Highly efficient and high overall performance welding method for subsea piping during rocking of pipelaying vessel

Abstract

The present invention relates to the field of welding technology, and specifically to a highly efficient and high overall performance welding method for submarine piping during the rocking of a pipelaying vessel. [Solution] In a welding method, ultra-short arc GMAW all-position welding is performed on subsea 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. The present invention creates a welding effect with low heat input overall and high heat input locally, ensuring the stability of all-position welding of subsea piping, thereby realizing stable welding of subsea piping even under conditions where the pipe-laying ship is rocking, and improving the fatigue resistance and corrosion resistance of the subsea piping.

Description

[Technical field]

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

[0002] Since its first use on the tension leg platform Auger in the Gulf of Mexico in 1994, steel catenary risers (SCRs) have been gaining attention in deepwater development due to their advantages such as high resistance to high temperatures and pressures, simple manufacturing process, and low cost. However, complex marine environments and increasing production demands have brought more challenges to the design and manufacturing of deepwater steel catenary risers.

[0003] As the water depth increases and the length of the riser increases, the marine environment becomes harsher, and the occurrence of underwater vortex excitation vibration causes severe vibration perpendicular to the water flow and the axial direction of the cylindrical body, and the action of alternating loads is also doubled when the steel catenary riser is connected to the platform through a joint. If the riser is in this state for a long time, the life of the riser will be shortened and fatigue damage may occur due to frequent operation. Meanwhile, during the use of the piping, the root pass is in direct contact with the internal gas or liquid, which generates large pressure and strong corrosion in the piping, and cracks will develop from the root defects, which will eventually cause the piping to break. In addition, frequent waves cause the pipe laying ship to rock, which has a great impact on the all-position welding process of the subsea piping, making the welding of the subsea piping difficult. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention aims to provide a highly efficient and high-comprehensive performance welding method for submarine piping when a pipe-laying ship sways, thereby solving the problem that fatigue damage and corrosion fracture are easily caused in the submarine piping, and that it is difficult for the pipe-laying ship to weld the submarine piping when it sways.

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

[0007] More preferably, the welding process ensures that the height of the root reinforcement is 0.5 mm or less.

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

[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, and one-side groove angle: 2.5° to 3.5°.

[0010] More preferably, when welding submarine pipes by the ultra-short arc GMAW technique, the welding current is 160A to 200A, the welding voltage is 12V to 15V, and the welding speed is 450mm / min to 700mm / 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 produced 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 subsea piping under low heat input conditions, and optimizes the parameters in the GMAW waveform to form a welding effect with low overall heat input and high local heat input, thereby ensuring the stability of all-position welding of subsea piping, achieving stable welding of subsea piping under the condition of rocking of the pipe-laying ship, and improving the fatigue resistance and corrosion resistance of the subsea piping. 2. In particular, the present invention ensures that the root weld height is less than 0.5 mm 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 multi-pass single-pass welding process for a narrow-gap U-shaped groove instead of the multi-pass welding process for a V-shaped groove used in the prior art, and the suction effect of both sides of the auxiliary groove on the arc compression and the restraint effect on the flow range of the molten pool metal make it possible to avoid unfusion defects on the side walls, between passes, and between layers caused by turbulence in the molten pool metal under conditions when the ship hull is rocking. [Brief description of the drawings]

[0014] [Figure 1] 1 shows an arc form in Example 1 of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of groove design in Examples 1 to 5 of the present invention. [Diagram 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. [Diagram 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 SSC testing. [Figure 8] 1 shows side morphology after SSC testing of a joint in Example 1 of the present invention, 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 the crack extension of the welded joint at the 0 o'clock position after the SSC test of the joint in Comparative Example 1 of the present invention, where (a) is 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 enclosed area in (b). [Figure 14] 1 shows crack extension 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) is the crack morphology in the vicinity of 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 the crack extension of the welded joint at the 6 o'clock position after the SSC test of the joint in Comparative Example 1 of the present invention, where (a) is 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. 13 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 PREFERRED EMBODIMENTS

[0015] In order to clarify the object, technical means and advantages of the present invention, the present invention will be described in more detail with reference to the following 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] In one aspect of the present invention, a highly efficient and high overall performance welding method for submarine piping during rocking of a pipelaying ship is provided, which is specifically as follows: ultra-short arc GMAW all-position welding is performed on the submarine piping with 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 forming a welding effect with low heat input overall and high heat input locally, which in turn ensures the stability of all-position welding of the submarine piping under rocking conditions, and realizes the improvement of SSC (hydrogen sulfide stress corrosion cracking) performance.

