WO2022008750A1

WO2022008750A1 - Welding together of work-pieces

Info

Publication number: WO2022008750A1
Application number: PCT/EP2021/069234
Authority: WO
Inventors: Giorgio STEFANO; Simone Ciceri; Simone D'ARCANGELO; Ali Gökhan DEMIR; Tugay KURTAY; Barbara Previtali
Original assignee: Politecnico Di Milano; Saipem S.P.A.
Priority date: 2020-07-10
Filing date: 2021-07-09
Publication date: 2022-01-13
Also published as: GB202010648D0

Abstract

A first metal work-piece is welded to a second metal work-piece, for example as pipes (22, 28) in a method of laying pipeline, for example from a pipe-laying vessel (20) at sea. The metal pipes may have an outer diameter greater than 150mm and a pipe wall thickness of greater than 15mm. The work-pieces are brought together prior to welding so as to sandwich between them a third type of metal material (61). The third type of metal material (61) is deposited, for example using an additive manufacturing method such as laser metal deposition, on one or both work-pieces as multiple parallel tracks of material having a chemical composition which is different from that of the first and second materials. The thickness of the third type of material, immediately before welding is less than 2mm. The use of the third type of different material, may facilitate the use of a laser welding apparatus to perform an autogenous welding step, as it may be engineered to improve the quality and metallurgical properties of the material that forms the weld.

Description

WELDING TOGETHER OF WORK-PIECES

Field of the Invention

The present invention concerns methods and apparatuses relating to the welding together of work-pieces. More particularly, but not exclusively, this invention concerns the welding of pipes end-to-end, with a high energy welding apparatus, which induces high temperatures in the weld material and consequent rapid cooling in the weld joint and/or surrounding material, yet produces high quality welds for pipes that are suitable for use for conveying oil and/or gas.

Background of the Invention

Pipelines for the transportation of oil and gas must often be laid in water, for example at sea. Typically, when laying a pipeline at sea, one end of the pipeline (sometimes referred to as the string) is held by a pipeline laying vessel and a section of pipe is welded onto the end of the pipeline, at a location on the vessel commonly referred to as the firing line. In the oil and gas services industry, one of the main costs of any project is the time spent at sea. One of the main rate limiting steps, determining how long the pipe laying vessel must remain at sea, is the process of forming the pipeline in the firing line as described above. There is therefore a desire to increase the speed at which pipeline is laid.

However, quality is also key. Welded joints between sections of pipe in the pipeline must be of high quality. Ensuring extremely high weld quality and confidence in that quality is of the utmost importance when laying gas/oil pipeline at sea in circumstances when the pipeline will be under very high tension and/or will be subject to significant fatigue loading when being laid and/or when operational. Ensuring extremely high quality and confidence is also important when laying pipeline that will carry any highly corrosive substances in operation, such as so-called “sour” services. Sour services are typically carried by clad pipes (which may for example include a corrosion resistant inner lining) and/or pipes comprising CRA alloys (Corrosion Resistant Alloys)

In the field of application of the welding of a fixed length of pipe, the traditional type of welding process are: electric arc welding with filler material, Gas Metal Arc Welding (GMAW), Submerged Arc Welding (SAW), Flux Cored Arc Welding (FCAW), Shielded Metal Arc Welding (SMAW), or Gas Tungsten Arc Welding (GTAW), in which the two ends that are joined have chamfer edges (also called bevel edges) the function of which is to accommodate the metallic filler (molten metal) in the form of molten bath (pool).

The bath melts and solidifies along with the adjacent portion of pipeline through a series of weld beads that are wrapped around the circumference of the pipe. For example in GMAW technology the weld material is a continuous wire that acts as the first electrode to generate an electric arc with the base of the chamfer (which acts as second electrode) in this way the wire is unwound and melted continuously.

In GMAW technology the wire comes out continuously from a torch (welding gun) from which comes out that acts as a first electrode to generate an electric arc with the base of the chamfer (acting as a second electrode). In this way, a wire is unwound and melted continuously. Whilst the wire comes out continuously from the torch (welding gun), additionally a gas is released that settles on and protects the bath from adverse processes as oxidation.

Whilst GMAW technology is well understood and produces high quality weld joins, one of its main disadvantages is that several welding passes are required in order to maintain form a joint of a thick section of pipe.

In light of these disadvantages, in many heavy industries, research and development is focused substituting their conventional welding methods with high energy welding technologies, such as laser welding. However, in such applications that require thick-section welding, challenges remain yet in developing high energy welding techniques to compete with conventional welding methods.

The disadvantages of high energy welding technologies (such as laser welding or electron beam welding) include the safety associated with the high energy beam, the need to control any plasma effects which occur during the welding process, and metallurgy issues in the weld and the heat affected zone around the weld.

Undesirable effects, for example being plasma effects, may include the presence of an undercut (a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal) and/or the presence of an under-fill (a condition in which the weld face or root surface extends below the adjacent surface of the base metal) of the weld joint. There is some known prior art in the mitigation of the plasma effects of high- energy welding technologies. In Japanese patent application JP5724294, by JFE steel Corp., the plasma effects of the laser beam are controlled by the movement of the laser spot, the de-powering and defocusing of the laser beam, and the use of a specific angle of incidence of the laser beam on the joint surface. However, this prior art, whilst disclosing a method which may improve the quality of the weld join, has also disclosed something which adds complexity and possibly a longer time on the weld firing line. This piece of prior art may reduce the penetration depth of the welding source, reducing the thickness of the pipes which may be welded with this technology, a major disadvantage.

A typical problem of laser welding is of metallurgical type and it is caused by the high cooling rate of the material involved in the welding. This can cause defects in the welded material: the laser brings heat on a low volume of material with a high thermal power in a very short period of time. The resultant high cooling rates can form hard structures such as martensite on the carbon steels normally used in offshore pipeline manufacture. Consequently, unwanted mechanical characteristics, such as low toughness and resilience and/or surface defects can form. High cooling rates can also induce adverse grain growth paths during solidification process often resulting in solidification defects or other defects that are formed when the material is at a high temperature and then rapidly cools. The formation of such hot cracks, or solidification cracks, is a common issue in high energy welding followed by rapid cooling of the metal, once the heating energy is removed.

United States patent application US2005155960 describes a hybrid welding process employing a laser beam combined with an electric arc, with a supply of consumable welding wire and shielding gas, in which the said wire is melted by the said laser beam and/or the said electric arc so as to produce a weld on at least one steel work piece to be welded. However, this piece of prior art has clear disadvantage, in that the consumable wire used can only penetrate so far into the thickness of the pipe, putting an upper limit in the thickness of the pipes that this can be used on at under 10mm in thickness.

International patent application WO2015039154 proposes a welding system in which a ring of predefined chemical form and composition is inserted between the two pipes to assist the laser welding methodology. An issue with using prefabricated rings is that there are many different combinations of pipe joint during assembly and misalignment between the parts to be joined, which make it impracticable have a consumable ring available for every possible joint. Ensuring a good and accurate fit between each pipe end face and opposing side of the prefabricated ring is another potential disadvantage of this proposed solution.

International patent application W02017140805 (Saipem) describes a welding process with pre-heating by inductors that is applied on coupled joints in the presence of gap. This solution is particularly advantageous on thick pipes (20- 30mm) where the induction leads to a uniform temperature profile on the thickness and reduces the cooling speed. This piece of prior art also discloses the use of a spacer, which improves the coupling precision, and can provide additional material that forms part of the weld.

The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved welding method.

Summary of the Invention

In accordance with a first aspect of the present invention there is provided a method of joining a first work-piece to a second work-piece, the method comprising bringing the work-pieces together with a layer (preferably a relatively thin layer) of material positioned therebetween, thus forming a joint to be welded and then welding the work-pieces together, with the intermediate layer of material melting in the process, thus forming a joint between the two work-pieces. The first work-piece has a first portion made from a first metal material and the second work-piece has a second portion made from a second metal material, which may be the same type of material, for example a steel alloy. The intermediate layer of material is made of a third material having a chemical composition which is different from that of the first and the second metal materials. The intermediate layer of material (referred to herein also as the “intermediate material”, the “intermediate layer”, or the “third material”) is formed on one or both of the first and second portions, for example by means of a deposition method, such as a laser metal deposition method. In embodiments, the intermediate material comprises tracks of material, preferably multiple parallel tracks of deposited material. The height of such tracks, and their arrangement, may be such that the average thickness, and in certain embodiments the maximum thickness, of the intermediate layer is relatively low, for example 2mm or less. At least some of the tracks of material may be adjacent to each other, in the direction along the depth of the weld (for example, being side by side as opposed to a single track having a further track deposited directly on top of it).

