Crack welding repair method for communicating pipe from platen superheater to high-temperature superheater

Abstract

The invention relates to a crack welding repair method for a communicating pipe from a platen superheater to a high-temperature superheater, and relates to the technical field of pipeline repair. S2, digging out cracks; s3, groove processing; s4, welding material selection; s5, preparation before welding; s6, welding operation; s7, postweld heat treatment; and S8, detecting and accepting after repairing. According to the crack welding repair method for the communicating pipe from the platen superheater to the high-temperature superheater, by optimizing the welding process and the heat treatment process, the problem that welding stress is not fully released is effectively solved, cracks caused by stress concentration are reduced, then strict welding parameter control and a scientific welding sequence are adopted, and the welding repair efficiency is improved. And in addition, by combining nondestructive testing technologies such as penetration testing and ultrasonic testing, accurate positioning and thorough repairing of cracks are achieved, crack omission caused by insufficient detection is avoided, the quality of the repaired pipeline is improved, the service life of the repaired pipeline is prolonged, and the operation risk is reduced.

Description

Technical Field

[0001] This invention relates to the field of pipeline repair technology, specifically a method for welding and repairing cracks in the connecting pipe from a screen-type superheater to a high-temperature superheater. Background Technology

[0002] The main reasons for cracks in the connecting pipe between the screen-type superheater and the high-temperature superheater are multifaceted. First, because the wall thickness on the elbow side is greater than that on the straight pipe side, it is difficult to precisely control the heat treatment temperature and isothermal time during heat treatment, resulting in insufficient release of welding residual stress. This is the primary cause of crack formation. Second, the greater thickness on the elbow side increases the discontinuity of the weld, thereby increasing stress concentration, which is also a secondary cause of crack formation. In addition, the heavy on-site installation tasks and the welders' failure to strictly follow the welding process, as well as the influence of factors such as deep peak shaving after the unit is put into operation, cause the weld stress to change continuously and remain at a high level. These factors work together to lead to the generation and propagation of fatigue cracks. Over time, the cracks gradually increase and expand, ultimately affecting the integrity and safety of the pipeline.

[0003] Crack repair by welding is a crucial measure to ensure the safe operation of the connecting pipe from the screen-type superheater to the high-temperature superheater. The presence of cracks reduces the strength and rigidity of the welded joint, and the sharp notch at the crack end causes severe stress concentration, promoting further crack propagation and potentially leading to pipeline leaks. Leaks not only cause unplanned boiler shutdowns and significant economic losses but also pose a safety hazard of burns to personnel from leaking steam. Therefore, timely welding repair of cracks can effectively eliminate safety hazards, restore the integrity and load-bearing capacity of the pipeline, and ensure the safe and stable operation of power plant units. Through scientific and reasonable welding repair techniques, combined with strict testing and acceptance procedures, the quality and service life of the repaired pipelines can be significantly improved.

[0004] The existing technology has the following main drawbacks in dealing with cracks in the connecting pipe between the screen-type superheater and the high-temperature superheater: Insufficient release of residual welding stress: Since the wall thickness of the elbow is greater than that of the straight pipe, the selection of parameters such as temperature and isothermal time during heat treatment becomes more complicated. This leads to insufficient release of residual stress after welding, which is one of the main causes of fatigue cracks in the weld. Existing technology has not been able to effectively solve this problem, making the welded joint prone to cracking during long-term operation.

[0005] Increased weld discontinuity and stress concentration: The greater thickness on the elbow side increases weld discontinuity, further exacerbating stress concentration. This structural inhomogeneity and stress concentration are important factors leading to cracks in the weld and its surrounding area. Existing technologies lack effective means to reduce these adverse effects, making it difficult to avoid the occurrence and development of cracks.

[0006] On-site installation limitations: On-site installation tasks are heavy, and welders may not strictly follow welding process requirements, resulting in unstable welding quality. Especially in the process of infrastructure installation, if the welding process is not performed properly, it will directly affect the quality and service life of the welded joint. Existing technologies often ignore the impact of actual on-site operating conditions on welding quality and do not provide sufficient guidance and support.

[0007] Dynamic stress changes during unit operation: During the later stages of unit commissioning, factors such as deep peak shaving cause the weld stress to change continuously and remain at a high level, which is also an important reason for the gradual expansion of cracks. However, existing detection and maintenance strategies are usually unable to monitor and respond to these dynamic changes in real time, causing cracks to expand unnoticed until they cause serious consequences before they are discovered.

