IMPROVEMENTS IN THE WELDING OF PIPES

Abstract

A first metal pipe is welded to a second metal pipe in a method of laying pipeline, for example from a pipe-laying vessel at sea. The metal pipes may have an outer diameter greater than 150 mm and a pipe wall thickness of greater than 15 mm. The first pipe and the second pipe are brought together prior to welding so as to sandwich a third type of metal material between the pipe ends. The thickness of the third type of material, immediately before welding may be between 0.05 mm and 2 mm. The third metal material is melted together with the metal material of the first pipe and the second pipe.

Claims

1-19. (canceled)

20. A method of welding a first pipe and a second pipe end-to-end to form at least part of a pipeline that is suitable for use for conveying oil and/or gas, wherein the first pipe is made from a first metal material and the second pipe is made of a second metal material, the first pipe and the second pipe each having an end face, at least one of the end faces of the pipes having deposited thereon a layer of a third material having a chemical composition which is different from that of the first material and the second material, the layer having a thickness of 1 mm or less, and the method comprises the following steps: bringing the end face of the first pipe and the end face of the second pipe together with the third material forming an intermediate layer of material positioned between the end faces of the pipes, thus forming a joint to be welded; subsequently providing heating energy to the joint to be welded, thereby melting the intermediate layer of material and at least part of the first material and at least part of the second material; thereafter removing said heating energy; and allowing the heated material to solidify, so that a joint is made between the two pipes comprising a weld seam which has a thickness which is greater than the thickness of the intermediate layer of material.

21. A method according to claim 20, wherein the thickness of the layer of third material deposited on the end face of one of the pipes is less than or equal to 0.2 mm.

22. A method according to claim 20, wherein the thickness of the layer of third material deposited on the end face of one of the pipes is of the order of 10s of microns.

23. A method according to claim 20, wherein the third material is an alloy containing greater than 5% by weight Nickel and/or greater than 10% Manganese and/or the third material is an iron and/or steel alloy.

24. A method according to claim 20, wherein the bringing the end face of the first pipe and the end face of the second pipe together and the making of the joint between the two pipes occur at a single welding workstation.

25. A method according to claim 20, wherein the step of providing heating energy to the joint to be welded is performed by keyhole welding with a laser welding device.

26. A method according to claim 20, wherein the end face of the pipe has an annular shape and the overall shape of the intermediate layer of material between the end faces of the pipes corresponds to that of the end face of the pipe.

27. A method according to claim 20, wherein the first and second pipes each have an outer diameter greater than 150 mm and a pipe wall thickness of greater than 15 mm.

28. A method according to claim 20, wherein the step of providing heating energy to the joint is performed as a one-pass welding process with a welding apparatus to form a weld between the pipes having a depth of more than half of the thickness of the pipes.

29. A method according to claim 20, wherein the method includes a step of depositing the intermediate layer of material on at least one of the end faces of the pipes before the step of bringing the end faces of the pipes together.

30. A method according to claim 20, where the intermediate layer is deposited by means of an additive manufacturing technique.

31. A method according to claim 20, where the method is performed on a pipe-laying vessel at sea.

32. A pipe with an integrated layer of material on at least one end face of the pipe, the pipe and the integrated layer of material being configured for use as the first pipe and the intermediate layer of material as claimed in the method according to claim 20.

33. A method of depositing material on an end of a pipe so as to form a pipe according to claim 32 or a first pipe and intermediate layer of material, wherein the first pipe is made from a first metal material and the second pipe is made of a second metal material, the first pipe and the second pipe each having an end face, at least one of the end faces of the pipes having deposited thereon a layer of a third material having a chemical composition which is different from that of the first material and the second material, the layer having a thickness of 1 mm or less, and the method comprises the following steps: bringing the end face of the first pipe and the end face of the second pipe together with the third material forming the intermediate layer of material positioned between the end faces of the pipes, thus forming a joint to be welded; subsequently providing heating energy to the joint to be welded, thereby melting the intermediate layer of material and at least part of the first material and at least part of the second material; thereafter removing said heating energy; and allowing the heated material to solidify, so that a joint is made between the two pipes comprising a weld seam which has a thickness which is greater than the thickness of the intermediate layer of material.

