GTAW + FCAW composite welding method for X80 pipeline steel

Abstract

The invention discloses a GTAW + FCAW hybrid welding method for X80 pipeline steel, and belongs to the technical field of steel pipe welding. The process comprises the steps of pipe orifice cleaning, joint design, welding material management, pipe orifice pairing, interlayer temperature preheating, internal welding machine evacuation, welding, nondestructive testing and fracture toughness testing. According to the joint design, the X80 pipeline steel welding joint obtained through the composite groove machining and composite welding method is good in fracture toughness under the low-temperature condition of-10 DEG C, the CTOD value meets the requirement that the national pipe network DEC requirement is not lower than 0.254 mm, and the service performance of the X80 pipeline steel welding joint under the low-temperature environment of-10 DEG C is guaranteed; according to the process, the fracture toughness is good, the CTOD value is high, the mechanical property of a welded joint is excellent, the nondestructive testing result is qualified, the welding quality is improved, and the welding cost is saved while it is ensured that the welding quality meets the use performance requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of steel pipe welding, and specifically relates to a GTAW+FCAW composite welding method for X80 pipeline steel. Background Art

[0002] Pipeline transportation is the most economical and reasonable way to transport oil and natural gas. With the increasing development of science and technology and the continuous improvement of pipeline construction level, high-grade and large-diameter steel pipes play an important role in the construction of long-distance natural gas pipelines. my country's oil and gas pipeline network has spread across the country and connected the world, providing a steady stream of energy support for the national economy and national development.

[0003] During the manufacturing, forming and use of oil and gas steel pipes, melting welding processes such as tungsten inert gas welding and gas shielded welding are used. Due to the heat input and metallographic structure transformation during the welding process, the welded joints of X80 steel welded pipes are often dangerous locations where cracks initiate and fractures occur. At the same time, due to the differences in welding thermal cycles at different parts of the welded joints, their structures and properties are also distributed differently along the center of the weld. In addition, oil and gas pipelines often pass through cold regions and corrosive environments, which places higher requirements on the performance of pipeline steel welded joints. Fracture toughness is an important technical indicator of the performance of girth welds, which determines the crack arresting ability of girth welds and has an important impact on the safe service of pipelines. The inventors found that the prior art has at least the following problems: after welding the X80 pipeline steel pipe using the method provided by the prior art, the fracture toughness CTOD value of the weld fluctuates greatly, and the welded joints are prone to cracks and other defects, resulting in inconsistent mechanical properties of the welded joints and poor welding quality. Summary of the invention

[0004] The invention provides a GTAW+FCAW composite welding method for X80 pipeline steel, which solves the problems of the prior art and provides a GTAW+FCAW composite welding method for X80 pipeline steel with good welding quality, no defects such as oxidation and cracks, and good fracture toughness of the weld, wherein the welding method for the root welding layer and the hot welding layer is tungsten inert gas arc welding (GTAW for short), and the welding method for the filling layer and the surface layer is flux-cored arc welding (FCAW for short).

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a GTAW+FCAW composite welding method for X80 pipeline steel, comprising the following steps:

[0006] (1) Pipe cleaning: The grooves on the inner and outer surfaces of the steel pipe and the area within 150mm on both sides should be cleaned. There should be no scaling, wear, rust, slag, grease, paint or other harmful substances that affect the welding quality;

[0007] (2) Joint design: The pipe end bevel should be processed on site using a beveling machine;

[0008] (3) Welding material management: Welding wire should be stored in accordance with the manufacturer's product instructions. Welding wire that shows signs of damage or deterioration should not be used for welding;

[0009] (4) Pipe end assembly: When the internal welding machine is assembled, no scratches, abrasion marks or oil stains should be left on the inner surface of the steel pipe. The hammering method should not be used to correct the misalignment;

[0010] (5) Preheating interlayer temperature: the preheating temperature is controlled at 110-150°C, and the interlayer temperature is controlled at 80-150°C;

[0011] (6) Withdrawal of internal welding machine: When the steel pipe after root welding is completed is placed on the pipe pier, the steel pipe should not be subjected to vibration and impact;

[0012] (7) Welding: root layer welding method: GTAW, hot weld layer welding method: GTAW, filling layer welding method: FCAW, cover layer welding method: FCAW;

[0013] (8) Nondestructive testing: Nondestructive testing should follow up the work and provide timely feedback on the details of the unqualified welds, so as to facilitate the timely adjustment of welding parameters for automatic welding;

[0014] (9) Fracture toughness test and weld joint mechanical properties test: fracture toughness test and weld joint mechanical properties test shall be carried out in accordance with standard requirements.

