A welding method and product for improving the stress corrosion resistance of riser welded joints

Abstract

The present application belongs to the field of sea pipe welding, and specifically discloses a welding method and product for improving the stress corrosion resistance of the riser weld joint. The welding method is: in an atmosphere of 80% Ar + 20% CO2, the SCR riser is welded by CMT welding technology, wherein the welding current of the base layer and the filling layer is 180A-200A, the welding voltage is 20V-23V, and the welding speed is 400mm / min-500mm / min; the welding current of the cover layer is 130-150A, the welding voltage is 13-15V, and the welding speed is 245mm / min-255mm / min. The present application can reduce the hardness of the coarse-grained heat-affected zone of the weld joint, eliminate the negative influence of the martensitic structure, improve the stress corrosion cracking resistance of the pipeline steel, and realize the synergistic improvement of the corrosion fatigue resistance and stress corrosion cracking resistance of the marine oil and gas pipeline.

Description

Technical Field

[0001] The present application belongs to the field of sea pipe welding, and more specifically, to a welding method and product for improving the stress corrosion resistance of riser welded joints. Background Art

[0002] The development and transportation of offshore oil resources rely on submarine pipelines and marine risers. Steel Catenary Riser (SCR) is welded from some standard length steel pipes, integrating submarine pipelines and risers. It can operate in extreme working environments such as high temperature and high pressure and harsh marine environments, effectively solving the cost problem of deep-sea risers. It has a large tolerance for floating body drift and heave movement. Therefore, steel catenary risers have become an important component system of offshore floating platforms and submarine pipelines.

[0003] Submarine pipelines must first overcome the effects of harsh environmental factors such as waves, currents and corrosion, and H2S is increasingly present in oil and gas resources. When the H2S content in the medium transported by the oil and gas pipeline is high, the hydrogen in the H2S will be enriched in defects such as non-metallic inclusions and segregation zones, causing hydrogen-induced cracking and sulfide stress corrosion cracking (SSCC) in the pipeline. Pipelines serving on the seabed often face the problem of corrosion cracking, which brings higher quality requirements to marine oil and gas pipelines. If the pipeline is corroded and damaged and causes oil and gas leakage, it will not only stop the production of offshore oil fields and cause serious economic losses, but also cause serious marine pollution. This pollution is difficult to remove and its impact may last for decades, causing immeasurable damage to the marine ecology.

[0004] X65 is the main steel grade currently used in deep-sea acidic environments. For oil and gas transportation, welding is a common means of connecting pipelines, but the base material part adjacent to the fusion line forms a coarse grain heat affected zone (CGHAZ) due to the high peak temperature reached during the welding heating process. The grains in this area are severely coarsened, the brittleness of the transformation products is the greatest, and the toughness is deteriorated. This is the area most prone to failure in the welded joint.

[0005] Cold Metal Transfer (CMT) technology uses welding retraction technology to avoid the heating effect of short-circuit current on the molten pool, and has the characteristics of low heat input and stable arc, which can improve the forming quality of welded joints and improve welding efficiency. At present, CMT welding technology is gradually being applied to pipeline base welding. It reduces the stress concentration of joints and improves their corrosion fatigue life by optimizing the microstructure and reducing the stress concentration at the root of the weld. However, low heat input can easily lead to a large hydrogen diffusion coefficient of the welded joint and excessively high CGHAZ hardness, which in turn leads to an increase in the stress corrosion sensitivity of the welded joint. Summary of the invention

[0006] In view of the defects of the prior art, the present application provides a welding method and product for improving the stress corrosion resistance of riser weld joints, aiming to solve the problems of high hardness and high stress corrosion sensitivity of existing SCR riser weld joints.

[0007] According to one aspect of the present application, a welding method for improving the stress corrosion resistance of a riser weld joint is provided, specifically: in an atmosphere of 80% Ar + 20% CO2, the SCR riser is welded using CMT welding technology, wherein the welding current of the base layer and the filling layer is 180A to 200A, the welding voltage is 20V to 23V, and the welding speed is 400mm / min to 500mm / min; the welding current of the cover layer is 130 to 150A, the welding voltage is 13 to 15V, and the welding speed is 245mm / min to 255mm / min.

