BR112016030069B1 - MECHANICALLY COATED DUCT, METHOD OF MANUFACTURING THE SAME AND WINDING METHOD, SETTING ON THE COIL AND HYDROSTATIC TEST OF THE SAME - Google Patents

Abstract

improvements related to mechanically lined duct. mechanically lined duct (mlp) capable of being coiled, having a metallic outer tube and an internal metallic lining, where the inner lining is fixed to the outer tube through one or more welding beads extending longitudinally along the MLP. Weld beads are more efficient in manufacturing ducts, and in preventing ''wrinkling'' of the inner coating when the MLP undergoes bending, particularly when winding the MLP in and out of a coil. alternatively, any wrinkles formed are sufficiently smaller or smaller that they can be reduced or removed once the MLP is installed on the seabed or after the hydrostatic test step.

Description

[0001] The present invention reports on improvements related to a mechanically coated pipeline (MLP), particularly but not exclusively, to generate a subsea pipeline, and to methods of fabrication of structures such as an MLP. It also refers to the laying of MLP in coil laying methods, including those described in API 5L/ISO 3183:2007 Standard for seamless and welded steel pipelines, and in API 5LD for coated or clad pipelines.

[0002] Corrosion resistant pipelines for underwater transport or other types of underwater transport or conduction of corrosive fluids such as gas or crude oil may be provided by pipelines having a metallic inner lining. A double-walled or bi-metallic duct is usually composed of two metallic layers. The outer layer serves to generate resistance against buckling in the coil or the seabed and provides overall resistance to the pipeline designed in such a way as to withstand hydrostatic pressure, while the inner layer protects the outer layer from damage due to the chemical composition of the fluid that is being transported. The inner layer is also sometimes called a “cladding”. Likewise, such ducts are called bi-metallic cladding ducts. Since its primary purpose is to protect the outer layer from corrosion, a corrosion resistant alloy (CRA) is commonly chosen as the coating.

[0003] The minimum coating thickness in the API standard is 2.5mm, and the minimum coating thickness, according to the DNV standard, is 3mm.

[0004] There are two common methods of laying subsea or underwater pipelines. The so-called “pipe connection method” involves assembling piping stacked on a line launch vessel, and then welding each of these as the laying progresses. In the so-called “coil laying method”, the duct is mounted on dry land and wound into a large coil, sometimes also called a storage coil or drum. Once off shore, the pipeline is unrolled from the reel, stretched and/or lined up, and finally seated on the seabed. With this method, no drum welds. Once off shore, the pipeline is unrolled from the reel, stretched and/or lined up, and finally seated on the seabed. With this method, no welding is required during offshore operation, saving time for vessel operations.

[0005] The coil launching method is faster and more economical than the ducting method, such that it is preferred whenever possible, and the tubes and ducts that can be laid using this method are called " reelable” or “reelable”. However, the coil winding process obviously generates multiple bending stresses, which could cause a 2.5 to 3mm coating on a conventionally coated duct to wrinkle. And it is generally considered that wrinkles are harmful to an MLP. Therefore, it is generally preferable to have a thicker coating which would be less susceptible or likely to wrinkle during underwater bending, however this could significantly increase the budget (CAPEX), which is undesirable. Therefore, it is preferable, whenever possible, to use the thinnest possible coating.

[0006] For these reasons, there are currently only a few commercial modalities of the coil laying method for bi-metallic coated pipelines.

[0007] The application WO97/34101 A addresses the use of temporary joining in bi-metal lined ducts to control the separation between the coating and the outer layer during bending. This describes a duct comprising an outer tube of carbon steel and a corrosion resistant metallic coating, in which the coating is fixed along its length to the inner surface of the outer duct by circumferential fastening means having a circumferential shear force greater than the circumferential shear stress that could be induced to bend the tube to a predetermined minimum bending radius. There are several described circumferential fastening means, one of which is solid phase circumferential soldering. However, such circumferential joints require a large amount of soldering due to the fact that wrinkling is a periodic phenomenon with a very short wavelength; approximately 600 welds every 12m (40 ft) of pipe section length, which is economically difficult to justify for most pipeline manufacturing.