[0017] In general GMAW welding, the heat input is usually in the range of 0.8 kJ / mm to 1.5 kJ / mm, and in the GMAW waveform, the peak current is 250 A to 300 A, the peak current drop rate is 250 A / ms to 300 A / ms, and the necking time is 1.5 ms to 2.5 ms. In general GMAW process, the heat input is too high, and the root shape (too large root reinforcement height, too small transition radius) is one of the factors that cause stress concentration and fatigue fracture. In order to improve the fatigue resistance performance of subsea piping, the present invention improves the root shape by reducing the heat input. However, under low heat input conditions, the electromagnetic force and arc pressure generated when the arc is in all position welding, especially in the overhead position, are not enough to guarantee the stability of the welding process, and the gravity of the molten pool metal makes the magnetic field on both side walls of the groove uneven, causing arc deflection. In addition, under this condition, the rapid cooling action of the molten pool metal forms martensite structure, and the sulfide stress corrosion cracking performance of the joint is insufficient. Therefore, the present invention combines 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 caused by the retreat of the welding wire, extends the necking time to increase the duration of the arc's action on the droplet, and generates a larger electromagnetic force through the ultra-short arc technology to overcome the anti-gravity effect of the droplet.

[0018] Specifically, under the condition of low heat input, the GMAW waveform is adjusted to improve the peak current, reduce the peak current drop rate, and extend the necking time. Here, the increase in peak current can significantly increase the arc pressure and offset part of the gravitational effect of the molten pool metal, so that more molten pool liquid metal moves to the rear of the molten pool, which increases the time that the droplets remain on the welding wire. The decrease in peak current drop rate avoids the sudden change in current due to the retreat of the welding wire. The extension of the necking time increases the duration of the action of the arc on the droplets, which increases the time required for the droplets to fall off, and the sustained electromagnetic force can offset part of the effect of gravity on the molten pool. The combination of the above factors ensures the stability of all-position welding of subsea piping. In addition, the increase in peak current increases the average current and heat input, which is favorable to the reduction of joint hardness, and improves the SSC performance of the joint. Combined with ultra-short arc technology, it can generate a larger electromagnetic force than ordinary GMAW technology to overcome the effect of anti-gravity on the droplets and promote the short-circuit transfer of the droplets, and combined with waveform adjustment, it can ensure the stability of the all-position welding process of subsea pipes. Meanwhile, the action of the arc on the side wall is reduced, and the arc heat is locally compressed in the molten pool area, forming the effect of low heat input overall and high heat input locally. Combined with the improvement of peak current, the reduction of peak current drop rate and the extension of necking time, it can improve the stability of droplet transfer when the hull of the pipelaying ship is rocking, avoid the occurrence of unfused defects under low heat input, and achieve the maximum Vickers hardness of the joint ≦248HV10 and the corrosion SSC test meet the NACE0177 standard.

[0019] In addition, the welding process ensures that the root weld height is less than 0.5 mm, which reduces the stress concentration at the joint root and ensures that the fatigue resistance of the joint meets the requirements for use under alternating loads in subsea piping, thereby avoiding the occurrence of fatigue damage.

[0020] Furthermore, for the all-position welding process of submarine piping, frequent waves cause the pipe-laying ship to rock, and if a multi-pass GMAW welding process based on a normal V-groove is used, the molten pool metal will have significant turbulence under the condition of ship rocking, so the molten pool metal cannot fuse well with the side wall, and after flowing to the next pass area, it will affect the welding quality of the next pass and the next layer, and is very likely to cause side wall, inter-pass and inter-layer unfusion defects. Therefore, it is preferable to weld using a multi-pass single-pass welding process based on a narrow gap U-groove. Due to the suction effect of the side walls on both sides of the groove against the arc compression and the restraint effect on the flow range of the molten pool metal, the molten pool metal can be maintained in the center of the groove even under the condition of ship rocking, and the unfusion defects of the side wall, inter-pass and inter-layer caused by the turbulence phenomenon of the molten pool metal under the condition of ship rocking are avoided. Furthermore, the parameters of the narrow gap U-shaped groove are preferably a root face thickness of 1.0 mm to 1.6 mm, a circular 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 realized.

[0021] Furthermore, when welding subsea piping by 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.

