Analysis of compressor accident together

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According to the operator, the fault symptom is that the secondary exhaust temperature of the compressor is too high, exceeding 160°C. The operator stopped the machine, disassembled it for inspection, and found no abnormalities; after replacing the piston and cylinder liner, the machine was started up and operated again. A few minutes were enough to damage the top of the piston, and the exhaust temperature remained very high. The machine was shut down again for inspection and cleaning; the piston was replaced. After it was started up and operated for about an hour, a knocking sound came from the crankcase, so the machine was stopped immediately. Upon disassembly, it was found that the compressor’s cylinder head had been damaged and the cooling water jacket was leaking ； The piston, cylinder liner, intake and exhaust valve seats, as well as the connecting rods were all damaged. The crankshaft seized with its bearing shells. Even more seriously, the bolt holes used to fix the cylinder liner in the compressor housing were torn, resulting in a serious situation where the housing could no longer be used, and this led to the entire factory coming to a halt in production. After the accident, I was invited to help solve the problem. Based on the operator’s description, the accident analysis is as follows: The reasons for the excessively high exhaust temperature of the compressor are: (1) Excessive clearance in the compressor cylinder ； 　　(2) Damage to the suction and exhaust valves as well as piston rings in the compressor ； 　　(3) Leakage in the compressor safety bypass valve ； 　　(4) Excessively high compressor suction temperature ； 　　(5) Interruption of lubricating oil in the compressor cylinder ； 　　(6) The compressor’s suction pressure is too low, or the suction valve is opened too little ； (7) There is blockage in the compressor suction pipeline or filter, and the insulation layer is damaged ； 　　(8) Excessive resistance in the compressor return pipeline results in a slow gas flow rate, which can lead to overheating and an increase in exhaust temperature ； 　　(9) Excessively high condensation pressure ； There is oil scale or water scale in the condenser, etc ； 　　(10) Insufficient amount of cooling water in the compressor cylinder head water jacket ； Or the cooling water temperature is too high ； 　　(11) The cooling capacity of the compressor is lower than that of the warehouse equipment, such as when the evaporation area is too large ； 　　(12) Excessive resistance in the compressor exhaust pipeline ； 　　(13) The throttle valve is opened too wide or is blocked ； 　　(14) Poor efficiency of the compressor itself ； 　(15) The ammonia liquid separator is installed at too low a height ； Based on the above analysis, and taking into account the conditions at the site, items (1), (2), (3), (4), (5), (6), (7), (8), (9), and (10) were ruled out; only item (5) remained, namely that the operator failed to conduct a check. Upon inspection of the crankshaft, it was found to be an old crankshaft that had been repaired previously. The area where the seizure occurred was already worn out originally, and it was repaired by applying a filler material; this repaired crankshaft was in use for three months until the accident happened. At the scene, it was discovered that the filler layer in the originally repaired area had come loose, and these loose particles blocked the oil holes in the bearing shells, resulting in a lack of lubrication for the piston. The technicians conducted inspections only on the piston area earlier on, without properly checking the connecting rods, the crankshaft, and the bearing shells, which led to such severe damage. What’s even more frightening is that the operators in this team do not possess certification qualifications for operating refrigeration equipment. Solution: Replace the entire compressor, including the motor. From this accident, we should draw valuable lessons. In future work, we must strictly enforce the requirement that operators hold valid certificates to work. While strengthening management, companies should also properly implement systems for scheduled equipment maintenance and operational management, so as to prevent accidents from occurring in the first place.