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Control valve surfacing repair methods
High-pressure regulating valve open failure, seriously affecting the safe and stable operation of the unit. Disassembly of the valve inspection and found that high-pressure governor valve seat sink 10mm, resulting in valve disc guide shoulder off the guide groove, the steam can not be properly adjusted. In view of the short time of the unit repair, the seat sinking site is difficult to restore, the decision to use surfacing, increase the height of the guide shoulder to achieve the restoration of the original use of high pressure main steam valve function. High pressure main steam valve repair methods 1, valve disc guide shoulder working mechanism Unit 2 for the East Steam Turbine Works (N300-16.7 / 537 / 537-3 type) turbine, and its high pressure main steam valve is a The main steam valve and two control valves, high pressure control valve is used to regulate the intake cylinder pressure. When the unit is running, the oil motive serves as a mechanical lifting device, so that the valve disc guide shoulder moves up and down along the guide groove to control the opening of the valve disc. When the unit is running, the high-temperature steam of the regulating valve is 16.7MPa and 537 ℃. The guiding shoulder is mainly subjected to thermal stress and certain circumferential shearing stress. Valve No. 1 No. valve disc and valve seat with a diameter of 170mm, the valve disc structure shown in Figure 1, the guide shoulder size of 55mm × 30mm × 10mm (height × width × thickness). Disc material with 20Cr3MoWVA alloy steel, in order to improve the performance of valve disc cavitation erosion, the surface of the nitriding temperature treatment. 2, the choice of welding materials and welding equipment According to the working conditions of the control valve, valve disc guide shoulder both to ensure adequate high temperature strength, but also to meet a certain degree of wear resistance. In view of unit repair, can not be purchased to the best matching materials, reference to the principle of the choice of welding materials and mechanical properties of the welding material analysis, selection and the base material similar TIG-R34 (12Cr2MoWVTIB, Φ2.5mm) welding wire. Welding equipment used LincolnV300-1 and argon arc welding kit; temperature monitoring using the United States MX2 infrared thermometer. Analysis of welding performance According to the formula of carbon equivalent formula, the material 20Cr3MoWVA main features are more carbon and alloy elements, welding and heat treatment zone prone to harden the structure, when the weldment rigidity and joint stress is large, prone to cold crack. After nitriding valve disc, the surface hardness up to HV900, easy to crack when welding.