Belt Polishing Machine,Polishing Belt Machine,Concrete Polishing Machine,Grinding And Polishing Machine Foshan Youngmax Machine Co.LTD , https://www.ymaxmachine.com
ã€Abstract】 The paper analyzes in detail the reasons why the high pressure regulating door of Harbin-made domestic 300MW steam turbine unit is out of operation during the operation and causes the valve to close, and puts forward some countermeasures. The importance of improving the maintenance process to the safe operation of the unit is pointed out. Countermeasures 1, Situation: Hebei Xibaipo Power Co., Ltd. installed capacity of 4 × 300MW, Harbin N300-16.7 / 537 (538) / 537 (538), subcritical , Uniaxial, condensing steam turbine, high-pressure cylinder into the steam from the two high-pressure main steam door and six high-pressure regulating door (referred to as high-profile door) control, high-profile door operating mode according to load size using single valve or sequence valve. One # 1 unit put into operation in December 1993, after three major overhauls, six minor repairs, the last overhaul time in October 2002. 2, the cause of the incident 2.1, October 2002 # 1 unit overhaul, # 4 high-profile door disintegration found the head gate (there is no thread, but the processing of cross-dowel hole, Ñ„12mm, L = 120mm) occurred transverse fracture. Due to stop cross-off (referred to as horizontal pin) is not prolapse, so # 4 high-profile door before the operation of stable, no exception. 2.2, door head fracture analysis 2.2.1, force. Long-term operation of the steam generated on the door axial periodic excitation force, the connecting rod head and connecting parts prone to fatigue damage. 2.2.2, processing technology. The gate head horizontal cross hole is drilled and then reamed. The edge of the hole presents a blade-like shape, forming a typical stress concentration point. Once the crack is formed, it rapidly develops into a fracture. 2.2.3, material. Door material 2Cr12NiMoWV, work at high temperatures, in order to increase its high temperature oxidation ability, the surface of a special nitriding, the formation of a layer of about 0.5mm thick nitrogen and nitrogen compounds, its hardness, wear resistance, oxidation resistance greatly Increase, the corresponding increase of brittleness, reduce the toughness. 2.2.4, improper assembly process. Ha steam plant high-profile door assembly process requirements: Cold installation, the door lever into the guide sleeve, the need to exert a torque of 152N * M on the door, and then loaded into the horizontal pin. That is required after the cold installation of the door stem and guide sleeve completely tight contact, forbidden to leave a gap. Hot running, the door stem is wrapped inside the guide sleeve, the temperature is higher than the guide sleeve, the linear expansion of the axial direction is greater than the guide sleeve, the tight with the above can still be guaranteed. Therefore, when the door rod is hot, the door rod is subjected to the axial exciting force of the steam, which force is transmitted directly to the guide sleeve, so that the connecting rod of the door rod is not subjected to the exciting force because the threaded portion is more likely to occur Damage to the stress concentration point, thus preventing the fatigue of the thread. The actual situation is not the case, there are six high-profile doors do not meet the technical requirements of the phenomenon of varying degrees, that cold back door lever, 152N * M torque torque applied, the door cross pin hole and guide pin cross pin hole misplacement Phenomenon, horizontal pin can not be successfully loaded. In order to be able to successfully install the horizontal pin, the door must be slightly rotated backwards. If the cross pin hole is displaced by 2mm and the connecting rod thread is M50 * 2, the door rod needs to be withdrawn by about 0.025mm, that is 0.025mm mm gap, which in turn does not meet the technical requirements of the tight fit. If the maintenance staff ignored the technical requirements of the assembly, the figure effortless and hasty installation, it will leave a security risk. Cross hole pinhole two major reasons for dislocation: a parts factory processing size does not meet the technical requirements; b door long-term operation at high temperature, under stress, the connection thread by the tensile stress, compressive stress, vibration and fatigue damage and high temperature Oxidation and other effects, the surface deformation, defects, assembly gap will change. 2.2.5, horizontal pin deformation. After the cross-section stress, it will be slightly bent and distorted, and it will not be replaced during maintenance. Due to the large squeezing force at the edge of the pin hole due to misalignment, the stress on the edge of the pin hole further deteriorates and the possibility of cracking may be caused Sharply increased. 