[0008] WO2008/072970 A1 addresses a method for laying a duct having a corrosion-proof inner metallic lining that is held within an outer pipe material by interference stresses. In this method, a section of duct is wound onto a duct-setting drum, while an overpressure is maintained within the section by means of a pressurized fluid. When the duct is stopped, the overpressure is relieved, and an additional section of duct is joined to the first section. A new overpressure is then applied within the sections, and the additional section is wound onto a duct-setting coil.

[0009] While this method can help prevent wrinkling when the duct sections have “mechanical movement” (defined in application WO2008/072970 A1 as significant duct winding into one or duct unwinding from the duct laying drum) , this method requires the overpressure and relief steps every time two sections of duct are joined. Duct laying is described in application WO2008/072970 A1 as typically having installed “many” prefabricated sections, requiring significant repetition of the overpressure and relief steps.

[0010] The application WO2011/048430 A1 describes methods of laying on the coil of an MLP including the steps of winding and unwinding in the complete absence of internal pressure based on the thickness of the coating being calculated by a specific formula capable of obtaining an MLP only having wrinkles smaller than 2mm after winding, especially after hydrostatic testing of the seated MLP.

[0011] One of the objectives of the present invention is to provide an MLP and a more practical method of fabrication such that an MLP suitable for winding, in particular the MLP winding and unwinding on a coil, through better control of any separation between the coating and the outer layer during bending.

[0012] According to a first aspect of the present invention, there is provided a mechanically coated duct (MLP) capable of being coiled having a metallic outer tube and a metallic inner lining, where the inner lining is fixed to the outer tube by one or more weld beads extending longitudinally along the MLP.

[0013] Longitudinal welds are more efficient in the fabrication of ducts, and in preventing the wrinkling of the inner liner when the MLP undergoes bending, in particular, winding the MLP and unwinding it on a coil. Alternatively, any wrinkles formed are sufficiently small or smaller that they can be reduced or removed once the MLP is installed on a seabed or after the hydrostatic testing step.

[0014] Mechanically coated ducts (MLP) are formed by any number of layers, coatings, coverings, etc., known in the state of the art, including, however, at least: a metallic outer tube, sometimes called, in the state of the art, as an "outer lining" or "hosting tube", such as an outer tube of carbon steel, and here generally called an "outer tube", attached to at least one metallic inner lining, sometimes called, in the prior art , as a "liner" or an inner layer", and here generally referred to as an "inner liner".

[0015] Any reference in the text to the term "metal" or "metallic" includes alloys, or components formed from an alloy.

[0016] According to an embodiment of the present invention, the inner liner is fixed to the outer tube by 4 to 20 weld beads extending longitudinally along the MLP, possibly equally or regularly spaced radially around the MLP. The invention is not limited to the number of longitudinal weld beads, and the larger the diameter of the outer tube and inner duct, the greater the number of longitudinal weld beads expected to be required or needed. Therefore, the inner liner can be attached to the outer tube using 4, 6, 8, 10, 12, 14, 16, 18 or 20 weld beads, or any variation based on these numbers.

[0017] The number of longitudinal weld beads can be partially based on the thickness of the inner liner. A thicker inner liner requires more weld beads. For example, a 3mm inner liner can have the same number of weld beads per diameter (in ft) as the MLP, ie 12” (3.66m) = 12 longitudinal weld beads, but a 5mm liner for the same diameter MLP can be smaller, for example only 6 or 8 longitudinal weld beads.

[0018] The present invention is not limited by the diameters of the outer tube and the inner liner. For example, the outer tube can have a diameter of any size from at least 12”(323.9mm) outside diameter to values greater than 20”(508mm) outside diameter. MLP pipelines for use in transporting gas or crude oil are commonly supplied in medium sized diameters, usually measured in inches (“), such as 12” (323.9mm) outside diameter, 14” (355.6mm) of outside diameter and 16” (406.4mm) outside diameter. Generally, the size used is commonly expressed as nominal diameter; that is, a “nominal diameter 12”” corresponds to an outside diameter of 12.75” outside diameter (323.9 mm).

[0019] A preferred inner liner is formed of a corrosion resistant alloy (CRA), for example a liner such as a 316L, 825, 625 or 904L alloy.

