings, etc. The term "pipe joint" is intended to refer to all types of joints formed by pipes welded together in accordance with known techniques. Pipeline can be laid either by welding short lengths of pipe together (J-lay), or welding together longer pipe lengths deployed from a reel (reel lay). With reel-lay pipe, the required pipeline length may be formed from several reels of pipe, each welded together. Pipe joints formed on a marine vessel are generally known in the industry as field joints, and are put together on a workstation on a pipelay ramp on the vessel. A typical reel lay system is shown in Figure 1. Such a system comprises a ramp/tower 1 comprising a curved guide 7 and A&R (Abandonment and Recovery) winch system 10, mounted on a pipe-lay vessel 2, equipped with a straightener 3, tensioner 4, work station 5, hold off clamp (HOC) 6 and reeled pipe storage reel 8, for laying and welding reeled pipe 9. Typical J-lay systems use similar equipment to that shown in Figure 1 , except that instead of a reel, the pipe lengths are held in suitable racks, and fed individually to the ramp.

Exploration and recovery of oil and gas is being conducted in ever increasing depths of water; consequently pipelines are being laid in these deep waters.

The lower ambient temperature of the depths at which some subsea pipelines are laid may be such that the oil becomes too viscous to flow at an economic rate, and ultimately the flow may be blocked by the formation of hydrates and the like. To ensure that the oil continues to flow, subsea pipelines are generally covered with a thick thermally insulating outer layer.

The laying of pipeline in deep waters results in large suspended weights of pipe between the pipe-lay vessels and the seabed. This, in turn, increases the stresses on the welded pipe joints. These welds must be of high quality. In anticipation of increased stress levels on these pipe joints, inspection can involve searching for weld defects with a length of 0.5mm or less, which exceeds the discrimination capabilities of the equipment and systems currently used for N on -destructive Testing (NDT), in particular, of those that are based on ultra-sonic techniques, which are the ones most commonly used in the Oil and Gas Industry for such work.

The problem lies with the known limitations of the currently used NDT equipment in detecting small defects. Reinforcing the joint means that larger defects can be tolerated in the welded joints of otherwise highly stressed pipe, and being of a larger size, means they can be detected by existing NDT systems.

Thus there is a need for reducing the stress on welded pipe joints, particularly in deep-water applications. There is also a need for reducing the sensitivity of a welded pipe joint to the failures that may be induced by small defects introduced during the welding process.

The present invention solves or alleviates the problems of the prior art. In broad terms, the present invention provides an apparatus and method for reducing stress across welded pipe joints in pipelines for subsea use, whereby the pipe joint is reinforced locally by replacing standard thermal pipe insulation at the welded field joints, either wholly or partially, with a suitably shaped higher modulus material. By reducing the stress across welded pipe joints, in particular, stress caused by bending, the present invention allows for a longer fatigue life of the joints and reduces the number of joint weld repairs required. Furthermore, by decreasing the pipe joint sensitivity to failure caused by small defects in the welding process, the chance of detecting significant defects (i.e. with dimensions greater than 0.5mm) using nondestructive techniques becomes greater. Thus, the present invention allows the use of high grade welding skills, to industry norms, for the pipe joints, and may allow the use of the current range of non-destructive testing equipment to find significant defects in the welds. It will be appreciated that the present invention may reduce other kinds of stress across welded pipe joints. For instance, the present invention may reduce hoop stress local to the reinforcement, thus providing additional resistance to an external pressure when laying un-pressurised pipe, and additional strength when the pipe is in use on the seabed whilst carrying oil at pressures of thousands of psi (pounds per square inch). The present invention may reduce axial stress local to the reinforcement, although the reduction in axial stress may well depend on how well the reinforcing material is adhered to the pipe.

As used herein, the term deep water means depths of water equal to or greater than 1000 metres. As used herein the term modulus is a measure of extension (strain) versus the applied stress. Thus, for instance, a material having low modulus exhibits more strain for a given stress than one having a high modulus.