[0008] In summary, existing technologies have significant shortcomings in addressing cracks in the connecting pipes from the screen-type superheater to the high-temperature superheater, particularly in areas such as residual welding stress management, stress concentration reduction, adaptation to on-site installation conditions, and handling dynamic stress changes during operation. These issues not only affect the safety and reliability of the equipment but may also lead to higher maintenance costs and economic losses. Therefore, a more scientific, systematic, and efficient crack detection and repair method is needed to ensure the safe operation of pipelines. Consequently, this application proposes a method for welding and repairing cracks in the connecting pipes from the screen-type superheater to the high-temperature superheater to address the aforementioned deficiencies. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for welding and repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater. This method features optimized welding and heat treatment processes, strict control of welding parameters and sequence, and the integration of various non-destructive testing technologies. It achieves advantages such as precise crack location, complete removal, and high-quality repair. This method solves the problems of insufficient release of residual welding stress, stress concentration caused by weld discontinuity, and complex on-site installation conditions in existing technologies.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a method for welding and repairing cracks in the connecting pipe from a screen-type superheater to a high-temperature superheater, comprising the following steps: S1 Crack Detection and Assessment: A comprehensive inspection of the weld and base material of the connecting pipe is carried out using penetrant testing and ultrasonic testing methods. The locations of the detected cracks are then marked, and the severity of the cracks is assessed based on their characteristics and locations. S2 Crack Removal: Use a circumferential cutting machine to circumferentially cut the entire joint weld. For the part of the crack that extends into the base material, remove it by manual grinding. S3 beveling: Based on the depth and location of the crack after excavation, a suitable beveling shape is designed. The beveling is processed by mechanical processing and manual grinding. Then, penetrant testing with dye penetrant detection is performed after beveling. S4 Welding Material Selection: For circumferential welding, use φ2.5mm diameter TIG-R31 welding wire for argon arc welding root pass, φ3.2mm diameter R317 welding rod for root pass and cover pass welding, and φ4.0mm diameter R317 welding rod for fill pass. S5 welding preparation: Clean the area to be welded and the surrounding 10-15mm area with acetone or anhydrous ethanol. Preheat to 200℃-300℃ according to the welding characteristics of 12Cr1MoV material. S6 welding operation: Use TIG-R31 welding wire for argon arc welding to ensure root penetration of the weld, use R317 welding rod for filler welding, and use R317 welding rod for capping welding. S7 post-weld heat treatment: medium frequency heat treatment is adopted, the temperature is controlled at 720℃~730℃, and the temperature is held for 2~3 hours; S8 Post-repair inspection and acceptance: Use penetrant testing or ultrasonic testing to conduct a comprehensive inspection of the repaired weld and base material, checking that the weld is flat and smooth, without undercut or weld bead defects.

[0011] Furthermore, the penetrant detection method in step S1 crack detection and evaluation is as follows: 1) Clean the area to be tested with acetone and anhydrous ethanol to ensure it is clean, free of oil, rust, moisture, and impurities that would prevent the penetrant from penetrating the surface defects; 2) Apply the penetrant evenly to the surface to be inspected and allow it to remain for a sufficient time so that the penetrant can fully penetrate into the defects with surface openings; 3) Use appropriate cleaning agents or methods to remove excess penetrant from the surface, avoiding damage to the penetrant that has already entered the defect; 4) After cleaning, apply a developer to help pull out any penetrant left in the defects, making them more visible against a white background, and record any signs of defects that appear under appropriate lighting conditions.

[0012] Furthermore, the ultrasonic testing method in step S1 crack detection and evaluation is as follows: 1) Select a suitable probe and coupling agent, and adjust the ultrasonic testing equipment to the appropriate settings for the object being tested; 2) Move the probe along the predetermined path to scan the entire area to be inspected. Adjust the angle and position of the probe according to the inspection requirements to ensure that all potential internal defects can be detected. 3) Observe the echo signal on the screen, identify abnormal signals, and analyze the characteristics of the signal such as its location, size, and shape to assess the degree of defect; 4) Record defect information, including location, size, and nature.

[0013] Furthermore, during the crack removal process in step S2, a penetrant testing agent is used to test the polished area. The penetrant is evenly applied to the polished area, and after waiting for 10 to 15 minutes, excess penetrant is removed. Then, a developer is applied, and after developing for 10 to 15 minutes, it is observed whether there are any crack indications.

[0014] Furthermore, in step S4, the selection of welding materials: TIG-R31 welding wire is a low-alloy heat-resistant steel tungsten inert gas welding wire containing 1.25% Cr, 0.5% Mo, and V. R317 welding electrode is used for welding 12Cr1MoV low alloy heat-resistant steel. Its chemical composition includes, but is not limited to, C, Si, Mn, P, S, Mo, Cr, and V.

[0015] Furthermore, the specific steps for pre-welding preparation in step S5 are as follows: S51 defines the area to be welded and the cleaning area within a 10-15mm range; S52 is cleaned with acetone or anhydrous ethanol to remove oil, rust, moisture, and impurities; S53 checks the cleaning effect to ensure no residual contaminants remain; S54 Preheating is performed within a 100mm range on both sides of the weld; The S55 uses an electric heating element or medium-frequency induction heating to reach 200–300°C; S56 uses a temperature measuring instrument to detect and record the preheating temperature; Before welding S57, maintain the interpass temperature between 200 and 300°C.

[0016] Furthermore, the specific welding parameter control conditions during the welding operation in step S6 are as follows: TIG-R31 welding wire: welding current 80~120A, DC positive polarity, voltage 10~14V, welding speed 40~60mm / min; φ3.2mmR317 welding electrode: welding current 90~130A, DC reverse polarity, voltage 20~24V, welding speed 85~120mm / min; φ4.0mmR317 welding electrode: welding current 100~150A, DC reverse polarity, voltage 20~26V, welding speed 90~160mm / min.

