A method for repairing a desuperheater spray pipe

Abstract

Embodiments of the present disclosure provide a desuperheater water spray pipe repair method, which realizes on-site repair of larger defects in the water spray pipe part of the desuperheater by desuperheater cylinder repair welding, heat treatment, on-site secondary hole opening and water spray pipe installation, avoids direct replacement of a new desuperheater by optimizing the design of the water spray pipe to avoid direct action of desuperheated water on the inner wall of the desuperheater, and saves the replacement and maintenance period of the desuperheater.

Description

Technical Field

[0001] The embodiments disclosed herein belong to the field of welding technology, specifically relating to a method for repairing a desuperheater spray pipe. Background Technology

[0002] A desuperheater is a device that uses water as a cooling medium to regulate steam temperature. Its function is to control and maintain the temperature of superheated or reheated steam, and to prevent the temperature of the superheater and reheater tube walls from becoming too high. The desuperheater uses a cooling water spray system for internal cooling, with the cooling water delivered to the inside of the desuperheater through spray pipes. The internal walls of the desuperheater are often protected by stainless steel lining plates. However, these lining plates often have mounting holes at the spray pipe installation points. Due to factors such as operation, pipeline vibration, and user actions, cooling water can directly act on the desuperheater cylinder through these mounting holes, leading to cracks in the cylinder material or at the weld seams where the spray pipes are installed during use.

[0003] Regarding crack defects, most desuperheaters are replaced according to a planned schedule based on the results of regular inspections, which involves a long overall replacement cycle and high cost. However, there are also situations where larger crack defects are discovered during inspections, and no spare parts are available on site, requiring on-site repair. Currently, on-site repairs of desuperheaters mostly involve welding repairs for minor defects. Due to the limitations of the desuperheater's spray pipe installation and the irregular structure of the fillet welds, effective on-site repair methods are often lacking when cracks appear at the spray pipe installation welds, especially when the cracks extend to the base material surrounding the desuperheater cylinder. Summary of the Invention

[0004] The embodiments disclosed herein aim to at least solve one of the technical problems existing in the prior art, and provide a method for repairing the desuperheater spray pipe.

[0005] The embodiments of this disclosure provide a method for repairing a desuperheater spray pipe, the method comprising:

[0006] Surface non-destructive testing method was used to detect cracking defects in the fillet weld of the desuperheater spray pipe and the surrounding desuperheater cylinder base material to determine the location of the defects;

[0007] Based on the location of the defect, mechanical grinding was used to eliminate the crack defect, and subsequent treatment measures were determined according to the size of the grinding area after defect elimination.

[0008] Mechanical cutting was used to remove the butt weld, fillet weld, and installation weld of the fixing device of the desuperheater spray pipe. The desuperheater spray pipe was then removed and the relevant dimensions were remeasured.

[0009] The desuperheater cylinder and liner are fixed concentrically by spot welding with fixing blocks, and the installation center position of the desuperheater spray pipe is marked by using the mounting holes of the liner.

[0010] After the defects were eliminated, the desuperheater cylinder was overlaid with weld, and the overlaid area was subjected to local heat treatment.

[0011] After the local heat treatment is completed, the cylinder mounting hole is re-machined using a drilling machine according to the relevant dimensions obtained from the re-measurement, and a new water spray pipe is designed. The new water spray pipe is inserted into the re-machined cylinder mounting hole, ensuring that it is in close contact with the liner mounting hole and matches with the fixing device. Then, fillet welds, mounting welds of the fixing device and butt welds are welded and heat treatment is performed.

[0012] Repairs were completed after each weld was inspected for defects using surface non-destructive testing.

[0013] Optionally, determining subsequent processing measures based on the size of the polished area after defect removal includes:

[0014] If the defects are limited to the weld or the length and width of the desuperheater cylinder base material are no more than 20mm and the number of defects is no more than three, then the repair welding heat treatment can be carried out directly; otherwise, the area after defect elimination should be ground to prepare a weld bevel.

[0015] Optionally, removing the desuperheater spray pipe and re-measuring its dimensions includes:

[0016] The diameters A1 and A2 of the cylinder mounting hole and the liner mounting hole were remeasured, as were the internal length C1, middle length C2, and outer diameter C3 of the desuperheater spray pipe.

[0017] Optionally, the welding of the desuperheater cylinder after defect elimination includes:

[0018] Use argon arc welding to apply a 3mm-5mm thick base coat to the grinding area. Then use shielded metal arc welding to build up the base coat until the de-defect area and the mounting hole area of ​​the de-defector cylinder are completely filled. The weld should extend 1mm-1.5mm beyond the surface of the de-defector cylinder.