[0008] Through the above technical scheme conceived by the present application, compared with the prior art, since the present application proposes to improve the welding atmosphere and optimize its supporting welding parameters including welding current, welding voltage and welding speed, not only the arc is stable, the spatter is small, and the welding efficiency is high during the welding process, but also the obtained weld joint has good forming and small root excess height, and the hardness of the coarse grain zone is reduced, the negative influence of the martensitic structure is eliminated, the stress corrosion cracking resistance of the pipeline steel is improved, and the service life of the SCR riser is greatly improved.

[0009] As a further preferred embodiment, the shielding gas is supplied 1.5s to 2s in advance before welding, and the shielding gas is turned off with a delay of 1.2s to 1.5s after welding.

[0010] As a further preferred embodiment, the groove of the SCR riser adopts a U-shaped narrow gap groove.

[0011] As a further preferred embodiment, for a 6-inch to 18-inch SCR riser, the blunt edge thickness of the groove is 1.1 mm to 1.7 mm.

[0012] As a further preferred embodiment, an arc transition is designed between the blunt edge and the bevel edge of the groove, and the arc radius is 2.2 mm to 3.8 mm.

[0013] As a further preference, for a 6-inch SCR riser, the groove angle is set to 3°, and for a 12-inch SCR riser and an 18-inch SCR riser, the groove angle is set to 3.5°.

[0014] As a further preferred embodiment, the wire extension length is set to 12 mm when starting welding, and the wire extension length is 6 mm to 10 mm during welding.

[0015] As a further preferred embodiment, before welding, the part of the SCR riser to be welded is cleaned with acetone and then polished.

[0016] As a further preference, the SCR riser is preheated to 200° C. to 250° C. before welding.

[0017] According to another aspect of the present application, there is provided an SCR riser weld joint prepared by the above welding method.

[0018] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art:

[0019] 1. The present application adopts the high heat input CMT welding technology of 80% Ar + 20% CO2 shielding gas. The arc is stable and the spatter is small during the welding process. The welding wire is actively retracted to promote the shedding of the molten droplet, which can significantly improve the welding efficiency. At the same time, it can ensure that the weld joint is well formed and the root excess height is small, reducing the stress concentration at the weld joint. More importantly, it can reduce the hardness of the coarse-grained heat-affected zone of the weld joint, eliminate the negative influence of the martensitic structure, and improve the stress corrosion cracking resistance of the pipeline steel. The synergistic improvement of the corrosion fatigue resistance and stress corrosion cracking resistance of the marine oil and gas pipeline is achieved, and the service life of the SCR riser is greatly improved, while providing a scientific basis for the prevention and treatment of corrosion cracking;

[0020] 2. At the same time, the present application can avoid the problem of excessive root residual height or unstable penetration by optimizing the groove parameters of the SCR riser, and effectively improve the unfused defects that are prone to occur at the inflection point. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of a CMT weld provided in an embodiment of the present application;

[0022] Figure 2 The macroscopic morphology of the welded joints obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present application, wherein (a) is Comparative Example 1, (b) is Example 1, and (c) is Comparative Example 2;

[0023] Figure 3 Schematic diagram of the microstructure of the coarse grain zone of the welded joint obtained in Example 1 and Comparative Example 2 of the present application, wherein (a), (b), and (c) are respectively the 12 o'clock, 3 o'clock, and 6 o'clock positions of Example 1, and (d), (e), and (f) are respectively the 12 o'clock, 3 o'clock, and 6 o'clock positions of Comparative Example 2;

[0024] Figure 4 These are the test results of the base layer hardness of the welded joint obtained in Example 1 and Comparative Example 2 of the present application;

[0025] Figure 5 These are the SSC test results of the weld joint primer obtained in Example 1 and Comparative Example 2 of the present application, where (a) is Comparative Example 2 and (b) is Example 1;

[0026] Figure 6 These are the SSC test results of the weld joint primer obtained in Comparative Examples 3 to 5 of the present application, wherein (a) is Comparative Example 3, (b) is Comparative Example 4, and (c) is Comparative Example 5;