[0017] Furthermore, in step S7, during the post-weld heat treatment, the weld repair area is heated at a medium-frequency temperature of 300-400°C and held for 2-4 hours to increase hydrogen diffusion. After the post-heat treatment, when the temperature is cooled to 40-50°C, the beveling, alignment, preheating, and welding processes are carried out.

[0018] Furthermore, the post-weld heat treatment process in step S7 also includes the following specific parameters and steps: The heating rate should be controlled at ≤130℃ / h, and the temperature should be kept constant within the range of 720℃~730℃ for 2~3 hours. The cooling rate should be controlled at ≤100℃ / h to prevent rapid cooling. At the same time, appropriate insulation material should be used to cover the welding area throughout the heat treatment process.

[0019] Furthermore, the specific steps for post-repair inspection and acceptance in step S8 are as follows: S1 uses penetrant testing (PT) or ultrasonic testing (UT) to conduct a comprehensive inspection of the repaired weld and base material to ensure that there are no welding defects such as cracks, lack of fusion or porosity. S2 carefully inspects the surface quality of the weld to ensure that the weld is flat, smooth, and free of undercut, weld beads, and spatter; S3 performs hardness tests on the repaired weld and the adjacent base material to ensure that the hardness values ​​meet the relevant standard requirements; S4 further utilizes ultrasonic flaw detection technology to conduct a thorough inspection of the repaired area to ensure that there are no hidden micro-cracks or other discontinuities inside; For magnetic materials, S5 uses magnetic particle testing technology to confirm the presence of microcracks or surface defects.

[0020] Compared with the prior art, the technical solution of this application has the following beneficial effects: The method for welding and repairing cracks in the connecting pipe between the screen-type superheater and the high-temperature superheater effectively solves the problem of insufficient stress release during welding by optimizing the welding and heat treatment processes, thus reducing the generation of cracks caused by stress concentration. Secondly, the use of strict welding parameter control and a scientific welding sequence ensures the stability and reliability of the welding quality. In addition, the combination of non-destructive testing technologies such as penetrant testing (PT) and ultrasonic testing (UT) enables precise location and thorough repair of cracks, avoiding the omission of cracks due to insufficient detection. This significantly improves the quality and service life of the repaired pipeline and reduces operational risks.

[0021] This method for welding and repairing cracks in the connecting pipe between the screen-type superheater and the high-temperature superheater significantly improves repair efficiency while ensuring repair quality. Through a detailed welding repair technical plan, including crack detection, removal, beveling, selection of welding materials, pre-weld preparation, welding operation, post-weld heat treatment, and post-repair inspection and acceptance, the method achieves highly efficient crack repair. Especially under tight deadlines, this method can quickly complete the repair work, ensuring the normal operation of the unit. Furthermore, strict inspection and acceptance standards ensure that the repaired pipes are free of cracks, porosity, undercut, and other defects, significantly improving the safety and reliability of the pipelines, effectively preventing leakage accidents caused by cracks, and safeguarding the safe production and economic benefits of the power plant. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the steps of the crack welding repair method of the present invention; Figure 2 This is a schematic diagram of the chemical composition and structure of the material grade 12Cr1MoV of this invention; Figure 3 This is a schematic diagram of the chemical composition structure of the welding wire TIG-R31 of the present invention; Figure 4 This is a schematic diagram of the chemical composition and structure of material grade R317 of the present invention; Figure 5 This is a schematic diagram of the welding sequence and structure of the present invention; Figure 6 This is a schematic diagram showing the form and dimensions of the welding bevel processed according to the present invention; Figure 7 This is a schematic diagram of the permeability testing structure after the straight pipe side base material is repaired according to the present invention; Figure 8 This is a schematic diagram of the mating joint structure after the repair is completed according to the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figure 1-8 The present embodiment of a method for welding and repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater includes the following steps: S1 Crack Detection and Assessment: A comprehensive inspection of the weld and base material of the connecting pipe is carried out using penetrant testing and ultrasonic testing methods. The locations of the detected cracks are then marked, and the severity of the cracks is assessed based on their characteristics and locations. S2 Crack Removal: Use a circumferential cutting machine to circumferentially cut the entire joint weld. For the part of the crack that extends into the base material, remove it by manual grinding. S3 beveling: Based on the depth and location of the crack after excavation, a suitable beveling shape is designed. The beveling is processed by mechanical processing and manual grinding. Then, penetrant testing with dye penetrant detection is performed after beveling. S4 Welding Material Selection: For circumferential welding, use φ2.5mm diameter TIG-R31 welding wire for argon arc welding root pass, φ3.2mm diameter R317 welding rod for root pass and cover pass welding, and φ4.0mm diameter R317 welding rod for fill pass. S5 welding preparation: Clean the area to be welded and the surrounding 10-15mm area with acetone or anhydrous ethanol. Preheat to 200℃-300℃ according to the welding characteristics of 12Cr1MoV material. S6 welding operation: Use TIG-R31 welding wire for argon arc welding to ensure root penetration of the weld, use R317 welding rod for filler welding, and use R317 welding rod for capping welding. S7 post-weld heat treatment: medium frequency heat treatment is adopted, the temperature is controlled at 720℃~730℃, and the temperature is held for 2~3 hours; S8 Post-repair inspection and acceptance: Use penetrant testing or ultrasonic testing to conduct a comprehensive inspection of the repaired weld and base material, checking that the weld is flat and smooth, without undercut or weld bead defects.