Thus, in a first aspect of the invention, there is provided a pipe segment comprising at least two pipes welded together end-on-end at a pipe joint, and thermally insulating material covering the pipe joint and at least part of the pipe segment, wherein the thermally insulating material provides a reinforcing capability, or more specifically, acts as a joint reinforcement, at least in the region covering the pipe joint. The pipe segment may be made of short lengths of J-lay pipes or longer lengths of reeled pipes. The pipe segment may be particularly useful for subsea use, in particular, in deep water

The insulating material may comprise a reinforcing portion and a non- reinforcing portion. The reinforcing portion of the insulating material may be of a higher modulus than the non-reinforcing portion. The insulating material may comprise but is not limited to, a polyurethane or polypropylene foam. Preferably the material used for the reinforcing portion may be, but is not limited to, epoxy resin. The reinforcing material comprising epoxy resin may advantageously further comprise carbon reinforcement. The carbon reinforcement may comprise carbon fibre in cloth form or chopped stand mat. The carbon reinforcement may prevent the epoxy resin (which tends to the brittle) from cracking. Other materials could be used as the reinforcing portion, e.g. denser/higher modulus versions of the polyurethane or polypropylene foam, or other suitable higher modulus materials. The reinforcing portion at least covers the pipe joint, and is of a higher modulus compared to the non- reinforcing portion, such that stress is reduced across the welded pipe joint. This prolongs the fatigue life of the weld, and also reduces the weld defect acceptance criteria, and thus the frequency of any consequent weld repairs.

In another aspect of the invention, there is provided a method of reducing stress across a pipe joint, comprising forming a pipe segment from at least two pipes, by welding them together end-on-end at a pipe joint, and covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material acts as a joint reinforcement in at least the region covering the pipe joint.

In further aspect of the invention, there is provided a method of increasing the fatigue life a pipe joint, comprising forming a pipe segment from at least two pipes, by welding them together end-on-end at a pipe joint, and covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material acts as a joint reinforcement at least in the region covering the pipe joint.

In further aspect of the invention, there is provided a method of increasing a maximum allowable size of a weld defect in a welded pipe joint, comprising forming a pipe segment from at least two pipes, by welding them together end-on-end at a pipe joint, and covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material acts as a joint reinforcement at least in the region covering the pipe joint. In further aspect of the invention, there is provided a method of reducing a stringency of a weld defect acceptance criteria of a welded pipe joint, comprising forming a pipe segment comprising at least two pipes welded together end-on-end at a pipe joint; and covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material acts as a joint reinforcement in at least in the region covering the pipe joint. ^y

In further aspect of the invention, there is provided a method of facilitating the detection of a non-permissible weld defect in a welded pipe joint using a nondestructive testing technique, wherein the non-destructive testing technique comprises a detection limit, and wherein the non-destructive testing technique is capable of detecting weld defects having a length greater than or equal to a detection limit, the method comprising forming a pipe segment comprising at least two pipes welded together end-on-end at a pipe joint; and covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material acts as a joint reinforcement in at least in the region covering the pipe joint; wherein the reinforcing effect of the thermally insulating material is to increase the maximum allowable size of a weld defect in the pipe joint to greater than or equal to the detection limit.

In further aspect of the invention, there is provided a method of detecting a non-permissible weld defect of a welded pipe joint comprising: forming a pipe segment comprising at least two pipes welded together end-on-end at a pipe joint: and analysing the welded point joint using a non-destructive testing technique; and detecting a non-permissible weld defect, repairing the weld defect, and covering the pipe joint and at least part of the pipe segment with a thermally insulating material. wherein thermally insulating material acts as a joint reinforcement in at least in the region covering the pipe joint.

As described for the aspect of the invention above, pipe segment may comprise J -lay pipe and/or reeled pipe, and may be useful for subsea use. particularly deep water subsea use. The thermally insulating material may comprise a reinforcing portion and a non -reinforcing portion.

The welded pipe joints may be inspected using non-destructive testing techniques, for instance, ultra-sonic testing, and other non-destructive techniques (NDT) known in the art. Ultra-sonic testing is the particularly preferred NDT technique. Other NDT techniques for use in accordance with the present invention include those based on radiography, and those based on using dye penetrant; however, radiography is a slow technique, is not very discriminating and has associated radiation hazards. Dye penetrant testing is useful only for surface penetrating defects. The skilled person will appreciate the most appropriate technique for a given situation. Inspection using non-destructive testing techniques may preferably be carried out on the joint before the insulation is applied.