[0020] Preferably, the MLP comprises a CRA inner lining having a thickness greater than 2.5mm, preferably greater than 3mm.

[0021] According to a second embodiment of the present invention, the inner coating is fixed to the outer tube by at least two weld beads formed simultaneously along the MLP.

[0022] Simultaneous welding clearly saves time and reduces manufacturing costs. This can be clearly compared to the traditional method of creating circumferential weld beads, each of which is preferably formed individually as the union of the inner lining and outer tube, which is carried out along the length of the MLP. Even cases of simultaneous welding could be carried out, such operations are even more costly in terms of time due to the high number of weld beads required.

[0023] Preferably, all longitudinal weld beads are formed simultaneously along the length of the MLP.

[0024] Joining two metals through the act of welding is a well-known practice, usually by increasing the temperature in the joint regions and in its vicinity in such a way that the metals can be joined through fusion. There are several forms of welding including solid state welding.

[0025] The ability to join different metals and alloys together through soldering increases design and production flexibility. However, joining different metals can be a challenging task, usually due to the large differences in physicochemical properties that may be present.

[0026] Therefore, according to any modality of the present invention, the inner coating is preferably fixed to the outer tube by one or more laser weld beads extending longitudinally along the MLP.

[0027] Laser welding is a well-known form of joint that provides a number of particular advantages over conventional welding, including precise work, ie, exact positioning of the power location, welding of joints with complicated geometry, a low heat input and a smaller thermally affected zone (HAZ) (thus providing only minor local distortions), greater possible working distances, and a smaller mix of different materials (eg the lowest dilution of any CRA with the pipe metal external).

[0028] Preferably, the laser welds, longitudinally, are provided from within the MLP, and more preferably, such laser welds are provided simultaneously, for example by a multi-torch laser head, such a laser head it can be provided by a suitable internal duct equipment, device or means such as a pig.

[0029] According to any of the previous embodiments of the present invention, the MLP is a multi-section pipeline. For example, the MLP can be pre-assembled from a small number of tube sections. Such sections of pipeline can extend from many meters to approximately 1km, or greater than 1km in length. Methods and equipment for joining two tube sections are well known in the art and are not described in this document in detail. Generally, joints comprise one or more weld beads, such as association welds. The two duct sections form a combined tubular section. Typically, a coiled duct for subsequent laying using the coil laying method can be formed from many tubular sections, and can be many kilometers long.

[0030] Therefore, according to any modality of the present invention, a mechanically coated duct (MLP) capable of being coiled is provided, where the MLP comprises a series of welded duct sections, and the inner lining is fixed to the outer tube by one or more welds extending longitudinally and continuously along the MLP between the ends of the welded tube sections.

[0031] The MLP of the present invention may include one or more additional means of permanently and/or temporarily joining the outer tube to the inner liner, using one or more fastening methods known in the prior art to reduce, and hopefully prevent, the formation of wrinkles in an MLP at any bend.

[0032] It is also known from a previous patent application filed by the same applicant that the extent of the wrinkles formed in the winding of an MLP depends on one or more of the following group: the interference contact stresses in the coating, the thickness of the casing, radial insert clearance, casing yield stress, casing stress hardening; the response stress of the coating material, the applied bending stress, and the number of reverse bending cycles. There are two reverse bending cycles during a typical coil winding operation, there are more than five bending cycles during a contingency winding operation.

[0033] The present invention is not limited to the thickness of the inner liner. As mentioned above, API and DNV standard cite 2.5 or 3mm minimum thickness. Therefore, the minimum thickness is usually a thickness greater than 3mm, such as 4 or 5mm.

[0034] In application WO2011/048430 A1, the thickness of a minimum inner lining calculated by a formula involving maximum stress factors and radial insertion clearance. The maximum bending voltage (rated bending voltage) during coil winding depends on the outside diameter of the duct and coil or the alignment radius, whichever is smaller. The smallest radius of curvature of the coil means the radius of the coil on which the duct must be wound or the radius of the liner of the launching ship or any other coil on which the duct must be curved before being stretched and laid, whichever is smaller .