[0025] It should be noted that the method for repairing cracks in the connecting pipe between the screen-type superheater and the high-temperature superheater involves a systematic approach. This includes comprehensive crack assessment using penetrant testing and ultrasonic testing, thorough removal of the crack using a circumferential cutting machine and manual grinding, designing and fabricating a suitable bevel, selecting welding materials suitable for the properties of 12Cr1MoV material, rigorous pre-weld preparation and preheating, precise control of welding parameters to ensure high-quality welding, implementation of medium-frequency heat treatment to eliminate residual stress, and comprehensive inspection and acceptance to ensure the repair effect. This method effectively solves problems existing in current technologies, such as insufficient release of residual welding stress, stress concentration due to weld discontinuity, and complex on-site installation conditions. It significantly improves the quality and service life of the repaired pipe, reduces operational risks, and ensures the safety and reliability of the equipment. Furthermore, actual operation has verified that this method can effectively prevent crack regrowth, avoid leakage accidents and unplanned downtime, thereby significantly reducing maintenance costs and economic losses.

[0026] The specific penetrant testing method in step S1, crack detection and assessment, is as follows: 1) Clean the area to be tested with acetone and anhydrous ethanol to ensure it is clean, free of oil, rust, moisture, and impurities that would prevent the penetrant from penetrating the surface defects; 2) Apply the penetrant evenly to the surface to be inspected and allow it to remain for a sufficient time so that the penetrant can fully penetrate into the defects with surface openings; 3) Use appropriate cleaning agents or methods to remove excess penetrant from the surface, avoiding damage to the penetrant that has already entered the defect; 4) After cleaning, apply a developer to help pull out any penetrant left in the defects, making them more visible against a white background, and record any signs of defects that appear under appropriate lighting conditions.

[0027] It should be noted that the penetrant testing method in step S1, crack detection and assessment, ensures the accuracy and reliability of the detection through a systematic four-step operation. First, the area to be tested is thoroughly cleaned with acetone and anhydrous ethanol to remove oil, rust, moisture, and other impurities, ensuring that the penetrant can effectively penetrate the surface defects. Next, the penetrant is evenly coated on the test surface and given sufficient time to penetrate into all open defects. Then, an appropriate cleaning agent or method is used to remove excess penetrant from the surface, avoiding damage to the penetrant already penetrated into the defects, ensuring the authenticity and accuracy of the test results. Finally, after cleaning, a developer is applied to help pull out the penetrant remaining in the defects, making it more visible against a white background. Any visible defect signs are recorded under appropriate lighting conditions. This not only improves the sensitivity and accuracy of the detection but also ensures the effective identification of fine cracks and other surface defects, providing a solid foundation for subsequent repair work.

[0028] The ultrasonic testing method used in step S1, crack detection and evaluation, is as follows: 1) Select a suitable probe and coupling agent, and adjust the ultrasonic testing equipment to the appropriate settings for the object being tested; 2) Move the probe along the predetermined path to scan the entire area to be inspected. Adjust the angle and position of the probe according to the inspection requirements to ensure that all potential internal defects can be detected. 3) Observe the echo signal on the screen, identify abnormal signals, and analyze the characteristics of the signal such as its location, size, and shape to assess the degree of defect; 4) Record defect information, including location, size, and nature.

[0029] It should be noted that the ultrasonic testing method in step S1, crack detection and evaluation, ensures comprehensive and accurate detection of internal defects in the connecting pipe through a systematic four-step operation. First, a suitable probe and coupling agent are selected, and the ultrasonic testing equipment is adjusted to the appropriate settings for the object being tested to ensure optimal detection results. Next, the probe is moved along a predetermined path to scan the entire area to be tested, and the angle and position of the probe are flexibly adjusted according to the testing requirements to ensure that all potential internal defects can be detected. Then, the echo signals on the screen are carefully observed, and the location, size, and shape of abnormal signals are identified and analyzed to accurately assess the degree of defects. Finally, all defect information found is recorded in detail, including its specific location, size, and nature, providing detailed data support for subsequent repair work. This not only improves the comprehensiveness and accuracy of the detection but also provides a reliable basis for formulating a scientific and reasonable repair plan, significantly improving the quality and efficiency of the overall repair work.

[0030] In step S2, during the crack removal process, a penetrant testing agent is used to test the polished area. The penetrant is evenly applied to the polished area, and after waiting for 10 to 15 minutes, the excess penetrant is removed. Then, a developer is applied, and after developing for 10 to 15 minutes, it is observed whether there are any crack indications.