In an embodiment of the invention, the first and second work-pieces are pipes, the layer of material is deposited on at least one of the pipe ends before the welding step, the layer of material is of a different type of material from that of either pipe, and the welding is in the form of a keyhole laser welding process that melts not only the layer(s) of material between the pipes but also at least part of each pipe end. It may be that the welding process is performed in a way that requires no extra filler material to be added in order to form a satisfactory weld (i.e. an autogenous welding process in which there is no filler material in addition to the intermediate layer(s) of material between the pipe ends), at least insofar as the depth of the weld to be formed by the method. As will be described in further detail and more generally below, such an embodiment provides a very efficient and speedy method of joining a work-piece to another work-piece, for example in a method of laying pipeline from a vessel at sea. The intermediate layer being made by depositing tracks of material allows for a quick and straightforward deposition technique to be used in embodiments of the invention.

In examples, such a technique may also allow for a precise adjustment of, and control over, the amount of metal of the third material introduced into the weld, for example in different regions of the weld, as a result of tuning various controllable parameters of the metal deposition process as is described in further detail below.

In embodiments, the melting of the metal material (of the work-pieces and the intermediate layer of material) is performed by providing heating energy to the joint to be welded, for example with one or more welding torches. The heating energy is subsequently removed, and then the heated material solidifies, so that a solid weld joint (sometimes referred to as the weld seam) is made between the two work-pieces. The step of melting the intermediate layer of material to form the weld may be performed by an autogenous welding process, for example a keyhole welding process. The step of melting the intermediate layer of material may include using a laser welding device.

The intermediate material may be provided in the form of more than one layer. For example, one layer may be associated with, for example deposited on, the first portion of the first work-piece and another layer may be associated with, for example deposited on, the second portion of the second work-piece.

The weld joint that is formed as a result of performing the method of the invention contains both the base metal (e.g. of the first and second materials) and the intermediate layer. The proportions in which the base metal and intermediate layer make up the weld joint may affect the joint composition. In embodiments of the invention, the composition of the intermediate layer may be chosen (for example “tuned” or “engineered” in a particular way) to account for mixing with the base metal on welding, so that the final composition of the weld joint is of a specific composition or meeting certain criteria. An advantage of tuning the properties of the weld joint in this way may be to improve resistance to solidification cracking, which can be an issue in welding if the cooling of the molten metal is too rapid.

In some embodiments of the invention, the resultant composition of the mixing may have a higher percentage by weight of nickel than at least one of the first material and the second material. The third material may (before melting/mixing with the first or second materials) comprise more than 2% by weight nickel (optionally more than 5%). In some embodiments of the invention, the resultant composition of the mixing may be of greater than 1% by weight nickel, possibly greater than 2% by weight nickel. The inclusion of nickel can advantageously prevent the adverse grain growth paths, and inferior metallic structures, such as martensite, which can form because of high cooling rates. This is because nickel acts as a grain-refiner and promotes acicular ferrite formation which can be beneficial to weld toughness. Martensite is more brittle than austenitic steel, and has a much lower yield point. Reducing the likelihood of such structures from forming may therefore make a weld joint relatively stronger and more reliable.

In some embodiments of the invention, the weld joint may have a final composition similar to that of ER80SNi-2 (say, within +/- 10% of the amounts of any given constituent, on average). ER80SM-2 is a member of the family of alloys ER80SM as defined by the American Welding Society (AWS). Typically, such materials may contain between 2% and 2.75% nickel by weight, and between 0.4 and 0.8% silicon by weight.

The intermediate material may be a steel alloy. The steel alloy may comprise less than 90% weight iron, optionally less than 80% weight iron. The intermediate material may be an alloy comprising more than 30% weight iron. The intermediate material may have an alloy composition wherein at least 95% by weight (preferably at least 98%, and optionally at least 99%) is provided by only one or only two, or optionally only three, elements. In one embodiment of the invention, the intermediate layer of material used may be entirely elemental nickel (e.g. being at least 99% pure nickel). In some embodiments of the invention, it may be a nickel alloy containing above 50% by weight nickel. In another embodiment of the invention, the material used may be a steel and/or iron alloy containing greater than 2% by weight Nickel, for example greater than 5% or greater than 10% by weight, and possibly greater than 20% by weight Nickel (for example Invar, being -36% nickel and -64% iron). The intermediate layer of material may also be a steel alloy containing greater than 0.5% silicon. The intermediate layer of material may be a member of the family of alloys ER80SM, for example ER80SM-2.

The intermediate layer of material may be at least partially made of manganese carbon steel. The intermediate layer of material may be an alloy having at least 10% manganese. The inclusion of manganese and/or manganese carbon steel may increase the weldability and strength of the join made between the intermediate layer of material and the first and second work-pieces as unlike carbon steel, manganese carbon steel softens rather than hardens when rapidly cooled, restoring the ductility from a work-hardened state. This reduces the chance of solidification cracking occurring in the welded joint.

The intermediate layer material may include alloying elements such as one or more, preferably three of more of, the group consisting of manganese, nickel, chromium, molybdenum, copper, boron, titanium, niobium, and vanadium in order to improve the mechanical properties and corrosion resistance of the joint. The addition of chromium may increase the toughness of steel, as well as the wear resistance. Another potentially beneficial effect of adding chromium to the steel alloy is that it may impart resistance to staining and corrosion. Copper may also improve the corrosion resistance of the steel. Molybdenum may act to slow the critical quenching speed of the material, meaning the effects of rapid cooling are less negative on the intermediate layer of material. Niobium may act to control the grain structure of the steel. The addition of a very small percentage of boron can be used to tune the hardenability of the steel, along with titanium.

Embodiments of the invention may also include aluminium or silicon in the intermediate layer of material. These additions can act as deoxidising agents, which WO 2022/008750 . g . PCT/EP2021/069234 can remove oxygen from the melt during solidification of the intermediate layer. More or less aluminium or silicon can therefore be used in view of the volume percentage of pores or voids in the microstructure of the intermediate layer.

The intermediate layer material may have characteristics and/or a composition similar to the filler wire / properties thereof as referred to in the paper entitled “Hybrid welding possibilities of thick sections for arctic applications”, by Ivan Bunaziv et al (Physics Procedia 78 - 2015 - pages 74 to 83), the contents of which being incorporated herein by reference thereto.

The material of the intermediate layer may be weldable grade steel, preferably low carbon weldable grade steel. The steel material may have a carbon content of less than 0.5% by weight, and possibly -0.4% or less. The material may have a low equivalent carbon content, for example a CE value of less than 0.5% and optionally -0.4% or less. The CE value may be calculated as the percentage by weight of carbon plus 1/6 of the combined Mn and Si content, plus 1/5 of the combined Cr, Mo and V content plus 1/15 of the combined Cu and Ni content.

In some embodiments of the invention, the first material and second material are the same composition. In other embodiments of the invention, the first and second material may be of different compositions, therefore may melt to differing extents. In some embodiments of the invention, the first and second material may be steel.

It may be that the first and second material may be a steel of a quality grade of between X52 and X70. Here it should be noted that the steel quality grades as described in the form “Xn” where n is a number, are grades of pipe for the oil and gas industry, as regulated by API 5L, which adheres to the International Organization for Standardization ISO 3183. The ISO standard 3183 defines minimum mechanical properties for the steels used in the pipes. The number, n, denotes the minimum yield strength (being n multiplied by 1,000 pounds per square inch) of a pipe produced to this grade. The minimum yield strength for X52 pipes is 360MPa, and the minimum tensile strength is 460Mpa. For X70 pipes the minimum yield strength is 485 MPa and the minimum tensile strength is 570MPa. The requirements of the chemical composition of the base material also changes according to the grade specified. For example, X52 pipe may have no greater than 0.26% by weight carbon, or 1.40% Manganese. X70 pipe on the other hand, whilst having the same maximum limit on carbon content, allows for a percentage of manganese of no greater than 1.80%, depending on the delivery condition of the pipe. In any embodiment of the invention described herein, it is to be understood that the use of such classifications of pipe are in reference to ISO standard 3183 as in force on 1 October 2018.