[0019] Optionally, the local heat treatment of the weld-overlay area includes:

[0020] Four thermocouples are spot-welded to four areas of the overlay weld. The distance from the spot-welding position to the center of the cylinder mounting hole is D1 = (A1 + 4) / 2, and the angle is D2 = 45°. The four thermocouples are spliced ​​and heat-treated, and each thermocouple covers one-quarter of the overlay weld area.

[0021] Optionally, the criteria for completing the local heat treatment include:

[0022] After local heat treatment of the welded area for 24 hours, and after surface inspection and ultrasonic testing to confirm that there were no defects exceeding the standard in the weld, the weld surface was polished smooth.

[0023] Optionally, the diameter of the re-machined cylinder mounting hole is A3 = A1 + 6.

[0024] Optionally, the new water spray pipe has a diameter reduction structure between the re-machined cylinder mounting hole and the liner mounting hole:

[0025] The length of the variable diameter structure is C4 = 1 / 2C2, and the major diameter of the variable diameter structure is C5 = A3-1.

[0026] Alternatively, the new water spray pipes can be made of stainless steel.

[0027] Optionally, the weld bevel is a 45° bevel.

[0028] The desuperheater spray pipe repair method of the present disclosure achieves on-site repair of large defects in the desuperheater spray pipe by welding, heat treatment, on-site secondary drilling and spray pipe installation of the desuperheater cylinder. At the same time, the optimized design of the spray pipe avoids the desuperheating water from acting directly on the inner wall of the desuperheater, avoiding the need to replace the desuperheater directly and saving the desuperheater replacement and maintenance cycle. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the original structure of the desuperheater spray pipe involved in this application;

[0030] Figure 2 This is a flowchart illustrating a method for repairing a desuperheater spray pipe according to an embodiment of the present disclosure.

[0031] Figure 3 This is a schematic diagram of thermocouple arrangement in a heat treatment process according to an embodiment of the present disclosure;

[0032] Figure 4 for Figure 3 A schematic diagram showing the specific arrangement of thermocouples;

[0033] Figure 5 A schematic diagram of a partially optimized structure of the desuperheater spray pipe provided in the disclosed embodiment;

[0034] Figure 6 A macroscopic diagram of the defect in the desuperheater spray pipe of this implementation case;

[0035] Figure 7 for Figure 6 Non-destructive testing image after repair. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] like Figures 1 to 7As shown, a method for repairing a desuperheater spray pipe includes S110, using a surface non-destructive testing method to detect cracking defects in the fillet weld 2 of the desuperheater spray pipe 1 and the surrounding desuperheater cylinder 4 base material, and determining the specific location of the defect based on the test results.

[0038] S120. Based on the defect location, mechanical grinding is used to eliminate the crack defect, and subsequent treatment measures are determined according to the size of the ground area after defect elimination. Specifically, in this step, if the defect is limited to the weld (fillet weld 2), the grinding length of the base material of the desuperheater cylinder 4 does not exceed 20mm, the width does not exceed 20mm, and the number of defects does not exceed three, then direct welding heat treatment is performed. Otherwise, a weld bevel is prepared by grinding the area after defect elimination. As a specific example, the weld bevel is a 45° bevel.

[0039] S130. Using mechanical cutting, the butt weld 10, fillet weld 2, and installation weld 8 of the fixing device 9 of the desuperheater spray pipe are cut off, and the desuperheater spray pipe 1 is removed and its relevant dimensions are remeasured. Specifically, in this step, the remeasured dimensions include the diameter A1 of the cylinder mounting hole 3 and the diameter A2 of the liner mounting hole 5, as well as the internal length C1, middle length C2, and outer diameter C3 of the desuperheater spray pipe 1.

[0040] S140. Fix the desuperheater cylinder 4 and the liner 6 concentrically by spot welding with the fixing block 7, and use the liner mounting hole 5 to mark the center position of the desuperheater spray pipe 1.

[0041] S150. The degaussor cylinder 4, after defect removal, is overlaid with weld, and the overlaid area undergoes localized heat treatment. Specifically, in this step, an argon arc weld is first used to apply a 3mm-5mm thick base coat to the ground area. Then, shielded metal arc welding is used to overlay the base coat until the degaussor cylinder 4's defect removal area and the cylinder mounting hole 3 area are completely filled, with the weld extending 1mm-1.5mm beyond the surface of the degaussor cylinder 4. Next, four thermocouples are spot-welded to the four areas of the overlay weld 11. The distance from the spot-welding fixing position 12 to the center of the cylinder mounting hole 3 is D1 = (A1+4) / 2 (unit: mm), and the angle is D2 = 45°. The four thermocouples are then heat-treated together, with each thermocouple covering one-quarter of the overlay weld 11 area.