34. A method according to claim 33, where the material is deposited by means of a laser metal deposition additive manufacturing technique.

35. A kit of parts for laying a pipeline, the kit comprising multiple pipes, each being a pipe according to claim 32, and a welding apparatus for providing the heating energy required to perform the method of welding a first pipe and a second pipe end-to-end to form at least part of a pipeline that is suitable for use for conveying oil and/or gas, wherein the first pipe is made from a first metal material and the second pipe is made of a second metal material, the first pipe and the second pipe each having an end face, at least one of the end faces of the pipes having deposited thereon a layer of a third material having a chemical composition which is different from that of the first material and the second material, the layer having a thickness of 1 mm or less, and the method comprises the following steps: bringing the end face of the first pipe and the end face of the second pipe together with the third material forming an intermediate layer of material positioned between the end faces of the pipes, thus forming a joint to be welded; subsequently providing heating energy to the joint to be welded, thereby melting the intermediate layer of material and at least part of the first material and at least part of the second material; thereafter removing said heating energy; and allowing the heated material to solidify, so that a joint is made between the two pipes comprising a weld seam which has a thickness which is greater than the thickness of the intermediate layer of material.

36. A kit of parts for laying a pipeline, the kit comprising multiple pipes, and apparatus configured to perform the method of claim 33, and a laser welding apparatus for providing the heating energy required to perform the method of welding a first pipe and a second pipe end-to-end to form at least part of a pipeline that is suitable for use for conveying oil and/or gas, wherein the first pipe is made from a first metal material and the second pipe is made of a second metal material, the first pipe and the second pipe each having an end face, at least one of the end faces of the pipes having deposited thereon a layer of a third material having a chemical composition which is different from that of the first material and the second material, the layer having a thickness of 1 mm or less, and the method comprises the following steps: bringing the end face of the first pipe and the end face of the second pipe together with the third material forming an intermediate layer of material positioned between the end faces of the pipes, thus forming a joint to be welded; subsequently providing heating energy to the joint to be welded, thereby melting the intermediate layer of material and at least part of the first material and at least part of the second material; thereafter removing said heating energy; and allowing the heated material to solidify, so that a joint is made between the two pipes comprising a weld seam which has a thickness which is greater than the thickness of the intermediate layer of material.

37. A pipe-laying vessel including a kit of parts according to claim 35.

38. A method of laser welding a first pipe and a second pipe end-to-end to form at least part of an oil/gas pipeline, wherein the first pipe is made from a first metal material and the second pipe is made of a second metal material, the first pipe and the second pipe each having an end face, at least one of the end faces of the pipes has deposited thereon a layer of a third material having a chemical composition which is different from that of the first material and the second material, and the thickness of the layer of third material deposited on the end face of one of the pipes is less than or equal to 0.2 mm, and the method comprises the following steps: bringing the end face of the first pipe and the end face of the second pipe together, such that the third material, having previously been deposited on at least one of the end faces of the first pipe and the second pipe, forms an intermediate layer of material positioned between the end faces of the pipes, thus forming a joint to be welded; and subsequently welding the pipes together with a keyhole laser welding process, which melts the intermediate layer of material and at least part of the first material and at least part of the second material; thus forming a joint between the two pipes comprising a weld seam which has a thickness which is greater than the thickness of the intermediate layer of material.

39. A method according to claim 38, wherein the first and second pipes each have an outer diameter greater than 150 mm and a pipe wall thickness greater than 15 mm,

40. A method according to claim 38, wherein the thickness of the layer of third material deposited on the end face of one of the pipes is of the order of 10s of microns.