[0015] In the joint design process of step (2) described in the present invention, the groove processing dimensions are: misalignment: ≤2.0mm, the local length greater than 2.0mm and not greater than 2.5mm is not greater than 50mm; excess height: 0-2.0mm, the local length greater than 2.0mm and not greater than 3.0mm is not greater than 50mm; cover weld width: each side of the upper opening of the groove should be widened by 1.0-2.0mm.

[0016] In the joint design process (2) of the present invention, the angle and size of the pipe end groove should meet the following requirements: groove surface angle: β = 5° ± 1°, α = 45° ± 1°, γ = 37.5° ± 1°; blunt edge (P): 1.1 ± 0.2 mm, back pad: none, butt clearance (b): 0-0.5 mm; height from inflection point to inner wall (H): 5.1 ± 0.2 mm; half groove width (W): 3.4-4.1 mm, inner groove height (h): 1.6 ± 0.2 mm; the joint type is butt joint, and the groove type is composite.

[0017] In the welding process of step (7) of the present invention, the welding method of the root welding layer and the hot welding layer is argon tungsten arc welding (GTAW), and the welding method of the filling layer and the cover layer is flux-cored arc welding (FCAW).

[0018] In the welding process of step (7) of the present invention, the root welding layer welding process is: current: 126-176A, voltage: 9.9-14.3V, shielding gas flow rate 8-18L / min, welding speed 5.5-9.9cm / min, heat input 1.32-1.56kJ / mm.

[0019] In the welding process of step (7) of the present invention, the hot welding layer welding process is as follows: current: 162-214A, voltage: 10.3-14.8V, shielding gas flow rate 8-18L / min, welding speed 6.5-11cm / min, heat input 1.52-1.79kJ / mm, and the hot welding layer is welded with a single welding gun.

[0020] In the welding process of step (7) of the present invention, the filling layer welding process is as follows: current: 162-257A, voltage: 20.5-28V, swing width 3.6-11.5mm, edge dwell 180-297s, wire feeding speed 17-27cm / min, shielding gas flow 5.4-7.7L / min, welding speed 15.4-20.3cm / min, heat input 1.41-1.98kJ / mm, and the filling layer welding is a double welding gun.

[0021] In the welding process of step (7) of the present invention, the cover layer welding process is as follows: current: 142-214A, voltage: 20.6-26.4V, swing width 4.4-5.7mm, edge dwell 153-227s, wire feeding speed 17-27cm / min, shielding gas flow 5.3-6.8L / min, welding speed 15.8-20.3cm / min, heat input 1.22-1.52kJ / mm, and the cover layer welding is a double welding gun.

[0022] The fracture toughness of the weld of the welding method of the present invention is good under low temperature conditions of -10°C, and the fracture toughness CTOD value is ≥0.254mm.

[0023] According to the welding method of the present invention, the mechanical properties of the welded joint include tensile strength Rm≥625Mpa, impact energy Akv (J)≥60J, and no cracks in the bending test result.

[0024] The beneficial effect of adopting the above technical scheme is that the welding method of the present invention is a composite welding method, wherein the welding method of the root welding layer and the hot welding layer is tungsten inert gas arc welding (GTAW for short), and the welding method of the filling layer and the cover layer is flux-cored arc welding (FCAW for short). The X80 pipeline steel welded joint obtained by this composite welding method has good fracture toughness under low temperature conditions of -10°C, and the CTOD value meets the national pipeline network DEC requirement of not less than 0.254mm, ensuring the service performance of the X80 pipeline steel welded joint under low temperature environment of -10°C. The process of the present invention can ensure that the welding quality meets the performance requirements, while having good fracture toughness, excellent mechanical properties of the welded joint, and high CTOD value, thereby improving welding quality and saving welding costs. DETAILED DESCRIPTION