In some embodiments of the invention, the work-pieces are seamless pipes. The work-pieces may each be made from steel of grade X60QO or better, that may have been quenched and tempered in order to improve its mechanical properties. In other embodiments of the invention, the work-pieces are pipes which are longitudinally welded (i.e. with seams). The work-pieces may be thermo- mechanically formed into shape, before being provided for use in the method of the present invention. The first and second material may be of grade X60MO or better.

In the case where the work-pieces are pipes, the grade of steel used for first material and second material may be suitable for the type and pressure of the oil to be transported, and also the temperature of the environment in which the pipeline is to be laid. For example, the hardness of the pipes may be between 180HV10 to 300HV10 (as measured using a Vickers hardness test).

In examples, the intermediate layer of material is deposited on at least one of the portions of the work-pieces before the first and second work-pieces are brought together, and possibly before the method of the invention is performed. For example, the intermediate layer of material may be deposited on the work-piece by a different entity from the entity that performs the method and/or in a different territory.

A single layer of intermediate material need not be contiguously formed. A single layer of intermediate material may comprise multiple parallel and spaced apart tracks. A single layer of intermediate material may comprise at least five separate tracks of material. Each of the tracks may have a height (i.e. a measurement made in the same direction as the thickness of the intermediate layer of material) which is less than 1mm, optionally less than 0.5mm, and possibly less than 0.1mm. Each of the tracks may have a width (i.e. a measurement made in the same direction as the thickness of the intermediate layer of material) which is less than 10mm, optionally less than 3mm, and possibly less than 1mm. In the case where the tracks are spaced apart, the intermediate layer may thus have a thickness that varies across the layer of material (for example from the height of the highest track of the layer to effectively zero at regions in between spaced apart tracks). The individual tracks may be deposited in such a way that their height is not constant across the entire width of a given track. After the work-pieces have been brought together and immediately before commencement of the step of melting the intermediate layer of material, the intermediate layer of material positioned between work-pieces may have an average thickness (in the direction of the height of the tracks) of greater than 0.05mm, preferably greater than 0.1mm, and optionally greater than 0.2mm. It may be that the average thickness is less than 2mm, for example the thickness may be 1mm or less (optionally less than 0.1mm). In some embodiments of the invention, it may be advantageous to have a material thickness which is neither too thin nor too thick. A preferred range in certain embodiments is between 0.05mm and 1mm (another preferred range being between 0.02mm and 0.1mm), as this may result in the weld joint containing both the intermediate layer of material and the base material of the work-piece in appropriate proportions. As described elsewhere herein, this may allow for the altering of the chemical properties of the work-piece in a way which makes the join stronger and less susceptible to solidification cracking. Additionally, a thickness of between 0.05mm and 1mm or between 0.02mm and 0.1mm may allow for a fast deposition of the third material on the base material of the work-piece ends, which may allow for strong bonding of the material to the base material, as compared to the case when a thicker layer is used. It should be noted that the value of the average thickness of the intermediate layer is calculated by averaging the height of all the tracks that form the intermediate layer (over a representative sample unit area, say of 5cm² in area) and excluding any regions where the thickness is effectively zero.

In examples of the method of the invention, it will typically be the case that the weld formed has both a depth - e.g. into the work-piece(s) - and a length - e.g. along or parallel to an outer surface of the work-piece(s). Various features of the invention may conveniently be defined with reference to the directions of such a length and depth of the weld. It will be appreciated that the weld length and/or depth may have a direction that changes along the weld. For example, the length of a weld formed between the ends of two pipes extends circumferentially around the pipes whereas the depth of the weld is in the radial direction relative to the axis of the pipe. The tracks of the third material may extend in the same direction as the length of the weld to be formed. The height of tracks (the same direction in which the thickness of the intermediate layer would be measured) may be transverse (for example perpendicular) to both the length and the depth of weld. It may be that, immediately before the step of melting is performed, the amount of the third material per unit distance, in the direction of the depth of the weld, varies. It may be that, immediately before the step of melting is performed, the amount of a component of the third material per unit distance, in the direction of the depth of the weld, varies. For example, the amount of nickel, where tracks are present, may be distributed non-linearly, across the work-piece. Such a feature may have benefit in embodiments where the third material is deposited on the work-pieces by means other than parallel tracks of material.

There may be embodiments in which the amount of material welded varies in the direction of the depth of the weld. For example, more material may melt at the regions nearer a welding torch, than regions deeper in the weld. There may be embodiments in which the amount of material that melts is smaller in the middle of the weld, that is the middle as measured in the direction of the depth of the weld. In such cases, it may be desirable to have a weld joint with broadly the same average chemical composition, at all depths of the weld, which might require a greater amount of third material to be provided at those regions where greater amounts of the first and/or second materials are melted. It may be that the amount of the third material in the middle of the weld is less than, for example at least 10% less than (optionally at least 20% less than) the amount of the third material at a position corresponding to the upper or lower part of the weld. The amount of the third material at a certain position along the depth of the weld (to be measured immediately before welding) could be measured by considering the mass of the third material over a certain representative area of the first and/or second work-pieces, equal to say 5cm², centred at that depth. The amount of the third material at a certain position along the depth of the weld could alternatively be measured by considering the mass of the third material per unit distance at that depth, as measured over a certain representative distance in the direction of the length of the weld (say, over a distance of 5mm, or optionally over a distance of 2.5mm).

As mentioned above, it may be that at least some of the tracks of the third material are adjacent to each other in the direction along the depth of the weld. It may be that at least some of the adjacent tracks of the third material are directly adjacent to each other, for example, touching each other or close to touching each other. It may be that at least some of the adjacent tracks of the third material touch each other.

Some of the adjacent tracks of the third material may overlap each other. In some examples, tracks may be stacked one on top of the other, for example in addition to being adjacent to each other in the direction along the depth of the weld .

Alternatively or additionally, at least some adjacent tracks of the third material may be spaced apart from each other, across the direction along the depth of the weld to be formed. There may be a track (or a portion thereof) that is spaced apart from an adjacent track by a spacing of between 10 and 1,000 microns, for example, between 20 and 500 microns. There may be multiple such tracks (e.g. five or more) all being spaced apart from an adjacent track by such a spacing. Adjusting the spacing of the tracks, may provide a means of controlling / tuning the mix of first, second and third materials in the weld.

The tracks may be curved. There may be one or more tracks which follow a straight line. At least some of the tracks may be so arranged that the third material has a height (for example a non-zero height, as measured at the centre of the uppermost track on the work-piece) at one location along depth of the weld to be formed that is different from the height (for example a non-zero height, as measured at the centre of the uppermost track on the work-piece) at a different location along depth of the weld to be formed. The heights may differ by more than 10%, and possibly by more than 20% from each other. Having different heights of tracks may provide a means of controlling / tuning the mix of first, second and third materials in the weld. The height of one track may be different from the height of another track on the same work-piece. In the case where the heights of the tracks vary, it may nevertheless be the case in certain embodiments that the tops of the tracks are co- planar - this may be achieved by the portion of the work-pieces on which the tracks are deposited being non-planar and/or as a result of machining or other processing of the tracks after they have been deposited. It may be the case that in those embodiments where the tops of the tracks on one work-piece are co-planar, the plane in which the tops of the tracks lie is parallel to the abutting surface of the other work- piece (when the portions of the work-pieces are brought together ready for welding) - whether that abutting surface is defined by the tops of the tracks on that other work- piece, or defined by the shape of that other work-piece itself in the case where no tracks are deposited thereon.

The thickness of the layer of the third material, where non-zero, may be substantially constant, across the direction along the depth of the weld to be formed. It may be that each of the tracks is the same height and the same width. Such uniformity may simplify the device(s) / apparatus used to deposit the tracks. Other means may, as explained herein, be used to control / tune the mix of first, second and third materials in the weld where that is so desired.

It may be that some of the tracks have a different chemical composition from other tracks. Having different chemical compositions of tracks may provide a means of controlling / tuning the mix of first, second and third materials in the weld.

It may be that the amount of a component of the third material of the tracks varies (e.g. across the depth of the weld to be formed) as a result of any of the following six parameters varying: (a) the height of the track, (b) the width of the track, (c) the pitch distance between the centres of the tracks, (d) the gap between adjacent tracks, (e) the number of tracks stacked on top of each other, and (f) the relative concentration of the component of the third material. It may be that only one (or optionally only two) of those six parameters are varied on a given work-piece, with the remaining parameters being substantially constant (i.e. the values of those other remaining parameters not forming part of the mechanism by which the amount of the component of the third material of the tracks is controlled/tuned). It may be that at least two (or optionally three or more) of those six parameters are kept substantially constant on a given work-piece. It may be that one or more of those six parameters are varied on a given work-piece, with at least two or more of the remaining parameters (optionally three, and possibly four) being substantially constant.