[0035] The radius of curvature of a coil can be less than 1.5m, and it can be greater than 10m or more. The radius of the coil and the duct wound obviously grows as the duct is wound on the spool. A typical example of a coil for laying a marine pipeline has a coil bend radius of 8.23m.

[0036] However, using the present invention, the coating thickness can now be less than the previously calculated minimum coating. This is due to local longitudinal welds which are beneficial for wrinkle sensitivity. It has been found that longitudinal welds generally increase the bendability of an MLP without risk of wrinkling the coating.

[0037] Therefore, according to another particular modality of the present invention, the thickness of the inner lining is smaller than "t" calculated through the formula:

[0038] where:

[0039] t is expressed in mm;

[0040] a00, a01,... are constants defined by table 1:

[0041] is the maximum coil voltage or rated voltage that can be calculated as follows:

[0042] is is the transverse insertion clearance in mm; and

[0043] D =DH – 2tH is the outer diameter of the casing in mm, where DH and tH are the outer diameter and the wall thickness of the receptacle or the outer duct of the MLP in mm, respectively.

[0044] Using the index notation, the formula can also be written as: t = αij(εDft7S)i g} + 0.16

Tabela 1: Constantes da fórmula para cálculo de espessura de revestimento mínima[0045] where i=0.1.2 and j=0.1

Table 1: Formula constants for calculating minimum coating thickness

[0046] While this formula can calculate a variety of coating thicknesses and, in particular, a minimum wall thickness coating, one or more requirements or requirements may still result in the use in practice of a wall coating thickness greater than The least possible. Although, it is clearly beneficial that the present invention can achieve a coating thickness less than that previously recognized by patent application WO2011/048430 A1 and therefore reduce the budget (CAPEX).

[0047] As longitudinal weld beads benefit from wrinkling sensitivity, a skilled team can verify that the number of longitudinal weld beads can be balanced with the inner liner. That is, the more weld beads used in the present invention, the smaller or thinner the coating thicknesses can be, and vice versa. Therefore, it is possible to compute the number of longitudinal weld beads required to use a 3mm thick liner without wrinkling the coating, or the possibility of using a slightly thinner liner such as 4mm, with fewer longitudinal weld beads. Other parameters affected in this computation include the materials used and the outside diameter of the ducts, but a skilled team can consider the balance between using a coating thickness that is thinner than what was previously considered a minimum thickness, and the required OPEX to achieve a number of welds to weld the casing to the outer tube of the MLP during its fabrication.

[0048] In this way, the two factors of the number of longitudinal weld beads and the possible thickness of the coating can be, but not limited to, inversely proportional.

[0049] By way of example only, twelve longitudinal weld beads could be used to secure a 3mm thick CRA coating to a 12" OD outer tube, or eight longitudinal weld beads could be used to secure a thick CRA coating 5mm to the same outer tube.

[0050] The present invention also allows for faster winding and unwinding to be performed faster, safer and, therefore, more economical than rewinding an MLP. In particular, such an MLP can be designed and manufactured to be loaded directly onto a coil in a conventional manner without requiring any internal pressure on the complete assembly or its sections.

[0051] In another aspect of the present invention, a method of manufacturing a mechanically coated duct (MLP) having an outer tube and a metallic inner lining for coil laying is provided comprising the steps of:

[0052] provide the metallic inner lining;

[0053] provide the metallic outer tube; and

[0054] locally weld the inner liner, longitudinally, to the outer tube to form the MLP.

[0055] Preferably, the method comprises laser welding, longitudinally, the inner coating to the outer tube to form the MLP.

[0056] Optionally, the method provides 4 to 20 laser weld beads, which weld the inner liner onto the outer tube to form the MLP.

[0057] Optionally, the method provides a laser welding head of multiple torches along the inner casing to weld the inner casing to the outer tube to form the MLP.

[0058] Optionally, the MLP comprises an outer tube and/or inner liner as defined in one or more embodiments described above in this document.

