Precautions for manhole maintenance of high-voltage equipment

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Leakage on the sealing surface is mainly caused by defects on the sealing surface, poor assembly of the gasket, or insufficient or uneven preload force. Precautions for maintenance of manhole sealing surfaces of high-pressure equipment are as follows:: a. During maintenance, the sealing surface must be carefully checked for scratches, corrosion pits and other defects. And check for cracks with tint. For deep scratches and corrosion pits, local repair welding can be carried out. The cracks should be polished first and the cracks should be polished and eliminated before repair welding. It is best to use manual argon arc welding for repair welding. The repair welding area is small and can be smoothed by manual filing and grinding. ； If the repair welding area is large, it can be processed on a lathe or with a special tool holder. When high-pressure studs and nuts have defects such as slight bites or naps, they can be repaired by adding a small amount of abrasive sand. If magnetic particle inspection finds cracks in the studs or nuts that affect their strength, they should be replaced. b. After long-term use, the sealing surfaces on the manhole cover and tower flange will become deformed and the seal will fail. During maintenance, the manhole cover can be put on a lathe, or a special tool holder can be installed on the tower flange to level the sealing surface with a light knife. After passing through the light knife, the sealing surface must be inspected with a calibrated ferrite meter to ensure that the material within 3mm from the surface meets the corrosion resistance requirements. c. For asbestos stainless steel toothed composite pads, the asbestos pad should be carefully removed after removal, and the toothed pad should be carefully inspected. If there are no defects that affect the sealing effect, it can still be reused. If the toothed pad or lens pad has defects that affect the sealing effect, it should be replaced. The new gasket material should comply with the relevant standards of the original design. ； If it is a titanium lens pad, it should be carefully inspected after removal. If there are no defects that affect the sealing effect, it can still be reused. The requirements for manhole sealing structure assembly are as follows:: (1) Before assembly, the sealing surface and stainless steel toothed gasket must be cleaned, and there should be no dirt on the sealing surface. (2) The manhole cover should be lifted smoothly and slowly to prevent jamming when falling. After the manhole cover is in place, its sealing surface and the sealing surface on the tower flange and the combined gasket should be basically evenly connected before using the hydraulic unloading device to add pressure. (3) The outer surface around the bolt hole on the manhole cover and the plane of the main nut should be smooth and free of burrs. Otherwise, it will affect the even force of the gasket. (4) To facilitate disassembly, the threads of the main bolts should be painted with molybdenum disulfide. (5) Tighten the main bolts (according to the ammonia stripper maintenance regulations). 1) First tighten the nut by hand or a simple tool until the bottom surface of the nut contacts the flange surface. 2) Use hydraulic fastening devices to tighten the bolts according to the equipment manufacturer or the drawings. Fasten four bolts at the same time in each step. The bolt pre-tightening force is divided into four steps to gradually tighten the manhole main bolts. The tightening oil pressure in each step is 50%, 71%, 100%, and 100% of the final pressure. ； For each step of oil pressure value, the bolts must be tightened in groups in the specified order. ； During the tightening process, the gap between the flange surfaces should be measured every time the bolt is tightened, and the difference should be controlled within 0.3mm. ； After tightening in the third step, use the oil pressure value in the third step to tighten the entire circle of bolts evenly. 3) After the system is heated and passivated, the bolts should be heat-tightened once, and the hot-tightening oil pressure should be the final oil pressure value. (6) In order to ensure reliable sealing, pre-tighten the bolts again after 24 hours of tightening, or after heat passivation. When the system has the opportunity to stop and discharge, it should also be pre-tightened to the same oil pressure value. This can ensure the long-term safe operation of the device. (7) When removing the manhole cover, the nuts should also be loosened in the same order, but the oil pressure for the first time can be slightly higher than the final pressure when tightening.