A method for repairing a medium-pressure cylinder inner cylinder crack

Abstract

The application discloses a kind of medium-pressure cylinder inner cylinder crack repair method, comprising the following steps: step one: construction preparation;Step two: before defect cleaning, stop crack hole, then clean crack defect, after defect cleaning, grind out U-shaped groove, the size of groove angle is determined according to depth;Step three: preheating before welding;Step four: before welding, check again to confirm that defect has been cleaned, according to workpiece material selects appropriate welding material and welding parameter and carries out welding;Step five: after welding, first clean slag and welding spatter, then carry out post-heat hydrogen removal treatment to weld joint.The application completes the repair of steam turbine cylinder body crack major defect by construction preparation, defect cleaning, preheating before welding, welding and hydrogen removal treatment after welding, and the repair period is short, and the quality is good.Not only does it save high maintenance cost for power plant, reduce power generation loss, but also provides guarantee for unit to complete maintenance on schedule.

Description

Technical Field

[0001] This invention relates to the technical field of crack repair, and in particular to the technical field of repairing cracks in the inner cylinder of a medium-pressure cylinder. Background Technology

[0002] Steam turbine units in power plants require routine maintenance. When cracks are found in the cylinder body of large steam turbines during maintenance, they should be repaired promptly to avoid significant economic losses caused by the cracks expanding. However, currently, there is no complete technical solution for repairing cracks in the cylinder bodies of such large steam turbines, especially cracks in the intermediate-pressure cylinder body. Therefore, a method for repairing cracks in the intermediate-pressure cylinder body is needed. Summary of the Invention

[0003] The purpose of this invention is to solve the problems in the prior art and propose a method for repairing cracks in the inner cylinder of a medium-pressure turbine. This method can successfully repair major defects in turbine cylinder block cracks, with a short repair period, good repair quality, and mitigation of economic losses caused by cracks.

[0004] To achieve the above objectives, this invention proposes a method for repairing internal cylinder cracks in medium-pressure cylinders, comprising the following steps: Step 1: Construction Preparation: Determine the power supply location at the construction site, especially the power supply location of the heat treatment machine; when placing the medium-pressure cylinder workpiece to be repaired, the weld seam should be in a flat welding position, and the workpiece should be placed stably, and a platform of appropriate height should be set up on the work surface; the welding machine and heat treatment machine should be in place and have passed inspection and be in normal condition; consumables should be in place, and the welding materials should be dried; wind and rain protection measures should be taken at the construction site. Step 2: Defect cleaning: Before cleaning the defects, drill anti-crack holes, then clean the cracks and defects. After cleaning the defects, grind out a U-shaped bevel. The size of the bevel angle depends on the depth. Step 3: Preheating before welding: For small-sized crack defects, oxyacetylene flame preheating is used, with a preheating range of not less than 3-5 times the workpiece thickness and not less than 300mm on one side, and a preheating temperature of 100℃; For large-sized crack defects, electric heating preheating is used, with a preheating width of not less than 4 times the workpiece thickness on one side, and a preheating temperature of 100℃. Step 4: Welding Before welding, double-check that defects have been cleaned, and clean the oil and rust on the base material within 20mm of the bevel surface until the metal luster is exposed; check the inside of the bevel with an air hammer to ensure there are no defects; select appropriate welding materials and welding parameters according to the workpiece material; During welding, segmented welding is adopted according to the length of the weld, with the length of each segment based on the length of one welding rod; after each segment is welded, stress is relieved by hammering immediately. During welding, while ensuring welding quality, reduce welding parameters, decrease electrode oscillation amplitude, and increase welding speed to reduce welding line energy; the thickness of a single weld bead should not exceed the electrode diameter plus 2, and the width of a single weld bead should not exceed 4 times the electrode diameter. During welding, the weld joints should be staggered, and the crater should be filled when the weld is finished. When welding, use multi-layer, multi-pass welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the bevel and press the passes towards the middle. Before welding a secondary pass or layer, the weld should be cleaned and inspected to ensure there are no defects before welding. The weld should be 2-3mm higher than the base metal. Step 5: Post-weld hydrogen removal treatment: After welding, first clean the slag and welding spatter, and then perform post-heat hydrogen removal treatment on the weld. The heating width on one side should not be less than 4 times the thickness of the workpiece. Use a medium-pressure cylinder to heat both sides at the same time. The heating rate is 60℃ / h. After heating to 350℃, hold the temperature for 2 hours. After holding the temperature, cool down to below 300℃ at a rate of 60℃ / h and then furnace cool to room temperature.