[0059] According to any other aspect of the present invention, there is provided a method of winding, coiling and hydrostatic testing an MLP as defined herein, comprising the steps of: a) winding the MLP on a coil in the complete or substantial absence of internal pressure above ambient pressure in the MLP; b) unwinding the MLP from the coil at complete or substantial absence of internal pressure above ambient pressure in the MLP; c) stretching the MLP discharged from step (b); d) laying the MLP from step (c); and e) hydrostatic testing of the seated MLP to provide a fully or substantially seated MLP having creases less than 2mm in height.

[0060] After the hydrostatic test, any residual wrinkling in the MLP will be less than 2mm high and preferably less than 1mm high, at least in the case of incompatible ducts where the wrinkling site may increase due to incompatibility.

[0061] Preferably, step (e) comprises the hydrostatic testing of the MLP at a maximum test pressure in accordance with the DNV-OS-F101 standard (offshore standard, Det Norske Veritas, DNV-OS-F101, subsea pipeline systems , October 2007) where the internal pressure applied for the hydrostatic test depends on the duct diameter and wall thickness.

[0062] The term "internal pressure" as used in this document to describe the pressure within the MLP during the winding and unwinding method such as an MLP on a coil, during a full or complete process thereof, as opposed to winding processes and/or unwinding involve one or more cases of shutdown or periods of time requiring internal pressure or internal pressure change to bend or stretch the MLP. The winding of step (a) is preferably wholly or substantially continuous or otherwise perennial or interruptible, compared to previous stop-start winding processes.

[0063] The term "stretching" as used above includes one or more processes or steps of causing the MLP to be stretched after it has been wound or unwound from the reel, and before the MLP is delivered to its desired seating position or location. This can include one or more cycles of bending steps, alignments and/or stretches, usually before the MLP enters the marine environment. The coil laying method involves at least the steps of aligning and stretching the MLP.

[0064] The present invention encompasses all combinations of various embodiments or aspects of the invention described herein. It is understood that any or all of the embodiments of the present invention may be considered in conjunction with any of the embodiments to describe additional embodiments of the present invention. In addition, any elements of one modality can be combined with any or all of the other elements of any one of the modes to describe additional modalities.

[0065] Therefore, several aspects of the present invention can be practiced individually or in combination with one or any other aspects, as will be verified by a team versed in the state of the art. The various aspects of the invention may optionally be provided in combination with one or more of the optional components of other aspects of the invention. Furthermore, additional components described in relation to one embodiment can typically be combined individually or together with any other components in different embodiments of the invention.

[0066] Various embodiments or aspects of the invention will now be described in detail with reference to the attached figures. Still, other aspects, components and advantages of the present invention are readily apparent from the full description thereof, including the figures, which illustrate a number of exemplary embodiments and aspects of implementations. The invention is also capable of other and different modalities and aspects, and its various details can be modified in various ways, all without departing from the spirit and scope of the present invention. Therefore, figures and descriptions are referred to as forms of illustration in nature, and are not restrictive. Furthermore, the terminology and phraseology used in this document is used for descriptive purposes only and should not be construed as limiting the scope. Language such as "include", "understand", "have", "contain" or "involve", and variations thereof, should be understood comprehensively and encompass the subject matter shown in the figures, additional subject matter and equivalents not mentioned, and it is not intended to exclude other additives, components, integral or partial. For example, the term “comprising” is considered synonymous with the terms “include” and “contain” for purposes of legal application.

[0067] Modalities of the present invention will now be described by way of example only, and with reference to the accompanying figures, in which: a. Figure 1 is a schematic cross-sectional view of an MLP;b. Figure 2 is a diagrammatic view of a method of winding an MLP onto a coil; ç. Figure 3 is a diagrammatic view of the coil laying method which illustrates the unwinding, alignment, stretching and laying of an MLP from a coil;d. Figure 4 is a longitudinal cross-sectional diagram view of a prior art MLP prior to welding, and just after welding the inner liner circumferentially to an outer tube; e. Figures 5a and 5b are diagrammatic views of cross-sections and longitudinal respectively of an MLP according to an embodiment of the present invention after welding an inner liner, longitudinally, to an outer tube;f. Figure 6 is a cross-sectional view of the longitudinal weld bead of Figures 5a/b; eg. Figure 7 is a longitudinal cross-sectional view of a method of manufacturing an MLP according to any of the embodiments of the present invention.