In an embodiment, the insulation may be applied in a manner described as follows. Non-reinforcing insulating material, i.e. the non-reinforcing portion of insulating material, may be applied to the pipe segment, except for a section which includes the pipe joint. This section may be in the range of from 0.3 to 3 metres, preferably 0.5 to 2 metres, and most preferably about 1 metre, either side of the joint. The reinforcing portion of the insulating material may then be applied using a mould, by clamping or securing the mould around the pipe joint, injecting a settable material into the mould, forming the reinforcing insulating material from the settable material, and then removing the mould. The mould may be provided with at least one hole to allow the air to vent so that the mould is filled completely and the moulded material is without voids. Once the reinforcing portion of the material has been applied, the non- reinforcing material may also be applied to the section so as to encapsulate the reinforcing portion. The reinforcing portion of the insulating material may be of a higher modulus than the non-reinforcing portion. The insulating material ma}¹ comprise a polyurethane or polypropylene foam, or a mixture thereof. The reinforcing portion may comprise a polyurethane foam or. more preferably, the reinforcing material may comprise epoxy resin. The epoxy resin may advantageously further comprise carbon reinforcement. The carbon reinforcement may comprise carbon fibre in cloth form or chopped stand mat. In another aspect of the invention, there is provided a use of an insulating material comprising a reinforcing portion and a non-reinforcing portion to reinforce a joint between two welded pipes. In a further aspect of the present invention, there is provided a use of an insulating material comprising a reinforcing portion and a non-reinforcing portion to reduce stress across a joint between two welded pipes.

In a further aspect of the present invention, there is provided a use of an insulating material comprising a reinforcing portion and a non-reinforcing portion to extend the fatigue life of a joint between two welded pipes.

As described for the aspect of the invention above, the pipe segments may comprise J-lay pipe and/or reeled pipe, and may be useful for subsea use, particularly deep water subsea use.

The welded pipe joints may be inspected using non-destructive testing techniques, for instance, ultra-sonic testing, and other non-destructive techniques known in the art. Inspection using non-destructive testing techniques is preferably carried out on the joint before the insulation is applied.

In an embodiment, the insulation may be applied in a manner described as follows. The non-reinforcing portion of the insulating material may be applied to the pipe segment, except for a section which includes the pipe joint. The section may be in the range of from 0.3 to 3 metres, preferably 0.5 to 2 metres, and most preferably about 1 metre, either side of the joint. The reinforcing portion of the insulating material may then be applied using a mould, by clamping or securing the mould around the pipe joint, injecting a settable material into the mould, forming the reinforcing portion of the insulating material from the settable material, and removing the mould. The mould may be provided with at least one hole to allow the air to vent so that the mould is filled completely and the moulded material is without voids. Once the non -reinforcing portion of the material has been applied, the non-reinforcing portion material may also be applied to the section so as to encapsulate the reinforcing portion.

The reinforcing portion of the insulating material may be of a higher modulus than the non -reinforcing portion. The insulating material may comprise a polyurethane foam or polypropylene foam, or a mixture thereof. The reinforcing portion may comprise a polyurethane foam or. more preferably, the reinforcing material may comprise epoxy resin. The epoxy resin may advantageously further comprise carbon reinforcement. The carbon reinforcement may comprise carbon fibre in cloth form or chopped stand mat.

The invention will be described further with reference to the drawings, in which:

Figure 1 shows a schematic view of a typical reel lay system which may be used to weld and prepare pipeline in accordance with the present invention;

Figure 2 A shows a cross-sectional view of a pipe segment and joint, reinforced in accordance with an embodiment of the present invention; Figure 2B shows the corresponding reduction in stress levels stress across the pipe joint of Figure 2 A;

Figure 3 shows a cross-sectional view of a pipe segment and pipe joint, before being reinforced in accordance with an embodiment of the present invention;

Figure 4 shows a cross-sectional view of a pipe segment and pipe joint being reinforced in accordance with an embodiment of the present invention; and

Figure 5 shows a cross-sectional view of a pipe segment and pipe joint reinforced in accordance with an embodiment of the present invention.

Figure 2A shows a cross-sectional view of a pipe segment 100 and joint 101 reinforced in accordance with an embodiment of the present invention. The pipe segment shows, by way of example, pipeline material 102, welded together end-on- end at welded joint 101. The pipeline material 102 can comprise short lengths of pipe or longer reeled lengths of pipe. Welded joint 101 is created at the workstation 5 on the pipe lay vessel 2 in accordance with techniques known in the art; such welded joints are known in the industry as field joints 103. The pipe segment 100 is provided with a reinforcing portion 104 of the thermally insulating material covering the welded joint 101. The remainder of the pipe is covered with a non-reinforcing portion

105 of thermally insulating material.