2.2.6, impact stress. Unit in the size of the late repair often do DEH mixed defense test, a large interlock test, do speed test at boot and emergency shutdown, high-profile door will be quickly closed within 0.3 to 0.5 seconds, the design due to the high-profile door and valve plate (Such as the high-pressure main valve spool installed inside) the buffer spring structure, making the door to be subjected to multiple strong impact, the impact of the gate head is particularly serious, further exacerbating the cross-hole crack. 3, measures: replace the new door pole. In view of the fact that the horizontal guide hole of the old guide sleeve may be drilled again, the inner diameter may be enlarged by the drill bit or the drill bit may deviate to cancel the horizontal pin hole, resulting in the assembly size of the horizontal pin not satisfying the requirements and the reworking of the horizontal pin hole at 20mm Department, the new door stem and guide sleeve after cold drilling installed once completed. 4, the development of the incident 4.1.1, April 8, 2003, the crew found # 1 machine # 4 high-profile door on-site valve opening (master monitor screen shows LVDT valve opening feedback has instructions), the closure of the valve after the command is issued But no response, suspected actuator servo valve failure, require maintenance personnel to deal with. # 4 high-profile door covered with a pin # 4 high-profile door covered with a pin when the inspection staff to check the gas side of the actuator was closed Child, confirm the gate rod and the guide sleeve horizontal pin prolapse, the door stem rotation from the guide sleeve down to close into the steam. 4.2 Analysis of reasons 4.2.1, after the cross-pin must be installed at both ends of the cross pin bore riveting stamping, the door rod sleeve of high hardness, sealing riveting difficult, sealing riveting point deformation is small, failed to play very Good sealing effect. 4.2.2, cross-pin length and pin hole length is almost the same, a small amount of sealing rivets, sealing riveting caused difficulties. If the cross is longer than the pin hole, you can not seal rivets. 4.2.3, around the guide pin hole due to repeated sealing riveting demolition, more defects in the base metal, seal riveting difficult. 4.2.4. The key reason is that in the original design, the guide pin hole is clamped by the lever arms on both sides, that is, the pin is observed from the outside. Due to the cover of the lever arm, only one half of the cross section of the cross pin can be seen. It can be understood that when the pin is loosened for various reasons and attempts to move to one side, it stops after reaching a lever arm after a small displacement. Overhaul in the re-processing of cross-hole sales as a whole down 20mm, cross-pin just from the lever arm protection, run-off can be successfully run out and lead to the valve stem down to close the valve. 5, processing steps 5.1, keep the unit running, single-valve mode of operation, the load limit below 220MW, turn off the # 4 high-profile door oil motive oil cut-off gate, cut off the oil. 5.2, remove the oil motive and the lever arm link pin, first with a jack to lift the lever arm, and in the lower part of the accumulator spring into the appropriate pad (square steel). 5.3, remove the pull spring, and then remove the jack, remove the lever arm and guide sleeve and the rear bearing coupling pin, remove the lever arm, the guide sleeve completely exposed. 5.4, ​​due to the valve butterfly is closed, the valve there is a huge vapor pressure before and after the difference, the valve butterfly is firmly pressed on the bottom of the mouth, the door will not easily move the rod, then turn the guide sleeve clockwise until the pin hole alignment, Reinstall the pins and seal the points firmly, restoring the rest of the connection. 5.5, closely monitor the load changes, open the oil into the oil gate, # 4 high-profile door into operation, remove the bottom of the pressure storage pad spring block. 6, Reflections 6.1, maintenance personnel on the structure and principles of the equipment must have a comprehensive understanding and mastery, requiring specific details of each problem. Any changes or changes to equipment (especially those imported or imported from abroad) must be justified by professional and technical personnel. Any unscientific act will be deservedly costly. 6.2, improve the high-profile door repair process is to ensure the long-term safe operation of the prerequisite, in which the quality of personnel occupy a leading position. To further strengthen the technical training of maintenance personnel to improve the overall level of skills should be the current important concern, the only way to ensure the quality of equipment maintenance.