Method for repairing ablation cracks of large elbow pipe

Abstract

The invention relates to a method for repairing ablation cracks of a large elbow, and relates to the technical field of repairing. The repair method provided by the invention comprises the following steps: (1) sealing and covering each communication interface of the large elbow before polishing, polishing to remove a crack defect area of the large elbow, and then cleaning and naturally drying; (2) performing welding repair on the crack defect area to obtain a repaired large elbow pipe, performing heat treatment on the repaired large elbow pipe, and then performing nondestructive inspection; the crack defect area is the junction of two materials in the large bent pipe, and the materials are GH3030 and GH3044. The welding repair effect is excellent. The hardness value of the completely repaired welding area meets the national standard and the national military standard, the welding area can be continuously used, the service life of the large bent pipe is prolonged, cost is reduced, efficiency is improved, and sustainable development is achieved.

Description

Technical Field

[0001] This invention relates to the field of repair technology, specifically to a method for repairing ablation cracks in a large bend pipe. Background Technology

[0002] The large bend is a crucial hot-end component of the X-engine, affecting the overall performance of the engine. It is welded from two materials: GH3044, which offers better high-temperature resistance in the high-temperature range, and GH3030, which offers lower cost and suitable low-temperature performance in the medium- and low-temperature range. During service, the large bend is susceptible to cracks (crack 1, crack 2) at the interface between the two materials (GH3030 and GH3044) due to high-temperature combustion gases and alternating thermal stress. Currently, the solution for these excessive cracks is replacement with new parts. However, new parts are expensive, with high procurement costs and long lead times, which cannot meet the X-engine's repair cycle and severely impacts the normal repair and delivery of this component. Therefore, independent maintenance and support are crucial and urgent. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a method for repairing ablation cracks in large bend pipes. This invention achieves excellent welding repair results. The hardness value of the fully repaired welded area meets national and military standards, allowing for continued service and extending the service life of the large bend pipe. This reduces costs, increases efficiency, and promotes sustainable development.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: The purpose of this invention is to provide a method for repairing ablation cracks in large bend pipes, comprising the following steps: (1) Before grinding, seal and cover all the connecting interfaces of the large bend, grind to remove the crack and defect area of ​​the large bend, and then clean and air dry. (2) The crack defect area is repaired by welding to obtain the repaired large bend pipe, the repaired large bend pipe is heat treated, and then non-destructive testing is performed. The crack defect area is the junction of two materials in the large bend pipe, and the materials are GH3030 and GH3044.

[0005] The beneficial effects of this invention are: Argon arc welding technology has the characteristics of good protection, high weld quality, high joint strength, and small deformation, and is widely used in manufacturing fields such as aerospace. For the repair of dissimilar material welds with excessive cracks in large bends, this invention achieves stable process, excellent weld quality, and short repair cycle. Specifically targeting the repair of excessive cracks in the large bends of X-engines, this invention develops an additive repair process for large bends based on Argon arc welding of dissimilar materials and post-weld heat treatment.

[0006] (1) This invention establishes a complete repair process for the ablation fault of the large bend of the aero-engine. In response to the excessive cracks that appear at the joint of dissimilar materials in the large bend, an additive repair process based on dissimilar material argon arc welding technology is proposed to ensure that the size and performance of the large bend after repair reach or exceed the original state.

[0007] (2) This invention utilizes HGH3044 for optimized welding of large bends made of GH3044 and GH3030 materials, resulting in excellent welding performance. After repair, the large bend is further heat-treated to remove residual stress, prevent deformation, and stabilize the dimensions of the parts. The fully repaired area of ​​the large bend can operate at a high temperature of 850℃. The hardness value of the welded area of ​​the fully repaired large bend meets national and military standards.

[0008] (3) After repair, the large bend was inspected for kerosene leakage, fluorescence, and X-ray, and the repair requirements were met. Fluorescence and X-ray inspection of the repaired area showed no brazing defects. The large bend repaired using this process showed no cracks after 50 cycles of 1100℃ water-cooled-room temperature thermal shock. It can continue to be used, extending the service life of the large bend, reducing costs and increasing efficiency, and achieving sustainable development.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, in step (1), paper tape is used for sealing and covering.

[0011] The advantages of adopting the above-mentioned further solution are: preventing metal shavings from entering, and allowing for removal after grinding.