[0031] It should be noted that during step S2, the crack removal process involves using a penetrant testing agent to inspect the ground area. A series of rigorous procedures ensure complete crack removal. First, the penetrant is evenly applied to the ground area and left for 10-15 minutes to allow it to fully penetrate any remaining microcracks. Then, excess penetrant is removed to avoid interfering with subsequent imaging. Next, a developer is applied to the ground area and left for 10-15 minutes to allow the developer to draw out any remaining penetrant within the defects, making it more visible against a white background. Finally, under appropriate lighting conditions, careful observation is conducted to check for crack indicators, ensuring all cracks have been completely eliminated. This process not only improves the sensitivity and accuracy of crack detection but also effectively verifies the thoroughness of crack removal, providing a solid foundation for subsequent beveling and welding repair, and significantly enhancing the reliability and safety of the repair work.

[0032] In step S4, the selection of welding materials includes: TIG-R31 welding wire is a low-alloy heat-resistant steel tungsten inert gas welding wire containing 1.25% Cr, 0.5% Mo, and V. R317 welding electrode is used for welding 12Cr1MoV low alloy heat-resistant steel. Its chemical composition includes, but is not limited to, C, Si, Mn, P, S, Mo, Cr, and V.

[0033] It should be noted that in step S4, the selection of welding materials, using TIG-R31 welding wire and R317 welding rod, ensures high-quality welding during the repair process. TIG-R31 welding wire is a low-alloy heat-resistant steel tungsten inert gas welding wire containing 1.25% Cr, 0.5% Mo, and V. It has excellent plasticity and toughness, is suitable for welding in high-temperature environments, and can provide good weld quality and crack resistance. R317 welding rod is specifically designed for welding 12Cr1MoV low-alloy heat-resistant steel. Its chemical composition includes, but is not limited to, C, Si, Mn, P, S, Mo, Cr, and V. These elements help improve the strength and heat resistance of the weld, ensuring that the welded joint maintains excellent mechanical properties under high temperature and high pressure environments. Through this carefully selected combination of welding materials, not only are the stress concentration and crack propagation problems that may occur during the welding process effectively solved, but the quality and service life of the repaired pipeline are also significantly improved, ensuring the safe and stable operation of the equipment. This provides a solid material foundation for the repair of cracks in connecting pipes, ensuring the reliability and long-term effectiveness of the repair work.

[0034] The specific steps for pre-welding preparation in step S5 are as follows: S51 defines the area to be welded and the cleaning area within a 10-15mm range; S52 is cleaned with acetone or anhydrous ethanol to remove oil, rust, moisture, and impurities; S53 checks the cleaning effect to ensure no residual contaminants remain; S54 Preheating is performed within a 100mm range on both sides of the weld; The S55 uses an electric heating element or medium-frequency induction heating to reach 200–300°C; S56 uses a temperature measuring instrument to detect and record the preheating temperature; Before welding S57, maintain the interpass temperature between 200 and 300°C.

[0035] It should be noted that step S5, pre-welding preparation, ensures the cleanliness and preheating of the welding area through a series of rigorous operations, thereby improving welding quality. First, the area to be welded and its surrounding 10-15mm area are designated as the cleaning zone. Then, the area is thoroughly cleaned with acetone or anhydrous ethanol to remove impurities such as oil, rust, and moisture. The cleaning effect is checked to ensure no residual contaminants remain. Next, preheating is performed within 100mm on both sides of the weld using electric heating belts or medium-frequency induction heating to 200-300℃. The preheating temperature is detected and recorded using a thermometer to ensure uniform preheating. Finally, the interpass temperature is maintained between 200-300℃ throughout the welding process to avoid welding defects caused by temperature fluctuations. This systematic pre-welding preparation not only effectively reduces the risk of residual welding stress and cold cracking but also significantly improves the quality and stability of the welded joint, ensuring that the repaired pipeline can operate safely for a long time under high temperature and high pressure conditions. This provides a solid foundation for subsequent high-quality welding and greatly enhances the reliability and durability of the repair work.

[0036] The specific welding parameter control conditions during the welding operation in step S6 are as follows: TIG-R31 welding wire: welding current 80~120A, DC positive polarity, voltage 10~14V, welding speed 40~60mm / min; φ3.2mmR317 welding electrode: welding current 90~130A, DC reverse polarity, voltage 20~24V, welding speed 85~120mm / min; φ4.0mmR317 welding electrode: welding current 100~150A, DC reverse polarity, voltage 20~26V, welding speed 90~160mm / min.

[0037] It should be noted that during the welding operation in step S6, precise control of welding parameters ensured a high-quality welding repair effect. Specifically, when using TIG-R31 welding wire, the welding current was set to 80–120A, with DC positive polarity, the voltage controlled at 10–14V, and the welding speed maintained at 40–60mm / min. These parameter settings help achieve uniform penetration and good weld formation. For φ3.2mmR317 welding rods, the welding current was set to 90–130A, with DC reverse polarity, the voltage controlled at 20–24V, and the welding speed at 85–120mm / min, ensuring… The stability and density of the filler layer are crucial. For φ4.0mmR317 welding electrodes, the welding current is set to 100-150A, DC reverse polarity, voltage controlled at 20-26V, and welding speed at 90-160mm / min to ensure the flatness and surface quality of the cover layer. By strictly controlling these welding parameters, not only are welding defects such as porosity and cracks effectively avoided, but the overall strength and durability of the weld are also significantly improved. This ensures that the repaired connecting pipe can operate safely for a long time under high temperature and high pressure, providing a reliable guarantee for high-quality welding and greatly improving the success rate of repair work and the safety of equipment.