[0025] Figure 1 This is the groove processing diagram;

[0026] Figure 2 is the weld distribution diagram;

[0027] Among them, 1 is the root welding layer, 2 is the hot welding layer, 3-1 is the filling layer, 3-2 is the filling layer, 4-1 is the filling layer, 4-2 is the filling layer, 5-1 is the cover layer, and 5-2 is the cover layer;

[0028] Figure 3 This is a picture of the specimen after fracture in the fracture toughness test of Example 1;

[0029] Figure 4 This is a picture of the specimen after fracture in the fracture toughness test of Example 2;

[0030] Figure 5 This is a picture of the specimen after fracture in the fracture toughness test of Example 3;

[0031] Figure 6 This is a picture of the sample after fracture in the fracture toughness test of Example 4;

[0032] Figure 7 This is a picture of the specimen after fracture in the fracture toughness test of Example 5;

[0033] Figure 8 This is a picture of the sample after fracture in the fracture toughness test of Example 6. DETAILED DESCRIPTION

[0035] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0036] A GTAW+FCAW composite welding method for X80 pipeline steel comprises the following steps:

[0037] (1) Pipe cleaning

[0038] The grooves on the inner and outer surfaces of the steel pipe and the area within 150mm on both sides should be cleaned and should not have scaling, wear, rust, slag, grease, paint or other harmful substances that affect the welding quality.

[0039] The groove and the area within 25mm on both sides should be cleaned mechanically until the metallic luster appears.

[0040] (2) Connector design

[0041] The pipe end bevel should be processed on site with a beveling machine. The angle and size of the pipe end bevel should comply with the attached Figure 1 requirements.

[0042] Joint type: Butt groove type: Composite

[0043] Bevel surface angle: β = 5° ± 1° α = 45° ± 1° γ = 37.5° ± 1°;

[0044] Blunt edge (P): 1.1±0.2mm Back pad: None Gap (b): 0-0.5mm;

[0045] Height from inflection point to inner wall (H): 5.1±0.2mm;

[0046] Half groove width (W): 3.4-4.1mm Inner groove height (h): 1.6±0.2mm;

[0047] Misalignment: ≤2.0mm, the local length of the misalignment greater than 2.0mm and less than 2.5mm is not greater than 50mm;

[0048] Residual height: 0~2.0mm, the local length exceeding 2.0mm and not exceeding 3.0mm shall not exceed 50mm;

[0049] Cover weld width: The upper edge of the groove should be widened by 1.0mm to 2.0mm on each side.

[0050] Before groove processing, the grinding condition of the inner and outer pipe welds at the pipe end should be checked to ensure that the inner and outer pipe welds within 150mm of the pipe end are ground to be flush with the parent material.

[0051] The processed welding groove surface should be visually inspected. The groove surface is required to be smooth and free of processed grooves, and should not have defects such as delamination and cracks.

[0052] The processed groove should be used within 24 hours to avoid the influence of rust and dirt corrosion on the welding quality.

[0053] For the pits on the surface of the steel pipe, the pits have sharp points or are located at the weld, or the pit depth exceeds 2% of the nominal diameter of the pipe, the pipe section should be removed. Figure 1Re-process the groove.

[0054] (3) Welding material management

[0055] Welding wire should be stored in accordance with the manufacturer's product instructions. Welding wire that shows signs of damage or deterioration should not be used for welding.

[0056] The welding wire that has been removed from the packaging should be used up continuously, and the damp or rusted welding wire should not be used.

[0057] Welding wire that is not used up on the same day does not need to be removed from the wire feeder, but rain and moisture-proof measures should be taken. When welding the next day, at least 2m of welding wire should be removed before welding can be carried out.

[0058] (4) Nozzle pairing

[0059] When the internal welding unit is aligned, no scratches, abrasion marks or oil stains should be left on the inner surface of the steel pipe. The hammering method should not be used to correct the misalignment.

[0060] The distance between adjacent circumferential welds should be greater than 1.0 times the diameter of the steel pipe. The weld of the straight seam pipe should be in the upper half of the circumference of the steel pipe.

[0061] The staggered edges should be evenly distributed along the circumference of the steel pipe.