[0012] Furthermore, the diameter of the cerium-tungsten electrode used for welding repair in step (2) is 1.0 mm to 2.5 mm, and the diameter of the welding wire is 1 mm to 2 mm.

[0013] The beneficial effects of adopting the above-mentioned further solutions are: ensuring arc stability and controllable molten pool.

[0014] Furthermore, the ambient temperature during welding is greater than or equal to 16°C, and the relative humidity is not greater than 60%.

[0015] The beneficial effects of adopting the above-mentioned further solutions are: reducing defects such as cracks and pores in the repaired area, and ensuring the stability of the quality of the repaired area.

[0016] Furthermore, the power source selected for welding is a DC power source with a steep drooping external characteristic.

[0017] The advantages of adopting the above-mentioned further solutions are: welding parameters can be easily adjusted, and the system can operate stably under the required parameter specifications.

[0018] Furthermore, the welding voltage in step (1) is between 330V and 430V.

[0019] Furthermore, the welding thickness is 0.3mm to 2.5mm.

[0020] The beneficial effects of adopting the above-mentioned further solutions are: ensuring stable operation of the welding machine and ensuring arc stability when welding materials of different thicknesses.

[0021] Furthermore, the welding in step (1) uses DC positive polarity, with a current of 10A~65A and a gas flow rate of 3L / min~28L / min.

[0022] The beneficial effects of adopting the above-mentioned further solutions are: ensuring appropriate penetration depth, controlling heat input, effectively isolating air, and preventing weld oxidation.

[0023] Furthermore, the equipment should operate normally and have functions such as early gas supply, delayed gas shut-off, high-frequency arc initiation, and current attenuation.

[0024] Furthermore, the welding torch should be lightweight, flexible, have good accessibility, and good conductivity. The nozzle and conductive parts should have good cooling, and the handle and conductive parts should have good insulation. The electrode chuck should reliably clamp the tungsten electrode. A heat-resistant ceramic nozzle should be used, and the shape of the nozzle cavity should allow the airflow to have a certain stiffness to obtain a good protective effect. There should be no draft in the welding room. Bottled argon or liquid argon canisters should be stopped and replaced when the pressure is below 1.0 MPa.

[0025] Furthermore, cerium tungsten electrodes are selected for the tungsten electrode. After grinding, the tip of the tungsten electrode should be a flat-headed cone with a diameter approximately half that of the tungsten electrode. When cleaning the welding wire, first use a white silk cloth soaked in anhydrous ethanol or acetone to remove oil and dirt from the surface of the welding wire. Then, use 240# metallographic sandpaper to clean the oxides on the surface of the welding wire. Finally, use a white silk cloth soaked in anhydrous ethanol or acetone to clean it again, and finally blow it dry with compressed air.

[0026] Furthermore, TIG welding is used, with HGH3044 welding wire. The tungsten electrode diameter is selected as Φ1.0mm~2.5mm, and the welding wire diameter is Φ1mm~2mm. During the welding process, argon gas is used for protection on the back side of the weld. When there are many welding parts, symmetrical welding, intermittent welding, or welding adjacent parts are carried out after the temperature of the previous weld has decreased before welding.

[0027] The beneficial effects of adopting the above-mentioned further solutions are: controlling heat input, reducing deformation during the repair process, and ensuring the compatibility of the chemical composition and overall performance of the weld with the base material.

[0028] Furthermore, in step (2), when the crack defect area is on the uncoated surface, mechanical grinding is used to remove the oxides of the crack defect area and the surrounding surface until the metallic luster is exposed.

[0029] The beneficial effects of adopting the above-mentioned further solutions are: reducing the impact of oxides on weld quality, preventing defects such as porosity, inclusions, and lack of fusion during welding, and ensuring reliable weld quality.

[0030] Furthermore, in step (2), when the crack defect area is on the coating surface, mechanical grinding is used to remove the coating around the crack defect area by 20mm to 40mm until the metallic luster is exposed.

[0031] The beneficial effects of adopting the above-mentioned further solutions are: reducing the impact of coatings and oxides on the quality of the weld, ensuring good weld formation and reliable quality.

[0032] Furthermore, the heat treatment described in step (2) specifically involves: holding the part at 840℃~860℃ for 30 minutes in an air atmosphere, followed by air cooling.

