Method for repairing cracks of inner cylinder of medium-pressure cylinder

Abstract

The invention discloses a method for repairing cracks of an inner cylinder of a medium-pressure cylinder. The method comprises the following steps that firstly, construction preparation is conducted; secondly, crack arrest holes are punched before defect cleaning, then crack defects are cleaned, a U-shaped groove is ground after the defects are cleaned, and the size of the groove angle is determined according to the depth; 4, checking again before welding to confirm that the defects are cleaned up, and selecting proper welding materials and welding parameters for welding according to the material of the workpiece; and fifthly, after welding is completed, medicine residues and welding spatter are removed, and then after-heat hydrogen elimination treatment is conducted on a welding seam. According to the method, through construction preparation, defect cleaning, preheating before welding, welding and hydrogen elimination treatment after welding, the major defects of cracks of the steam turbine cylinder body are repaired, the repairing period is short, and the quality is good. High maintenance cost is saved for a power plant, power generation loss is reduced, and guarantee is provided for a unit to complete maintenance on schedule.

Description

Technical Field

[0001] The present invention relates to the technical field of crack repair, in particular to the technical field of crack repair in a medium-pressure cylinder. Background Art

[0002] Steam turbine units in power plants require routine maintenance. When cracks are discovered within the cylinders of large steam turbines during this inspection, prompt repair is crucial to prevent the cracks from expanding and causing significant economic losses. However, currently, there is no comprehensive technical solution for repairing these large steam turbine cylinder cracks, particularly those within the intermediate-pressure cylinder. Therefore, a method for repairing cracks within the intermediate-pressure cylinder is needed. Summary of the Invention

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

[0004] To achieve the above object, the present invention proposes a method for repairing cracks in a medium pressure cylinder, 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; the medium-pressure cylinder workpiece to be repaired should be placed with the weld in the flat welding position, and the workpiece should be placed firmly, 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 inspected and in normal condition; consumables should be in place and the welding materials should be dried; take measures to protect the construction site from wind and rain; Step 2: Defect cleaning: Before defect cleaning, drill a stop hole, then clean the crack defect. After the defect is cleaned, grind out a U-shaped groove. The angle of the groove is determined by the depth. Step 3: Preheating before welding: For small-sized crack defects, use oxyacetylene flame to preheat, the preheating range is not less than 3-5 times the thickness of the workpiece on one side and not less than 300mm, and the preheating temperature is 100°C; for large-sized crack defects, use electric heating to preheat, the preheating width is not less than 4 times the thickness of the workpiece on one side of the weld, and the preheating temperature is 100°C; Step 4: Soldering: Before welding, check again to confirm that all defects have been cleaned up, and the oil, dirt and rust on the surface of the parent material within 20mm of the groove surface have been cleaned up until the metallic luster is exposed; the groove has been checked for defects with an air hammer; select appropriate welding materials and welding parameters according to the workpiece material; During welding, the weld seam is welded in sections according to its length. The length of each weld seam is based on the length of one welding rod. After each weld seam is welded, it is immediately hammered to relieve stress. When welding, under the premise of ensuring welding quality, reduce welding parameters, reduce the swing amplitude of the welding rod, and increase the welding speed to reduce the welding line energy; the thickness of a single layer weld should not exceed the diameter of the welding rod plus 2, and the width of a single weld should not exceed 4 times the diameter of the welding rod; During welding, the welding joints should be staggered and the arc pit should be filled when the welding arc is closed; Use multi-layer and multi-pass welding during welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the groove and press toward the middle. Before welding a 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 parent material; Step 5: Post-weld dehydrogenation treatment: After welding is completed, clean the slag and welding spatter first, and then perform post-heat dehydrogenation treatment on the weld. The heating width on one side during heating should not be less than 4 times the thickness of the workpiece. Both sides of the medium-pressure cylinder body should be heated simultaneously. The heating rate during heating is 60℃ / h. After heating to 350℃, keep the temperature constant for 2h. After the constant temperature is completed, cool it down to below 300℃ at a rate of 60℃ / h and then cool it to room temperature in the furnace.