[0027] Figure 7 These are the SSC test results of the weld joint primer layers obtained in Comparative Examples 6 and 7 of the present application, where (a) is Comparative Example 6 and (b) is Comparative Example 7. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0029] According to one aspect of the present application, a welding method for improving the stress corrosion resistance of a riser weld joint is provided, specifically: in an atmosphere of 80% Ar + 20% CO2, 5G welding of an SCR riser is performed using CMT welding technology, wherein the welding current of a base layer and a filling layer is 180A to 200A, the welding voltage is 20V to 23V, and the welding speed is 400mm / min to 500mm / min; the welding current of a cover layer is 130A to 150A, the welding voltage is 13V to 15V, and the welding speed is 245mm / min to 255mm / min.

[0030] The present application proposes to improve the welding atmosphere and optimize the supporting welding parameters including welding current, welding voltage and welding speed, which can not only ensure the arc stability, small spatter and high welding efficiency in the welding process, but also ensure that the obtained welded joint has good forming and small root excess height, and reduces the hardness of the coarse grain zone, eliminates the negative influence of the martensitic structure, improves the stress corrosion cracking resistance of the pipeline steel, and greatly improves the service life of the SCR riser.

[0031] Furthermore, the shielding gas is supplied 1.5s to 2s in advance before welding, and the shielding gas is turned off 1.2s to 1.5s after welding, thereby ensuring that the welding is completely carried out in a shielding gas atmosphere of 80% Ar + 20% CO2.

[0032] Furthermore, the groove of the SCR riser adopts a U-shaped narrow gap groove, which can reduce the number of welding passes and the filling amount of welding wire while ensuring the welding quality, thereby shortening the welding time and construction cost and improving the welding efficiency.

[0033] Furthermore, for 6-inch to 18-inch SCR risers, the blunt edge thickness of the groove is 1.1mm to 1.7mm. Among them, when the blunt edge thickness is small, the excessive root height will increase the stress concentration factor and seriously shorten the service life of the SCR riser; when the blunt edge thickness is large, the CMT process is difficult to ensure stable penetration of the blunt edge in different positions of flat welding, overhead welding, and vertical welding.

[0034] Furthermore, an arc transition is designed between the blunt edge and the bevel edge of the groove, and the arc radius R=3±0.8mm, thereby increasing the space at the root of the groove and effectively improving the unfused defects that are prone to occur at the turning point.

[0035] Further, for the 6-inch SCR riser, the groove angle is set to 3°, and for the 12-inch SCR riser and 18-inch SCR riser, the groove angle is set to 3.5°, thereby ensuring sufficient fusion of the weld to improve welding quality and effectively control thermal stress and deformation.

[0036] Furthermore, the wire extension length is set to 12mm when starting welding, and 6mm to 10mm during welding. If the extension length is too long, the instantaneous current will increase, which is very likely to cause defects and wire sticking problems; if the extension length is too short, the conductive tip will be easily burned, resulting in welding defects.

[0037] Furthermore, before welding, the SCR riser is cleaned with acetone to remove surface oil stains and dust, and then the surface of the SCR riser is polished. At the same time, the SCR riser needs to be preheated before welding, the preheating temperature is 200℃~250℃, and each weld needs to be polished and cleaned with a grinder.

[0038] Furthermore, the welding wire brand is selected as PIPELINER or SUPRA MIG. According to the strength level of API 5L X65 steel and the high matching principle, the yield strength of the welding material is required to be greater than 450MPa and the tensile strength is greater than 570MPa. In addition, the DNV OSF101 standard recommends high matching, and the yield strength of the welding material is as high as possible higher than the yield strength of the parent material by 80MPa. In addition, the use of low-hydrogen electrodes can effectively avoid welding hot cracks. The DNV OS F101 standard requires that the diffusible hydrogen of the welding material is less than 5ml / 100g. The welding wires of PIPELINER and SUPRAMIG meet the above requirements.

[0039] According to another aspect of the present application, there is provided an SCR riser weld joint prepared by the above welding method.

[0040] The technical solution provided by this application is further described below based on specific embodiments.

