Welding method for subsea pipeline with high efficiency and comprehensive performance under shaking of pipe-laying ship

Abstract

To provide a technique belonging to a field of welding technology, in particular, a welding method for a subsea pipeline with high efficiency and comprehensive performance under shaking of a pipe-laying ship.SOLUTION: A welding method according to the present invention performs ultra-short arc GMAW all-position welding on a subsea pipeline within a range of heat input of 0.2 kJ / mm to 0.3 kJ / mm, while setting, in a GMAW waveform, a peak current from 285 A to 370 A, setting a peak current descent rate from 50 A / ms to 70 A / ms, and setting a necking time from 3 ms to 7 ms. A welding effect of overall low heat input and partial high heat input is formed, and stability of all-position welding of the subsea pipeline is guaranteed, which realizes stable welding of the subsea pipeline under a condition of pipe-laying ship shaking, and improves fatigue resistance and corrosion resistance of the subsea pipeline.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of welding technology, and more particularly to a highly efficient and comprehensive welding method for submarine piping during the rocking of a pipelaying vessel. [Background technology]

[0002] Steel catenary risers (SCRs) have been attracting attention in deepwater development since they were first used on the Auger tension leg platform in the Gulf of Mexico in 1994. Their advantages include high resistance to high temperatures and pressures, simple manufacturing processes, and low costs. However, complex marine environments and increasing production demands pose additional challenges to the design and manufacturing of deepwater steel catenary risers.

[0003] As the water depth and riser length increase, the marine environment becomes more severe. Underwater vortex-induced vibrations cause severe vibrations perpendicular to the water flow and the axis of the cylindrical body. Furthermore, when steel catenary risers are connected to the platform via joints, the alternating load effect is also doubled. If the riser is in this condition for a long period of time, frequent operation can shorten its lifespan and cause fatigue damage. Meanwhile, during pipe use, the root pass comes into direct contact with the internal gas or liquid, generating high pressure and severe corrosion within the pipe, leading to cracks from root defects and ultimately pipe failure. Furthermore, frequent wave motions cause the pipe-laying vessel to rock, significantly affecting the all-position welding process for subsea pipes, making subsea pipe welding difficult. Summary of the Invention

[0004] In response to the deficiencies of the prior art, the present invention provides a highly efficient and comprehensive welding method for submarine pipes when the pipe-laying vessel is oscillating, thereby solving the problems that the submarine pipes are prone to fatigue damage and corrosion fractures, and that the pipe-laying vessel has difficulty welding the submarine pipes when oscillating.

[0005] In one embodiment of the present invention, a highly efficient and comprehensive welding method for submarine pipes during rocking motion of a pipelaying vessel is provided as follows: ultra-short arc GMAW all-position welding is performed on submarine pipes with a heat input in the range of 0.2 kJ / mm to 0.3 kJ / mm, the peak current in the GMAW waveform is set to 285 A to 370 A, the peak current fall rate is set to 50 A / ms to 70 A / ms, and the necking time is set to 3 ms to 7 ms, thereby achieving a welding effect with low overall heat input and high localized heat input, and thus ensuring the stability of all-position welding of submarine pipes under rocking motion conditions.

[0006] With the above-mentioned technical means of the present invention, compared with the prior art, the present invention can perform ultra-short arc GMAW all-position welding with low heat input, and by optimizing the parameters in the GMAW waveform, can ensure the stability of all-position welding of subsea piping.

[0007] More preferably, the height of the root reinforcement during the welding process is ensured to be 0.5 mm or less.

[0008] More preferably, the welding is performed by a narrow gap U-groove multi-layer single pass welding process.

[0009] More preferably, the parameters of the narrow gap U-shaped groove are: root face thickness: 1.0 mm to 1.6 mm, arc transition radius: 2.4 mm to 3.2 mm, one-side groove angle: 2.5° to 3.5°.

[0010] More preferably, when welding submarine piping by the ultra-short arc GMAW technique, the welding current is 160 A to 200 A, the welding voltage is 12 V to 15 V, and the welding speed is 450 mm / min to 700 mm / min.

[0011] More preferably, the arc length of the ultra-short arc is 1.5 mm to 2.5 mm.

[0012] In another aspect of the present invention, there is provided a welded joint for subsea piping manufactured by the above welding method.