Description

DESCRIPTION OF THE DRAWINGS

[0066] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0067] FIG. 1 shows a side view of a pipeline laying vessel according to a first embodiment of the invention;

[0068] FIG. 2 shows a side view of two ends of pipe being welded together on the vessel of FIG. 1;

[0069] FIG. 3 shows part of the end of a pipe, which has been coated with filler material in accordance with the first embodiment;

[0070] FIG. 4 shows a partial cross-section of the end of the pipe shown in FIG. 3;

[0071] FIG. 5 shows the bringing of the pipes together according to the first embodiment;

[0072] FIGS. 6 to 8 are various cross-sections showing the ends of the pipes being brought together and illustrating typically axial and radial misalignments and how those are reduced by the first embodiment;

[0073] FIG. 9 shows the pipe joint once welded according to the first embodiment, the weld seam extending beyond the original extent of the filler material;

[0074] FIG. 10 shows a welded pipe joint once welded, the weld seam being narrow than the extent of the material sandwiched between the pipes;

[0075] FIG. 11 shows pipe being prepared by depositing filler material on the end of the pipe in accordance with a second embodiment,

[0076] FIG. 12 shows a partial cross-section of the end of the pipe shown in FIG. 11;

[0077] FIGS. 13 and 14 illustrate a method according to a third embodiment, in which material is deposited with the use of an additive manufacturing technique; and

[0078] FIG. 15 show a pipe welding method according to a fourth embodiment, in which filler material is supplied separately as a gasket.

DETAILED DESCRIPTION

[0079] FIG. 1 shows a pipe laying vessel 20 laying a pipeline 22 in water 24 using an S-lay process. It will be seen that the pipeline 22 forms the general shape of an “S” as it is laid off the vessel 20 towards the seabed 26. The first embodiment concerns welding successive sections 28 of pipe to the end of the pipeline 22 as the pipeline is laid from the vessel 20.

[0080] The sections 28 of pipe added to the pipeline 22 (string) are each 12 m long (but could be multiples of 12 m in other embodiments, or any other length). Each pipe has an outer diameter of 1000 mm. The sections 28 of pipe (and the resulting pipeline) are steel pipes having a relatively low carbon content. The steel is low carbon weldable grade steel having a relatively low effective carbon content (CE).

[0081] The alloying composition of the steel pipe in this embodiment (as ascertained using the ASTM E415-17 “standard test method for analysis of carbon and low-alloy steel by spark atomic emission spectrometry” made available by ASTM International—www.astm.org) complies with the following limits: Fe ˜97.5%, C≤0.1%, Mn ≤1.40%, P≤0.030%, S≤0.030%, Cr 0.18%, Mo 0.12%, V 0.027%, Ni 0.26%, Cu 0.13%, Si 0.27%, Al 0.032%, Co 0.01%, Nb 0.02%, Sn 0.01%, Zr 0.01%; with a CE value (as defined herein) of ˜0.4%. For example, such a composition may have the following proportions (in decreasing order): Fe (97.5%), Mn (1.08%), Si (0.27%), Ni (0.26%), Cr (0.18%), Cu (0.13%), Mo (0.12%), C (0.087%), Al (0.032%), V (0.027%), Nb (0.02%), Co (0.01%), Zr (0.01%), Sn (0.01%), P (0.008%), S (0.003%), Ti (0.003%), other/margin of error (0.25% of total mass). The pipeline 22 and pipe sections 28 being welded to it are of the same material.

[0082] The processes associated with the laying of the pipeline are divided across several working stations 30, 32, equi-spaced with respect to the conventional joint length and included within the string production line (firing line). In this case, a first working station is in the form of a pipe coupling station 30, at which a new section 28 of pipe is welded to the free end of the pipeline 22. A second working station is in the form of a non-destructive testing (NDT) station 32, at which the quality of the weld joint is tested. Tensioners 34 hold the pipeline 22 under tension.