[0022] In addition, the arc length of the ultra-short arc is 1.5mm~2.5mm, which can generate a larger electromagnetic force to overcome the antigravity effect of the droplet, promote the short-circuit transfer of the droplet, locally compress the arc heat in the molten pool area, and improve the stability of the arc.

[0023] Furthermore, the present invention can realize fully automatic 5G position welding of subsea piping using a robot, and can also realize fully automatic welding of subsea piping using a track vehicle.

[0024] In another aspect of the present invention, a welded joint for submarine piping is provided, which is manufactured by the above welding method. The submarine piping having the welded joint for submarine piping has fatigue resistance performance superior to BS7608D grade and E grade inspection curves, fatigue strength about 40% higher than BS7608E curve, maximum Vickers hardness of the joint is ≦248HV10, and corrosion SSC test meets 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 FIG. 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 molten pool metal was located at the center of the groove, and no arc deflection occurred (Fig. 1). No unfused defects were found in the joint macromorphology (Fig. 3). In terms of microstructure, the structure of the coarse-grained heat-affected zone at the 0 o'clock position was mainly lath bainite, ferrite and chain-like MA components, while the structure of the coarse-grained zone at the 3 o'clock position and 6 o'clock position was mainly granular bainite, ferrite and chain-like MA components, and no hard and brittle structure such as martensite appeared at any of the positions (Fig. 4). The maximum hardness value <235HV10 appeared in the heat-affected zone (Fig. 5). As can be seen from the SN curves with 95% confidence interval, no fatigue damage occurred after reaching the runout value at medium and low stress levels, and fatigue fracture occurred at a high stress level of 172MPa, and the fatigue resistance performance was superior to the BS 7608 D grade and E grade acceptance curves, and the fatigue strength was 38% higher than the BS7608E curve (Fig. 6). For the SSC sample, after 720 hours of testing, the tensile surface of the sample was inspected under a low-power microscope with a magnification of 10x, and the tensile surface had no fractures or cracks (Figure 7). This indicates that the sample is not sensitive to sulfur-induced stress corrosion cracking or stress-dominated 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 (Figure 8).

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

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

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

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

[0032] Comparative Example 1 Comparative Example 1 was similar to 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). As for the microstructure, the structure of the coarse-grained heat-affected zone at the 0 o'clock position was mainly granular bainite and coarse chain-like MA components, the structure of the coarse-grained zone at the 3 o'clock position was mainly martensite and chain-like MA components, and the structure of the coarse-grained zone at the 6 o'clock position was mainly granular bainite, lath bainite, and martensite (Fig. 11). Due to the formation of martensite, the maximum hardness of the joint reached 260HV10, both of which appeared in the heat-affected zone (Fig. 12).

[0033] After testing the SSC samples for 720 hours, the tensile surfaces of the samples were examined under a low-magnification microscope with a magnification of 10x, and microcracks were found on the load-bearing side of the weld root. The samples were cut to observe the root cross section, and the cracks in the weld joint at 0 o'clock mainly initiated from the coarse-grained martensite and extended along the martensite and bainite, and stopped growing when they extended to the acicular ferrite of the weld or when the extension direction was perpendicular to the lath bainite direction (Figure 13). The cracks in the weld joint at 3 o'clock and 6 o'clock mainly initiated from the coarse-grained martensite and extended along the martensite or bainite, and stopped growing when the crack at 3 o'clock extended perpendicular to the lath bainite (Figure 14), and the crack at 6 o'clock extended to the weld and then stopped growing due to the inhibiting effect of 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 260A, the peak current fall rate was 280A / ms, and the necking time was 2ms. 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 285HV10. After the SSC sample was tested for 720 hours, the tensile surface of the sample was inspected under a low-magnification microscope with a magnification of 10x, and significant cracks were found on the load-bearing side of the weld root (Figure 16).

[0035] As can be understood by those skilled in the art, 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 high overall performance welding method for subsea piping during rocking of a pipelaying vessel, comprising: The welding method is characterized in that, in the above welding method, ultra-short arc GMAW all-position welding is performed on the submarine pipe 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, the necking time is set to 3 ms to 7 ms, and welding is performed by a narrow gap U-groove multi-layer single pass welding process, and the root reinforcement height is guaranteed to be 0.5 mm or less during the welding process, thereby forming a welding effect of low heat input overall and high heat input locally, and ensuring the stability of all-position welding of the submarine pipe under rocking conditions.

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 by 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.

Images