Turbine high pressure control valve surfacing repair program
Introduction Zhanjiang Power Plant No. 2 Turbine No. 1 high pressure control valve fails to open, 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. 1 high-pressure main steam valve repair program 1.1 valve disc guide shoulder working mechanism Unit 2 for the East Turbine Factory (N300-16.7 / 537 / 537-3 type) turbine, its high pressure main steam valve Is composed of a main steam valve and two regulating valves, high pressure regulating 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. 1.2 The choice of welding materials and welding equipment According to the working conditions of the regulating 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. 2 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. 3 surfacing process 3.1 process route polished before cleaning - preheating - surfacing - welding heat treatment - after welding turning. 3.2 Welding preparation First of all, with the angular grinding wheel to thoroughly clean the nitrided layer to remove the surfacing within the range of 20mm, grinding depth should be greater than 0.4mm, measuring the hardness of polished parts, and to ensure that the welding area to HB185 ~ 321 Request. According to JB4730-94 testing standards, check the quality of the polished guide shoulder surface without cracks, slag and other defects, to meet the level â… standard. Then clean the valve plate with acetone acetone welding area and the surrounding area of ​​50mm, to ensure that no water, oil, etc .; with sandpaper to remove oil and rust stains on the surface of TIG wire and other dirt. 3.3 Welding process and parameters Using oxyacetylene flame heating preheating before welding, preheating temperature of 350 ~ 400 ℃, with a thermometer to measure the preheating temperature. Valve plate exposed welding parts, other parts covered with asbestos cloth to prevent electric arc burns. Process parameters I = 80 ~ 90A, argon flow rate 8 ~ 10L / min, DC is positive, the voltage range of 10 ~ 15V, welding speed 30 ~ 45mm / min, swing width ≤ 10mm, welding thickness ≤ 4mm. Preheat temperature reaches after the start of welding, the interlayer temperature control at 300 ~ 400 ℃, the welding process is not allowed to produce any defects, focus on inspection lead, Arc Department, found defects immediately removed with the angle grinder. In order to ensure the machining allowance, according to figure surfacing size, diameter increase 5mm, diameter 5mm reduced, pile height 13mm. While surfacing is completed and then surfacing the other side. After welding, with aluminum silicate refractory cotton coated slow cooling, cold welding parts to 100 ~ 150 ℃, immediately after welding local heat treatment. Heat treatment using flame heating to 640 ~ 660 ℃, holding 30min, with thermometer monitoring, heating rate and cooling rate were <300 ℃ / h, cooling to below 300 ℃ can be controlled, cooling with aluminum silicate fiber blanket cold. 4 after-welding inspection Valve plate in accordance with the completion of the process of surfacing and mechanical processing, the penetration of flaw detection and ultrasonic flaw detection, weld no cracks, slag, porosity and other defects quality, surfacing quality JB4730-94 standard grade â… Requirements; hardness test on the processing surface, the average hardness value of HB241, and the hardness of the original base material close to meet the performance of the workpiece. 5 Conclusion Unit 1 No. 1 high-pressure main steam valve welding repair and operation of nearly 1 year after the dismantling of the unit overhaul inspection, surfacing of the valve plate shoulder running 5616h did not find any problems. Visible with TIG-R34 argon arc welding wire surfacing 20Cr3MoWVA material preheated 350 ~ 400 ℃, 640 ~ 650 ℃ after welding, heat treatment 30min welding process is reasonable and feasible. It not only solved the normal high pressure main steam regulating valve to regulate steam, but also saved tens of thousands of yuan of funds.
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