[0038] In step S7, during the post-weld heat treatment, the weld repair area is heated by medium frequency at a temperature of 300-400℃ and held for 2-4 hours to increase hydrogen diffusion. After the post-heat treatment, when the temperature is cooled to 40-50℃, the beveling, alignment, preheating and welding processes are carried out.

[0039] It should be noted that in step S7, the post-weld heat treatment process, by using medium-frequency heating to 300-400℃ and holding the temperature for 2-4 hours in the repaired area, significantly improved the quality and safety of the weld repair. This post-heat treatment not only helps increase hydrogen diffusion and reduce the risk of hydrogen-induced cracking, but also effectively alleviates residual welding stress and improves the microstructure of the weld and its heat-affected zone. After the post-heat treatment, when the temperature cools to 40-50℃, subsequent processes such as beveling, alignment, preheating, and welding are performed. Through strict temperature control and holding time settings, the effective release of internal stress in the weld is ensured, and the formation of hardened structures due to rapid cooling is prevented, thereby greatly reducing the probability of cold cracking. In addition, the meticulous operation steps provide a good foundation for subsequent welding, further improving the quality and service life of the repaired pipeline and ensuring the long-term stable operation of the equipment under high temperature and high pressure environments. Overall, this method significantly enhances the reliability and durability of weld repair and reduces potential safety hazards and maintenance costs.

[0040] The post-weld heat treatment process in step S7 also includes the following specific parameters and steps: The heating rate should be controlled at ≤130℃ / h, and the temperature should be kept constant within the range of 720℃~730℃ for 2~3 hours. The cooling rate should be controlled at ≤100℃ / h to prevent rapid cooling. At the same time, appropriate insulation material should be used to cover the welding area throughout the heat treatment process.

[0041] It should be noted that in step S7, the post-weld heat treatment process significantly improves the quality and reliability of weld repair by precisely controlling the heating rate, isothermal time, and cooling rate, and by using appropriate insulation material to cover the weld area. Specifically, the heating rate should be controlled at ≤130℃ / h to ensure uniform heating of the material and avoid stress concentration caused by rapid heating. Maintaining a constant temperature of 720℃~730℃ for 2~3 hours allows for sufficient annealing of the weld joint, effectively eliminating residual welding stress and improving the microstructure. The cooling rate should be controlled at ≤100℃ / h to prevent the formation of hardened structures caused by rapid cooling and reduce the risk of cold cracking. Simultaneously, using appropriate insulation material to cover the weld area throughout the heat treatment process ensures uniform heating and reduces heat loss. This not only effectively reduces residual stress and hydrogen embrittlement risk within the weld joint but also ensures the optimization of the microstructure of the weld and its heat-affected zone, thereby significantly improving the quality and service life of the repaired pipeline and ensuring long-term stable operation of the equipment under high temperature and high pressure environments. Overall, this method provides solid technical support for high-quality weld repair and significantly enhances the reliability and durability of the repair work.

[0042] The specific steps for post-repair inspection and acceptance in step S8 are as follows: S1 uses penetrant testing (PT) or ultrasonic testing (UT) to conduct a comprehensive inspection of the repaired weld and base material to ensure that there are no welding defects such as cracks, lack of fusion or porosity. S2 carefully inspects the surface quality of the weld to ensure that the weld is flat, smooth, and free of undercut, weld beads, and spatter; S3 performs hardness tests on the repaired weld and the adjacent base material to ensure that the hardness values ​​meet the relevant standard requirements; S4 utilizes ultrasonic flaw detection technology to conduct a thorough inspection of the repaired area, ensuring that there are no hidden micro-cracks or other discontinuities inside; For magnetic materials, S5 uses magnetic particle testing technology to confirm the presence of microcracks or surface defects.

[0043] It should be noted that the inspection and acceptance process after repair in step S8 involves a series of systematic inspection steps to ensure the quality and reliability of the weld repair. First, penetrant testing (PT) or ultrasonic testing (UT) is used to comprehensively inspect the repaired weld and base material to ensure there are no welding defects such as cracks, lack of fusion, or porosity, thereby verifying the elimination of surface and near-surface defects. Next, the surface quality of the weld is carefully inspected to ensure that the weld is flat and smooth, without undercut, weld beads, spatter, or other problems, ensuring that the appearance meets high standards. Finally, hardness testing is performed on the repaired weld and the nearby base material to ensure that the hardness values ​​meet relevant standards. The requirements include verifying whether the material properties have been restored to the expected level, further using ultrasonic flaw detection technology to conduct in-depth inspection of the repaired area to ensure that there are no hidden micro-cracks or other discontinuities inside, comprehensively assessing the internal quality of the weld, and finally, for magnetic materials, using magnetic particle testing technology to confirm the presence of micro-cracks or surface defects, providing additional assurance. These detailed inspection and acceptance steps not only improve the accuracy and completeness of the repair work, but also ensure the safety and reliability of the repaired pipeline in actual operation, significantly reducing potential safety hazards and maintenance costs, and providing a solid guarantee for the long-term stable operation of the equipment.