A variety of materials may be used as the thermally insulating material, including polyurethane foam or polypropylene foam. A variety of materials may be used as the reinforcing portion 104 of the insulating material, including, but not limited to. carbon reinforced epoxy, as long as the reinforcing portion 104 is of a higher modulus than the non-reinforcing portion material 105. In one embodiment, the reinforcing portion 104 is carbon-reinforced epoxy of a higher modulus than the non-reinforcing portion 105 used on the reminder of the pipe segment. Figure 2B shows the corresponding reduction in stress levels stress across the pipe joint of Figure 2A. The pipe segment comprising the reinforcing insulating material in accordance with the present invention exhibits a graded drop in the stress levels along the field joint, thereby allowing for a longer fatigue life of the welded joint and decreasing the pipe joint sensitivity to failure caused by small defects in the welding process.

The reinforcing portion 104 of the thermally insulating material in the drawings is shown shaped as a cylinder with a trapezium-like longitudinal cross- section; however, it will be appreciated by the person skilled in the art that a variety shapes in combination with a variety of reinforcing thermally insulating materials can be used, in order to achieve the desired smooth reduction in stress levels across the welded joint 101, and for a pre-determined length either side of the joint, typically but not necessarily to the faces of the insulation cut-back that is used to define the length of the pipe segment, in which the field joint is to be made. This is done without compromising the desired thermally insulating behaviour of the given pipe segment.

The application of the reinforced thermally insulating material to the pipe segment will be described as follows, with reference to Figures 3, 4 and 5.

Figure 3 shows a cross-sectional view of a pipe segment and pipe joint, before being reinforced in accordance with an embodiment of the present invention. A pipe segment 102 is prepared from individual lengths of pipe (stalks) or longer lengths of reeled pipe on a pipe lay marine vessel typically using equipment illustrated in Figure

1. The pipe is provided with the non-reinforced portion 105 of the thermally insulating material, except for a section 301 near the ends of the pipe. This section of pipe 301 not covered by insulation may vary in length, in the range of from 0.3 to 3 metres, preferably 1 metre. The two ends of the pipe are prepared for welding, butted together, and then welded using the equipment provided in the work station 5 in accordance with techniques known in the art.

The weld is then be inspected using non-destructive testing techniques (NDT). for instance ultra-sonics testing or dye penetrant testing, for assessing the quality and integrity of the weld, which may be reworked if necessary.

The reinforcing portion 104 of the thermally insulating material would then be applied to the welded joint in accordance with an embodiment of the present invention, as schematically shown in Figure 4. In one embodiment, the reinforcing portion is moulded to the welded joint using two mould halves 401 and 402. The mould halves 401 and 402 are secured or clamped around the pipe joint 101. thereby defining a mould cavity 405 in the shape of the reinforcing portion of the thermally insulating material. A settable material is then used to fill the mould cavity 404 using a mould filling system 403. The settable material is then allowed to set, thereby forming the reinforcing portion 104 of the thermally insulating material. In one embodiment, the mould halves may be provided with at least one mould vent 404 to allow the mould cavity to be filled completely with the settable material, such that the moulded material in the cavity is then free of voids.

It will be appreciated that the NDT testing may need to be carried out before the reinforcing portion of the thermally insulating material is applied to the pipe joint. Thus the welded joint may need to be inspected according to criteria based on the expected drop in joint stress after application of the reinforcing material. As the present invention provides a reduction in the stress levels across the welded pipe joint, the criteria for an acceptable weld for a reinforced pipe joint in accordance with the present invention will be lower (i.e. less stringent) than the criteria for a non- reinforced pipe joint. The present invention thus allows the use of high grade welding skills, to industry norms, for the pipe joints, and because the pipe joint stress is attenuated, a larger flaw size becomes allowable. This in turn allows inspection using currently available NDT techniques, as the flaw size is well within their limits of discrimination.

Once the reinforcing portion 104 of the thermally insulating material has substantially set, the reinforcement mould is then removed, and the remainder of the field joint is filled to the outer diameter of the pipe with the non-reinforcing portion 105 of the thermally insulating material, as shown in Figure 5. It will be appreciated that the invention may be modified within the scope of the claims.

Claims

1 . A pipe segment comprising:

(a) at least two pipes welded together end-on-end at a pipe joint;

(b) thermally insulating material covering the pipe joint and at least part of the pipe segment, wherein the thermally insulating material acts as a joint reinforcement at least in the region covering the pipe joint.

2. A pipe segment according to claim 1 wherein the pipe segment comprises J-lay pipe and/or reeled pipe.

3. A pipe segment according to any preceding claim wherein the pipe segment is for subsea use.

4. A pipe segment according to any preceding claim wherein the insulating material comprises a reinforcing portion and a non-reinforcing portion.