The speed at which the tracks are deposited may be varied. A typical rate of deposition of a track may be at least lm/min. The rate of deposition may lOm/min or less.

The third material may be deposited to form a relatively thin coating of material on the work-piece. For example, the material deposited may have a typical thickness of 10s of microns (e.g. 20 to 90 microns). The thickness of the layer of material on the end face of one of the work-pieces may be less than 100 microns. The average thickness of the layer of material on the work-piece (taken as an average over the area of the end face on which the layer is present) may be less than 100 microns, for example 60 microns or lower. In embodiments, the thickness is preferred to be 30 microns or more and/or 100 microns or less. Different embodiments of the invention may utilise different means of depositing the tracks of material. The material may for example be deposited by any of sputtering, spraying, and/or additive manufacturing techniques such as laser metal deposition and electron beam melting deposition.

The weld joint that is made between the two work-pieces comprises a weld joint, which has a thickness that is greater than the thickness of the intermediate layer of material - typically at least 10 times, and possibly more than 50 times greater. The weld joint thickness is defined by those regions that have melted during the welding process, and therefore form some of the weld joint. The weld joint will typically be surrounded by a heat affected zone (HA Z), that being the regions of material, which have not melted but which have been otherwise affected by the welding heat (for example, material which has had its microstructure altered by the welding heat). For the purposes of measuring the thickness of a weld joint, which has different thickness at different locations, it may be that the thickness is defined as the average thickness of the weld joint (in a direction perpendicular both to the length and the depth of the weld) taken over the whole depth of the weld joint and along the entire length of the weld. The thickness of the intermediate layer of material (with which the weld joint thickness is compared) may be defined as the average height of the tracks that form the intermediate layer, as measured immediately before the work-pieces are brought together.

Some embodiments of the invention are particularly well suited to the use of high energy welding techniques. The step of melting the intermediate layer of material (and also melting at least part of the first and second materials) may be performed by keyhole welding, for example with a high energy welding device. The high energy welding device may be a laser welding device in some embodiments of the invention. In others, it may be an electron beam welding device. The welding device may use an electric arc. The high energy welding device may be a plasma welding device. The high energy welding device may comprise one or more welding torches. For example, the high energy welding device may be a laser welding device comprising one or more welding torches and/or optical heads. It will be understood that when employing a keyhole welding technique, a concentrated heat source penetrates deep within a work-piece, possibly through substantially the entire thickness of the work-piece, forming a hole at the leading edge of the molten weld metal at the surface of the work-piece to which the heat source is applied. As the heat source progresses, the molten metal fills in behind the hole to form the weld bead. This may be advantageous as a welding technique as it can produce narrow welds, with deep penetration and low distortion effects. The use of such highly focussed high energy welding devices can cause extremely high temperature gradients in the region of the weld and the surrounding material, and consequent rapid cooling rates after the source of the heating energy is removed. However, certain embodiments of the present invention are well suited to such techniques, with the use of the multiple tracks of intermediate material that can be engineered to mitigate against the disadvantageous effects of rapid cooling.

In some embodiments of the invention, the keyhole welding is performed with a laser with a spot size of less than 0.5mm. This is advantageous as a small spot size allows energy to be transferred quickly and efficiently, resulting in a shorter time required to complete a weld. In other embodiments of the invention, the spot diameter may be less than I,OOOmih. The spot diameter may be more than lOOpm. In these or other embodiments, a fibre optic cable may deliver the laser beam. This may be mounted on automated, or semi-automated, robotic equipment, which minimises the potential hazards of human exposure to a high energy source. It may be that the power density of the energy source is greater than 10k W/mm² at the surface of the work-pieces. It may be that the power density of the energy source is greater than 50kW/mm², for example around 70 kW/mm² or higher. This has the advantage that the keyhole welding of the work-pieces can occur at pace and at a stable rate.

In some embodiments of the first aspect of invention, welding is performed with a welding device which forms a weld in one-pass having a depth of more than half the thickness of the work-pieces, preferably more than 75% of the thickness. In certain examples, the weld may extend throughout substantially the entire depth of the thickness of the work-pieces.

It may be the case, for some embodiments of the invention, that the depth of welding achieved is greater than 10mm. In these or other embodiments of the invention, the depth of welding achieved may be higher, and be greater than 20mm. A deep weld may be advantageous, particular when welding work-pieces (e.g. pipes) together with thick walls as it means that the weld covers a higher proportion of the opposing faces of the welded work-pieces, forming a stronger join.

In some examples of the method of the invention, the portions of the work- pieces are provided with the tracks of the third material already deposited thereon. In other examples of the method of the invention, the method includes a step of depositing the intermediate layer of material on at least one of the first portion of the first work-piece and the second portion of the second work-piece before the step bringing the first portion and the second portion together. The deposition method may be a sputtering method. The intermediate layer of material may be deposited by means of an additive manufacturing technique. It may be that the additive manufacturing technique used is laser or electron beam melting deposition. It may be that the additive manufacturing technique used is a laser metal deposition process. The use of an additive manufacturing technique may be particularly useful in creating the tracks on the work-piece is a repeatable and controllable manner. It may be that multiple separate tracks of the intermediate layer are deposited simultaneously, for example by multiple deposition devices.

As acknowledged above, certain embodiments of the invention relate to welding pipes together. In accordance with a second aspect of the present invention there is provided a method of welding a first pipe and a second pipe end-to-end, comprising a step of bringing the end face of the first pipe and the end face of the second pipe together with an intermediate layer of material formed on at least one of the end faces of the pipes, thus forming a joint to be welded. The first pipe is made from a first metal material and the second pipe is made of a second metal material, which may be the same type of material, for example a steel alloy. The intermediate has a chemical composition which is different from that of the first material and the second material. The intermediate layer of material may be formed of multiple parallel tracks of a third material. There is a subsequent step of providing heating energy to the joint to be welded, for example with one or more welding torches, so that the intermediate layer of material melts together the first metal material and the second metal material. The heating energy is subsequently removed, and then the heated material solidifies, so that a joint is made between the two pipes. Immediately before the step of providing heating energy, the intermediate layer of material may have an average thickness of 2mm or less and/or the amount of at least one component of the third material per unit distance, in the direction of the depth of the weld to be formed, may vary.

In the case where the work-pieces are in the form of a first pipe and a second pipe, one of the pipes may form the end of a pipeline. The method may be performed on a pipe-laying vessel at sea. The method may be performed as part of a method of laying a gas or oil pipeline. The following text, referring to the welding of pipes together, applies to the first and/or second aspects of the invention.

The parallel tracks of the third material may be deposited on the pipe end so that each track extends circumferentially around the end face of the pipe. The tracks may be in the form of multiple concentric circles of progressively larger diameters, the circles for example being centred about the axis of the pipe. There may be a track which follows a spiral path.

In some embodiments of the invention, the bringing of 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. Performing all pipe alignment and welding steps at a single welding workstation allows for efficient usage of space on the vessel, for embodiments where the welding occurs at sea, and may also increase efficiency in other ways. For example, performing all of the principal welding steps at a single welding workstation may reduce complexity on the firing line and may also increase productivity. It may also reduce the amount of equipment that is required on a pipe laying vessel.

The making of the joint between the two pipes may occur in a single welding pass. The making of the joint between the two pipes may occur without using a rod of filler material, filler wire, or the like. The making of the joint between the two pipes may occur without using any extra filler material, over that provided by the intermediate layer(s).

It may be that the weld is performed on only one side of the pipe (for example from outside of the pipes - i.e. welding from the exterior rather from inside the pipes). For example, in some embodiments, a welding device forms a weld in one-pass which extends through substantially the entire thickness of the work-pieces (additionally or alternatively, at least 75% and possibly at least 90% of the thickness). This may result in a quicker speed of welding, as many current production lines require pipes to be welded on two sides in order to form a weld joint with sufficient strength and/or use multi-pass welding techniques where successive layers of welding material are laid down in a welding groove. Various embodiments of the invention have the advantage however of improving the speed at which the welding can take place on the firing line, by the use of such one-pass and/or full depth welding. It may be that the welding occurs only on the exterior side of the pipe. This may simplify the design of a firing line in comparison to current technologies, for example by reducing the number of robotic weld jigs required and/or avoiding the need for internal welding equipment for welding from inside the pipes. In certain embodiments of the invention, welding may occur from both sides (interior and exterior) of the pipe. In certain embodiments of the invention, autogenous one-pass laser welding may be performed in accordance with the method of the invention, with the root and/or cap of the weld being filled with filler material as a separate / additional step.