[0062] A track locator should be used to assist in the installation of the welding trolley track, and the welding gun should be ensured to be aligned with the center of the welding groove around the entire pipe circumference.

[0063] Before assembling the pipe mouths, the inspection reference line should be drawn according to the AUT inspection requirements.

[0064] (5) Preheating interlayer temperature

[0065] The preheating temperature is controlled at 110-150°C, and the interlayer temperature is controlled at 80-150°C;

[0066] The anti-corrosion layer of the steel pipe should not be damaged during preheating, and the surface dirt should be removed after preheating.

[0067] Use an infrared thermometer, contact thermometer or temperature pen to monitor whether the preheating temperature meets the requirements of the process regulations. The interlayer temperature should be monitored on the weld metal about 200mm in front of the welding direction.

[0068] When welding is interrupted and the interlayer temperature cools down to below the minimum temperature required by the welding procedure specification when welding is resumed, the weld should be reheated to the preheating temperature.

[0069] (6) Internal welding machine evacuation

[0070] The steel pipe being welded should be in a stable state.

[0071] When the steel pipe after root welding is completed is placed on the pipe pier, the steel pipe should not be subjected to vibration and impact.

[0072] (7) Welding

[0073] The welding operation of the external welding machine should be carried out in a fully enclosed windproof shed. Use a clamp to firmly contact the ground wire with the welded steel pipe, and no arc should be generated to burn the parent material. The arc should be struck in the groove or on the surface of the completed weld, and should not be struck on the surface of the steel pipe.

[0074] When the internal welding machine performs root welding, the pipe ends on both sides of the pipeline should be sealed to prevent the air in the pipe from flowing too quickly.

[0075] The pipelayer can only be adjusted after 100% of the root pass is completed. If there is a risk of cracking in the root weld, the pipelayer should not be adjusted or moved until 100% of the hot weld is completed. The support hoist cannot be withdrawn before the steel pipe is stabilized on the pier.

[0076] A composite welding method, wherein the root welding layer and the hot welding layer are welded by argon tungsten arc welding (GTAW for short), and the filling layer and the cover layer are welded by flux-cored arc welding (FCAW).

[0077] The root welding layer welding process is: current: 126-176A, voltage: 9.9-14.3V, shielding gas flow rate 8-18L / min, welding speed 5.5-9.9cm / min, heat input 1.32-1.56kJ / mm.

[0078] The welding process of the hot welding layer is as follows: current: 162-214A, voltage: 10.3-14.8V, shielding gas flow rate 8-18L / min, welding speed 6.5-11cm / min, heat input 1.52-1.79kJ / mm, and the hot welding layer is welded with a single welding gun.

[0079] The filling layer welding process is as follows: current: 162-257A, voltage: 20.5-28V, swing width 3.6-11.5mm, edge dwell 180-297s, wire feeding speed 17-27cm / min, shielding gas flow 5.4-7.7L / min, welding speed 15.4-20.3cm / min, heat input 1.41-1.98kJ / mm, and the filling layer welding is a double welding gun.

[0080] The welding process of the cover layer is as follows: current: 142-214A, voltage: 20.6-26.4V, swing width 4.4-5.7mm, edge dwell 153-227s, wire feeding speed 17-27cm / min, shielding gas flow 5.3-6.8L / min, welding speed 15.8-20.3cm / min, heat input 1.22-1.52kJ / mm, and the cover layer welding is a double welding gun.

[0081] When welding defects such as welding gun leakage, weld surface porosity, poor weld formation, etc. occur, internal repair welding should be carried out immediately and the welding process should be carried out as required.

[0082] Pay attention to the fusion of the arc on both sides of the groove and adjust the swing width of the welding gun at any time.

[0083] When the conductive nozzle is burned or hits the wall, it should be carefully polished and cleaned to completely remove copper contamination. If necessary, re-beveling and welding should be performed to avoid thermal cracks.

[0084] Before welding the next weld, use a powered angle grinder to grind away the dense pores, arc starting points or high convex parts of the completed weld. After the weld is completed, the spatter on the joint surface should be cleaned.

[0085] The welding of the next weld should be started after the previous weld is completed.

[0086] Interlayer welding defects found during the welding process should be repaired immediately by grinding, welding, etc.