[0005] Preferably, the processing method of the crack stop hole in step 2 is: according to the size of the crack defect, drill bits of different diameters are used to drill crack stop holes at both ends of the defect, and the crack stop hole is no more than 5mm away from the crack tip, and the depth of the crack stop hole is the detected crack depth plus 3-5mm. Cracks with larger depths should be drilled in sections.

[0006] Preferably, the crack defect cleaning in the step 2 is specifically as follows: the crack cleaning of the small-sized crack defects is carried out by using an angle grinder and an internal grinder, the cracks are cleaned first, and after visual inspection, the cracks are cleaned, and then PT / MT detection is used to confirm whether the cracks are cleaned; the large-sized crack defects are cleaned by using a carbon arc gouging to clean the defects, and after cleaning, the oxide layer produced by the carbon arc gouging is cleaned with an angle grinder or an internal grinder, and the cleaning thickness is more than 0.5 mm, and the defect cleaning status is checked in time during the cleaning process to prevent deviations during the cleaning process.

[0007] Preferably, in step 3, the small-sized crack defects are preheated by using 2-4 drying guns for simultaneous heating. During heating, the distance between the flame core and the workpiece is more than 10 mm, and the moving speed of the nozzle should be stable and must not stay at the same position.

[0008] Preferably, in step 3, for large-sized crack defects, a fixing tool for the heating plate is made according to the characteristics of the workpiece before the preheating operation to ensure that the heater is in close contact with the workpiece during preheating. The heating rate during preheating of large-sized crack defects is not greater than 60°C / h. After the temperature reaches 100°C, it is kept constant for 4 hours to ensure that the workpiece temperature reaches 100°C uniformly. Preferably, the welding materials and welding parameters in step 4 are as follows:

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

[0010] The present invention has the following beneficial effects: Through construction preparation, defect cleaning, pre-weld preheating, welding, and post-weld hydrogen removal, it can complete the repair of major cracks in steam turbine cylinders with a short repair period and high quality. This not only saves the power plant high maintenance costs and reduces power generation losses, but also ensures that the unit maintenance is completed on schedule.

[0011] The features and advantages of the present invention will be described in detail through embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of defect locations in a method for repairing cracks in a medium-pressure cylinder according to the present invention; Figure 2 This is a schematic diagram of the locations of crack arrest holes in a method for repairing cracks in a medium-pressure cylinder according to the present invention; Figure 3 This is a method for repairing cracks in a medium-pressure cylinder of a steam turbine according to the present invention. Three replicated samples are taken from the crack area of the medium-pressure cylinder of the steam turbine for microstructural analysis. Figure 4 This invention Figure 3 The area map of sample A in ; Figure 5 This invention Figure 3 The regional diagram of sample B and sample C in the figure; Figure 6 This is a set of crack metallographic analysis images of sample A of a medium-pressure cylinder inner cylinder crack repair method of the present invention; Figure 7 This is a set of crack metallographic analysis images of sample B of a medium-pressure cylinder inner cylinder crack repair method of the present invention; Figure 8 This is a set of crack metallographic analysis images of sample C of a medium-pressure cylinder inner cylinder crack repair method of the present invention. DETAILED DESCRIPTION