[0068] The present invention provides an MLP suitable for winding, unwinding, aligning, stretching and pre-commissioning as a subsea pipeline.

[0069] Figure 1 shows a schematic cross-sectional view of parts of a mechanically coated pipeline (MLP) 2. MLP 2 generally comprises a number of layers (including coating), only two of these are shown in figure 1 for clarity, comprising a metallic outer layer 4, which may be a carbon steel duct, and a metallic inner lining 6 being formed from a corrosion resistant alloy (CRA), such as a 316L alloy. The relative dimensions shown in Figure 1 are not to scale, and are provided for clarity of representation.

[0070] Figure 2 shows a diagram of a coil 10 having a minimum bending radius "R", and a mechanically coated duct (MLP) 12 having a duct outer diameter "D". MLP can be formed into sections joined together to form a single pipe. Sections are normally 1km in length but can be longer or shorter as needed. Figure 2 shows a winding of MLP 12 on coil 10.

[0071] By way of example only, coil 10 may have a radius of curvature R of 8.23m, and MLP 12 may have a diameter D of 12.75" (323.9mm) and a wall thickness of 15.9mm.

[0072] Figure 3 shows a method of unwinding a reeled MLP 12 of Figure 2 from the reel 10, now located on a suitable ship 14, from the sea surface 16 to a seabed 18; commonly known as the coil laying method. The unrolled MLP provides a seated marine duct 12a after it has been lined up by passing a liner 20 and drawn by passing through a stretcher comprising multiple modules 22, before passing below the vessel 14 to be laid on the seabed 18.

[0073] Pre-commissioning the seated MLP 12a (not shown) typically involves pressurizing the MLP 12a in a manner known as "hydrostatic testing". Just as pressurization can generally be generated from the passage of a pressurized fluid such as water through duct 12a, generally at a pressure that depends on duct size and wall thickness such as 30 to 40 MPa.

[0074] In particular, a combination of figures 3 to 4 show a method of laying a mechanically lined duct (MLP) 12 in a marine environment comprising: i. wind the MLP 12 onto a coil 10;ii. unwind the MLP 12 of step (i) from the coil 10 and direct the MLP 12 to the liner 20 of a launching tower 24 (during which the MLP 12 undergoes a plastic bend such that the MLP 12 is or can be almost completely stretched in the space between the coil 10 and the liner 20, and then the stretch module 22 of the launch tower 24 in order to seat the MLP 12 in a marine environment such as a marine pipeline 12a; eiii. perform hydrostatic testing (not shown) in the MLP seated in step (ii) to remove any ridges in the MLP 12a once it is on the seabed 18.

[0075] It may be useful to note that the hydrostatic test during the pre-commissioning of the pipeline is done to check its integrity after installation, this is also useful for removing wrinkles.

[0076] However, the bending of a duct formed from two layers shown in Figure 1, such as winding or unwinding on the coil, can create wrinkles, which are harmful to the laid duct. Therefore, increasing the bond, even if it is a temporary bond, to reduce or prevent wrinkling of the inner liner compared to the outer layer during wrinkling, would clearly be beneficial.

[0077] Figure 4 shows an MLP 30 having only two layers for clarity of understanding, as in figure 1. The MLP 30 comprises an outer layer 32 and an inner liner 34 in longitudinal cross section. The lower part of Figure 4 shows a known method of applying a series of circumferential weld beads 36 to assist in securing the inner liner 34 to an outer tube 32 to prevent separation during bending of the MLP.

[0078] However, it can be seen that the number of circumferential weld beads 36 per length of MLP required to avoid wrinkling, which is a periodic phenomenon, can be substantial. Such a high number entails significant time and effort required during the manufacturing process. The number of weld beads required clearly depends on several factors including duct diameter, etc., however a typical MLP duct requires one weld bead every 20 to 30mm, resulting in the need to make approximately 600 circumferential weld beads for a typical 12m (40 ft) duct length section.

[0079] In addition, wrinkles can be significantly formed radially or circumferentially, forming weld beads circumferential to the outer tube, and the inner liner can create locations along the MLP 30 that can aid in the "initialization" of wrinkles, particularly, where any weld bead or weld material induces or creates a circumferential embrittlement line in the inner liner 34.