[0083] It is desirable to improve the speed at which sections 28 of pipe can be welded onto the pipeline 22, as this can be the principal limitation on the rate at which pipeline can be laid from the vessel. In this embodiment, the weld joint is quickly and efficiently performed in one welding-pass with the use of a laser welding apparatus, as shown in more detail in FIGS. 2 to 4.

[0084] FIG. 2, shows a welding bug 78, incorporating a laser-based welding torch, travelling in a circumferential direction around the joint to be formed between a pipe section 28 and the end of the pipeline 22 (“the pipes”). The welding bug 78 is attached and guided by a welding belt 77, which is clamped to one of the pipes 22, 28. The ends of the pipes are prepared before welding by means of a method carried out at a location different from the pipe coupling station 30, as will now be described with reference to FIG. 3.

[0085] FIG. 3 shows an end 60 of a pipe 28 on which there has been deposited a layer 61 of filler material. The filler material of layer 61 is made of a different material than the pipes 22, 28, has a higher Nickel content in particular. In this embodiment, the material of layer 61 has an alloying composition as follows: Fe (95.8%), Mn (1.1%), Si (0.6%), Ni (2.4%), and C (0.1%).

[0086] In the first embodiment of the invention, the layer 61 is applied and coated on the ends of the pipes (both ends of all pipe sections 28) to be welded, long before the welding process begins, for example at a location on-shore, before the pipes are loaded onto the vessel. The material 61 is deposited on the end of the pipe across the entire cross-sectional area of the end 60 of the pipe, as shown in FIGS. 3 and 4. FIG. 4 is a partial cross section of the pipe representing the area marked by the box A shown in FIG. 3. The axis of the pipe is horizontal in FIG. 4, and an exterior surface 66 of the pipe is shown at the top of the FIG. 4. The depth (thickness, d1) of the layer 61 (as measured in the direction parallel to the axis of the pipes) is ˜0.3 mm on each pipe end. Each pipe has a wall thickness, t, of ˜30 mm.

[0087] The relatively thin depth of the layer 61 allows for a quick deposition of the material on the pipe end during preparation, and also results in a welded joint which comprises both the base pipe material and the material deposited 61. In this first embodiment of the invention, the intermediate material 61 is deposited on the ends of the pipes 60 by means of cold spray deposition, on land in a factory.

[0088] FIG. 5 shown the pipe 28 with its coated end 60 being moved towards the end 60 of the pipeline 22, which is also coated. Thus, the pipe pieces 22 and 28 are brought together, so that their ends 60 touch. Each end face of the pipes will have imperfections so that the surfaces deviate from the desired result of having two perfectly flat and parallel end faces. The pipes are urged together with sufficient force that some of the material 61 on the ends of the pipes deforms, effectively being squeezed from regions on the opposing end faces that are closer together to regions on the opposing end faces that are further apart. Thus, some of the material 61 moves to reduce the size of cavities or gaps that would otherwise exist without such material deformation.

[0089] FIG. 6 shows a partial cross section view of the pipes 22, 28 having been brought into contact with each other and approximately aligned but before the third material has deformed. The pipes 22, 28 are arranged end-to-end, with the exterior (outside) of the pipe being denoted by the reference “E” and the interior (inside) of the pipe being denoted by the reference “I”. The ends of pipes have been machined flat and coated with filler material 61. A joint 14 to be welded is defined between the ends of the sections of pipe. FIG. 7 is an enlarged view of the portion labelled as 7 in FIG. 6. Thus, the exterior E of the pipe is uppermost in FIG. 7 and the interior I of the pipes is lowermost. The shapes of the end faces of the pipes shown in FIG. 7 are distorted for the sake of illustrating misalignment of the pipes. One such measure of pipe alignment, at a given location on the joint to be welded, is the “high-low value” (or just “hi-lo”). The hi-lo is the distance, in the radial direction, between two corresponding positions on two adjacent pipe end-faces. FIG. 7 shows two measures of external misalignment in the radial direction: a step of depth h1 between the outside diameters of the pipe ends (the “external cap hi-lo”) and a step of depth h2 between the inside diameters of the pipe ends (the “internal hi-lo”). The values of hi-lo h1 and h2 may vary around the circumference of the pipes. This may be due to misalignment of the pipes' axes and/or deviations of the pipes' perimeters from a circular shape (“Out Of Roundness” which may sometimes be abbreviated to “OOR”).