[0013] See Figures 1-8 , the present invention comprises 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; the medium-pressure cylinder workpiece to be repaired should be placed with the weld in the flat welding position, and the workpiece should be placed firmly, 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 inspected and in normal condition; consumables should be in place and the welding materials should be dried; take measures to protect the construction site from wind and rain; Step 2: Defect cleaning: Before defect cleaning, drill a stop hole, then clean the crack defect. After the defect is cleaned, grind out a U-shaped groove. The angle of the groove is determined by the depth. Step 3: Preheating before welding: For small-sized crack defects, use oxyacetylene flame to preheat, the preheating range is not less than 3-5 times the thickness of the workpiece on one side and not less than 300mm, and the preheating temperature is 100°C; for large-sized crack defects, use electric heating to preheat, the preheating width is not less than 4 times the thickness of the workpiece on one side of the weld, and the preheating temperature is 100°C; Step 4: Soldering: Before welding, check again to confirm that all defects have been cleaned up, and the oil, dirt and rust on the surface of the parent material within 20mm of the groove surface have been cleaned up until the metallic luster is exposed; the groove has been checked for defects with an air hammer; select appropriate welding materials and welding parameters according to the workpiece material; During welding, the weld seam is welded in sections according to its length. The length of each weld seam is based on the length of one welding rod. After each weld seam is welded, it is immediately hammered to relieve stress. When welding, under the premise of ensuring welding quality, reduce welding parameters, reduce the swing amplitude of the welding rod, and increase the welding speed to reduce the welding line energy; the thickness of a single layer weld should not exceed the diameter of the welding rod plus 2, and the width of a single weld should not exceed 4 times the diameter of the welding rod; During welding, the welding joints should be staggered and the arc pit should be filled when the welding arc is closed; Use multi-layer and multi-pass welding during welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the groove and press toward the middle. Before welding a 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 parent material; Step 5: Post-weld dehydrogenation treatment: After welding is completed, clean the slag and welding spatter first, and then perform post-heat dehydrogenation treatment on the weld. The heating width on one side during heating should not be less than 4 times the thickness of the workpiece. Both sides of the medium-pressure cylinder body should be heated simultaneously. The heating rate during heating is 60℃ / h. After heating to 350℃, keep the temperature constant for 2h. After the constant temperature is completed, cool it down to below 300℃ at a rate of 60℃ / h and then cool it to room temperature in the furnace.

[0014] Working process of the present invention: The working process of a method for repairing cracks in a medium-pressure cylinder of the present invention is described with reference to the accompanying drawings.