5. A pipe segment according to claim 4 wherein the reinforcing portion of the insulating material is of a higher density than the non-reinforcing portion.

6. A pipe segment according to claim 4 or 5 wherein the reinforcing portion of the insulating material is of a higher modulus than the non- reinforcing portion.

7. A pipe segment according to any preceding claim wherein the insulating material comprises a polyurethane foam.

8. A pipe segment according to claim 4. 5 or 6, or claim 7 when dependent on claim 4, wherein the reinforcing portion of the insulating material comprises a polyurethane foam, polypropylene foam, or a mixture thereof.

9. A pipe segment according to any of claims 4 to 8, wherein the reinforcing portion comprises an epoxy resin.

10. A pipe segment according to claim 9 wherein the reinforcing portion further comprises carbon reinforcement.

] 1 . A pipe segment according to claim 9 wherein the carbon reinforcement carbon fibre in cloth form, chopped stand mat, or a combination thereof.

12. A method of reducing stress across a pipe joint, comprising:

(a) forming a pipe segment comprising at least two pipes welded together end- on-end at a pipe joint; and

(b) covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material acts as a joint reinforcement at least in the region covering the pipe joint.

13. A method of increasing the fatigue life of a pipe joint, comprising: (a) forming a pipe segment comprising at least two pipes welded together end- on-end at a pipe joint:

(b) covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material is acts as a joint reinforcement at least in the region covering the pipe joint.

14. A method of increasing a maximum allowable size of a weld defect in a welded pipe joint, comprising:

(a) forming a pipe segment comprising at least two pipes welded together end- on-end at a pipe joint; and (b) covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein the thermally insulating material acts as a joint reinforcement in at least in the region covering the pipe joint.

15. A method of reducing a stringency of a weld defect acceptance criteria of a welded pipe joint, comprising: (a) forming a pipe segment comprising at least two pipes welded together end- on-end at a pipe joint; and

(b) covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein thermally insulating material acts as a joint reinforcement in at least in the region covering the pipe joint.

16. A method of facilitating the detection of a non-permissible weld defect in a welded pipe joint using a non-destructive testing technique, wherein the nondestructive testing technique comprises a detection limit, and wherein the nondestructive testing technique is capable of detecting weld defects having a length greater than or equal to a detection limit the method comprising (a) forming a pipe segment comprising at least two pipes welded together end- on-end at a pipe joint; and

(b) covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein the thermally insulating material acts as a joint reinforcement in at least in the region covering the pipe joint; (c) wherein the thermally insulating material increases a maximum allowable size of a weld defect in the pipe joint to greater than or equal to the detection limit.

17. A method of detecting a non-permissible weld defect of a welded pipe joint comprising: (a) forming a pipe segment comprising at least two pipes welded together end- on-end at a pipe joint: and

(b) analysing the welded point joint using a non-destructive testing technique; and (c) detecting a non-permissible weld defect,

(d) repairing the weld defect, and

(e) covering the pipe joint and at least part of the pipe segment with a thermally insulating material, wherein the thermally insulating material acts as a joint reinforcement in at least in the region covering the pipe joint.

18. A method according to any of claims 12 to 17 wherein the pipe segment comprises J-lay pipe and/or reeled pipe.

19. A method according to any of claims 12 to 18 wherein the pipe segment is for subsea use.

20. A method according to any of claims 12 to 19 wherein the thermally insulating material comprises a reinforcing portion and a non -reinforcing portion.

21. A method according to any of claims 12 to 20 wherein after the step of welding the two pipes together, the pipe joint is inspected by non-destructive testing.

22. A method according to claim 21 wherein the non-destructive testing comprises ultra-sonic testing, dye-penetrant testing or radiography.

23. A method according to claim 21 wherein the non-destructive testing comprises ultra-sonic testing.

24. A method according to any of claims 20 to 23, wherein the covering step comprises applying the non-reinforcing portion to the pipe segment except for a section including the pipe joint.

25. A method according to claim 24. wherein the section extends in the range of 0.3 to

3 metres, preferably 0.5 to 2 metres, either side of the pipe joint.

26. A method according to claim 24, wherein the section extends 1 metre either side of the pipe joint.

27. A method according to any of claims 20 to 26, wherein the covering step further comprises the steps of:

(a) installing a mould around the welded pipe joint;

(b) injecting a settable material into the mould;

(c) forming the reinforcing portion from the settable material; and

(d) removing the mould.

28. A method according to claim 27 wherein the mould is provided with at least one vent to allow the mould to be filled completely.