[0090] Furthermore, a gap or cavity may exist between the end faces of the sections of pipe prior to welding. The “gap” (see for example the gap labelled g in FIG. 7) may be defined as the distance between two pipe end faces in a direction approximately parallel to the axes of the sections of pipe. The gap may vary around the joint to be welded in both the radial distance from the pipes' axes and around the circumference of the pipes' end faces. It will be appreciated that a gap of zero will indicate that the sections of pipe are touching at that point. FIG. 7 shows the gap and a corresponding cavity 36 at the time at which the layers 61 have first touched.

[0091] In this embodiment, the intermediate material 61 is engineered to have a lower hardness and/or stiffness than the material used to make the pipe. Further movement of the pipes towards each other thus deforms the layers 61, as shown in FIG. 8. (The pipes 22 and 28 are brought together with sufficient force so that the intermediate material 61 deforms). The cavity 36 of FIG. 7 is now filled with material 61, or viewed another way, the cavity 36 no longer exists. It may also be the case that the intermediate layer deforms at the outer and inner diameter of the pipe so as to reduce the internal hi-lo and the external hi-lo, immediately before welding. Thus, in this embodiment, the material 61 deforms in such a way as to reduce the effect of gaps between the ends 60 of the pipes and to reduce the effect of radial off-sets (hi-lo parameters h1, h2).

[0092] On welding of the pipes together all of the intermediate layer 61 melts and forms part of the weld joint. With reference again to FIG. 2, the welding apparatus used incorporates a laser source which performs a keyhole welding of the full thickness of the pipes as it travels around the joint in a circumferential direction. The spot size of the laser may have a diameter of about 400 μm delivering heat energy at a density of about 70 kW/mm.sup.2.

[0093] FIG. 9 shows a side view of the pipes once welded together, with the size of the intermediate layers 61 before welding being overlaid, showing schematically their thickness as measured in the direction parallel to the axis P.sub.axis of the pipe. The thickness of the weld seam w1 (being ˜3 mm) is sufficiently large that it encompasses all of the intermediate material (the two layers 61 having a combined thickness of ˜0.6 mm) and a portion of the material of each pipe 22, 28. The thickness of the heat affected zone is of course greater than the thickness of the weld seam, as is shown schematically in FIG. 9 by the double-headed arrow labelled HAZ. Mixing of the base pipe material and the intermediate material occurs during welding. The composition of the welded material can be controlled as a result of the relatively even distribution of filler material 61 and the consistent welding process used. The weld joint may have a composition such that the components in the weld itself are as follows: Fe (97.16%), Mn (1.084%), Si (0.336%), Ni (0.688%), Cr (0.144%), Cu (0.104%), Mo (0.096%), C (0.0896%), Al (%), V (0.0216%), Nb (0.016%), Co (%), Zr (%), Sn (%), P (0.0064%), S (0.0024%), Ti (0.0024%). The material structure of the weld is such that the crystallographic grains which form in the material when subjected to a high cooling rate grow in such a way that the likelihood for crack formation in the material is reduced in comparison to the likelihood of crack formation occurring in the pipe material when the same cooling rate is applied.

[0094] In this first embodiment of the invention, the properties of the intermediate material 61 are tailored for the purpose of welding, and the steel material is similar in make-up to the base material of the pipes. The intermediate material has a melting point which correlates well with the incident energy from the welding source.