[0013] The above technical means of the present invention have the following technical advantages over the prior art. 1. The present invention performs ultra-short arc GMAW all-position welding on submarine pipes under low heat input conditions, and optimizes the parameters in the GMAW waveform to achieve a welding effect with low overall heat input and high local heat input, thereby ensuring the stability of all-position welding of submarine pipes, achieving stable welding of submarine pipes even under the conditions of rocking of the pipe-laying vessel, and improving the fatigue resistance and corrosion resistance of the submarine pipes. 2. In particular, the present invention ensures that the root weld height is 0.5 mm or less during the welding process, thereby reducing the stress concentration at the joint root and improving the fatigue resistance of the joint. 3. Furthermore, the present invention uses a narrow-gap U-groove multi-pass single-pass welding process instead of the V-groove multi-pass welding process used in the prior art. The suction effect of the side walls of the auxiliary groove on arc compression and the restraint effect on the flow range of the molten pool metal make it possible to avoid unfused defects on the side walls, between passes, and between layers caused by turbulence in the molten pool metal when the ship is rocking. [Brief explanation of the drawings]

[0014] [Figure 1] 1 shows an arc form in Example 1 of the present invention. [Figure 2] FIG. 2 is a schematic diagram of groove design in Examples 1 to 5 of the present invention. [Figure 3] 1 shows the macromorphology of a joint in Example 1 of the present invention. [Figure 4] 1 shows the microstructure of the joint in Example 1 of the present invention, where (a) is a diagram of the heat-affected coarse-grained region (CG) at the 0 o'clock position, (b) is a diagram of the CG at the 3 o'clock position, (c) is a diagram of the CG at the 6 o'clock position, (d) is a diagram of the weld (WM) at the 0 o'clock position, (e) is a diagram of the WM at the 3 o'clock position, and (f) is a diagram of the WM at the 6 o'clock position. [Figure 5] 1 shows the microhardness distribution of a joint in Example 1 of the present invention. [Figure 6] 1 is an SN curve of a fatigue test of a joint in Example 1 of the present invention. [Figure 7] 1 shows the surface morphology of the joint in Example 1 of the present invention after the SSC test. [Figure 8] 1 shows the side morphology of the joint in Example 1 of the present invention after the SSC test, where (a) is the 0 o'clock position, (b) is the 3 o'clock position, and (c) is the 6 o'clock position. [Figure 9] 1 shows the arc forms in Comparative Examples 1 and 2 of the present invention. [Figure 10] 1 shows the macromorphology of a joint in Comparative Example 1 of the present invention. [Figure 11] 1 shows the joint microstructure in Comparative Example 1 of the present invention, where (a) is a diagram of the heat-affected coarse-grained region (CG) at the 0 o'clock position, (b) is a diagram of the CG at the 3 o'clock position, (c) is a diagram of the CG at the 6 o'clock position, (d) is a diagram of the weld (WM) at the 0 o'clock position, (e) is a diagram of the WM at the 3 o'clock position, and (f) is a diagram of the WM at the 6 o'clock position. [Figure 12] 1 shows the microhardness distribution of a joint in Comparative Example 1 of the present invention. [Figure 13] 1 shows crack propagation in a welded joint at the 0 o'clock position after an SSC test for a joint in Comparative Example 1 of the present invention, where (a) shows the crack morphology near the coarse grain region in the heat-affected zone, (b) is an enlarged view of the crack morphology in (a), and (c) and (d) are enlarged views of the circled area in (b). [Figure 14] 1 shows crack propagation in a welded joint at the 3 o'clock position after an SSC test for a joint in Comparative Example 1 of the present invention, where (a) shows the crack morphology near the coarse grain region in the heat-affected zone, (b) is an enlarged view of the crack morphology in (a), (c) is an enlarged view of the part framed in red in (b), (d) is an enlarged view of the part framed in yellow in (b), and (e) is an enlarged view of the part framed in blue in (b). [Figure 15]1 shows crack propagation in a welded joint at the 6 o'clock position after an SSC test for a joint in Comparative Example 1 of the present invention, where (a) shows the crack morphology in the vicinity of the coarse grain region in the heat-affected zone, (b) is an enlarged view of the part framed in red in (a), (c) is an enlarged view of the part framed in yellow in (a), and (d) is an enlarged view of the part framed in blue in (a). [Figure 16] FIG. 10 is a diagram showing the surface morphology of a joint in Comparative Example 2 of the present invention after an SSC test. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to clarify the objectives, technical means and advantages of the present invention, the present invention will be described in more detail below with reference to the drawings and examples. Note that the specific examples described in this specification are merely for interpreting the present invention and are not intended to limit the present invention.