In certain embodiments of the invention, welding may be performed with multiple welding heads, for example each welding head working on a different sector of the pipe circumference. Multiple welding heads may perform welding at the same time. Each welding head may comprise one or more welding torches. In certain embodiments of the invention, welding may be performed with multiple welding torches, for example the multiple welding torches performing welding at the same time. The welding heads may be spaced apart equally along the pipe circumference, or alternatively be spaced relatively proximal to one another in a queue.

The intermediate layer of material between the end faces of the pipes may be sized and shaped to extend over the entirety of the annular end face of at least one of the pipes. It may be that no part (e.g. no non-negligible part) of the end face is left uncovered by the extent of the intermediate layer of material, once the pipes have been brought together. The intermediate layer of material may be deposited over a part of the inside (interior) surface of the pipe in the region of the end face. The intermediate layer of material may be deposited over a part of the outside (exterior) surface of the pipe in the region of the end face.

The intermediate layer of material may have a shape having an outer diameter that is the same as the outer diameter of the pipes (for example within a margin of +/- 5%). The intermediate layer of material may have a shape having an inner diameter that is the same as the inner diameter of the pipes (for example within a margin of +/- 5%). The intermediate layer of material may cover the whole area of the face of the pipe end. Alternatively, the intermediate layer of material could be slightly smaller than the whole area of the face of the pipe end and yet still have an annular shape that is sized to broadly correspond to that of the end face of the pipe.

Embodiments of the invention may be of particular application in relation to metal pipes which have an outer diameter greater than 150mm, possibly greater than 500mm. It may be that the pipes are such that the pipe wall has a thickness, t, of greater than 15mm, possibly greater than 25mm. The pipe wall may have a thickness of 50mm or less (possibly less than 45mm). The average thickness of the third type of metal material, (a) once sandwiched between the pipes and/or (b) immediately before the welding step is performed, may be greater than 0.005mm (possibly greater than 0.01mm and optionally greater than 0.05mm) and/or may be less than 2mm (optionally less than 1mm and possibly less than 0.1mm). The welding may be performed without using extra filler wire, filler rods or other extra filler material (other than the layer(s) of third material sandwiched between the pipes).

The present invention also provides, according to a third aspect of the invention, a work-piece material being configured for use in the method according to other aspects of the present invention. Such a work-piece may for example include a portion made from a first metal material on which there are deposited multiple parallel tracks of material of a different chemical composition from the first metal material.

According to the present invention, there is also provided a method of depositing material on a work-piece so as to form a work-piece being configured for use in the method according to other aspects of the present invention. This aspect of the invention does not necessarily require the performance of the other steps of the first or second aspects of the invention mentioned herein. The material may be deposited by means of an additive manufacturing technique, for example a laser metal deposition technique. The laser metal deposition technique may be powder fed. The laser metal deposition technique may be wire fed. Wire fed laser metal deposition is known as laser metal wire deposition LMWD or micro LMWD (pLMWD). The wire diameter may be less than 2mm, optionally less than 1mm, and possibly less than 0.8mm. The method may include a step of flattening the layer of tracks after it has been deposited, for example by means of the use of a milling tool or by melting the layer before the main welding step. The method may include a step of machining a work-piece to provide a non-planar surface ready for the deposition of the tracks thereon.

The present invention also provides an apparatus for depositing material on the end of a work-piece so as to form a work-piece, configured for use in the method according to other aspects of the present invention. Such an apparatus may include one, and preferably more than one (for example, at least five or more than five), additive manufacturing devices each arranged to deposit metal along a track. Said one or more additive manufacturing devices may comprise one or more laser metal deposition devices. Said one or more additive manufacturing devices may comprise one or more laser metal wire deposition devices. The apparatus may comprise multiple spaced apart additive manufacturing devices. The additive manufacturing devices may be supplied with heat power, for example laser light, from a common source. The additive manufacturing devices may be supplied with metal material from a common source. The additive manufacturing devices may each comprise its own source of metal, for example metal in powder form or in wire form. The additive manufacturing devices may each comprise a respective nozzle and/or outlet for metal material to be outputted therefrom. In some embodiments, there may be a single body with multiple such nozzles and/or outlets. The additive manufacturing devices may be arranged such that the spacing between tracks when deposited is controllable by physical adjustment of the relative spacing and/or orientation of one or more nozzles and/or outlets.

The additive manufacturing device(s) of the apparatus may be independently controllable, so as to vary the rate of deposition of the metal track. The additive manufacturing devices may mounted for movement relative to the work-piece, for example movement along the length of the tracks to be deposited. Two or more additive manufacturing devices may mounted for movement together relative to the work-piece. The additive manufacturing devices may configured for rotation about an axis, which for example coincides with the centre of curvature of one or more of the tracks to be deposited. In other embodiments, the work-piece may be moveable such that the one or more additive manufacturing devices deposit tracks onto the work- piece as it moves along a path. A work-piece, particularly when in the form of a pipe, may be rotated relative to the additive manufacturing device(s), such that the one or more additive manufacturing devices deposit circumferential tracks onto pipe ends as the pipe rotates. The apparatus may be provided on a pipe laying vessel.

The present invention also provides a kit of parts for use in a method of laying a pipeline. The kit may comprise multiple pipes, each being a pipe being configured for use in the method according to other aspects of the present invention, and a welding apparatus (for example a laser welding apparatus). The kit may comprise multiple pipes, a welding apparatus (for example a laser welding apparatus) and apparatus for depositing material on the end of a pipe so as to form a pipe configured for use in the method according to the present invention. The kit of parts may be provided on a pipe-laying vessel. It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

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

Figure 1 shows a side view of a pipeline laying vessel according to a first embodiment of the invention;

Figure 2 shows a side view of two ends of pipe being welded together on the vessel of Figure 1;

Figure 3 shows part of the end of a pipe, on which material has been deposited in accordance with the first embodiment;

Figure 4 shows a partial cross-section of the end of the pipe shown in Figure 3;

Figure 5 shows the bringing of the pipes together according to the first embodiment;

Figure 6 shows the pipe joint once welded according to the first embodiment, the weld seam extending beyond the original extent of the filler material;

Figure 7 shows an apparatus according to a second embodiment for depositing filler material as parallel tracks on the end of a pipe;

Figures 8 to 10 show cross-sections of various configurations of tracks able to be deposited by the apparatus of Figure 7;

Figures 11 to 16 illustrate some non-linear aspects of the weld joint profile and possible ways in which to address that;

Figures 17 and 18 show cross-sections of some further configurations of deposited tracks;

Figure 19 shows an apparatus being a variant of that shown in Figure 7;

Figure 20 shows an apparatus as an alternative to the second embodiment

Figure 21 shows an apparatus as a further alternative to the second embodiment; and Figure 22 is a flowchart of a method according to an embodiment in which filler material is deposited on at least a first work-piece before being welded to a second work-piece.

Detailed Description

Figure 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. The pipe laying vessel and type of pipeline, and other details of the present invention and embodiments thereof, including any optional features, may be as described and/or illustrated in PCT Application No. PCT/EP2020/050589, the contents of which being incorporated herein by reference.

The sections 28 of pipe added to the pipeline 22 (string) are each 12m long (but could be multiples of 12m in other embodiments, or any other length). Each pipe has an outer diameter of 1000mm. 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).

The base material of the pipes may be of X60 grade material having the following (non-exhaustive list of) constituents: Fe (97.5%), C (0.087%), Mn (1.08%), Si (0.27%), Ni (0.26%), Cr (0.18%), Cu (0.13%), Mo (0.12%), and A1 (0.032%). The pipeline 22, and pipe sections 28 being welded to it, are of the same material.

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.

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 Figures 2 to 4.

Figure 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 Figure 3.

Figure 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 is Invar, which has an alloying composition as follows -36% nickel and -63 to 64% iron (more specifically, Fe (63.2%), Mn (0.2%), Si (0.15%), Ni (36.4%).