[0042] As a specific example, the thermocouple can use heating elements, such as four heating elements of the same size and power, such as heating element 13, heating element 14, heating element 15, and heating element 16, which are spliced ​​together and heat-treated, with each heating element covering one-quarter of the area of ​​the overlay weld 11.

[0043] S160. After the local heat treatment is completed, the cylinder mounting hole is re-machined using a drilling machine according to the relevant dimensions obtained from the re-measurement, and a new water spray pipe is designed. The new water spray pipe is inserted into the re-machined cylinder mounting hole, ensuring that it is in close contact with the liner mounting hole 5 and matches with the fixing device 9. Then, fillet weld 2, mounting weld 8 of fixing device 9 and butt weld 10 are welded and heat-treated.

[0044] Specifically, in this step, the criteria for completing the local heat treatment include: after performing local heat treatment on the weld overlay area for 24 hours, and after surface inspection and ultrasonic testing confirm that the weld overlay 11 has no defects exceeding the standard, the weld surface is ground smooth, thus completing the local heat treatment. Afterwards, a drilling machine is used to re-machine the cylinder mounting hole and design and manufacture a new water spray pipe. The diameter of the re-machined cylinder mounting hole is A3 = A1 + 6 (unit: mm). The new water spray pipe has a diameter-changing structure between the re-machined cylinder mounting hole and the liner mounting hole 5: that is, the length of the diameter-changing structure is C4 = 1 / 2 C2 (unit: mm), the major diameter of the diameter-changing structure is C5 = A3 - 1 (unit: mm), and the remaining dimensions and structure remain unchanged.

[0045] The newly processed water spray pipe is inserted into the newly processed cylinder mounting hole, ensuring tight contact with the liner mounting hole 5 and good fit with the fixing device 9. Then, the new water spray pipe fillet weld 2, the fixing device 9 mounting weld 8, and the butt weld 10 are welded and heat-treated.

[0046] S170. After inspecting each weld for defects using surface non-destructive testing, the repair is completed. Specifically, in this step, surface non-destructive testing is continued to be used to inspect the new water spray pipe fillet weld 2, the installation weld 8 of the fixing device 9, and the butt weld 10. Once the inspection results show that there are no defects, the entire repair process is completed.

[0047] It should be noted that the new water spray pipes can be made of stainless steel.

[0048] The desuperheater spray pipe repair method of the present disclosure achieves on-site repair of large defects in the desuperheater spray pipe by welding, heat treatment, on-site secondary drilling and spray pipe installation of the desuperheater cylinder. At the same time, the optimized design of the spray pipe avoids the desuperheating water from acting directly on the inner wall of the desuperheater, avoiding the need to replace the desuperheater directly and saving the desuperheater replacement and maintenance cycle.

[0049] As a specific implementation case, the repair process of the desuperheater spray pipe is as follows:

[0050] A crack appeared in the fillet weld of the desuperheater spray pipe. The defect was removed by mechanical grinding, and non-destructive testing confirmed that the crack had extended to the base material, with a length of 50mm. Subsequently, mechanical cutting was used to remove the butt weld, fillet weld, and fixing device of the spray pipe, and the spray pipe was removed. The diameter of the cylinder mounting hole was re-measured as 120mm, the diameter of the liner mounting hole was 120mm, the internal length of the spray pipe was 440mm, the middle length was 40mm, and the outer diameter was 118mm. The positions of the cylinder mounting holes were marked on the cylinder using the liner mounting holes.

[0051] A 3mm thick base layer was deposited in the ground area using argon arc welding, followed by shielded metal arc welding until it protruded 1mm above the cylinder surface. The area after the weld repair was then subjected to localized heat treatment. The thermocouple was fixed 64mm from the center of the cylinder mounting hole at a 45° angle to the horizontal. Four identical 5kW heating elements were used for heat treatment, each covering one-quarter of the weld area. 24 hours after heat treatment, surface inspection and ultrasonic testing confirmed that the weld had no defects exceeding the standard, and the weld surface was polished smooth.

[0052] Subsequently, a new cylinder mounting hole with a diameter of 126mm was machined at the original cylinder mounting hole using a drilling machine. A new stainless steel water spray pipe was designed and machined, with a variable diameter structure between the new cylinder mounting hole and the liner mounting hole. The variable diameter structure is used in the section between the new cylinder mounting hole and the liner mounting hole, with a major diameter of 125mm and a length of 20mm at the variable diameter section, while the remaining dimensions and structure remain unchanged.