[0087] When performing repair welding, the defects should be completely removed and the original automatic welding process should be used for the repair work.

[0088] The length of each repair should be greater than 100mm. If the distance between two adjacent repairs is less than 50mm, it should be repaired as one defect. During the repair welding process, the interlayer temperature should be guaranteed to meet the requirements of the welding process regulations.

[0089] When welding the cover weld, the subsequent weld should cover at least 1 / 3 of the width of the previous weld.

[0090] Each weld should be completed continuously. Welds that cannot be completed on the same day should be welded to 50% of the steel pipe wall thickness and placed in a windproof shed. Before welding the next day, it should be preheated to the minimum preheating temperature required by the welding procedure specification.

[0091] Each construction unit should not leave more than 5 openings in the windbreak shed on the same day.

[0092] When the gas pressure in the welding shielding gas bottle is lower than 0.98MPa, the use should be stopped.

[0093] The gas flow of each welding gun of the internal welding machine shall be monitored for compliance at least once a day using a portable gas flow meter.

[0094] When the weld excess height is too high, grinding should be carried out to avoid damaging the base material. If grinding damages the base material, the wall thickness of the steel pipe after grinding should not be less than 95% of the nominal wall thickness of the steel pipe.

[0095] When the weld needs to be cut on site, the cutting width should be at least 5mm wider than the cover weld on each side to remove the heat affected zone of the original weld.

[0096] The measuring instruments used on site should comply with relevant national regulations.

[0097] (8) Nondestructive testing

[0098] Carry out appearance inspection and non-destructive testing according to the design documents adopted for this project.

[0099] Nondestructive testing should follow up the work and provide timely feedback on the details of unqualified welds to facilitate timely adjustment of welding parameters by automatic welding.

[0100] (9) Fracture toughness test

[0101] Conduct fracture toughness tests and mechanical properties tests on welded joints.

[0102] Examples 1-6

[0103] A GTAW+FCAW composite welding method for X80 pipeline steel comprises the following steps:

[0104] Prepare the base material, an X80 steel pipe with a wall thickness of 18.4 mm and a pipe diameter of 1219 mm, and the mass percentages of the main chemical components are: C: 0.04-0.08%, Si: 0.15-0.30%, Mn: 1.50-1.90%, P≤0.015%, S≤0.005%, Cr: 0.20-0.40%, Mo: 0.08-0.30%, Ni: 0.10-0.30%, Al: 0.03-0.05%, Nb: 0.05-0.08%, and Ti: 0.010-0.025%.

[0105] (1) Pipe cleaning

[0106] The grooves on the inner and outer surfaces of the steel pipe and the area within 150mm on both sides should be cleaned to be free of scaling, wear, rust, slag, grease, paint and other harmful substances that affect the welding quality. The grooves and the area within 25mm on both sides should be cleaned mechanically until the metallic luster is revealed.

[0107] (2) Joint design

[0108] The pipe end bevel should be processed on site with a beveling machine. The angle and size of the pipe end bevel should meet the following requirements (see Appendix Figure 1 Requirements):

[0109] Joint type: butt joint, groove type: composite;

[0110] The processing dimensions of the groove are as follows: groove surface angle: β = 5° ± 1° α = 45° ± 1° γ = 37.5° ± 1°; blunt edge (P): 1.1 ± 0.2 mm back pad: no gap (b): 0-0.5 mm; height from inflection point to inner wall (H): 5.1 ± 0.2 mm; half groove width (W): 3.4-4.1 mm inner groove height (h): 1.6 ± 0.2 mm. Misalignment: ≤ 2.0 mm, the local length greater than 2.0 mm and not greater than 2.5 mm is not greater than 50 mm; excess height: 0-2.0 mm, the local length greater than 2.0 mm and not greater than 3.0 mm is not greater than 50 mm; cover weld width: each side of the groove upper opening should be widened by 1.0 mm to 2.0 mm, and the control parameters of each embodiment are shown in Table 1.

[0111] Table 1 Groove processing dimensions of Examples 1-6

[0112]

[0113]

[0114] Table 1: Groove processing dimensions of embodiments 1-6

[0115]

[0116] Before groove processing, the grinding condition of the inner and outer pipe welds at the pipe end should be checked to ensure that the inner and outer pipe welds within 150mm of the pipe end are ground to be flush with the parent material.