In the first embodiment of the invention, the layer 61 is applied as parallel tracks 64 of material (as shown in the magnified section 63 shown in Figure 3), in a manner described in further detail below, on the ends of the pipes (both ends of all pipe sections 28) to be welded. The pipes are machined and tracks 64 deposited on their ends 60, separately from and before the start of the welding process, 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 Figures 3 and 4. Figure 4 is a partial cross section of the pipe representing the area marked by the box as shown in Figure 3. As can be seen from the magnified section shown in Figure 3, the parallel tracks 64 of deposited material are directly adjacent to each other, in the direction along the depth of the weld. It will be understood that in this embodiment, the depth of the weld is parallel to direction of the thickness, t, of the pipe. In at least this embodiment, each parallel track 64 has a length which extends in the same direction as the direction of the length of the weld to be formed. The tracks 64 of deposited material are shown in the magnified section of Figure 3 as being parallel and spaced apart in the direction along the depth of the weld. The axis of the pipe is horizontal in Figure 4, and an exterior surface 66 of the pipe is shown at the top of the Figure 4. The depth (thickness, dl) of the layer 61 (as measured in the direction parallel to the axis of the pipes) is ~50pm (0.05mm) on each pipe end. Each pipe has a wall thickness, t, of ~30mm.

The thin depth of the layer 61 allows results in a welded joint which comprises both the base pipe material (of both pipes) 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 an additive manufacturing technique, on land in a factory.

Figure 5 shows the pipe 28 with its end 60 (having been pre-treated by means of deposition of the intermediate material 61 thereon) being moved towards the end 60 of the pipeline 22, which is similarly treated. Thus, the pipe pieces 22 and 28 are brought together, so that their ends 60 touch.

On welding of the pipes together all of the intermediate layer 61 melts and forms part of the weld joint. With reference again to Figure 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 pm delivering heat energy at a density of about 70 kW/mm². The welding process is autogenous - no further filler material is required in addition to the material already deposited on the pipe ends.

Figure 6 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_axiS of the pipe. The thickness of the weld seam d2 (being ~3mm) is sufficiently large that it encompasses all of the intermediate material (the two layers 61 having a combined thickness of ~0.1mm) 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 Figure 6 by the double-headed arrow labelled HA Z. 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 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 brittle microstructures formation in the material is reduced in comparison to the likelihood of brittle microstructures formation occurring in the pipe material when the same cooling rate is applied. In particular, in this first embodiment of the invention, the properties of the intermediate material 61 are tailored such that the resultant weld seam comprises a steel containing a higher weight percentage of nickel, which gives improved fracture toughness in comparison to a join made out of only the base 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.

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 substantially consistent across the full depth of the weld. It works well with welding thick pipes, with a thickness of, say, greater than 20mm.

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.

A second embodiment of the invention relates solely to the preparation of the pipes, by depositing tracks of material on a pipe end to form an integrated layer on the end of the pipe. The second embodiment is illustrated with reference to Figure 7.

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.

Figure 7 shows a deposition apparatus comprising multiple additive manufacturing nozzles 70 each of which being fed by a respective source 71 of metal powder and a common source of laser light 72. The apparatus is configured to lay down parallel tracks of material onto the end of the pipe 28, using a laser metal deposition (“LMD”) technique which has the advantage of being a readily well understood and controllable process. The nozzles are held in position as a set of tracks are laid down, while the pipe is rotated about its axis by the use of a spin roller. The radial position of the nozzles may be adjusted between runs so as to allow multiple circumferential tracks to be laid down in the case where the number of tracks required is greater than the number of nozzles provided. It will be appreciated that the apparatus of Figure 7 includes other elements not shown for the sake of clarity including a chiller, sources of process gas, position sensors, profilometers, cameras, motors, thermometers, fume extraction system, and the like. Position sensors may for example be configured to enable the position / orientation of the nozzles relative to the pipe end to be ascertained. Adjustable optics are provided for focusing the laser beam in the desired position on the pipe end.

The flow of metal powder from the source 71 is provided by a system (not shown) of pumping or pushing or suctioning powder towards the laser head (not separately shown). The powder flow is coaxial with the laser beam. The rate of powder deposition achieved per nozzle is ~ 3.6 m/min (linear speed), which allows for a pipe end to be coated with tracks within at most 10 minutes and preferably less than 6 minutes.

Only two nozzles are shown in Figure 7, but more than two may be provided - for example four or more. Such nozzles may be provided close together such that parallel tracks are deposited substantially next to each other, or in quick succession, side by side. Alternatively, the nozzles may be spaced apart around the circumference of the pipes end such multiple tracks are deposited simultaneously but at different positions around pipe circumference.

Figures 8 to 10 shows some example layouts of the tracks 64 that can be laid with the apparatus of Figure 7. In each Figure, the tracks 64 have a width, w, a height, h (in these cases also equal to the depth dl of the layer 61) and a pitch or separation, s. In Figure 8, adjacent tracks are separated by a gap, g (such that g = s - w). An example might be for the tracks to have a width of ~0.6mm, a height of ~0.05mm, and a pitch / separation of 1 2mm. Seven parallel tracks may then be deposited to cover a pipe wall thickness of ~8mm. In an experiment with such a set up, where the base material of the pipes was of X60 grade material (in this case, A1 - 0.03%, Si - 0.27%, Cr - 0.18%, Mn - 1.08%, Fe - 97.37%, C - <0.1%, Ni - 0.26%,

Cu - 0.13%, Mo - 0.12%) and the tracks were of Invar material (in this case, Si - 0.15%, Mn - 0.22%, Fe - 63.23%, Ni - 36.4%), the composition of the resulting weld was found to be as follows: A1 - 0.03%, Si - 0.27%, Cr - 0.18%, Mn - 1.06%, Fe - 97.03%, C - <0.1%, Ni - 0.99%, Cu - 0.13%, Mo - 0.12%).

In Figure 9, adjacent tracks are touching such that g = 0 and s = w). An example might be for the tracks to have a width of ~0.6mm, a height of ~0.05mm, and a pitch / separation of 0.6mm. Thirteen parallel tracks may then be deposited to cover a pipe wall thickness of ~8mm. In an experiment with such a set-up, where the material of the pipes and of the tracks being the same as described in relation to Figure 8, the composition of the resulting weld was found to be as follows: A1 - 0.03%, Si - 0.27%, Cr - 0.18%, Mn - 1.04%, Fe - 96.3%, Ni - 1.73%, Cu - 0.13%, Mo - 0.12%).

In Figure 10, the tracks overlap, such that s < w (which in the case that the tracks have the same volume of material per unit length as the tracks of Figure 9, inevitably leads to the overlapping tracks forming a layer 61 having a greater depth dl than in Figure 9.

Thus, it can be seen that by changing such parameters as the pitch (separation s) of the adjacent tracks it is possible to control the amount of intermediate material deposited on the ends 60 of the pipes head in a controlled manner, without necessarily needing to change the rate of flow of metal material or the travel speed of the nozzles relative to the pipe ends 60. Thus, the “apparent density” or coverage of the layer 61 over the pipe end may be controlled and engineered as desired. The layer need not cover the entire surface of the pipe end - there may be gaps between adjacent tracks (as shown in Figure 8). Laying down fewer tracks in the pipe wall thickness direction (t) may save time in deposition process and/or require fewer deposition nozzles.

Track height (h) and width (w) can also be independently controlled by appropriate selection of the LMD parameters. The pitch (s) can be controlled by changing the relative positions of the depositing nozzles 70.

It has been observed that the weld shape typically achieved with use of embodiments of the invention has a width / thickness (“d2”) which varies with the depth of the weld (in the pipe wall thickness direction, t). With reference to Figure 11, the weld tends to be thinner in the middle with the thickness, d2, being wider towards the outer surface of the pipe wall (towards either the pipe inner diameter or the outer diameter). The weld thus has an hourglass shape. If the intermediate layer material 61 is distributed evenly over the pipe end, the concentration of that material in the weld joint may be higher in the middle of the weld and less concentrated at the outer regions. It may be desirable for the weld joint to have a substantially uniform chemical composition. Thus, it may be desirable to have a relatively higher amount of material deposited at the regions of the pipe end that will correspond to the root of the weld and the cap of the weld and a relatively lower concentration of material deposited at the regions of the pipe end that will correspond to the middle of the weld. Figure 12 illustrates schematically how the amount of material 61 deposited on the pipe end 60 might need to vary for the resultant weld to have a uniform composition. This may be achieved in a variety of different ways, as shown in Figures 13 to 16, all of which could be achieved using the apparatus of the embodiment shown in Figure 7.