[0005] Preferably, the method for processing the crack-stopping hole in step two is as follows: according to the size of the crack defect, drill crack-stopping holes at both ends of the defect using drill bits of different diameters, and the distance between the crack-stopping hole and the crack tip is no more than 5mm. The depth of the crack-stopping hole is the detected crack depth plus 3-5mm. For cracks with larger depths, the holes should be drilled in sections.

[0006] Preferably, the crack defect cleaning in step two is specifically as follows: for small-sized crack defects, an angle grinder and an internal grinder are used for cleaning. The crack is cleaned first, and after visual inspection, a PT / MT test is used to confirm whether the crack is clean. For large-sized crack defects, a carbon arc gouging is used to clean the defects. After cleaning, an angle grinder or an internal grinder is used to clean the oxide layer produced by the carbon arc gouging. The thickness of the cleaning layer should be more than 0.5 mm. During the cleaning process, the defect cleaning status should be checked in a timely manner to prevent deviations from occurring.

[0007] Preferably, in step three, when preheating the small-sized crack defects, 2-4 heating guns are used simultaneously. During heating, the distance from the flame core to the workpiece should be more than 10mm, and the moving speed of the nozzles should be stable, without staying in the same position.

[0008] Preferably, in step three, before preheating, a fixing tool for the heating element is made according to the characteristics of the workpiece to ensure that the heater is in close contact with the workpiece during preheating. The heating rate for preheating large-sized cracks should not exceed 60℃ / h, and after reaching 100℃, the temperature is held constant for 4 hours to ensure the workpiece temperature reaches 100℃ uniformly. Preferably, the welding materials and welding parameters in step four are as follows:

[0009] Preferably, the thermocouples used for heating in step five are arranged in a representative position according to the actual situation. The insulation width during constant temperature is measured from the center of the weld, and each side should be at least twice the workpiece thickness compared to the heating width, and not less than 150mm.

[0010] The beneficial effects of this invention are as follows: This invention repairs major defects in the turbine cylinder block through construction preparation, defect cleaning, preheating before welding, welding, and post-weld hydrogen removal treatment. The repair process is short and of high quality. This not only saves power plants significant maintenance costs and reduces power generation losses, but also ensures that the unit can complete its maintenance on schedule.

[0011] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0012] Figure 1 This is a set of schematic diagrams showing the defect locations in a method for repairing internal cylinder cracks in a medium-pressure cylinder according to the present invention; Figure 2 These are schematic diagrams showing the location of the crack arresting holes in a method for repairing internal cylinder cracks in a medium-pressure cylinder according to the present invention. Figure 3 This invention relates to a method for repairing cracks in the inner cylinder of a medium-pressure steam turbine, which involves taking three replicated samples from the cracked area of ​​the inner cylinder of the medium-pressure steam turbine and performing microstructure analysis. Figure 4 This is the present invention. Figure 3 Region map of sample A in the image; Figure 5 This is the present invention. Figure 3 Region maps of samples B and C in the image; Figure 6 These are metallographic images of sample A, which is a method for repairing cracks in the inner cylinder of a medium-pressure cylinder according to the present invention. Figure 7 These are metallographic images of sample B, representing a method for repairing cracks in the inner cylinder of a medium-pressure cylinder according to the present invention. Figure 8 These are metallographic images of sample C, representing a method for repairing cracks in the inner cylinder of a medium-pressure cylinder according to the present invention. Detailed Implementation