[0015] During the overhaul of Unit 2 of a power plant, a crack was found in the lower cylinder of the intermediate pressure cylinder. The location of the crack is shown in the attached figure. Figure 1 Schematic diagram of the defect locations in the image. According to the material composition analysis report and on-site spectral analysis results, the steel's composition is close to the national standard ZG15Cr1MoV steel. According to the flaw detection report, defect #1 is 200mm long, 78mm deep at the joint surface, and 20mm deep on the outer surface (the crack extends from the outside to the inner surface of the bolt hole). Defect #2 is 80mm long 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 workpiece, try to keep the weld in the flat welding position, and the workpiece must be placed firmly, and the work surface must be built with a platform of appropriate height; the welding machine and heat treatment machine must be in place and inspected and in normal condition; consumables must be in place and the welding materials must be dried; wind and rain protection measures must be taken at the construction site; Step 2: Defect cleaning: Drill crack-stop holes before defect cleaning. Use a Φ5mm diameter drill bit to drill crack-stop holes at both ends of defect #2, and use a Φ12mm diameter drill bit to drill crack-stop holes at both ends of defect #1. The distance between the crack-stop holes and the crack tip should not exceed 5mm, and the depth should be 3-5mm more than the detected crack depth. Deeper cracks should be drilled in sections. Small-sized defects such as defect #2 should be cleaned with an angle grinder and an internal grinder. Clean the cracks first, visually check that the cracks are clean, and then use PT / MT to confirm whether the cracks are clean. After cleaning, a U-shaped groove is ground. The angle of the groove is determined by the depth (refer to the Electric Power Industry Standard DL / T869-2021 of the People's Republic of China, Technical Specification for Welding of Thermal Power Plants). The large-sized defect crack #1 is cleaned with carbon arc air gouging. After cleaning, the oxide layer produced by the carbon arc gouging is cleaned with an angle grinder or internal grinder. The cleaning thickness should be at least 0.5mm. The defect cleaning status should be checked in time during the cleaning process to prevent deviations during the cleaning process. A U-shaped groove is used here, and the angle of the groove is determined by the depth. Step 3: Preheating before welding: Use oxyacetylene flame for preheating at defect #2. The preheating range is no less than 3-5 times the thickness of the workpiece on one side and no less than 300mm. The preheating temperature is 100℃. It is advisable to use 2-4 drying guns for simultaneous heating. The distance between the flame center and the workpiece should be more than 10mm during heating. The movement speed of the nozzle should be stable and should not stay in the same position. Electric heating is used for preheating at defect #1. 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 close to the workpiece. The preheating width of the weld seam on one side should be no less than 4 times the thickness of the workpiece. The heating rate during preheating should not exceed 60℃ / h. After the temperature reaches 100℃, keep the temperature constant for 4 hours. Welding can only be started after the workpiece temperature reaches 100℃ uniformly. Step 4: Welding: Before welding, check again to confirm that the defects have been cleaned up, and the oil, dirt and rust on the surface of the base material within 20mm of the groove surface are cleaned until the metallic luster is exposed; the groove has been checked for defects such as looseness and disorganization with an air hammer; The selection of welding materials and welding parameters are as follows: When welding, the weld should be welded in sections according to the length of the weld. The length of each weld section is based on the length of one welding rod. After each weld section is welded, hammer stress relief should be performed immediately. When welding, under the premise of ensuring welding quality, the welding parameters should be reduced, the electrode swing amplitude should be reduced, and the welding speed should be increased to reduce the welding line energy; the thickness of a single layer weld should not be greater than the diameter of the electrode used plus 2, and the width of a single weld should not be greater than 4 times the diameter of the electrode used; During welding, the welding joints should be staggered and the arc pit should be filled when the welding arc is closed; Use multi-layer and multi-pass welding during welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the groove and press toward the middle. Before welding the next pass (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 parent material to allow for sufficient machining allowance; Step 5: Post-weld dehydrogenation treatment: After welding is completed, clean the slag and welding spatter first, and then perform post-heat dehydrogenation treatment on the weld; the heating width on one side should not be less than 4 times the thickness of the workpiece, and both sides of the cylinder should be heated simultaneously; the thermocouples should be arranged in more representative positions according to actual conditions; the insulation width is measured from the center of the weld, and each side should be at least 2 times the thickness of the workpiece longer than the heating width, and not less than 150mm; the heating rate is 60℃ / h, and after heating to 350℃, keep the temperature constant for 2h. After the constant temperature is completed, cool it down to below 300℃ at a rate of 60℃ / h and then cool it to room temperature in the furnace.

[0016] The above embodiments are intended to illustrate the present invention, not to limit the present invention. Any solution that is a simple transformation of the present invention falls within the protection scope of the present invention.