[0033] The beneficial effects of adopting the above-mentioned further solutions are: In view of the influence of post-weld thermal stress and subsequent coating repair processes, the present invention uses heat treatment for stress relief annealing after dissimilar material welding of large bends, thereby further weakening the workpiece deformation problem. Attached Figure Description

[0034] Figure 1 The flowcharts for repairing large bends in Embodiments 1 and 2 of the present invention are shown. Figure 2 This is a schematic diagram of the coating surface of the large bent pipe part in Embodiment 1 of the present invention; Figure 3 This is a drawing of the large bend pipe component from Embodiment 1 of the present invention; Figure 4 Metallographic images of welds made of GH3030 and GH3044 base materials in this invention; Figure 5 Metallographic image of the weld seam of the GH3044 base material of this invention; Figure 6 This is a diagram showing the dimensions of the room temperature tensile specimen of the present invention. Figure 7 This is a dimensional diagram of the high-temperature tensile specimen of the present invention; Figure 8 This is a diagram showing the average tensile strength of each specimen at room temperature in this invention. Figure 9 This is a graph showing the average high-temperature tensile strength of each specimen in this invention. Figure 10 This is a diagram showing the dimensions of the thermal shock specimen of the present invention. Figure 11 The inner cavity shape of the heat-resistant ceramic nozzle in Embodiment 1 of the present invention is shown. Detailed Implementation

[0035] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0036] Example 1: like Figure 1 As shown: (1) Before grinding, seal all connecting joints of the large bend with masking tape to prevent metal shavings from entering. Remove the tape after grinding. For cracks on the non-coated surface of the large bend, use a Saint-Nair S-6633 pneumatic grinder to completely grind away the crack defects and the surface oxides around the crack within 10mm~20mm until the metal luster is exposed; for cracks on the coated surface (such as the coated surface of the large bend part), use a Saint-Nair S-6633 pneumatic grinder to completely grind away the crack defects and the surface oxides within 10mm~20mm around the crack until the metal luster is exposed; for cracks on the coated surface (such as the coated surface of the large bend part), use a masking tape to seal all connecting joints of the large bend with masking tape to prevent metal shavings from entering. Figure 2 As shown in the figure, the coating around the crack (20mm~40mm) is completely removed by using a Saint-Nair S-6633 pneumatic grinder until the metal luster is exposed. Then, the brazed area is cleaned with a white silk cloth soaked in acetone or anhydrous ethanol and then allowed to dry naturally. (2) Cracks 1 appearing at the joint of the two materials GH3044 and GH3030 in the large bend (e.g. Figure 3 The welding repair was performed using a DC power supply with a steep droop characteristic (as shown). The equipment operated normally and had functions such as pre-gas supply, delayed gas cut-off, high-frequency arc initiation, and current attenuation. The grid voltage of the welding power supply was within the range of (380±50)V. The welding torch was lightweight, flexible, and had good weld accessibility and conductivity. The nozzle and conductive parts had good cooling, and the handle and conductive parts had good insulation. The electrode chuck reliably clamped the tungsten electrode. A heat-resistant ceramic nozzle was used, and the nozzle's internal cavity shape (as shown) Figure 11 (As shown) The airflow should have a certain stiffness to achieve a good protective effect; the indoor temperature of the welding room should not be lower than 16℃, the relative humidity should not be greater than 60%, and cross drafts are not allowed; bottled argon or liquid argon tanks should be stopped and replaced when the pressure is lower than 1.0MPa. Cerium tungsten electrodes should be used. After grinding, the tip of the tungsten electrode should be a flat-headed cone with a diameter approximately half that of the tungsten electrode; protective goggles should be worn during grinding to prevent metal particles from entering the eyes; when cleaning the welding wire, first use a white cloth soaked in anhydrous ethanol or acetone to degrease and clean the surface of the welding wire, then use 240# metallographic sandpaper to clean the oxides on the surface of the welding wire, and finally clean it again with a white cloth soaked in anhydrous ethanol or acetone, and finally dry it with compressed air; Welding was performed using TIG welding (welding wire grade HGH3044), with a welding thickness of 0.3mm~2.5mm, a current of 10A~65A, a gas flow rate of 3L / min~28L / min, DC positive polarity, a tungsten electrode diameter of Φ of 1.0mm~2.5mm, and a welding wire diameter of Φ of 1mm~2mm. During welding, argon gas was used for protection on the back side of the weld. When there were multiple welding sections, symmetrical welding, intermittent welding, or welding adjacent sections after the temperature of the preceding weld had decreased were used to obtain the repaired large bend. (3) The repaired large bend was inspected using a customized fluorescent flaw detector from Shanghai Cihai Nondestructive Testing Equipment Manufacturing Co., Ltd. and an ISOVOLT320HS industrial X-ray flaw detector from General Electric. No cracks or defects were found. For the welding of the U-shaped groove and the outlet groove, kerosene penetration testing was performed. Kerosene was injected into the welding area for 30 minutes. There were no signs of kerosene leakage, such as discoloration or wet spots, in the chalk dust around the welded area. After the inspection, the kerosene and chalk dust were cleaned up. After welding, stress relief heat treatment and dimensional stabilization were performed. The parts were held at 830℃~850℃ for 30 minutes in an air atmosphere and then air-cooled.