[0013] See Figures 1-8 The present invention includes the following steps: Step 1: Construction Preparation: Determine the power supply location at the construction site, especially the power supply location of the heat treatment machine; when placing the medium-pressure cylinder workpiece to be repaired, the weld seam should be in a flat welding position, and the workpiece should be placed stably, and a platform of appropriate height should be set up on the work surface; the welding machine and heat treatment machine should be in place and have passed inspection and be in normal condition; consumables should be in place, and the welding materials should be dried; wind and rain protection measures should be taken at the construction site. Step 2: Defect cleaning: Before cleaning the defects, drill anti-crack holes, then clean the cracks and defects. After cleaning the defects, grind out a U-shaped bevel. The size of the bevel angle depends on the depth. Step 3: Preheating before welding: For small-sized crack defects, oxyacetylene flame preheating is used, with a preheating range of not less than 3-5 times the workpiece thickness and not less than 300mm on one side, and a preheating temperature of 100℃; For large-sized crack defects, electric heating preheating is used, with a preheating width of not less than 4 times the workpiece thickness on one side, and a preheating temperature of 100℃. Step 4: Welding Before welding, double-check that defects have been cleaned, and clean the oil and rust on the base material within 20mm of the bevel surface until the metal luster is exposed; check the inside of the bevel with an air hammer to ensure there are no defects; select appropriate welding materials and welding parameters according to the workpiece material; During welding, segmented welding is adopted according to the length of the weld, with the length of each segment based on the length of one welding rod; after each segment is welded, stress is relieved by hammering immediately. During welding, while ensuring welding quality, reduce welding parameters, decrease electrode oscillation amplitude, and increase welding speed to reduce welding line energy; the thickness of a single weld bead should not exceed the electrode diameter plus 2, and the width of a single weld bead should not exceed 4 times the electrode diameter. During welding, the weld joints should be staggered, and the crater should be filled when the weld is finished. When welding, use multi-layer, multi-pass welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the bevel and press the passes towards the middle. Before welding a secondary pass or layer, the weld should be cleaned and inspected to ensure there are no defects before welding. The weld should be 2-3mm higher than the base metal. Step 5: Post-weld hydrogen removal treatment: After welding, first clean the slag and welding spatter, and then perform post-heat hydrogen removal treatment on the weld. The heating width on one side should not be less than 4 times the thickness of the workpiece. Use a medium-pressure cylinder to heat both sides at the same time. The heating rate is 60℃ / h. After heating to 350℃, hold the temperature for 2 hours. After holding the temperature, cool down to below 300℃ at a rate of 60℃ / h and then furnace cool to room temperature.

[0014] Working process of this invention: The present invention provides a method for repairing internal cylinder cracks in a medium-pressure cylinder, which is described in conjunction with the accompanying drawings during operation.