[0041] The following materials are used in both the embodiment and the comparative example: the parent material is an X65 grade SCR riser with a diameter of 12 inches, a wall thickness of 27 mm, and a length of 200-250 mm. The chemical composition of the parent material is shown in Table 1, and the mechanical properties are shown in Table 2. The composition design of this X65 pipeline steel follows the composition design principle of the previous pipeline steel, that is, reducing the carbon content and increasing the content of alloy elements such as Mn and Mo. In addition to adopting reasonable metallurgical technology, the composition of pipeline steel must also be strictly controlled.

[0042] The welding method uses CMT welding technology, which has the characteristics of low heat input, high cladding efficiency and no spatter. The welding system is as follows Figure 1 As shown; the welding material is ER70S~6 low carbon steel welding wire with a diameter of 1mm and the brand is PIPELINER or SUPRA MIG.

[0043] Table 1 Chemical composition of X65 base material (mass fraction%)

[0044]

[0045] Table 2 Mechanical properties of X65 base material (mass fraction %)

[0046]

[0047] Example 1

[0048] For the base material, a U-shaped narrow gap groove is used. The blunt edge thickness of the groove is 1.4mm. A circular arc transition with a radius of 3.4mm is designed between the blunt edge and the bevel edge of the groove. After removing the surface oil stains and dust with acetone, place the riser on the welding bracket to ensure the alignment of the groove. Set the welding parameters at the welding power supply and control box. The welding current of the base layer and the filling layer is 185A~195A, the welding voltage is 21V~22V, and the welding speed is 450mm / min; the welding current of the cover layer is 135A~145A, the welding voltage is 13V~14V, and the welding speed is 250mm / min. When welding at different positions, the welding parameters can fluctuate around the above point values. Welding is carried out in a protective gas atmosphere of 80% Ar+20% CO2, and the dry extension of the welding wire is 10mm. The number of welding layers is as follows: Figure 1 As shown, before each welding, the groove and the layers need to be grinded with an angle grinder.

[0049] Example 2

[0050] For the base material, a U-shaped narrow gap groove is used. The blunt edge thickness of the groove is 1.1mm. A circular arc transition with a radius of 2.2mm is designed between the blunt edge and the bevel edge of the groove. After removing the surface oil stains and dust with acetone, place the riser on the welding bracket to ensure the alignment of the groove. Set the welding parameters at the welding power supply and control box. The welding current of the base layer and the filling layer is 180A~190A, the welding voltage is 21V~22V, and the welding speed is 440mm / min; the welding current of the cover layer is 130A~135A, the welding voltage is 13V~14V, and the welding speed is 248mm / min. When welding at different positions, the welding parameters can fluctuate around the above point values. Welding is performed in a protective gas atmosphere of 80% Ar+20% CO2, and the dry extension of the welding wire is 6mm. The number of welding layers is as follows: Figure 1 As shown, before each welding, the groove and the layers need to be grinded with an angle grinder.

[0051] Example 3

[0052] For the base material, a U-shaped narrow gap groove is used. The blunt edge thickness of the groove is 1.7mm. A circular arc transition with a radius of 3.8mm is designed between the blunt edge and the bevel edge of the groove. After removing the surface oil stains and dust with acetone, place the riser on the welding bracket to ensure the alignment of the groove. Set the welding parameters at the welding power supply and control box. The welding current of the base layer and the filling layer is 190A~200A, the welding voltage is 22V~23V, and the welding speed is 500mm / min; the welding current of the cover layer is 140A~150A, the welding voltage is 14V~15V, and the welding speed is 254mm / min. When welding at different positions, the welding parameters can fluctuate around the above point values. Welding is carried out in a protective gas atmosphere of 80% Ar+20% CO2, and the dry extension of the welding wire is 10mm. The number of welding layers is as follows: Figure 1 As shown, before each welding, the groove and the layers need to be grinded with an angle grinder.