[0095] The laser welding method of the first embodiment has many advantages. It is quick and efficient and enables faster production in the firing line. The weld joint has a composition that is consistent across the full depth of the weld. It works well with welding thick pipes, with a thickness of, say, greater than 20 mm. The method represents a way of efficiently forming quality welds with a one-pass laser welding method. The problems typically associated with rapid cooling of weld material that has been heated to the very high temperatures associated with deep full penetration laser welding are mitigated. The problems typically associated with misalignment of pipes ends, for example relatively hi-lo values and/or gaps between the pipes, can be mitigated by means of the deformable filler material.

[0096] FIG. 10 illustrates, by way of a contrast, a method of joining pipes, similar to that of the first embodiment of the invention, except that a super abundant thickness of filler material 61 is used, which results in a weld joint whereby the only material in the weld joint that is melted during the laser welding process is the deposited material 61. The fact that the weld joint comprises only one material may have the benefit that the material composition is better defined, and allows for the tailoring of the material properties to be optimum for welding at the point where the welding takes place. This could also improve the quality of weld, as the weld-ability of the steel usually used in the construction of pipelines can sometimes be poor. FIG. 10 shows the relative thickness of the weld seam w1 where the intermediate material 61 is applied, before welding, superabundantly. In this case, intermediate material 61 is applied by means of a prior hot deposition process (using an arc welding process) which melts the surface of the base material during application, with a slow cooling process, to allow a strong junction between the intermediate material 61 and the base material of the pipe. This deposition process may be known as “buttering” in the art. (The general concept of “buttering” of work piece surfaces in this manner before forming a joint between the work pieces is known in the prior art.) The deposition process could be performed in a purpose built prefabrication line on the pipe laying vessel. The intermediate material used in this example is an alloy of steel containing manganese, silicon and a high percentage by weight of nickel. Other elements included in non-negligible quantities the intermediate material in this example of the invention include chromium, molybdenum, vanadium, copper, titanium and niobium. In this illustrated example, the thickness of the material used to coat the pipes is applied on the end edges of both of the pipes at a thickness of 3 mm, so the total thickness of the intermediate material is 6 mm. The use of the material in a super abundant manner allows for the most control of the chemical properties of the weld joint. In this example, the pipes that are welded together have a thickness of 35 mm, and a tube outer diameter (of the steel pipe) of 120 cm. Aspects of this example are included in the present disclosure as they may be combined with features of other embodiments of the invention.

[0097] A second embodiment of the invention relates solely to the preparation of the pipes, by depositing material on a pipe end to form an integrated filler layer on the end of the pipe. The second embodiment is illustrated with reference to FIG. 11. The method of the second embodiment of the invention may be used to prepare pipes to be used as the pipes of the first embodiment or of the example of FIG. 10. FIG. 11 shows a different way of depositing material on the pipe end, however. FIG. 11 shows both intermediate 61 applied as a covering on the end face of the pipe 28 but the coating also extends along the inside (coating layer 62) and the outside surface of the pipe (coating layer 65). This ensures that there is still sufficient filler material when the intermediate material melts during welding and the material in the region between the two pipes effectively shrinks. In this embodiment, the outer diameter of the filler material is greater than the outer diameter of the pipe, before welding, but after welding the joint between the two pipes may have an outer diameter which is substantially the same as the outer diameter of the pipes. FIG. 11 shows a filler layer deposition device in the form of a spray gun 70, which is spraying, in a controlled manner, filler material onto the end of the pipe 28. In this embodiment of the invention, the hardness of the intermediate material is at least an order of magnitude lower than the hardness of the pipe material, which in this embodiment of the invention is 300HV10. FIG. 12 shows a section of the end of the pipe in cross-section and can be compared and contrasted with FIG. 4 showing a similar view of the pipe of the first embodiment. According to this second embodiment, the thickness (d2) of the deposited material is ˜0.1 mm on each end of the pipe, and about 80 μm on each of the outer and inner surfaces. The total thickness of the intermediate material when the pipe ends are brought together is thus ˜0.2 mm.