[0015] During the overhaul of Unit 2 at a power plant, a crack was found in the lower cylinder block of the intermediate pressure cylinder. The location of the crack is shown in the attached image. Figure 1 A schematic diagram of the defect locations is provided. Based on the material composition analysis report and on-site spectral analysis results, the steel composition is close to that of national standard ZG15Cr1MoV steel. According to the flaw detection report, defect #1 is 200mm long, with a mating surface depth of 78mm and an outer surface depth of 20mm (the crack extends from the outside to the inner surface of the bolt hole). Defect #2 has a length of 80mm at the R-angle where the boss meets the cylinder block, with a depth ranging from 6mm to 12mm. The specific repair steps are as follows: Step 1: Construction Preparation: Determine the power supply location at the construction site, especially the power supply location of the heat treatment machine; when placing the workpieces, try to place the weld seam in the flat welding position, and the workpieces should be placed stably, and a platform of appropriate height should be set up on the work surface; the welding machine and heat treatment machine are in place and have passed inspection and are in normal condition; consumables are in place and the welding materials have been dried; wind and rain protection measures have been taken at the construction site. Step Two: Defect Cleaning: Before cleaning the defects, drill arrest holes. Use a Φ5mm drill bit to drill arrest holes at both ends of defect #2, and use a Φ12mm drill bit to drill arrest holes at both ends of defect #1. The distance between the arrest holes and the crack tip should not exceed 5mm, and the depth should be the detected crack depth plus 3-5mm. For deeper cracks, drill in sections. For small-sized defects, use an angle grinder and an internal grinder to clean the #2 crack. Clean the crack first, and after visually inspecting whether the crack is clean, use PT / MT to confirm whether the crack is clean. After cleaning, a U-shaped bevel is ground, with the bevel angle determined by the depth (refer to the People's Republic of China Electric Power Industry Standard DL / T869-2021 Welding Technical Specification for Thermal Power Plants); for large-sized defects and cracks, carbon arc gouging is used to clean the defects at #1. After cleaning, an angle grinder or internal grinder is used to remove the oxide layer produced by the carbon arc gouging, with a thickness of more than 0.5 mm; the cleaning process should be checked regularly to prevent deviations; a U-shaped bevel is used at this location, with the bevel angle determined by the depth; Step 3: Preheating before welding: For defect #2, use an oxyacetylene flame for preheating. The preheating range should be no less than 3-5 times the workpiece thickness on one side and no less than 300mm. The preheating temperature should be 100℃. During preheating, it is advisable to use 2-4 heating guns simultaneously. The distance from the flame core to the workpiece should be more than 10mm. The moving speed of the nozzle should be stable and should not stay in the same position. For defect #1, use electric heating for preheating. Before operation, a fixing tool for the heating plate should be made according to the characteristics of the workpiece to ensure that the heater can be in close contact with the workpiece. The preheating width of the weld should be no less than 4 times the workpiece thickness on one side. The heating rate during preheating should not exceed 60℃ / h. After reaching 100℃, maintain the temperature for 4 hours to ensure that the workpiece temperature reaches 100℃ uniformly before welding can begin. Step 4: Welding: Before welding, check again to confirm that the defects have been cleaned. Clean the oil and rust on the base material surface within 20mm of the bevel surface until the metal luster is exposed; the inside of the bevel has been checked with an air hammer to check for defects such as loose structure. The selection of welding materials and welding parameters are as follows: Welding should be performed in sections according to the length of the weld, with the length of each section based on the length of one welding rod. After each section is welded, stress should be relieved by hammering. During welding, while ensuring welding quality, welding parameters should be reduced, electrode oscillation amplitude should be decreased, and welding speed should be increased to reduce welding heat input. The thickness of a single weld bead should not exceed the electrode diameter plus 2, and the width of a single weld bead should not exceed 4 times the electrode diameter. During welding, the weld joints should be staggered, and the crater should be filled when the weld is finished. When welding, use multi-layer, multi-pass welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the bevel and press the passes towards the middle. Before welding the secondary pass (layer), the weld should be cleaned and inspected, and welding should only be carried out after confirming that there are no defects. The weld should be 2-3mm higher than the base metal to allow for sufficient machining allowance; Step 5: Post-weld hydrogen removal treatment: After welding, first clean the slag and welding spatter, and then perform post-heat hydrogen removal treatment on the weld. The heating width on one side should not be less than 4 times the workpiece thickness, and both sides of the cylinder should be heated simultaneously. Thermocouples should be placed in representative positions according to the actual situation. The heat preservation width should be measured from the center of the weld, and each side should be at least twice the workpiece thickness than the heating width, and not less than 150mm. The heating rate is 60℃ / h, and after heating to 350℃, the temperature should be held for 2 hours. After holding the temperature, the temperature should be reduced to below 300℃ at a rate of 60℃ / h, and then furnace cooled to room temperature.