[0044] Understandably, refer to the appendix Figure 5 The welding repair sequence for the straight pipe side base material is ①→③→⑤→②→④, and the welding sequence for the elbow side base material is ①→③→⑤→②→④→⑥. The straight pipe side base material and the elbow side base material are welded and repaired simultaneously. After the repair is completed, the butt joint between the straight pipe and the elbow is welded.

[0045] This method for welding and repairing cracks in the connecting pipe between the screen-type superheater and the high-temperature superheater comprehensively solves various problems existing in the current technology through systematic steps and technical means, and significantly improves the quality and reliability of the repair work, as detailed below: Comprehensive Inspection and Assessment: A combination of penetrant testing (PT) and ultrasonic testing (UT) is used to conduct a comprehensive inspection of the weld and base material, ensuring accurate assessment of crack location, depth, and severity. This multi-layered inspection approach improves the sensitivity and accuracy of defect identification.

[0046] Complete crack removal: Using a combination of circumferential cutting machine and manual grinding, the portion of the crack extending into the base material is completely removed, and penetrant testing is used to confirm that the crack has been completely eliminated, ensuring a solid foundation for subsequent welding repairs.

[0047] Precision beveling: Design a suitable beveling shape based on the specific conditions after crack removal, and perform fine processing using machining or manual grinding. Then, confirm the absence of defects through penetrant testing with dye penetrant detection, providing good preparation conditions for high-quality welding.

[0048] Scientific material selection: TIG-R31 welding wire and R317 welding rod, which are suitable for the characteristics of 12Cr1MoV material, are selected to ensure that the welded joint has excellent strength and heat resistance, and effectively avoid stress concentration and crack propagation problems that may occur during the welding process.

[0049] Strict pre-welding preparation: The area to be repaired is cleaned with acetone or anhydrous ethanol and precisely preheated to ensure that the welding area is clean and the temperature is uniform, reducing the risk of residual welding stress and cold cracking.

[0050] Precise welding operation: Strict control of welding parameters, including current, voltage and welding speed, ensures consistent welding quality of each layer, avoids welding defects such as porosity and cracks, and improves the overall performance of the weld.

[0051] Effective post-weld heat treatment: Medium-frequency heating is used and the heating, constant temperature and cooling rate are controlled to ensure that the weld joint is fully annealed, reduce residual stress and improve the microstructure, and further enhance the reliability and durability of the weld.

[0052] Comprehensive post-repair inspection and acceptance: The repaired welds are thoroughly inspected using various methods such as penetrant testing, ultrasonic testing, hardness testing, and magnetic particle testing to ensure that there are no defects and that they meet relevant standards, providing a solid guarantee for the safe and stable operation of the equipment.

[0053] This welding repair method not only solves the problems of insufficient release of residual welding stress and stress concentration caused by weld discontinuity in existing technologies, but also ensures the stability and reliability of repair quality through detailed pre-inspection and evaluation, beveling after crack removal, and comprehensive subsequent inspection and acceptance. Actual operation has verified that this method can effectively prevent crack propagation, avoid leakage accidents and unplanned downtime, thereby significantly reducing maintenance costs and economic losses. Overall, it significantly improves the safety and service life of equipment, providing valuable practical experience and technical reference for similar projects.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater by welding, characterized in that: Includes the following steps: S1 Crack Detection and Assessment: A comprehensive inspection of the weld and base material of the connecting pipe is carried out using penetrant testing and ultrasonic testing methods. The locations of the detected cracks are then marked, and the severity of the cracks is assessed based on their characteristics and locations. S2 Crack Removal: Use a circumferential cutting machine to circumferentially cut the entire joint weld. For the part of the crack that extends into the base material, remove it by manual grinding. S3 beveling: Based on the depth and location of the crack after excavation, a suitable beveling shape is designed, and the beveling is processed by mechanical processing and manual grinding. Then, penetrant testing with dye penetrant detection is performed after beveling. S4 Welding Material Selection: For circumferential welding, use φ2.5mm diameter TIG-R31 welding wire for argon arc welding root pass, φ3.2mm diameter R317 welding rod for root pass and cover pass welding, and φ4.0mm diameter R317 welding rod for fill pass. S5 welding preparation: Clean the area to be welded and the surrounding 10-15mm area with acetone or anhydrous ethanol. Preheat to 200℃-300℃ according to the welding characteristics of 12Cr1MoV material. S6 welding operation: Use TIG-R31 welding wire for argon arc welding to ensure root penetration of the weld, use R317 welding rod for filler welding, and use R317 welding rod for capping welding. S7 post-weld heat treatment: medium frequency heat treatment is adopted, the temperature is controlled at 720℃~730℃, and the temperature is held for 2~3 hours; S8 Post-repair inspection and acceptance: Use penetrant testing or ultrasonic testing to conduct a comprehensive inspection of the repaired weld and base material, checking that the weld is flat and smooth, without undercut or weld bead defects.