[0098] A third embodiment of the invention is illustrated by FIGS. 13 and 14. In this embodiment, the intermediate material 61 is deposited on the ends 60 of the pipes as a porous material having multiple voids formed therein. Such voids may comprise at least some that are in fluid communication with each other. Such voids may comprise at least some that are closed voids. In this embodiment of the invention, the coating of the pipes performed in a factory on land. The intermediate material 61 is deposited as a lattice-type material having voids 68 that collapse as the surrounding material deforms when the pipe ends are brought together. Such voids 68 are evenly distributed to ensure an even distribution of the filler material between the faces of the ends 60 of the pipes when fully brought together. This may assist in accommodating for misalignment in the axial and radial direction of the pipe end faces. Each of the voids may have a volume of between 0.001 mm.sup.3 and 1 mm.sup.3. There may therefore be thousands of such voids distributed within the layers of material deposited on each end face of each pipe. The material may be deposited on the pipe ends using an additive manufacturing technique, for example using a laser metal deposition technique.

[0099] FIG. 15 illustrated a fourth embodiment of the invention, which incorporates the features of previous embodiments, except that the intermediate material is not coated on either of the ends 60 of the pipes. Instead, it is provided as a thin layered gasket 63 which in use is inserted between the pipes, mechanically by a device 64, as the two pipes are brought together. This has the benefit that the pipes do not have to be pre-coated before welding. The gasket 63 is made of material that is softer than the pipe material and is thus able to deform in the manner described above to reduce the effects of misalignment of the pipe end faces.

[0100] A fifth embodiment of the invention, not separately illustrated, incorporates the features of the first embodiment, except that the intermediate material is substantially entirely nickel (purity >99%), and is applied at a minimal thickness, 0.1 mm on one pipe end face only meaning that the total thickness of filler material sandwiched between the pipe end faces is 0.1 mm. The weld seam has a thickness of 5 mm. The base material of the pipes has the following (non-exhaustive list of) constituents: Fe (97.5%), Mn (1.08%), Si (0.27%), Ni (0.26%), Cr (0.18%), Cu (0.13%), Mo (0.12%), and C (0.087%). The resultant weld seam comprises a steel containing a higher weight percentage of nickel, which gives improved resistance to solidification cracking in comparison to a join made out of only the base material. The weld once formed has reduced amounts of at least Fe (95.5%) and Mn (1.06%) and an increased Ni content (2.25%). Use of a minimum thickness of filler material allows for speedy deposition of the material during manufacturing, and results in a weld join which comprises both the base pipe material and the material deposited.

[0101] A sixth embodiment of the invention, not separately illustrated, is similar to the first embodiment apart from the differences that are now described. The layer applied to both pipe ends is a steel alloy having about 65-70% by weight iron and deposited at a thickness of the order of about 50 microns. Suitable alloys include FeMn (which includes about 35% Manganese), AISI 304 (which includes about 18% Chromium and 10% Nickel) and Invar (which includes about 36% Nickel). The layer has a hardness that is harder than the base material. When the pipes are forced together, the steel pipe material may deform more than the layer of intermediate material. Despite the low volume of intermediate material provided having a different chemical composition from the pipe steel, there are, perhaps surprisingly, sufficient levels of non-iron metal to improve the quality of the weld caused by the subsequent laser welding.

[0102] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0103] The filler material (intermediate material) may be a steel alloy of chromium, molybdenum, and vanadium. These materials are particularly resistant to long term plastic deformation (known as creep), so make a good choice as an intermediate material for a pipeline as they rest the long-term undesirable effects of heating and cooling cycles in the pipe.

[0104] The additive manufacturing technique described above could be an electron beam melting deposition.

[0105] The filler material may include aluminium and/or silicon in its composition. Such additions may act as deoxidising agents as the weld forms, reducing the presence of oxygen in the melt as the metal solidifies. This may in turn lower the number and/or size of voids and/or pores in the welded joint, which might otherwise weaken its mechanical properties.