[0016] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A method for repairing internal cylinder cracks in a medium-pressure cylinder, characterized in that: Includes the following steps: Step 1: Construction Preparation: Determine the power supply location and the power supply location of the heat treatment machine at the construction site; when placing the medium-pressure cylinder workpiece to be repaired, the weld seam should be in a flat welding position, and the workpiece should be placed stably, and a platform of appropriate height should be set up on the work surface; the welding machine and heat treatment machine should be in place and have passed inspection and be in normal condition; consumables should be in place, and the welding materials should be dried; wind and rain protection measures should be taken at the construction site. Step 2: Defect cleaning: Before cleaning the defects, drill anti-crack holes, then clean the cracks and defects. After cleaning the defects, grind out a U-shaped bevel. The size of the bevel angle depends on the depth. Step 3: Preheating before welding: For small-sized crack defects, oxyacetylene flame preheating is used, with a preheating range of not less than 3-5 times the workpiece thickness and not less than 300mm on one side, and a preheating temperature of 100℃; For large-sized crack defects, electric heating preheating is used, with a preheating width of not less than 4 times the workpiece thickness on one side, and a preheating temperature of 100℃. Step 4: Welding Before welding, double-check that defects have been cleaned, and clean the oil and rust on the base material within 20mm of the bevel surface until the metal luster is exposed; check the inside of the bevel with an air hammer to ensure there are no defects; select appropriate welding materials and welding parameters according to the workpiece material; During welding, segmented welding is adopted according to the length of the weld, with the length of each segment based on the length of one welding rod; after each segment is welded, stress is relieved by hammering immediately. During welding, while ensuring welding quality, reduce welding parameters, decrease electrode oscillation amplitude, and increase welding speed to reduce welding line energy; the thickness of a single weld bead should not exceed the electrode diameter plus 2, and the width of a single weld bead should not exceed 4 times the electrode diameter. During welding, the weld joints should be staggered, and the crater should be filled when the weld is finished. When welding, use multi-layer, multi-pass welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the bevel and press the passes towards the middle. Before welding a secondary pass or layer, the weld should be cleaned and inspected to ensure there are no defects before welding. The weld should be 2-3mm higher than the base metal. Step 5: Post-weld hydrogen removal treatment: After welding, first clean the slag and welding spatter, and then perform post-heat hydrogen removal treatment on the weld. The heating width on one side should not be less than 4 times the thickness of the workpiece. Use a medium-pressure cylinder to heat both sides at the same time. The heating rate is 60℃ / h. After heating to 350℃, hold the temperature for 2 hours. After holding the temperature, cool down to below 300℃ at a rate of 60℃ / h and then furnace cool to room temperature.

2. The method for repairing internal cylinder cracks in a medium-pressure cylinder as described in claim 1, characterized in that: The method for processing the crack arresting hole in step two is as follows: Crack arresting holes are drilled at both ends of the defect using drill bits of different diameters according to the size of the crack defect, and the distance between the crack arresting hole and the crack tip is no more than 5mm. The depth of the crack arresting hole is the detected crack depth plus 3-5mm. For cracks with larger depths, the holes should be drilled in sections.

3. The method for repairing internal cylinder cracks in a medium-pressure cylinder as described in claim 1, characterized in that: The crack defect cleaning in step two is specifically as follows: For small-sized crack defects, an angle grinder and an internal grinder are used for cleaning. The crack is cleaned first, and after visual inspection, a PT / MT test is used to confirm whether the crack is clean. For large-sized crack defects, a carbon arc gouging is used to clean the defects. After cleaning, an angle grinder or an internal grinder is used to clean the oxide layer produced by the carbon arc gouging. The thickness of the cleaning layer should be more than 0.5 mm. During the cleaning process, the defect cleaning status should be checked in a timely manner to prevent deviations from occurring.

4. The method for repairing internal cylinder cracks in a medium-pressure cylinder as described in claim 1, characterized in that: In step three, when preheating the small-sized crack defects, 2-4 heating guns are used simultaneously. During heating, the distance from the flame core to the workpiece should be more than 10mm, and the moving speed of the nozzle should be stable, without staying in the same position.

5. The method for repairing internal cylinder cracks in a medium-pressure cylinder as described in claim 1, characterized in that: In step three, before the preheating operation, a fixing tool for the heating element is made according to the characteristics of the workpiece to ensure that the heater of the preheating device is in close contact with the workpiece. The heating rate of the large-sized crack defect during preheating is no more than 60℃ / h. After the temperature reaches 100℃, it is kept at a constant temperature for 4 hours to make the workpiece temperature uniformly reach 100℃.

6. The method for repairing internal cylinder cracks in a medium-pressure cylinder as described in claim 1, characterized in that: The welding materials and welding parameters in step four are as follows: 。 7. The method for repairing internal cylinder cracks in a medium-pressure cylinder as described in claim 1, characterized in that: In step five, the thermocouples used for heating are arranged in representative positions according to the actual situation. The insulation width during constant temperature is measured from the center of the weld, and each side should be at least twice the workpiece thickness compared to the heating width, and not less than 150mm.

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