[0080] Circumferential welding can generate local coating jolt due to thermal distortion, causing the coating to become more susceptible to wrinkling when the MLP is subject to bending during its installation.

[0081] Figures 5a and 5b show an MLP according to an embodiment of the present invention. Figures 5a and 5b show a windable mechanically lined duct (MLP) having a metallic outer tube 42 and a metallic inner lining 44, where the inner lining 44 is secured to the outer tube 42 by a series of weld beads 46 which extend longitudinally along the MLP 40.

[0082] As shown in Figures 5a and 5b, the inner liner 44 is secured to the outer tube 42 by 8 longitudinal weld beads 46 which extend continuously along the MLP 40, and preferably between the ends of the duct sections welded as described herein in relation to Figure 7. The longitudinal welds 46 are spaced radially around the MLP 40, and their dimensions in Figure 5b are for clarification and location purposes only, and do not represent their extent from the casing. 44 in practice.

[0083] Figure 6 shows, more typically, an enlarged part of a weld bead of Figure 5b, and the extent of penetration of the longitudinal weld 46 from the inner liner 44 to the outer tube 42. Figure 6 also shows a graduated scale 48 to show the relative penetration of the longitudinal weld 46 relative to the thickness or height of the inner liner 44.

[0084] Figure 7 shows a method of manufacturing a mechanically lined pipe (MLP) comprising a series of welded tube sections. In figure 7, a first tubular section 40 as shown in figure 5a is shown, and a second tubular section 41 to be joined to the first tubular section 40 in a manner known in the prior art, such as circumferential welding, and not described in more detail in the present document. The inner liner 44 of each section 40, 41 is or will be attached to the outer tube 42 of each section by one or more weld beads which extend longitudinally 46 and continuously along the MLP 40 between the ends 48 of each section. welded tubular 40, 41.

[0085] The longitudinal weld is provided by a pig 50. Pigs are able to cross internally along lengths of duct or tubular section and are well known in the art, and generally comprise a central body 51, and one or more, generally, a regular series of wheels 56 or rollers capable of traversing along the inner surface of the duct or tubular section and support for the body of the pig 51.

[0086] The pig in Figure 7 supports a multiple torch head 52 having a series of laser welders 54 arranged circumferentially around it, and capable of providing simultaneous formation of the longitudinal welds 46 as the pig 50 traverses along the MLP 40 in the direction of arrow A shown in figure 7. In this way, all longitudinal welds 46 are formed simultaneously by a single pass of the pig 50, which is also ready to pass through the next tubular section 41, once the tubular sections 40, 41 are joined.

[0087] In addition, the MLP 40, or an MLP formed by a series of tubular sections such as 40 and 41, is then applicable in a coil laying method and hydrostatic testing of an MLP as described herein in relation to figures 2 and 3.

[0088] The speed and power of laser welding is dependent on the nature and dimensions of the inner tube and inner lining. A typical laser welding for the method is the Ytterbium fiber laser (YLR-15,000 IPG), with a laser power ranging from 3 to 6 KW. The welding speed can be less than 1m/min or even less than that, and greater than 6, 7, 8m/min or even greater.

[0089] Typically, longitudinal welding only needs to extend into the outer tube (ie weld depth) by 1 or 2mm or less.

[0090] A team versed in the art can use these parameters, and knowing the nature of the outer tube and inner lining, calculate the required power and usable welding speeds.

[0091] The present invention provides a simple method of manufacturing an MLP that achieves at least good temporary unions between the inner lining and the outer tube for bending, in particular for winding and unwinding a coil, optionally with a thickness thinner coating than previously considered possible. The manufacturing method is relatively quick and simple, especially when it can be applied to supply all welds simultaneously without affecting other steps in the manufacturing process.

[0092] In particular, longitudinal welds avoid the problem of circumferential welds by providing a place for the initialization of wrinkles.