29. A method according to any of claims 24 to 28, wherein the non-reinforcing portion is applied to the section after the reinforcing portion has been applied.

30. A method according to any of claims 20 to 29 wherein the reinforcing portion is of a higher density than the non-reinforcing portion.

31. A method according to any of claims 20 to 30 wherein the reinforcing portion is of a higher modulus than the non-reinforcing portion.

32. A method according to any of claims 12 to 31 wherein the thermally insulating material comprises a polyurethane foam.

33. A method according to any of claims 20 to 32, wherein the reinforcing portion comprises an epoxy resin.

34. A method according to claim 33, wherein the reinforcing portion further comprises carbon reinforcement.

35. A pipe segment according to claim 34 wherein the carbon reinforcement carbon fibre is in cloth form, chopped stand mat. or a combination thereof.

36. A use of a thermally insulating material comprising a reinforcing portion and a non-reinforcing portion to reinforce a joint between two welded pipes.

37. A use of a thermally insulating material comprising a reinforcing portion and a non-reinforcing portion to reduce stress across a joint between two welded pipes.

38. A use of a thermally insulating material comprising a reinforcing portion and a non-reinforcing portion to extend the fatigue life of a joint between two welded pipes.

39. A use according to any of claims 36 to 38, wherein the pipes comprise J-lay pipe and/or reeled pipe.

40. A use according to any of claims 36 to 39 wherein the pipes are for subsea use.

41. A use according to any of claims 36 to 40 comprising inspecting the welded joint using non-destructive testing techniques.

42. A use according to claim 41 wherein the non-destructive testing techniques comprise ultra-sonic testing, dye-penetranl testing or radiography.

43. A use according to any of claims 36 to 42 wherein the non-reinforcing portion is applied to the pipes except for a section including the pipe joint.

44. A use according to claim 43 wherein the section extends 0.3 to 3 metres, preferably 0.5 to 2 metres, either side of the welded joint.

45. A use according to claim 43 wherein the section extends 1 metre either side of the welded joint.

46. A use according to any of claims 36 to 45 comprising: (a) installing a mould around the welded pipe joint; (b) injecting a settable material into the mould;

(c) forming the reinforcing portion of the insulating material from the settable material; and

(d) removing the mould.

47. A use according to claim 46 wherein the mould is provided with at least one vent to allow the mould to be filled completely.

48. A use according to claim 46 or 47 wherein the non-reinforcing portion is applied to the section after the reinforcing portion has been applied.

49. A use according to any of claims 36 to 48 wherein the reinforcing portion is of a higher density than the non-reinforcing portion.

50. A use according to any of claims 36 to 49 wherein the reinforced portion is of a higher modulus than the non-reinforced portion.

51. A use according to any of claims 36 to 50 wherein the insulating material comprises a polyurethane foam.

52. A use according to any of claims 36 to 51 wherein the reinforcing portion of the insulating material comprises a polyurethane foam.

53. A use according to any of claims 36 to 52 wherein the reinforcing portion comprises an epoxy resin.

54. A use according to any of claims 36 to 53. wherein the reinforcing portion further comprises carbon reinforcement.

55. A use according to any of claims 36 to 54 wherein the carbon reinforcement carbon fibre in cloth form, chopped stand mat. or a combination thereof.

56. A pipe segment, substantially as herein described, and/or with reference to and as shown in the accompanying drawings.

57. A method of reducing stress across a pipe joint, as substantially as herein described, and/or with reference to and as shown in the accompanying drawings

58. A method of increasing the fatigue life of a pipe joint, as substantially as herein described, and/or with reference to and as shown in the accompanying drawings

59. A method of increasing a maximum allowable size of a weld defect in a welded pipe joint, as substantially as herein described, and/or with reference to and as shown in the accompanying drawings

60. A method of reducing the stringency of a weld defect acceptance criteria of a welded pipe joint, as substantially as herein described, and/or with reference to and as shown in the accompanying drawings

61. A method of facilitating the detection of a non-permissible weld defect in a welded pipe joint using a non-destructive testing technique, as substantially as herein described, and/or with reference to and as shown in the accompanying drawings

62. A method of detecting a non-permissible weld defect in a welded pipe joint, as substantially as herein described, and/or with reference to and as shown in the accompanying drawings

63. A use of a thermally insulating material comprising a reinforcing portion and a non-reinforcing portion to reinforce a joint between two welded pipes, substantially as herein described, and/or with reference to and as shown in the accompanying drawings.