[0053] Example 4

[0054] For the base material, a U-shaped narrow gap groove is used. The blunt edge thickness of the groove is 1.6mm. A circular arc transition with a radius of 3.2mm is designed between the blunt edge and the bevel edge of the groove. After removing the surface oil stains and dust with acetone, place the riser on the welding bracket to ensure the alignment of the groove. Set the welding parameters at the welding power supply and control box. The welding current of the base layer and the filling layer is 185A~195A, the welding voltage is 22V~23V, and the welding speed is 490mm / min; the welding current of the cover layer is 140A~150A, the welding voltage is 14V~15V, and the welding speed is 255mm / min. When welding at different positions, the welding parameters can fluctuate around the above point values. Welding is carried out in a protective gas atmosphere of 80% Ar+20% CO2, and the dry extension of the welding wire is 10mm. The number of welding layers is as follows: Figure 1 As shown, before each welding, the groove and the layers need to be grinded with an angle grinder.

[0055] Example 5

[0056] For the base material, the groove is processed with a U-shaped narrow gap groove. The thickness of the blunt edge of the groove is 1.2mm. A circular arc transition with a radius of 2.4mm is designed between the blunt edge and the bevel edge of the groove. After removing the surface oil stains and dust with acetone, place the riser on the welding bracket to ensure the alignment of the groove. Set the welding parameters at the welding power supply and control box. The welding current of the base layer and the filling layer is 180A~190A, the welding voltage is 20V~21V, and the welding speed is 400mm / min; the welding current of the cover layer is 130A~140A, the welding voltage is 13V~14V, and the welding speed is 245mm / min. When welding at different positions, the welding parameters can fluctuate around the above point values. Welding is carried out in a protective gas atmosphere of 80% Ar+20% CO2, and the dry extension of the welding wire is 6mm. The number of welding layers is as follows: Figure 1 As shown, before each welding, the groove and the layers need to be grinded with an angle grinder.

[0057] Comparative Example 1

[0058] Same as Example 1, except that the protective gas atmosphere is 100% Ar.

[0059] Comparative Example 2

[0060] Same as Example 1, except that the protective gas atmosphere is 50% Ar+50% CO2.

[0061] Comparative Example 3

[0062] Same as in Example 1, only the welding current of the base layer and the filling layer is set to 130A-140A, the voltage is 12.5V-13.5V, the protective gas atmosphere is 50% Ar+50% CO2, and the welding speed is 320mm / min respectively.

[0063] Comparative Example 4

[0064] Same as in Example 1, only the welding current of the base layer and the filling layer is set to 130A-140A, the voltage is 12.5V-13.5V, the protective gas atmosphere is 50% Ar+50% CO2, and the welding speed is 450mm / min.

[0065] Comparative Example 5

[0066] Same as in Example 1, only the welding current of the base layer and the filling layer is set to 130A-140A, the voltage is 12.5-13.5V, the protective gas atmosphere is 50% Ar+50% CO2, and the welding speed is 700mm / min.

[0067] Comparative Example 6

[0068] Same as Example 1, only the shielding gas was 50% Ar+50% CO2, and the welding speed was 450 mm / min.

[0069] Comparative Example 7

[0070] Same as Example 1, only the shielding gas was 50% Ar+50% CO2, and the welding speed was 700 mm / min.

[0071] The macroscopic morphology of the welded joints obtained in Example 1, Comparative Example 1 and Comparative Example 2 is as follows: Figure 2 As shown, it can be observed that the base layer of comparative example 1 is not fully welded in the pure argon atmosphere, while the joints obtained in embodiment 1 and comparative example 2 are well formed.