2. The method for repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater according to claim 1, characterized in that: The specific penetrant testing method used in step S1, crack detection and evaluation, is as follows: 1) Clean the area to be tested with acetone and anhydrous ethanol to ensure it is clean, free of oil, rust, moisture, and impurities that would prevent the penetrant from penetrating the surface defects; 2) Apply the penetrant evenly to the surface to be inspected and allow it to remain for a sufficient time so that the penetrant can fully penetrate into the defects with surface openings; 3) Use appropriate cleaning agents or methods to remove excess penetrant from the surface, avoiding damage to the penetrant that has already entered the defect; 4) After cleaning, apply a developer to help pull out any penetrant left in the defects, making them more visible against a white background, and record any signs of defects that appear under appropriate lighting conditions.

3. The method for repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater according to claim 1, characterized in that: The ultrasonic testing method used in step S1, crack detection and evaluation, is as follows: 1) Select a suitable probe and coupling agent, and adjust the ultrasonic testing equipment to the appropriate settings for the object being tested; 2) Move the probe along the predetermined path to scan the entire area to be inspected. Adjust the angle and position of the probe according to the inspection requirements to ensure that all potential internal defects can be detected. 3) Observe the echo signal on the screen, identify abnormal signals, and analyze the characteristics of the signal such as its location, size, and shape to assess the degree of defect; 4) Record defect information, including location, size, and nature.

4. The method for repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater according to claim 1, characterized in that: In step S2, during the crack removal process, a penetrant testing agent is used to test the polished area. The penetrant is evenly applied to the polished area, and after waiting for 10 to 15 minutes, excess penetrant is removed. Then, a developer is applied, and after developing for 10 to 15 minutes, it is observed whether there are any crack indications.

5. The method for repairing cracks in the connecting pipe from a screen-type superheater to a high-temperature superheater according to claim 1, characterized in that: In step S4, the selection of welding materials: TIG-R31 welding wire is a low-alloy heat-resistant steel tungsten inert gas welding wire containing 1.25% Cr, 0.5% Mo, and V. R317 welding electrode is used for welding 12Cr1MoV low alloy heat-resistant steel. Its chemical composition includes, but is not limited to, C, Si, Mn, P, S, Mo, Cr, and V.

6. The method for repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater according to claim 1, characterized in that: The specific steps for pre-welding preparation in step S5 are as follows: S51 defines the area to be welded and the cleaning area within a 10-15mm range; S52 is cleaned with acetone or anhydrous ethanol to remove oil, rust, moisture, and impurities; S53 checks the cleaning effect to ensure no residual contaminants remain; S54 Preheating is performed within a 100mm range on both sides of the weld; The S55 uses an electric heating element or medium-frequency induction heating to reach 200–300°C; S56 uses a temperature measuring instrument to detect and record the preheating temperature; Before welding S57, maintain the interpass temperature between 200 and 300°C.

7. The method for repairing cracks in the connecting pipe from a screen-type superheater to a high-temperature superheater according to claim 1, characterized in that: The specific welding parameter control conditions during the welding operation in step S6 are as follows: TIG-R31 welding wire: welding current 80~120A, DC positive polarity, voltage 10~14V, welding speed 40~60mm / min; φ3.2mmR317 welding electrode: welding current 90~130A, DC reverse polarity, voltage 20~24V, welding speed 85~120mm / min; φ4.0mmR317 welding electrode: welding current 100~150A, DC reverse polarity, voltage 20~26V, welding speed 90~160mm / min.

8. The method for repairing cracks in the connecting pipe from a screen-type superheater to a high-temperature superheater according to claim 1, characterized in that: In step S7, during the post-weld heat treatment, the weld repair area is heated by medium frequency at a temperature of 300-400℃ and held for 2-4 hours to increase hydrogen diffusion. After the post-heat treatment, when the temperature is cooled to 40-50℃, the beveling, alignment, preheating and welding processes are carried out.

9. A method for repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater according to claim 1, characterized in that: The post-weld heat treatment process in step S7 also includes the following specific parameters and steps: The heating rate should be controlled at ≤130℃ / h, and the temperature should be kept constant within the range of 720℃~730℃ for 2~3 hours. The cooling rate should be controlled at ≤100℃ / h to prevent rapid cooling. At the same time, appropriate insulation material should be used to cover the welding area throughout the heat treatment process.

10. A method for repairing cracks in the connecting pipe between a screen-type superheater and a high-temperature superheater according to claim 1, characterized in that: The specific steps for post-repair inspection and acceptance in step S8 are as follows: S1 uses penetrant testing (PT) or ultrasonic testing (UT) to conduct a comprehensive inspection of the repaired weld and base material to ensure that there are no welding defects such as cracks, lack of fusion or porosity; S2 carefully inspects the surface quality of the weld to ensure that the weld is flat, smooth, and free of undercut, weld beads, and spatter; S3 performs hardness tests on the repaired weld and the adjacent base material to ensure that the hardness values ​​meet the relevant standard requirements; S4 further utilizes ultrasonic flaw detection technology to conduct a thorough inspection of the repaired area to ensure that there are no hidden micro-cracks or other discontinuities inside; For magnetic materials, S5 uses magnetic particle testing technology to confirm the presence of microcracks or surface defects.

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