[0037] Example 2: The only difference between this embodiment and embodiment 1 is that the area to be repaired is crack 2 at the junction of GH3044 and GH3030 materials. All other conditions and steps are the same as in embodiment 1.

[0038] Comparative Examples 1-2: The only difference between Comparative Examples 1 and 2 and Example 1 is that the polishing range of the oxide in step (2) is different. The polishing range of Comparative Examples 1 and 2 is shown in Table 1: Table 1 Performance testing: 1. Oxide and coating removal experiments As shown in Examples 1 and Comparative Examples 1, 2, 3, and 4, a pneumatic grinder is used to remove oxides and coatings from the repair area. When the oxide removal range is less than 10 mm and the coating removal range is less than 20 mm, some oxides and coatings will enter the weld during the welding process, resulting in unqualified weld appearance and defects such as porosity, inclusions, cracks, and incomplete penetration on the weld surface. When the oxide removal range is 10mm~20mm and the coating removal range is 20mm~40mm, the weld appearance is good, with no defects such as porosity, inclusions, cracks, or incomplete penetration. When the oxide removal is above 20mm and the coating removal is above 40mm, the weld appearance is good, but the grinding range is increased, and the purpose of cost reduction and efficiency improvement is not achieved.

[0039] 2. Metallographic Experiment Rectangular specimens containing complete fusion lines were cut from the center region of the weld of the GH3030+GH3044 weld joint using an electrical discharge wire cutting machine. The observation surfaces were ground and polished, and then etched using a solution of 1g CuCl2 + 20 ml C2H6O + 20 ml HCl. Microstructure analysis was performed using a GP-L700 metallographic microscope from Kunshan Gaopin Precision Instruments Co., Ltd. After processing the GH3044 material, butt welding was performed, and the microstructure of the weld joint was observed. The metallographic examination results are as follows: Figure 4 , Figure 5 As shown.

[0040] Depend on Figure 4 , Figure 5 We can obtain: (1) Figure 4 (a) is a microstructure diagram of the GH3030 substrate, whose matrix is ​​a typical austenitic structure. Figure 4 (b) is a microstructure diagram of the GH3044 matrix, which has an equiaxed crystal structure with relatively uniform carbides distributed at the grain boundaries. Figure 4 (e) is a metallographic image of the weld area, showing that the entire weld has a uniform equiaxed grain structure. The weld near the fusion line exhibits typical columnar and dendritic grains. During welding, the molten pool cools rapidly, and the columnar and dendritic grains gradually grow into equiaxed grains, such as... Figure 4 As shown in (c) and (d), the metallographic test results show that after argon arc welding, the entire welded area of ​​GH3030 and GH3044 materials is free of cracks, porosity, and slag inclusions, meeting the technical requirements.

[0041] (2) Figure 5 (a) is a microstructure diagram of the GH3044 matrix, which has an equiaxed crystal structure with some carbides distributed at the grain boundaries. Figure 5 (b) is a metallographic image of the weld area, showing that the entire weld has a uniform equiaxed grain structure. The weld near the fusion line exhibits typical columnar grains; during welding, the molten pool cools rapidly, and the columnar grains gradually grow into equiaxed grains, such as... Figure 5 As shown in (c), the metallographic test results show that after argon arc welding, the entire welded area of ​​GH3044 material is free of cracks, pores, and slag inclusions, meeting the technical requirements.