[0072] Metallographic samples were taken from the welded joints obtained in Example 1 and Comparative Example 2 at the 12th, 3rd and 6th points of the weld, and the metallographic samples were polished flat with 240#-2000# sandpaper, and polished with 1.0W diamond grinding paste until the surface was bright and without marks, and then corroded with 4% nitric acid alcohol solution. Since stress corrosion cracking mainly occurs in the coarse-grained heat-affected zone of the welded joint, the microstructure of the coarse-grained zone of the samples obtained under different protective gas atmospheres was observed under a metallographic microscope, as shown in FIG. Figure 3 As shown. Comparative Example 2, i.e., the coarse grain zone structure obtained by welding under 50% Ar + 50% CO2 protective gas atmosphere is mainly lath martensite (M), lath bainite (LB) and a small amount of granular bainite (GB). X65 is a ferritic steel. The mechanical properties of martensite and matrix are quite different. Under the action of hydrogen, it is easier to cause the separation of martensite and matrix, resulting in a large stress and strain concentration, causing fracture failure. In addition, martensite has a high carbon content, and there is a potential difference between it and low-carbon phases such as ferrite, so it is easy to form micro-batteries and accelerate corrosion. The coarse grained zone structure obtained by welding in Example 1, i.e., 80% Ar + 20% CO2 protective gas atmosphere, is mainly composed of acicular ferrite (AF), granular bainite (GB) and lath bainite (LB). The high dislocation density of acicular ferrite will reduce the concentration of hydrogen in the dislocation, so that the hydrogen molecules combined with a single dislocation are less and insufficient to reach the threshold value for hydrogen-induced cracking, thereby making the distribution of hydrogen more diffuse and thus weakening the damage caused by hydrogen absorption to the material. Therefore, the appearance of AF greatly improves the hydrogen-induced cracking resistance of the welded joint. In summary, 80% Ar + 20% CO2 protective gas improves the crack resistance of the welded joint by obtaining acicular ferrite and eliminating martensite.

[0073] Considering that failure mainly occurs in the base layer in practical applications, the Vickers hardness of the base layer of the welded joint obtained in Example 1 and Comparative Example 2 was measured using a HVA-10A Vickers hardness tester at a load of 10 kg. The test results are as follows: Figure 4As shown in Table 3. From the test results, it can be seen that there is basically no difference in the weld hardness values ​​of the joints obtained by welding in the two protective gas atmospheres, while the hardness values ​​of the heat-affected zones are quite different. This is because the coarse-grained zone structure obtained by welding in the traditional 50% Ar + 50% CO2 protective gas atmosphere is mainly martensite, which has a high carbon content and contains a high density of dislocations in the structure, so it has a very high hardness. The coarse-grained structure of the joint obtained by welding in the 80% Ar + 20% CO2 protective gas atmosphere specified in the present invention is mainly acicular ferrite and granular bainite. Compared with martensite, the acquisition of these two structures requires a longer cooling time, so that the carbon inside the sample is more fully diffused, which leads to a decrease in hardness. The NACEMR0175~2009 standard stipulates that the metal hardness in an acidic hydrogen sulfide environment should not exceed 248HV 10 It can be seen from the test results that the welded joint obtained by welding with the shielding gas specified in the present invention meets the standard requirements, while conventional shielding gases cannot meet the standard requirements.

[0074] Table 3 Hardness values ​​of welded joints with different shielding gases (HV 10 )

[0075]

[0076] The welded joints obtained in Example 1 and Comparative Example 2 were subjected to a base layer stress corrosion test, and the welded joint samples with a certain deflection were subjected to a 720-hour test under the test conditions of NACE TM0177-Solution A, 99.5% hydrogen sulfide gas, 1 bar pressure, and 24°C ± 3. The sample was subjected to deflection loading with the weld root side as the tensile surface, and the loading load was 80% of the yield strength of the parent material. The loading formula is as follows:

[0077]

[0078] After 720 hours of testing, the tensile surface of the two welded joint samples was inspected under a low-power microscope with a magnification of ×10. Figure 5 As shown, all the joint specimens welded in 50% Ar + 50% CO2 protective gas atmosphere are broken, so the resistance of the specimen to stress corrosion cracking is unqualified, and by observing the fracture positions, it can be found that the fractures all occur in the heat affected zone; there are no cracks or cracks on the tensile surface of the joint welded in 80% Ar + 20% CO2 protective gas atmosphere, so the specimen is not sensitive to hydrogen sulfide stress corrosion cracking.

[0079] Comparative Examples 3 to 5 were carried out under low heat input conditions. The welded joints obtained in Comparative Examples 3, 4, and 5 were subjected to hardness tests and primer SSC tests. The hardness test results are shown in Table 4, and the primer SSC test results are shown in Table 4. Figure 6As shown in Table 4, it can be seen that the hardness values ​​of the rough area of ​​the welded joints obtained under the three process parameters are relatively high, far higher than the standard requirement of 248HV 10 ,It can be seen from Table 4 that the SSC resistance of the welded joints obtained under the three process parameters is unqualified.