[0117] The processed welding groove surface is visually inspected and the groove surface is required to be smooth, without processing grooves, delamination, cracks and other defects.

[0118] The processed groove should be used within 24 hours to avoid the influence of groove rust and dirt corrosion on welding quality.

[0119] (3) Welding material management

[0120] The root welding layer and the hot welding layer are tungsten inert gas arc welding (GTAW), the welding material is Atlantic welding wire ER55-Ni1, and the welding wire diameter is Φ2.5mm. The filling and cover welding layers are flux-cored arc welding (FCAW), and the welding wire is American HOBART FABCO91K2-M, with a diameter of Φ1.2.

[0121] The storage of welding wire should be carried out in accordance with the requirements of the manufacturer's product manual. The unpacked welding wire should be used up continuously and not be damp or rusted. When welding the next day, at least 2m of welding wire should be removed before welding.

[0122] (4) Nozzle pairing

[0123] When the internal welding machine is aligned, no scratches, abrasion marks or oil stains are left on the inner surface of the steel pipe. The distance between adjacent circumferential welds should be greater than 1.0 times the diameter of the steel pipe. The weld of the straight seam pipe should be in the upper half of the circumference of the steel pipe. The track positioner should be used to assist in the installation of the welding trolley track to ensure that the welding gun is aligned with the center of the welding groove around the entire pipe. Before the pipe mouth is aligned, the inspection reference line should be marked according to the AUT inspection requirements.

[0124] (5) Preheating interlayer temperature

[0125] Preheating interlayer temperature: the preheating temperature is controlled between 110 and 150°C, the interlayer temperature is controlled between 80 and 150°C, the heating method is electric induction heating, and the control parameters of each embodiment are shown in Table 2.

[0126] Table 2 Preheating interlayer temperature of Examples 1-6

[0127] Example Preheating temperature (℃) Interlayer temperature (℃) 1 110 80 2 120 100 3 125 120 4 130 130 5 140 140 6 150 150

[0128] The anti-corrosion layer of the steel pipe is not damaged during preheating, and the surface dirt should be removed after preheating. Use an infrared thermometer, contact thermometer or temperature pen to monitor whether the preheating temperature meets the requirements of the process regulations. It is advisable to monitor the interlayer temperature on the weld metal about 200mm in front of the welding direction. Interrupt welding, and when the interlayer temperature cools down to below the minimum temperature required by the welding process regulations when resuming welding, reheat the weld to the preheating temperature.

[0129] (6) Internal welding machine evacuation

[0130] The steel pipe being welded should be in a stable state. When the steel pipe after the root welding is completed is placed on the pipe pier, the steel pipe is not subjected to vibration and impact.

[0131] (7) Welding

[0132] A composite welding method, wherein the root welding layer and the hot welding layer are welded by argon tungsten arc welding (GTAW for short), and the filling layer and the cover layer are welded by flux-cored arc welding (FCAW).

[0133] The root welding layer welding process is: current: 126-176A, voltage: 9.9-14.3V, shielding gas flow rate 8-18L / min, welding speed 5.5-9.9cm / min, heat input 1.32-1.56kJ / mm.

[0134] The welding process of the hot welding layer is as follows: current: 162-214A, voltage: 10.3-14.8V, shielding gas flow rate 8-18L / min, welding speed 6.5-11cm / min, heat input 1.52-1.79kJ / mm, and the hot welding layer is welded with a single welding gun.

[0135] The filling layer welding process is as follows: current: 162-257A, voltage: 20.5-28V, swing width 3.6-11.5mm, edge dwell 180-297s, wire feeding speed 17-27cm / min, shielding gas flow 5.4-7.7L / min, welding speed 15.4-20.3cm / min, heat input 1.41-1.98kJ / mm, and the filling layer welding is a double welding gun.

[0136] The welding process of the cover layer is as follows: current: 142-214A, voltage: 20.6-26.4V, swing width 4.4-5.7mm, edge dwell 153-227s, wire feeding speed 17-27cm / min, shielding gas flow 5.3-6.8L / min, welding speed 15.8-20.3cm / min, heat input 1.22-1.52kJ / mm. The cover layer welding is a double welding gun. The control parameters of each embodiment are shown in Table 3.