[0042] 3. Hardness test Microhardness was measured using a Vickers microhardness tester on the cross-section of the weld repair area. The load was 1 kgf, and the loading time was 10 s. At least five points were drilled on each specimen cross-section, covering the weld area, heat-affected zone, and substrate. The average hardness values ​​of GH3044 and GH3030 specimens are shown in Tables 2 and 3. Table 2 Average Hardness Test Table for GH3044+GH3044 Table 3 Average Hardness Test Table for GH3030+GH3044 From Tables 2 and 3, we can obtain: The hardness test results show that the Vickers hardness of the GH3044 and GH3030 base materials is basically the same before and after the stress-relief heat treatment, indicating that the stress-relief heat treatment did not affect the original heat treatment state of the base materials. For GH3044 welded joints of the same metal, the hardness of the weld and heat-affected zone is lower than that of the base material. This may be because heating the base material during welding causes some of the carbides in the base material to dissolve, thereby reducing the hardness of the weld and heat-affected zone.

[0043] According to the "China Aviation Materials Handbook: Deformed High-Temperature Alloys, Cast High-Temperature Alloys, 2nd Edition" and GB / T 1172-1999 "Conversion Values ​​of Hardness and Strength of Ferrous Metals", the hardness of the GH3044 base material should not exceed 285 HBS, i.e., not exceed 288 HV. The hardness value of GH3044 materials welded using argon arc welding meets the standard requirements. Due to the influence of material composition, thermal cycling differences, and other factors, the Vickers hardness of different areas of the welded joint of dissimilar materials exhibits different characteristics. According to GJB 1952A-2020 "Specification for Cold-Rolled High-Temperature Alloy Sheets for Aerospace Use", only the tensile strength of GH3030 is required. Under the condition of meeting the tensile strength requirement, the hardness value is based on the measured value and is not used as a basis for judgment. The hardness values ​​of GH3030 and GH3044 materials welded using argon arc welding meet the technical standard requirements.

[0044] 4. Strength Test Tensile properties were assessed using a universal tensile testing machine to determine the impact of weld repair on the mechanical properties of the large bend. All specimens were prepared by wire cutting and mechanically ground to remove weld excess, ensuring the weld repair area was flush with the substrate. Burrs were then removed with sandpaper. The test temperatures were divided into two groups: room temperature and 850℃. The dimensions of the room temperature tensile specimens are shown below. Figure 6 As shown, the dimensions of the tensile specimen at 850℃ are as follows: Figure 7 As shown, the test speed was 0.5 mm / min, and the specimen condition and test results are as follows. Figure 8 , Figure 9 As shown.

[0045] Depend on Figures 6-9 We can obtain: The room temperature tensile strength of the GH3044 specimen decreased from 886.67 MPa before welding to 764.33 MPa after TIG welding, indicating that the strength after TIG welding repair was 86.2% of the original strength. The room temperature tensile strength of the GH3044+GH3044 specimen decreased from 679.33 MPa before welding to 587.33 MPa after TIG welding, indicating that the strength after TIG welding repair was 86.4% of the original strength. The high-temperature tensile strength of the GH3044 specimen at 850℃ decreased from 283.29 MPa before welding to 242.13 MPa after TIG welding, indicating that the strength after TIG welding repair was 85.5% of the original strength. The high-temperature tensile strength of the GH3044+GH3044 specimen at 850℃ decreased from 157.72 MPa before welding to 155.25 MPa after TIG welding, indicating that the strength after TIG welding repair was 98.4% of the original strength. According to the HB5456-90 standard "Quality Inspection of High Temperature Alloy Tungsten Inert Gas Welding", the tensile strength of the welded joint after removing the excess weld height shall not be less than 85% of the lower limit of the base material strength. The large bend crack repaired by argon arc welding meets the technical standard requirements.

[0046] 5. Thermal shock test Large bends are subjected to prolonged exposure to high-temperature combustion gases and alternating thermal stress, resulting in significant thermal shock and temperature gradients on their surface. This, combined with component expansion and contraction and boundary constraints, creates severe thermal stress on the surface and within the structure, potentially leading to cracks. To simulate the working environment of large bends, the thermal shock resistance of component materials before and after repair was compared under rapid cooling and heating conditions to assess the feasibility of the repair process.