Claims

1. A method for repairing cracks in a medium-pressure cylinder, characterized by: The following steps are involved: Step 1: Construction Preparation: Determine the power supply location at the construction site, especially the power supply location of the heat treatment machine; the medium-pressure cylinder workpiece to be repaired should be placed with the weld in the flat welding position, and the workpiece should be placed firmly, 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 inspected and in normal condition; consumables should be in place and the welding materials should be dried; take measures to protect the construction site from wind and rain; Step 2: Defect cleaning: Before defect cleaning, drill a stop hole, then clean the crack defect. After the defect is cleaned, grind out a U-shaped groove. The angle of the groove is determined by the depth. Step 3: Preheating before welding: For small-sized crack defects, use oxyacetylene flame to preheat, the preheating range is not less than 3-5 times the thickness of the workpiece on one side and not less than 300mm, and the preheating temperature is 100°C; for large-sized crack defects, use electric heating to preheat, the preheating width is not less than 4 times the thickness of the workpiece on one side of the weld, and the preheating temperature is 100°C; Step 4: Soldering: Before welding, check again to confirm that all defects have been cleaned up, and the oil, dirt and rust on the surface of the parent material within 20mm of the groove surface have been cleaned up until the metallic luster is exposed; the groove has been checked for defects with an air hammer; select appropriate welding materials and welding parameters according to the workpiece material; During welding, the weld seam is welded in sections according to its length. The length of each weld seam is based on the length of one welding rod. After each weld seam is welded, it is immediately hammered to relieve stress. When welding, under the premise of ensuring welding quality, reduce welding parameters, reduce the swing amplitude of the welding rod, and increase the welding speed to reduce the welding line energy; the thickness of a single layer weld should not exceed the diameter of the welding rod plus 2, and the width of a single weld should not exceed 4 times the diameter of the welding rod; During welding, the welding joints should be staggered and the arc pit should be filled when the welding arc is closed; Use multi-layer and multi-pass welding during welding. The subsequent weld should cover 1 / 3 to 1 / 2 of the previous weld. When welding, start from both sides of the groove and press toward the middle. Before welding a 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 parent material; Step 5: Post-weld dehydrogenation treatment: After welding is completed, clean the slag and welding spatter first, and then perform post-heat dehydrogenation treatment on the weld. The heating width on one side during heating should not be less than 4 times the thickness of the workpiece. Both sides of the medium-pressure cylinder body should be heated simultaneously. The heating rate during heating is 60℃ / h. After heating to 350℃, keep the temperature constant for 2h. After the constant temperature is completed, cool it down to below 300℃ at a rate of 60℃ / h and then cool it to room temperature in the furnace.

2. A method for repairing cracks in a medium-pressure cylinder according to claim 1, characterized in that: The processing method of the crack stop hole in the step 2 is: according to the size of the crack defect, drill bits of different diameters are used to drill crack stop holes at both ends of the defect, and the crack stop hole is no more than 5mm away from the crack tip. The depth of the crack stop hole is the detected crack depth plus 3-5mm. Cracks with larger depths should be drilled in sections.

3. The method for repairing cracks in a medium-pressure cylinder according to claim 1, characterized in that: The crack defect cleaning in the step 2 is specifically as follows: the cracks of small sizes are cleaned by using an angle grinder and an internal grinder, the cracks are cleaned first, and after visual inspection, the PT / MT test is used to confirm whether the cracks are cleaned; the cracks of large sizes are cleaned by using a carbon arc gouging, and after cleaning, the oxide layer produced by the carbon arc gouging is cleaned with an angle grinder or an internal grinder, and the cleaning thickness is more than 0.5 mm. In the cleaning process, the defect cleaning status is checked in time to prevent deviations in the cleaning process.

4. The method for repairing cracks in a medium-pressure cylinder according to claim 1, characterized in that: In the step 3, 2-4 drying guns are used to heat the small-sized crack defects simultaneously. During heating, the distance between the flame center and the workpiece is more than 10 mm, and the moving speed of the nozzle should be stable and must not stay in the same position.

5. The method for repairing cracks in a medium-pressure cylinder according to claim 1, characterized in that: In the step three, a fixing tool for the heating plate is made according to the characteristics of the workpiece before the preheating operation to ensure that the heater of the preheating device is close to the workpiece. The heating rate of the large-sized crack defect during preheating is not more than 60°C / h. After the temperature reaches 100°C, the temperature is kept constant for 4 hours to ensure that the temperature of the workpiece reaches 100°C evenly.

6. The method for repairing cracks in a medium-pressure cylinder according to claim 1, characterized in that: The welding materials and welding parameters in step 4 are as follows: 。 7. The method for repairing cracks in a medium-pressure cylinder according to claim 1, characterized in that: The thermocouples used for heating in step 5 are arranged at more representative positions according to actual conditions. The insulation width during constant temperature is measured from the center of the weld, and each side should be at least twice the thickness of the workpiece larger than the heating width, and not less than 150 mm.

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