[0137] Single-pass or multi-pass welding for each layer: 2 passes for 1 layer of cap welding, and single pass for the rest of the layers; single-wire or multi-wire filling: single wire (per welding gun); wire dry extension length: 10-15mm; welding gun swing mode: root welding - no swing / hot welding, filling, capping - flat swing; post-weld insulation, slow cooling and heat treatment: not required; arc starting or arc ending requirements: it is strictly forbidden to start the arc on the pipe wall outside the groove, and the arc starting or arc ending points of adjacent welds in different layers should be staggered by more than 30mm; the time interval between the end of root welding and the start of hot welding: ≤16min.

[0138] Table 3 Welding process of Examples 1-6

[0139]

[0140] Table 3: Welding process of embodiments 1-6

[0141]

[0142]

[0143] After welding is completed, the order of the welds is as shown in the attached Figure 2 As shown, 1 is the root welding layer, 2 is the hot welding layer, 3-1 is the filling layer, 3-2 is the filling layer, 4-1 is the filling layer, 4-2 is the filling layer, 5-1 is the covering layer, and 5-2 is the covering layer.

[0144] (8) Nondestructive testing

[0145] The non-destructive testing results are qualified.

[0146] (9) Fracture toughness test and weld joint mechanical properties test: fracture toughness test and weld joint mechanical properties test shall be carried out in accordance with standard requirements.

[0147] The fracture toughness test results are shown in Table 4. The CTOD value meets the national pipeline network DEC requirement of not less than 0.254 mm. The corresponding fracture morphology of Examples 1-6 is shown in Table 4. Figure 3-8 As shown in the figure, the fracture form is ductile fracture, with obvious macroscopic plastic deformation, large plastic deformation, irregular fracture shape, equiaxed dimples, and large and deep dimples are evenly distributed and numerous, indicating good fracture toughness. The mechanical properties of the welded joint are shown in Table 5.

[0148] Table 4 Fracture toughness test results of Examples 1-6

[0149]

[0150] Table 5 Mechanical properties test results of welded joints of Examples 1-6

[0151]

[0152]

[0153] The joint of the present invention is designed to process a composite groove, and the welding method is a composite welding method, namely, tungsten inert gas arc welding (GTAW for short) and flux-cored arc welding (FCAW for short). The obtained X80 pipeline steel welded joint has good fracture toughness under low temperature conditions of -10°C, and the CTOD values ​​of the weld center and the heat-affected zone at the three positions of 0, 9 and 6 meet the national pipeline network DEC requirement of not less than 0.254 mm, thereby ensuring the service performance of the X80 pipeline steel welded joint under low temperature conditions of -10°C. The fracture form of the fracture is ductile fracture, indicating that the fracture toughness is good. Among the mechanical properties of the welded joint, the tensile strength meets the standard requirement of being greater than 625Mpa, the impact energy is much greater than the standard requirement of Akv (J)>60J, the bending test result is free of cracks and qualified, and the non-destructive testing result is qualified.

[0154] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A GTAW+FCAW composite welding method for X80 pipeline steel, characterized in that: The following steps are involved: (1) Pipe mouth cleaning: The grooves on the inner and outer surfaces of the steel pipe and the area within 150mm on both sides should be cleaned. There should be no scaling, wear, rust, slag, grease, paint or other harmful substances that affect the welding quality; (2) Joint design: The pipe end bevel should be processed on site using a beveling machine; (3) Welding material management: The storage of welding wire should be carried out in accordance with the requirements of the manufacturer's product instructions. Welding wire that shows signs of damage or deterioration should not be used for welding; (4) Pipe end assembly: When the internal welding machine is used for assembly, no scratches, abrasion marks or oil stains should be left on the inner surface of the steel pipe. The hammering method should not be used to correct the misalignment; (5) Preheating interlayer temperature: the preheating temperature is controlled at 110-150°C, and the interlayer temperature is controlled at 80-150°C; (6) Evacuation of the internal welding machine: When the steel pipe after the root welding is completed is placed on the pipe pier, the steel pipe should not be subjected to vibration and impact; (7) Welding: root welding layer welding method: GTAW, hot welding layer welding method: GTAW, filling layer welding method: FCAW, cover layer welding method: FCAW; (8) Nondestructive testing: Nondestructive testing should follow up the work and provide timely feedback on the details of the unqualified welds to facilitate the timely adjustment of welding parameters by automatic welding; (9) Fracture toughness test and weld joint mechanical properties test: fracture toughness test and weld joint mechanical properties test shall be carried out according to standard requirements.