Figure 13 shows how the amount of material 61 deposited on the pipe end 60 could be varied across the pipe wall thickness direction by varying the height h of the tracks whilst keeping the pitch and width constant. Thus, the track in the middle has a height hi that is lower than the height h2 of the tracks immediately adjacent to the outer diameter and to the inner diameter.

Figure 14 shows how the amount of material 61 deposited on the pipe end 60 could be varied across the pipe wall thickness direction by varying the gap between the tracks whilst keeping the width and height constant. Thus the track in the middle is further away (gap g2) to the adjacent track than the separation gl of a track immediately adjacent to the outer diameter or the inner diameter.

Figure 15 shows how the amount of material 61 deposited on the pipe end 60 could be varied across the pipe wall thickness direction by varying the width w of the tracks whilst keeping the gap and height constant. Thus the track in the middle has a width w2 that is lower than the width wl of the tracks immediately adjacent to the outer diameter and to the inner diameter.

Figure 16 shows how the amount of material 61 deposited on the pipe end 60 could be varied across the pipe wall thickness direction by varying the number of tracks deposited on top of each other, whilst keeping the pitch, width, and height of each individual track constant. Thus, the layer 61m in the middle is formed of a single track having a height h, whereas the layer 61e immediately adjacent to the outer diameter and to the inner diameter is formed of the three tracks in a stack, thus having a height of 3 x h.

A further way in which the resultant weld may have a uniform composition, at least insofar as percentage nickel content is concerned for example, would be for the nickel content of the tracks per unit length to be changed according to location of the track along the thickness of the pipe. The track laid directly adjacent to the outer diameter or the pipe may for example have a higher concentration of nickel than tracks nearer to the midway point between the inner and outer diameter. The tracks could otherwise have a uniform shape and distribution across the end of the pipe.

It may be convenient to change only one or perhaps two of the controllable parameters in order to achieve the desired material concentration profile of the deposited material across the depth of the weld to be formed, while keeping the values of other parameters substantially constant.

In the examples of Figures 13 and 16, the thickness of the layer increases from the centre outwards such that the pipe ends are not as flat as they might previously have been. A non-flat geometry of the pipe ends may create gaps between the touching pipes when brought together for welding. If the gaps are significant in size, weld quality could be affected. As an alternative, the pipe end could be machined before the tracks are deposited so that the profile of the end of the pipe after the layer has been deposited is flatter (as measured by the heights of the tracks thus laid - ignoring any gaps in between) than immediately before the layer is deposited on the pipe end. Additionally or alternatively, there may include a step of flattening the layer of tracks after it has been deposited, for example by milling or by re-melting the layer before the weld joint is formed. Figure 17 and 18 are two schematic illustrations each showing a cross-section of the pipe wall at the pipe ends showing an example profile. In Figure 17, the pipe end is machined with four flat sections, arranged so that the pipe end has a generally convex shape. The amount of material 61 deposited on the pipe end 60 is varied such that the track in the middle has a lower track height than the tracks immediately adjacent to the outer diameter. The pipe ends are machined again after the tracks have been deposited so that the end face is flat and perpendicular to the pipe axis (as shown in Figure 17). Figure 18 shown a variation of the profile shown in Figure 17, in that the pipe wall ends are machined before the tracks are deposited to have two flat sections 60f, instead of four. Other profiles and shapes are also envisaged.

Figure 19 shows schematically an additive manufacturing apparatus for depositing parallel tracks of material, as a modification of the embodiment of Figure 7. In the additive manufacturing apparatus shown in Figure 19 multiple streams of material 7G and laser light 72’ are outputted from a single nozzle device 70 which is fed by a common source 71 of metal powder and a common high power source of laser light 72. The laser light passes through a beam shaping optic device 73 which creates multiple beams of laser light, one beam per output. These laser beams are combined with streams 7 of metal powder which are melted to form the parallel tracks on the pipe end 60, thus depositing a volume of intermediate material 61 on the pipe end. As a modification to the apparatus for depositing parallel tracks of material of Figure 19, the nozzle device may be configured such that the same apparatus can be employed to control the amount and type of material sent to each output of the nozzle. This may allow for combining different powder types for alloying in situ and/or allowing for graded depositions for a greater control of the chemistry of the material deposited for example.

In the apparatus of Figure 19, the nozzle device 70 is mounted for rotation relative to the pipe 28. This may be achieved by means of the device being part of a larger assembly that is clamped to the pipe, for example by means of an internal pipe clamp, in a manner similar to a portable pipe-bevelling machine. Alternatively, the nozzle device 70 may be movably mounted on an externally mounted band which is clamped to the pipe end, in a manner similar to a travelling welding bug.

Figure 20 shows a single high productive deposition apparatus according to a further embodiment, which provides an alternative to the apparatus shown in Figure 7. The main differences are now described. The apparatus comprises a single additive manufacturing dispensing device 170 with multiple outputs 174. The device has a single source of laser light 172 and a single source 171 of metal powder. The device 170 is configured to lay down parallel tracks of material, side by side, onto the end of a work-piece, using a laser metal deposition (“LMD”) technique. The nozzle outputs are arranged so that they can be manipulated in space to adjust the position of the flow, and the separation/pitch between adjacent tracks. The laser light may be provide from the single source as a single strip of laser light that fuses/melts the powder from the multiple nozzles simultaneously (i.e. the strip of laser light extending in a direction perpendicular to the length of the tracks).

Figure 21 shows a single deposition apparatus according to a further embodiment, which provides an alternative to the apparatus shown in Figures 7 or 20. The main differences are now described. The apparatus of Figure 21 can be incorporated on a pipe-laying vessel so that pipe sections can have intermediate layers deposited on the pipe ends on the same vessel as is laying the pipeline being formed of such pipe sections, for example during prefabrication on the vessel and/or in the firing line. If required, the deposition of material onto the pipe ends can be achieved without rotating the pipe about its axis. It is thus possible to use the apparatus of Figure 21 to deposit material directly onto the end of the pipe section 228 that forms the end of the pipeline that is at sea level (i.e. the end held / clamped in position on the vessel) which cannot, of course, be rotated about its axis. Figure 21 shows two deposition tools 270 mounted on robot arms 275, the tools each being in the form of a micro LMWD device which can be more productive than powder-based laser deposition processes. The micro LMWD (pLMWD) process uses a laser source and thin gauge wire as a consumable (wire diameters typically being 0.8mm or less). The pipe 228 is fixed in position (e.g. on the end of the pipeline) and the deposition heads 270 are configured to move around the pipe end. The robot arms 275 are articulated and mounted for vertical movement on vertical rails 276. The robot arms are illustrated schematically and could have at least 6-axis movement enabled. The robot arms are able to follow the pipe geometry such that a pipe which is not perfectly round can nevertheless have material deposited on the pipe ends so that the material is accurately and precisely deposited in the desired quantities at the desired locations. There may be more than two robot arms - for example, there could be four robot arms, such that a single micro LMWD device on each robot arm operates to deposit tracks in its own 90 degree sector of the pipe end. Such a deposition could be controlled such that tracks are deposited in both directions around the pipe, possibly each successive track in a given sector being deposited in an opposite direction to the previous track. The robot arms may be controlled to be at least 60 degrees apart from each other at any given moment of material deposition.

A further 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 thickness of 0.1mm on one pipe end face only meaning that the total thickness of filler material sandwiched between the pipe end faces is 0.1mm. The tracks of material are laid down next to each other such that the entire face is of the end of the pipe is covered with what appears like a continuous layer of material having a substantially constant and uniform thickness (track height). The weld seam has a thickness of 5mm. The base material of the pipes has the following (non-exhaustive list of) constituents: Fe (97.4%), 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%).

A further embodiment of the invention, not separately illustrated, incorporates the features of the first embodiment, layer applied to both pipe ends is in the form of multiple concentric circular beads of material, each bead being about 50 microns high and about 1mm wide, and separated from an adjacent bead by about 1mm. The bead is made of a steel alloy having about 65-70% by weight iron. Suitable alloys include FeMn (which includes about 35% Manganese), AISI 304 (which includes about 18% Chromium and 10% Nickel).

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.