[0047] The sample dimensions are 30mm × 7mm × 1mm, such as Figure 10 As shown, an artificial V-shaped defect was created on the unwelded raw material sample, and one V-shaped defect was created on both the weld and the base material of the welded sample. The specific dimensions are as follows. Figure 10 As shown. A high-temperature box furnace was used for the experiment. The furnace temperature was set to 1100℃, and the holding time after reaching the specified temperature was no less than 30 minutes. The sample was placed in the furnace and held for 4-5 minutes after reaching the specified temperature. Then, the sample was quickly immersed in water at 10℃-30℃ for 5-8 seconds to cool. The immersion depth of the sample (distance from the top of the sample to the water surface) should be greater than 100 mm. This constitutes one cycle. After each cycle, the surface condition of the sample was inspected with a 10x magnifying glass and recorded. Photographs were taken after every five cycles until cracks appeared in the sample, at which point the thermal shock test was stopped.

[0048] The test pieces were divided into four groups, with three test pieces in each group (DWG: large bend pipe, YC: raw material, YHH: argon arc welding, TH: stress relief annealing, RCJ: thermal shock).

[0049] Table 4 Comparison of Thermal Shock Experiments As shown in Table 4, no cracks were found in any group after 50 impacts, indicating that the thermal shock resistance of the base material and the weld is basically the same at 1100℃, which meets the technical requirements.

[0050] 6. Size inspection The dimensions of the large bends repaired in Examples 1 and 2 were inspected, and the requirements and results are shown in Table 5. Table 5 Large Bend Pipe Dimension Inspection Checklist Table 5 shows that the repaired large bend meets the engine assembly requirements and drawing requirements.

[0051] 7. Test drive and testing The repaired large bends from Examples 1 and 2 were assembled into the engine for test runs. The engine's performance was tested during emergency, takeoff, rated, idle, and cruise phases. The test results are shown in Table 6. It can be seen that the repaired large bends do not affect engine performance and can meet the service requirements of the engine at each stage.

[0052] Table 6 Engine Test Parameters 8. Post-test run inspection The large bends repaired in Examples 1 and 2 were assembled onto the engine for testing. After the test, the large bends were removed for fluorescent flaw detection, X-ray flaw detection, and kerosene penetration testing. The repaired area of ​​the large bends showed no cracks and no kerosene leakage, which met the requirements for normal product use.

[0053] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for repairing ablation cracks in a large bend pipe, characterized in that, Includes the following steps: (1) Before grinding, seal and cover all the connecting interfaces of the large bend, grind to remove the crack and defect area of ​​the large bend, and then clean and air dry. (2) The crack defect area is repaired by welding to obtain the repaired large bend pipe, the repaired large bend pipe is heat treated, and then non-destructive testing is performed. The crack defect area is the junction of two materials in the large bend pipe, and the materials are GH3030 and GH3044.

2. The method for repairing ablation cracks in a large bend pipe according to claim 1, characterized in that, In step (1), paper tape is used for sealing and covering.

3. The method for repairing ablation cracks in a large bend pipe according to claim 1, characterized in that, The diameter of the cerium-tungsten electrode used for welding repair in step (2) is 1.0 mm to 2.5 mm, and the diameter of the welding wire is 1 mm to 2 mm.

4. The method for repairing ablation cracks in a large bend pipe according to claim 3, characterized in that, The ambient temperature during the welding repair is greater than or equal to 16℃ and the relative humidity is not greater than 60%.

5. The method for repairing ablation cracks in a large bend pipe according to claim 1, characterized in that, The voltage for welding repair described in step (2) is 330V~430V.

6. The method for repairing ablation cracks in a large bend pipe according to claim 1, characterized in that, The welding thickness for the welding repair described in step (2) is 0.3mm to 2.5mm.

7. The method for repairing ablation cracks in a large bend pipe according to claim 1, characterized in that, The welding repair described in step (2) uses DC positive polarity, with a current of 10A~65A and a gas flow rate of 3L / min~28L / min.

8. The method for repairing ablation cracks in a large bend pipe according to claim 1, characterized in that, In step (2), when the crack defect area is on the uncoated surface, the crack defect area and the surrounding surface oxides are removed by grinding until the metallic luster is exposed.

9. The method for repairing ablation cracks in a large bend pipe according to claim 1, characterized in that, In step (2), when the crack defect area is on the coating surface, the crack defect area and the surrounding 20mm~40mm of coating are removed by grinding until the metallic luster is exposed.

10. A method for repairing ablation cracks in a large bend pipe according to any one of claims 1 to 9, characterized in that, The heat treatment described in step (2) is as follows: the part is kept at 840℃~860℃ for 30 minutes in an air atmosphere, and then air-cooled.

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