[0106] The filler material may be made of manganese carbon steel. Manganese carbon steel is particularly resistant to solidification cracking, as well as being very resistant to abrasion, so makes a good choice of material for an intermediate material of use in the welding of pipes.

[0107] The composition of the filler material (intermediate material) may be tailored to be resistant to the corrosive effects that often occur in joints of welded pipes that are required to carry “sour” services (oil/gas products having a high Hydrogen Sulphide content—H.sub.2S). This may be achieved by reducing the hardenability (i.e. ensuring that the joint formed has a low carbon content (or low CE value)—for example, lower than the alloy from which the steel pipes are made. Alternatively, or additionally, the S content and/or P content may be reduced. The Nickel content of the weld joint may need to be kept below 1% for sour service pipelines. The corrosive effects to be mitigated against may be the “inclusion” of sulphur based compounds, from the so-called sour services, into the microstructure of the material, causing weaker mechanical properties, and cracking.

[0108] In may be that the intermediate material is held in place by a spacer arrangement, as described in WO2017140805. The welding apparatus may be as described and claimed in WO2017140805. The contents of that application are fully incorporated herein by reference. The claims of the present application may incorporate any of the features disclosed in that patent application. In particular, the claims of the present application may be amended to include features relating to the laser beam welding equipment of WO2017140805 and/or the induction heating method employed.

[0109] The chemical composition of the filler material may be engineered to reduce the effect of impurities by adding into the filler material alloying elements, such as for example manganese and/or silicon, which induce grain toughness or refinement.

[0110] The filler material when porous/comprising voids may comprise, at least in part, an open cell solid foam. The material may comprise, at least in part, a closed cell solid foam.

[0111] Voids and/or pores may comprise about 5% of the sum volume of the filler material (that sum volume including both the volume of the solid material and the volume of the gaps defined by the voids/pores, at the stage immediately before any deformation of the filler material).

[0112] As an alternative to forming the intermediate material as a void-containing porous structure (as shown in FIGS. 13 and 14) so that the material has macroscopic properties facilitating deformation of the material when the pipe ends are brought together, other structures could be deposited having similar macroscopic material properties. For example, the intermediate material could be laid down as an array of multiple discrete structures that are readily deformable when the pipe ends are brought together. Such structures may crush and/or readily deform as the pipes are brought together, to ensure an even distribution of the filler material between the faces of the ends of the pipes. Such structures could have an irregular shape and form what might be described as a dendritic pattern. The structures may be similarly sized in cross-sectional shape but may have varying heights (as measured in the direction of the pipe axis). The structures may each have a cross-section being no more than about 1 mm.sup.2 in area. There may therefore be thousands of such structures distributed across each end face of each pipe. Such structures could take various shapes, and be distributed and arranged in various ways. For example, the array of structures may appear as a bed of needles. The array of structures may look like a distribution of hairs. The structures may be take the form of a distribution of columns, which protrude at different distances and angles from the pipe end face. A reticular pattern of structures is also possible. Such structures may be deposited on the pipe ends using an additive manufacturing technique.

[0113] While the filler material is in many embodiments expected to be deposited on the entirety of the end face of a pipe, and be present along the whole circumference of the face and across the full thickness of the pipe, it will be appreciated that there may be small areas, and/or negligible gaps, on the end face not being covered by the deposited material. This may be the case in particular where the material is deposited as a distribution of many small structures across the surface of the end face.

[0114] It is understood that the intermediate material, as shown in FIG. 15, could be held in between the pipes in ways other than by using the mechanical apparatus described. For example, clamps, or chemical adhesive, may be used to hold the intermediate material in place.

[0115] The pipes may be coated with other materials such as concrete and/or plastic coverings, before and/or after welding.

[0116] The welding steps may be performed in separate stages at separate welding stations. There may be multiples welding passes performed at a single weld station. Multiple welding torches may be used at a single weld station. There may be multiple welding heads.

[0117] There may be application in relation to other types of welding, not being girth welding of pipes, as shown in the drawings.

[0118] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.