[0016] One aspect of the present invention provides a highly efficient and comprehensively effective welding method for submarine piping during oscillating motion of a pipelaying vessel, specifically as follows: ultra-short arc GMAW all-position welding is performed on submarine piping with a heat input in the range of 0.2 kJ / mm to 0.3 kJ / mm, the peak current in the GMAW waveform is set to 285 A to 370 A, the peak current fall rate is set to 50 A / ms to 70 A / ms, and the necking time is set to 3 ms to 7 ms, thereby achieving a low heat input overall and a high heat input locally, thereby ensuring the stability of all-position welding of the submarine piping under oscillating motion conditions and improving SSC (hydrogen sulfide stress corrosion cracking) performance.

[0017] In typical GMAW welding, the heat input is typically within the range of 0.8 kJ / mm to 1.5 kJ / mm. The GMAW waveform has a peak current of 250 A to 300 A, a peak current ramp rate of 250 A / ms to 300 A / ms, and a necking time of 1.5 ms to 2.5 ms. In typical GMAW processes, excessively high heat input leads to root shaping (too large root reinforcement height, too small transition radius), which is one of the factors that cause stress concentration and fatigue fracture. To improve the fatigue resistance of subsea piping, the present invention reduces the heat input to improve the root shape. However, under low heat input conditions, the electromagnetic force and arc pressure generated in all-position arc welding, especially in overhead welding, are insufficient to ensure the stability of the welding process. The gravity of the molten pool metal causes non-uniform magnetic fields on both sides of the groove, resulting in arc deflection. Furthermore, under these conditions, the rapid cooling of the molten pool metal leads to the formation of martensitic structures, resulting in poor sulfide stress corrosion cracking resistance of the joint. Therefore, the present invention combines a GMAW waveform and ultra-short arc technology under low heat input, improves the peak current to increase the arc pressure, reduces the peak current drop rate to avoid sudden changes in current due to the retreat of the welding wire, extends the necking time to increase the duration of the arc's action on the droplet, and uses ultra-short arc technology to generate a larger electromagnetic force to overcome the anti-gravity effect of the droplet.

[0018] Specifically, under low heat input conditions, the GMAW waveform is adjusted to increase the peak current, decrease the peak current drop rate, and extend the necking time. Here, increasing the peak current significantly increases the arc pressure, partially offsetting the gravitational effect of the weld pool metal, moving more liquid metal to the rear of the weld pool and thereby lengthening the time the droplets remain on the welding wire. Reducing the peak current drop rate prevents sudden changes in current due to the retraction of the welding wire. Prolonging the necking time increases the duration of the arc's action on the weld droplets, lengthening the time required for the droplets to detach, and the sustained electromagnetic force partially offsets the effect of gravity on the weld pool. The combination of the above factors ensures the stability of all-position welding of subsea piping. Furthermore, increasing the peak current increases the average current and heat input, which is beneficial for reducing joint hardness and improving the joint's SSC performance. By combining with ultra-short arc technology, it can generate a larger electromagnetic force than conventional GMAW technology, overcome the anti-gravity effect of droplets, and promote short-circuiting droplet transfer. Combined with waveform adjustment, this technology ensures the stability of the all-position welding process for subsea pipes. Meanwhile, the arc's effect on the sidewall is reduced, and the arc heat is locally compressed in the weld pool area, resulting in low overall heat input and high localized heat input. Combined with increased peak current, slower peak current drop rate, and longer necking time, this technology improves droplet transfer stability even when the pipelaying vessel is oscillating, avoiding the occurrence of unfused defects under low heat input conditions. The joint achieves a maximum Vickers hardness of ≦248HV10 and meets the NACE0177 standard for corrosion SSC testing.

[0019] Furthermore, the welding process ensures that the root weld height is no more than 0.5 mm, which reduces stress concentration at the joint root and ensures that the joint's fatigue resistance meets the requirements for use under alternating loads in subsea piping, thereby avoiding fatigue damage.

[0020] Furthermore, for all-position welding of submarine piping, frequent wave motions of pipelaying vessels cause significant turbulence in the weld pool. Therefore, using a conventional multi-pass GMAW welding process based on a V-groove results in significant turbulence in the weld pool, preventing it from fusing well with the sidewalls. After flowing to the next pass, the weld quality of the next pass and layer is affected, resulting in significant defects in the sidewalls, between passes, and between layers. Therefore, a multi-pass single-pass welding process based on a narrow U-groove is preferable. The sidewalls on both sides of the groove act to suppress arc compression and restrict the flow of the weld pool, thereby maintaining the weld pool in the center of the groove even under ship rocking conditions. This avoids defects in the sidewalls, between passes, and between layers that would otherwise be caused by turbulence in the weld pool. Furthermore, the parameters of the narrow gap U-shaped groove are preferably a root face thickness of 1.0 mm to 1.6 mm, an arc transition radius of 2.4 mm to 3.2 mm, and a one-side groove angle of 2.5° to 3.5°. Under these conditions, multi-layer single-pass welding is achieved.

