The E-GT501 turbine of the compression system of the ethylene plant is the driver of the vertical centrifugal pump (designation: E-GA501A). It is responsible for the timely discharge of the condensed water of the propylene refrigeration compressor to ensure the normal operation of the unit, the E-GT501 turbine worm gear failed in June 1998. Although the results were not satisfactory after repeated maintenance, the service life of the new worm gear was very short, the longest being no more than 20 hours, resulting in the turbine not working normally. The chemical pump driven by another motor (bit number: E-GA501B) has been running as a single unit without a backup pump. If the E-GA501 water pump fails suddenly, it will inevitably cause the propylene compressor unit to stop, and the entire ethylene plant will be affected. The stable production poses a great threat. We analyzed and found the root cause of the failure of the turbine worm gear, and successfully solved the problem by changing the material of the worm gear.
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Analysis of the first failure of the worm gear
After the first failure of the worm gear in June 1998, we found during the inspection of the turbine that there was a lot of free water in the turbine lubricating oil tank. Since the transmission of the worm gear and worm is realized by the meshing of the tooth surfaces, its friction surface must establish an extreme pressure lubricating film, which is a lubricating film generated by the reaction between the extreme pressure agent in the lubricating oil and the metal surface. It has high strength and can withstand The load generated by the meshing of the worm gear. The presence of water in the lubricating oil will cause the inactivation of the extreme pressure agent, so that the meshing surface cannot form a lubricating film, resulting in direct contact with the surface of the worm gear and worm, resulting in surface wear. Since the worm gear is made of tin bronze (code ZQSn10-1), its allowable contact stress is 220MN/m2, while the worm is made of alloy steel (steel number: 35CrMo), and its allowable contact stress is 850MN/m2. Soft, so the form of failure is the wear of the worm gear teeth.
We conducted a comprehensive analysis of the lubricating oil system, and finally confirmed that the water in the oil system comes from the condensed water formed by the leaking steam of the turbine seal. Due to the very good thermal insulation of the turbine, part of the leaked steam will inevitably enter the lubricating oil system through the bearing oil seal.
In view of the problem of failure of the worm gear due to water in the lubricating oil, according to the requirements of the random operation manual of the turbine, we sample and analyze the water content of the lubricating oil every month, drain water from the bottom of the oil tank regularly, and formulate a relevant management system.
After the above improvement measures, the E-GT501 turbine has been put into use since October 2000, and it has been running normally for more than 2 years, and there is still no sign of damage, which provides a strong guarantee for the stable operation of the device. More than 8,000 tons of medium-pressure steam can save 15Kw×8,000h=120,000 kWh of electricity every year. Calculated at 0.6 yuan per kWh, it can save 72,000 yuan in electricity bills a year, and the economic benefits are very obvious.
Since the original design of the condensate pump turbine worm gear has no margin for the contact strength of the teeth, it frequently fails, and the problem is solved by changing the material of the worm gear and formulating the relevant management system according to the requirements. With the increase in the introduction of foreign equipment in my country, the original design conditions should be checked according to the differences in national conditions, which should be paid attention to in the process of localization of spare parts. The process of solving the failure problem of the turbine worm gear of the condensate pump has certain reference significance.