2. The X80 pipeline steel GTAW+FCAW composite welding method according to claim 1, characterized in that: In the step (2) of the joint design process, the groove processing dimensions are as follows: misalignment: ≤2.0mm, the local length greater than 2.0mm and not greater than 2.5mm is not greater than 50mm; excess height: 0-2.0mm, the local length greater than 2.0mm and not greater than 3.0mm is not greater than 50mm; cover weld width: each side of the groove top should be widened by 1.0-2.0mm.

3. The X80 pipeline steel GTAW+FCAW composite welding method according to claim 1, characterized in that: In the joint design process (2), the angle and size of the pipe end groove should meet the following requirements: groove surface angle: β = 5° ± 1°, α = 45° ± 1°, γ = 37.5° ± 1°; blunt edge (P): 1.1 ± 0.2 mm, backing pad: none, butt clearance (b): 0-0.5 mm; height from inflection point to inner wall (H): 5.1 ± 0.2 mm; half groove width (W): 3.4-4.1 mm, inner groove height (h): 1.6 ± 0.2 mm; joint type is butt joint, and groove type is composite.

4. The X80 pipeline steel GTAW+FCAW composite welding method according to claim 1, characterized in that: In the welding process of step (7), the root welding layer and the hot welding layer are welded by tungsten inert gas arc welding, and the filling layer and the cover layer are welded by flux-cored arc welding.

5. A GTAW+FCAW composite welding method for X80 pipeline steel according to any one of claims 1 to 4, characterized in that: In the welding process of step (7), the root welding layer welding process is: current: 126-176 A, voltage: 9.9-14.3 V, shielding gas flow rate 8-18 L / min, welding speed 5.5-9.9 cm / min, heat input 1.32-1.56 kJ / mm.

6. A GTAW+FCAW composite welding method for X80 pipeline steel according to any one of claims 1 to 4, characterized in that: In the welding process of step (7), the hot welding layer welding process is as follows: current: 162-214A, voltage: 10.3-14.8V, shielding gas flow rate 8-18L / min, welding speed 6.5-11cm / min, heat input 1.52-1.79kJ / mm, and the hot welding layer is welded with a single welding gun.

7. A GTAW+FCAW composite welding method for X80 pipeline steel according to any one of claims 1 to 4, characterized in that: In the welding process of step (7), the filling layer welding process is as follows: current: 162-257A, voltage: 20.5-28V, swing width: 3.6-11.5mm, edge dwell time: 180-297s, wire feeding speed: 17-27cm / min, shielding gas flow rate: 5.4-7.7L / min, welding speed: 15.4-20.3cm / min, heat input: 1.41-1.98kJ / mm, and the filling layer welding is performed with a double welding gun.

8. A GTAW+FCAW composite welding method for X80 pipeline steel according to any one of claims 1 to 4, characterized in that: In the welding process of step (7), the welding process of the cover layer is as follows: current: 142-214A, voltage: 20.6-26.4V, swing width 4.4-5.7mm, edge dwell 153-227s, wire feeding speed 17-27cm / min, shielding gas flow 5.3-6.8L / min, welding speed 15.8-20.3cm / min, heat input 1.22-1.52kJ / mm, and the cover layer welding is performed with a double welding gun.

9. A GTAW+FCAW composite welding method for X80 pipeline steel according to any one of claims 1 to 4, characterized in that: Under the low temperature condition of -10°C, the fracture toughness CTOD value of the weld of the welding method is ≥0.254mm.

10. A GTAW+FCAW composite welding method for X80 pipeline steel according to any one of claims 1 to 4, characterized in that: The welding method has the following mechanical properties: the tensile strength Rm≥625Mpa, the impact energy Akv (J)≥60J, and the bending test result shows no cracks.

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