[0021] Furthermore, when welding submarine pipes using the ultra-short arc GMAW technology, the welding current is 160A to 200A, the welding voltage is 12V to 15V, and the welding speed is 450mm / min to 700mm / min.

[0022] Furthermore, the ultra-short arc length is 1.5mm to 2.5mm, which generates a larger electromagnetic force to overcome the anti-gravity effect of the droplets, promotes the short-circuit transfer of the droplets, locally compresses the arc heat in the weld pool area, and improves the arc stability.

[0023] Furthermore, the present invention can realize fully automatic 5G position welding of submarine pipes using robots, and can also realize fully automatic welding of submarine pipes using track vehicles.

[0024] Another aspect of the present invention provides a welded joint for submarine piping manufactured by the above welding method. The submarine piping having this welded joint for submarine piping has fatigue resistance performance superior to the BS7608D grade and E grade acceptance curves, fatigue strength approximately 40% higher than the BS7608E curve, a maximum Vickers hardness of the joint ≦248HV10, and corrosion SSC test results satisfying the NACE0177 standard. Therefore, the submarine piping manufactured by the welding method provided in the present invention can meet the requirements for use under alternating loads.

[0025] The technical solutions provided by the present invention are further illustrated below through specific examples.

[0026] Example 1 The material to be welded in this example was 12-inch API 5L X65 riser. The narrow gap U-shaped opening used is shown in Figure 2. The root welding process parameters were: welding current 185 A, welding voltage 13.5 V, welding speed 500 mm / min, and heat input 0.24 kJ / mm. The GMAW waveform had a peak current of 360 A, a peak current ramp rate of 60 A / ms, a necking time of 4.8 ms, and an arc length of 2 mm.

[0027] The welding process was stable, the weld pool metal was centered in the groove, and no arc deflection occurred (Fig. 1). The joint macromorphology showed no unfused defects (Fig. 3). Microstructurally, the coarse-grained HAZ at the 0 o'clock position consisted primarily of lath bainite, ferrite, and chain-like MA components. The coarse-grained HAZ at the 3 o'clock and 6 o'clock positions consisted primarily of granular bainite, ferrite, and chain-like MA components. Hard, brittle structures such as martensite were not present at either position (Fig. 4). Maximum hardness values ​​of <235 HV10 were observed in the HAZ (Fig. 5). As can be seen from the SN curves with 95% confidence intervals, no fatigue damage occurred after the runout value was reached at medium and low stress levels. At a high stress level of 172 MPa, fatigue fracture occurred. The fatigue resistance performance was superior to the BS 7608 D and E grade acceptance curves, and the fatigue strength was 38% higher than the BS 7608 E curve (Fig. 6). For the SSC sample, after 720 hours of testing, the tensile surface of the sample was examined under a low-magnification microscope with a magnification of 10x, and no cracks or fractures were found on the tensile surface (Fig. 7). This indicates that the sample is not susceptible to sulfur-induced stress corrosion cracking or stress-controlled hydrogen-induced cracking under the above test conditions and meets the DNV-OS-F101 standard. After cutting the sample, the cross section of the root was observed and no microcracks were found (Fig. 8).

[0028] Example 2 In this example, the material being welded was a 12-inch API 5L X65 riser, and the narrow U-groove used had backing welding process parameters of 160 A welding current, 15 V welding voltage, 450 mm / min welding speed, and 0.26 kJ / mm heat input. The GMAW waveform had a peak current of 285 A, a peak current ramp rate of 65 A / ms, a necking time of 6 ms, and an arc length of 1.5 mm.

[0029] Example 3 In this example, the material being welded was a 12-inch API 5L X65 riser, and the narrow U-groove used had backing welding process parameters of 170 A welding current, 12 V welding voltage, 500 mm / min welding speed, and 0.23 kJ / mm heat input. The GMAW waveform had a peak current of 300 A, a peak current ramp rate of 50 A / ms, a necking time of 3 ms, and an arc length of 2.5 mm.