[0080] Table 4 Hardness values ​​of welded joints at different welding speeds with low heat input (HV 10 )

[0081]

[0082] Comparative Examples 6 and 7 were carried out under high heat input conditions. The welded joints obtained in Comparative Examples 6 and 7 were subjected to hardness tests and primer SSC tests. The hardness test results are shown in Table 5, and the primer SSC test results are shown in Table 5. Figure 7 As shown in Table 5, it can be seen that the hardness values ​​of the rough area of ​​the welded joint obtained under the two process parameters are lower than the standard 248HV, although the heat input process is lower. 10 From Table 5, it can be seen that the SSC performance of the welded joints obtained under the two process parameters is unqualified, but the hardness is slightly lower than that of the low heat input process (i.e., Comparative Examples 3 to 5), and no 300HV 10 The above hardness values.

[0083] Table 5 Hardness values ​​of welded joints at high heat input and different welding speeds (HV 10 )

[0084]

[0085] In the prior art, CMT welding is usually carried out in a 50% Ar + 50% CO2 protective gas atmosphere. However, whether it is low heat input or high heat input, only improving the welding parameters cannot solve the problem of high hardness and high stress corrosion sensitivity of the SCR riser welded joint. The present application proposes to improve the protective gas atmosphere, and at the same time optimize the welding parameters under the atmosphere, including welding current, welding voltage, and welding speed, which can effectively reduce the hardness of the SCR riser welded joint and obtain better anti-SSC performance, and can meet the special requirements of oil and gas transportation in deep-sea acidic environments. In addition, the present application also optimizes the structural parameters of the groove, which can further improve the welding effect. The high heat input CMT welding technology using 80% Ar + 20% CO2 protective gas not only has a stable arc, small spatter, and high welding efficiency during the welding process, but also has a good welded joint with a small root excess height, and reduces the hardness of the coarse grain zone, eliminates the negative effects of the martensitic structure, improves the resistance of pipeline steel to stress corrosion cracking, and greatly improves the service life of the SCR riser.

[0086] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the feature. In the description of the present application, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0087] In addition, references throughout this specification to "one embodiment"; "one embodiment", "an example" or similar language indicate that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present application. Thus, appearances of the phrase "in one embodiment"; "in one embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0088] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A welding method for improving the stress corrosion resistance of a riser weld joint, characterized in that: The welding method is as follows: in a protective gas atmosphere of 80% Ar+20% CO2, the CMT welding technology is used to perform 5G welding on the SCR riser, wherein the welding current of the base layer and the filling layer is 180A-200A, the welding voltage is 20V-23V, and the welding speed is 400mm / min-500mm / min; the welding current of the cover layer is 130-150A, the welding voltage is 13-15V, and the welding speed is 245mm / min-255mm / min. The groove of the SCR riser adopts a U-shaped narrow gap groove. For 6-inch to 18-inch SCR risers, the blunt edge thickness of the groove is 1.1mm-1.7mm.

2. The welding method according to claim 1, characterized in that Supply the shielding gas 1.5s to 2s before welding, and turn off the shielding gas 1.2s to 1.5s after welding.

3. The welding method according to claim 1, characterized in that An arc transition is designed between the blunt edge and the bevel edge of the groove, and the arc radius is 2.2 mm to 3.8 mm.

4. The welding method according to claim 1, characterized in that: For the 6-inch SCR riser, the bevel angle is set to 3°, and for the 12-inch SCR riser and 18-inch SCR riser, the bevel angle is set to 3.5°.

5. The welding method according to any one of claims 1 to 4, characterized in that: When starting welding, set the wire extension length to 12mm, and during welding, the wire extension length is 6mm to 10mm.

6. The welding method according to any one of claims 1 to 4, characterized in that: Before welding, the part of the SCR riser to be welded is cleaned with acetone and then polished.

7. The welding method according to any one of claims 1 to 4, characterized in that: The SCR riser is preheated to 200°C to 250°C before welding.

8. An SCR riser weld joint prepared by the welding method according to any one of claims 1 to 7.

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