[0053] The new water spray pipe is inserted into the new cylinder mounting hole, with the diameter change point tightly contacting the liner mounting hole. It is then inserted into the fixing device. Subsequently, the fillet welds of the water spray pipe, the mounting welds of the fixing device, and the butt welds are welded and heat-treated. After 24 hours of heat treatment, non-destructive testing of the fillet welds of the water spray pipe, the mounting welds of the fixing device, and the butt welds shows no defects, and the repair is complete.

[0054] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A method for repairing a desuperheater spray pipe, characterized in that, The method for repairing the desuperheater spray pipe includes: Surface non-destructive testing method was used to detect cracking defects in the fillet weld of the desuperheater spray pipe and the surrounding desuperheater cylinder base material to determine the location of the defects; Based on the location of the defect, mechanical grinding was used to eliminate the crack defect, and subsequent treatment measures were determined according to the size of the grinding area after defect elimination. Mechanical cutting was used to remove the butt weld, fillet weld, and installation weld of the fixing device of the desuperheater spray pipe. The desuperheater spray pipe was then removed and the relevant dimensions were remeasured. The desuperheater cylinder and liner are fixed concentrically by spot welding with fixing blocks, and the installation center position of the desuperheater spray pipe is marked by using the mounting holes of the liner. After the defects were eliminated, the desuperheater cylinder was overlaid with weld, and the overlaid area was subjected to local heat treatment. After the local heat treatment is completed, the cylinder mounting hole is re-machined using a drilling machine according to the relevant dimensions obtained from the re-measurement, and a new water spray pipe is designed. The new water spray pipe is inserted into the re-machined cylinder mounting hole, ensuring that it is in close contact with the liner mounting hole and matches with the fixing device. Then, fillet welds, mounting welds of the fixing device and butt welds are welded and heat treatment is performed. Repairs were completed after each weld was inspected for defects using surface non-destructive testing.

2. The method for repairing the desuperheater spray pipe according to claim 1, characterized in that, The determination of subsequent processing measures based on the size of the polished area after defect removal includes: If the defects are limited to the weld or the length and width of the desuperheater cylinder base material are no more than 20mm and the number of defects is no more than three, then the repair welding heat treatment can be carried out directly; otherwise, the area after defect elimination should be ground to prepare a weld bevel.

3. The method for repairing the desuperheater spray pipe according to claim 1, characterized in that, The step of removing the desuperheater spray pipe and re-measuring the relevant dimensions includes: The diameters A1 and A2 of the cylinder mounting hole and the liner mounting hole were remeasured, as were the internal length C1, middle length C2, and outer diameter C3 of the desuperheater spray pipe.

4. The method for repairing the desuperheater spray pipe according to claim 1, characterized in that, The process of overlaying welds onto the desuperheater cylinder after defect elimination includes: Use argon arc welding to apply a 3mm-5mm thick base coat to the grinding area. Then use shielded metal arc welding to build up the base coat until the de-defect area and the mounting hole area of ​​the de-defector cylinder are completely filled. The weld should extend 1mm-1.5mm beyond the surface of the de-defector cylinder.

5. The method for repairing the desuperheater spray pipe according to claim 3, characterized in that, The local heat treatment of the area after welding includes: Four thermocouples are spot-welded to four areas of the overlay weld. The distance from the spot-welding position to the center of the cylinder mounting hole is D1 = (A1 + 4) / 2, and the angle is D2 = 45°. The four thermocouples are spliced ​​and heat-treated, and each thermocouple covers one-quarter of the overlay weld area.

6. The method for repairing the desuperheater spray pipe according to claim 1, characterized in that, The criteria for completing the localized heat treatment include: After local heat treatment of the welded area for 24 hours, and after surface inspection and ultrasonic testing to confirm that there were no defects exceeding the standard in the weld, the weld surface was polished smooth.

7. The method for repairing the desuperheater spray pipe according to claim 3, characterized in that, The diameter of the re-machined cylinder mounting hole is A3 = A1 + 6.

8. The method for repairing the desuperheater spray pipe according to claim 7, characterized in that, The new water spray pipe features a diameter reduction structure between the re-machined cylinder mounting holes and the liner mounting holes: The length of the variable diameter structure is C4 = 1 / 2C2, and the major diameter of the variable diameter structure is C5 = A3-1.

9. The method for repairing the desuperheater spray pipe according to claim 8, characterized in that, The new water spray pipes are made of stainless steel.

10. The method for repairing the desuperheater spray pipe according to claim 2, characterized in that, The weld bevel is a 45° bevel.

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