[0030] Example 4 In this example, the material being welded was a 12-inch API 5L X65 riser, and the narrow U-groove used had backing welding process parameters of 200 A welding current, 15 V welding voltage, 700 mm / min welding speed, and 0.21 kJ / mm heat input. The GMAW waveform had a peak current of 370 A, a peak current ramp rate of 70 A / ms, a necking time of 5 ms, and an arc length of 1.8 mm.

[0031] Example 5 In this example, the material being welded was a 12-inch API 5L X65 riser, and the narrow U-groove used had backing welding process parameters of 190 A welding current, 13 V welding voltage, 600 mm / min welding speed, and 0.20 kJ / mm heat input. The GMAW waveform had a peak current of 320 A, a peak current ramp rate of 55 A / ms, a necking time of 7 ms, and an arc length of 2.2 mm.

[0032] Comparative Example 1 Comparative Example 1 was the same as Example 1, except that the arc length was 4 mm. During the welding process, the arc was attracted and deflected by the side wall (Fig. 9). The macromorphology of the joint showed significant unfused defects (Fig. 10). Regarding the microstructure, the coarse-grained HAZ at the 0 o'clock position was mainly composed of granular bainite and coarse chain-like MA components. The coarse-grained region at the 3 o'clock position was mainly composed of martensite and chain-like MA components. The coarse-grained region at the 6 o'clock position was mainly composed of granular bainite, lath bainite, and martensite (Fig. 11). Due to the formation of martensite, the maximum hardness of the joint reached 260 HV10, both of which appeared in the HAZ (Fig. 12).

[0033] After 720 hours of testing, the tensile surfaces of the SSC samples were examined under a 10x microscope. Microcracks were observed on the load-bearing side of the weld root. The samples were cut and the root cross-sections were examined. The cracks in the weld joint at the 0 o'clock position primarily initiated from the coarse-grained martensite and propagated along the martensite and bainite. The cracks stopped growing when they reached the acicular ferrite in the weld or perpendicular to the lath bainite direction (Figure 13). The cracks in the weld joints at the 3 and 6 o'clock positions primarily initiated from the coarse-grained martensite and propagated along the martensite or bainite. The crack at the 3 o'clock position stopped growing when it reached the lath bainite direction (Figure 14). The crack at the 6 o'clock position propagated to the weld and then stopped growing due to the inhibiting effect of the acicular ferrite (Figure 15).

[0034] Comparative Example 2 Comparative Example 2 was similar to Comparative Example 1, except that the peak current in the waveform was 260 A, the peak current decline rate was 280 A / ms, and the necking time was 2 ms. During the welding process, the arc was attracted and deflected by the side wall (Figure 9). The maximum hardness of the joint was higher than that of Comparative Example 1, reaching 285 HV10. After the SSC sample was tested for 720 hours, the tensile surface of the sample was examined under a low-magnification microscope with 10x magnification, and significant cracking was observed on the load-bearing side of the weld root (Figure 16).

[0035] Those skilled in the art can understand that the above description is only a preferred embodiment of the present invention, and does not limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A highly efficient and comprehensive welding method for subsea piping during rocking of a pipelay vessel, comprising: In the above welding method, ultra-short arc GMAW all-position welding is performed on submarine piping with a heat input in the range of 0.2 kJ / mm to 0.3 kJ / mm, the arc length of the ultra-short arc is 1.5 mm to 2.5 mm, the peak current in the GMAW waveform is set to 285 A to 370 A, the peak current fall rate is set to 50 A / ms to 70 A / ms, and the necking time is set to 3 ms to 7 ms. Welding is performed using a narrow gap U-groove multi-pass single-pass welding process, and it is ensured that the root reinforcement height is 0.5 mm or less during the welding process, thereby forming a welding effect with low heat input overall and high heat input locally, and ensuring the stability of all-position welding of submarine piping under swinging conditions.

2. 2. The welding method according to claim 1, characterized in that the parameters of the narrow gap U-shaped groove are a root face thickness of 1.0 mm to 1.6 mm, an arc transition radius of 2.4 mm to 3.2 mm, and a one-side groove angle of 2.5 ° to 3.5 °.

3. The welding method according to claim 1, characterized in that, when welding submarine pipes using ultra-short arc GMAW technology, the welding current is 160A-200A, the welding voltage is 12V-15V, and the welding speed is 450mm / min-700mm / min.

4. A welded joint for submarine piping manufactured by the welding method according to any one of claims 1 to 3.

Images