Claims (18)

1. Mechanically coated duct (MLP) (2) capable of being wound, characterized by the fact that it has a metallic outer tube (4) and a metallic inner coating (6), in which the inner coating is fixed to the outer tube by 4 to 20 weld beads (36) extending longitudinally along the MLP (2). 2. Mechanically coated duct (MLP) (2) capable of being wound, according to claim 1, characterized in that the inner coating (6) is fixed to the outer tube (4) through at least two cords of solder (36) formed simultaneously along the MLP. 3. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 1 to 2, characterized in that the inner coating (6) is fixed to the outer tube (4) through one or more laser weld beads (36) extending longitudinally across the MLP. 4. Mechanically coated duct (MLP) (2) capable of being wound, according to claim 3, characterized in that the laser weld beads (36) are supplied from the interior of the MLP. 5. Mechanically coated duct (MLP) (2) capable of being wound, according to claim 4, characterized in that the laser weld beads (36) are provided, simultaneously, by a laser head of multiple torches. 6. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 1 to 5, characterized in that the MLP (2) comprises a series of welded duct sections, and the coating ( 6) inner is fixed to outer tube (4) by one or more weld beads (36) extending longitudinally and continuously along the MLP (2) between the ends and sections of welded duct. 7. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 1 to 6, characterized in that the MLP comprises an outer tube (4) of carbon steel. 8. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 1 to 7, characterized in that the MLP comprises a coating (6) of Corrosion Resistant Alloy (CRA). 9. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 1 to 8, characterized in that the coating (6) has a thickness ranging from 2.5mm to 10mm. 10. Mechanically coated duct (MLP) (2) capable of being wound, according to claim 9, characterized in that the coating (6) has a thickness ranging from 2.5 to 5mm. 11. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 1 to 10, characterized in that the thickness of the inner coating (6) is smaller than "t" calculated through the formula:t = a00(εD0.75)0 g0 + a01(εD0.75)0 g1 + a02(εD0'75)0 g2 + aioCεD0.75)1 g0 + a^CεD0.75)1 g1 + a12(εD0 .75)1 g2 + 0.16 where:t is expressed in mm;a00, a01,... are constants defined by table 1:

is the maximum voltage on the coil; is the transverse insertion clearance in mm; e- 2 - is the outer diameter of the casing in mm, where DH and tH are the outer diameter and the wall thickness of the MLP receptacle or outer duct in mm, respectively. 12. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 9 to 11, characterized in that the inner coating (6) is a 316L, 825, 625 or 904L alloy. 13. Mechanically coated duct (MLP) (2) capable of being wound, according to any one of claims 1 to 12, characterized in that the MLP (2) is a multi-section duct. 14. Method of manufacturing a mechanically coated duct (MLP) (2) capable of being wound, as defined in any one of claims 1 to 13, having an outer tube (4) metallic and a metallic inner lining for winding, characterized by fact to understand the steps: provide an inner metal casing (6); provide an outer tube (4) metal; locally weld the inner liner longitudinally to the outer tube to form the MLP. 15. Method of manufacturing a mechanically coated duct (MLP) (2) capable of being wound, according to claim 14, characterized in that it comprises the step of: laser welding, longitudinally, the coating (6) inner tube (4) to form the MLP. 16. Method of manufacturing a mechanically coated duct (MLP) (2) capable of being wound, according to claim 14 or 15, characterized in that it comprises the step of: providing 4 to 20 weld beads (36) to weld the inner casing (6) to the outer tube (4) to form the MLP. 17. Method of manufacturing a mechanically coated duct (MLP) (2) capable of being wound, according to claim 15 or 16, characterized in that it comprises the step of: providing a multiple torch laser welding head to the along the inner casing (6) to weld the inner casing to the outer tube (4) to form the MLP. 18. Coil winding-setting method and hydrostatic testing of an MLP (2) capable of being wound as defined in any one of claims 1 to 13, characterized in that it comprises the steps of: (a) winding the MLP (2) in a coil (10) in the absence of internal pressure above the ambient pressure in the MLP (2); (b) unwind the MLP (2) from the coil (10) in the absence of internal pressure above the ambient pressure in the MLP (2 );(c) drawing the MLP (2) discharged from step (b); (d) laying the MLP (2) from step (c); and (e) hydrostatic testing of the seated MLP to provide a seated MLP having creases less than 2mm in height.

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