Figure 22 shows a flowchart of a method 1000 of an embodiment for welding together work-pieces (e.g. pipes). A first step 1002, which may be performed separately from the welding step (for example at a different much earlier time, in a different country, by a different person and/or under the control of a completely different undertaking) includes depositing a thin layer of material (<2mm) on the end/face (partly or wholly across such end/face) of at least one of the work-pieces.

The thin layer so deposited is of a material different from the base material of the work-pieces to be welded together. The material is deposited in tracks and/or is deposited in a manner such that the amount of at least one component of the material per unit distance, in the direction of the depth of the weld to be formed, varies. The work-pieces are brought together (step 1004) with the thin layer of material forming an intermediate layer therebetween. As step 1006, the work-pieces are welded together, for example with a laser welding apparatus, such that the intermediate layer of material is melted and mixes with molten material from both the work-pieces, thus forming a weld joint between the work-pieces. The weld joint has a chemical composition that is different from the base material of the unwelded material of the work-pieces immediately adjacent to the weld joint.

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.

The additive manufacturing technique described above could be an electron beam melting deposition. Rather than using metal powder, metal wire may be used to deposit the filler material as the intermediate layer. The wire need not be thin gauge for certain embodiments and could have a diameter of up to 2mm.

The filler material (intermediate 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.

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.

The composition of the filler 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 - H2S). 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. 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. For example, the composition of the filler material may be an alloy of steel containing manganese, silicon and a high percentage by weight of nickel. Other elements included in non-negligible quantities in the filler material may include one or more of chromium, molybdenum, vanadium, copper, titanium and niobium.

The alloying composition of the steel pipe (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) may comply with the following limits: Fe -97.5%, C <0.1%, Mn <1.40%, P <0.030%, S <0.030%, Cr O.18%, Mo 0.12%, V 0.027%, Ni 0.26%, Cu 0.13%, Si 0.27%, A1 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%), A1 (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 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%), A1 (%), V (0.0216%), Nb (0.016%), Co (%), Zr (%), Sn (%), P (0.0064%), S (0.0024%), Ti (0.0024%).

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

The welding apparatus may be as described and claimed in W02017140805. 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 W02017140805 and/or the induction heating method employed.

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. In the case of laser welding, an optical head may be considered to be equivalent to a welding torch.

It may be that the filler material is deposited not only on the end face of the pipe but may in certain examples also extend along the inside and the outside surface of the pipe.

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

It will be appreciated that adjacent tracks need not be exactly parallel (in the precise mathematical sense) to each other for the benefits of the embodiments described above to be realised and/or for the tracks to be considered as sufficiently parallel to each other, in the context of the present invention. The tracks may be substantially parallel to each other. Alternatively or additionally, there may be extra non-parallel tracks deposited. The tracks may follow a straight line. The intermediate material need not, in all embodiments, be deposited as tracks. There may for example be benefit in embodiments in which metal work-pieces are welded together wherein there is an intermediate layer of a third material having a thickness of 2mm or less, and immediately before the step of melting, the amount of at least one component of the third material per unit distance, in the direction of the depth of the weld to be formed, varies despite not being deposited as separate parallel tracks.

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.

Claims

1. A method of welding a first work-piece to a second work-piece, wherein the first work-piece has a first portion made from a first metal material and the second work-piece has a second portion made from a second metal material, at least one of the first and second portions has deposited thereon a layer of a third material, and the method comprises the following steps: bringing the first portion and the second portion together, thus forming a joint to be welded, with the third material forming an intermediate layer of material positioned between the first portion and the second portion; and melting the intermediate layer of material, at least part of the first material, and at least part of the second material, to form a weld between the first portion and the second portion; wherein immediately before the step of melting, the intermediate layer of material has an average thickness of 2mm or less and is formed of multiple parallel tracks of deposited material having a chemical composition which is different from that of the first material and the second material, and wherein at least some of the tracks of material are adjacent to each other, in the direction along the depth of the weld.

2. A method according to claim 1, wherein the weld so formed has a depth and a length and the tracks of the third material extend in the same direction as the length of the weld to be formed.

3. A method according to claim 1 or claim 2, wherein the weld so formed has a depth and a length and, immediately before the step of melting, the amount of at least one component of the third material per unit distance, in the direction of the depth of the weld to be formed, varies.

4. A method according to claim 3, wherein the way in which the amount of the component of the third material of the tracks varies is by varying no more than two of the following six parameters according to the position of the track in the direction of the depth of the weld to be formed: (a) the height of the track, (b) the width of the track, (c) the pitch distance between the centres of the tracks, (d) the gap between adjacent tracks, (e) the number of tracks stacked on top of each other, and (f) the relative concentration of the component of the third material.

5. A method according to claim 3 or 4, wherein the amount of the third material at a position corresponding to the centre of the weld, in the direction of the depth of the weld to be formed, is less than the amount of the third material at a position which corresponds to the upper or lower part of the weld.

6. A method according to any preceding claim, wherein the weld so formed has a depth and a length and at least some of the tracks of the third material are spaced apart across the direction along the depth of the weld to be formed.

7. A method according to any preceding claim, wherein the weld so formed has a depth and a length and at least some of the tracks are so arranged that the third material has a height at one location along depth of the weld to be formed that is different from the height at a different location along depth of the weld to be formed.

8. A method according to any preceding claim, wherein the each of the tracks is the same height and same width.

9. A method according to any preceding claim, wherein some of the tracks have a different chemical composition from other tracks.

10. A method according to any preceding claim, wherein the third material is an alloy containing greater than 5% by weight nickel and/or greater than 10% manganese.

11. A method according to any preceding claim, wherein the step of melting the intermediate layer of material to form the weld between the first portion and the second portion is performed by an autogenous keyhole welding process using a laser welding device.

12. A method according to any preceding claim, wherein the method includes a step of depositing the intermediate layer of material on at least one of the first portion and second portion before the step bringing the first portion and the second portion together.

13. A method according to claim 12, where the intermediate layer is deposited by means of an additive manufacturing technique.

14. A method according to claim 12 or claim 13, where multiple separate tracks of the intermediate layer are deposited simultaneously.

15. A method according to any preceding claim, wherein the work-piece are each pipes, and the first portion comprises at least part of one end face of a first pipe, and the second portion comprises at least part of one end face of a second pipe, to be welded end-to-end to the first pipe.

16. A method according to claims 15, wherein each of the parallel tracks extend circumferentially around the end face of the first and/or second pipe.

17. A method according to claim 15 or claim 16, wherein the first and second pipes each have an outer diameter greater than 150mm and a pipe wall thickness of greater than 15mm.

18. A method according to any preceding claim, where the method is performed on a pipe-laying vessel at sea.

19. A method of welding together work-pieces, wherein the work-pieces are a first pipe and a second pipe, 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 2mm 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, melting the intermediate layer of material, at least part of the first material, and at least part of the second material, to form a weld between the pipes; and wherein immediately before the step of melting, the amount of at least one component of the third material per unit distance, in the direction of the depth of the weld to be formed, varies.

20. A work-piece with a portion made from a first metal material on which there are deposited multiple parallel tracks of material of a different chemical composition from the first metal material, the work-piece and the multiple parallel tracks of material being configured for use as the work-piece and intermediate layer of material as claimed in the method of any preceding claim.

21. A method of depositing material on the end of a work-piece so as to form a work-piece according to claim 20.

22. A method according to claim 21, where the material is deposited by means of a laser metal deposition additive manufacturing technique.

23. Apparatus for performing the method of claims 21 or 22.

24. Apparatus according to claim 23, wherein the apparatus comprises multiple spaced apart laser metal deposition devices.

25. Apparatus according to claim 24, wherein the laser metal deposition devices are supplied with laser light from a common source.

26. Apparatus according to claim 24 or claim 25, wherein the multiple spaced apart laser metal deposition devices are configured for rotation about an axis, said axis coinciding with the centre of curvature of one or more of the tracks to be deposited.

27. A kit of parts for laying a pipeline, the kit comprising multiple pipes, each being in accordance with claim 20 and a welding apparatus for performing the step of melting the intermediate layer of material to form a weld according to any of claims 1 to 19.

28. A kit of parts for laying a pipeline, the kit comprising a laser welding apparatus for performing the step of melting the intermediate layer of material to form a weld according to any of claims 1 to 19, multiple pipes, and apparatus according to any of claims 23 to 26.

29. A pipe-laying vessel including a kit of parts according to claim 27 or 28.