Abstract: The propylene outflow pump of ethylene plant is a GSB type high-speed pump, the seal frequently leaks. Through the calculation and analysis of the specific pressure of the mechanical seal end face, the cause of the seal failure is found by analyzing the material and structure of the mechanical seal moving ring. Targeted to its comprehensive transformation, received good results. Keywords: High Speed ​​Pump Mechanical Seal Leakage Analysis Modification Ethylene Unit The propylene delivery pump (designation E-GA301A / B) supplies raw material for the downstream polypropylene unit. The pump has an extremely important role for the entire polypropylene unit. The liquid used for the reaction All of propylene is supplied by it, so once the pump has a problem, it will cause the entire ethylene and polypropylene plant to stop. Since the pump was put into use in April 2001, the two pumps have had many lubricating oil and sealing liquid and Propylene leakage problem. Despite repeated maintenance, replace the new mechanical seal components, but little effect. Frequent failure of the pump, not only the loss of a large number of propylene, an increase of maintenance costs, but also to the entire polypropylene plant has brought great risks for the stable production. By analyzing the causes of its leakage, we conducted a comprehensive reform in a targeted manner and achieved good results. First, the basic situation: E-GA301 pump model GSB vertical high-speed pump, Aerospace Industries Corporation XI Institute of manufacturing. By the motor, gearbox, pump, forced lubrication system, sealing liquid circulation system and other components. Gearbox for the two gear growth, the input shaft speed that is motor speed 2950r / m, the output shaft speed 10275r / m, two shaft seal with a different form. The shaft seal (ie, the input shaft seal) is a lip seal (rubber skeleton lip seal). The lower shaft seal (ie, the output shaft seal) is a mechanical seal, code 60C, Forced lubrication system for circulation, the lower part of the mechanical seal lubrication, cooling. The shaft seal for the pump body is two sets of mechanical seals in series, with the upper mechanical seal code 60B and the lower mechanical seal code 60A. The sealed chamber between the two mechanical seals is filled with sealing oil and circulated in the sealing liquid supply circulation system (including a sealed oil tank) to lubricate and cool the mechanical seal. The three sets of mechanical seals are composed of the following components: moving ring, static ring, push ring, spring, spring seat, auxiliary seal, snap ring and so on. The rings, springs, spring washers and snap ring, the auxiliary seal has "O" shaped rubber ring and PTFE wedge ring, the stationary ring material is graphite (M106K). The moving ring material is different, 60A and 60C moving ring are made of cemented carbide YG6, and 60B of the moving ring, the base material is oCrl8N112M02Ti, welded on the sealed end of a layer of thickness 1.5mm Carbide. Second, the mechanical seal leakage analysis: There is a cavity between the high-speed pump gearbox and the pump body, the leakage of lubricating oil and sealing oil are accumulated here, lead to the oil cup outside the pump through the oil drain hole. After the pump is put into use, there is leakage of oil to the oil cup, every 3-5 days to pump additional gearbox oil. After 1-2 months of operation, the sealing performance of the mechanical seal begins to deteriorate, the sealing oil leaks outward, the color of the oil in the oil cup and the sealing oil tank changes to black, and propylene starts to enter the sealing chamber and enters the sealing oil tank and oil Cup, the pump vibration increased, the last a large number of propylene leaks, leading to high pressure alarm sealed oil tanker parking. The high-speed pump disintegration inspection and found that the mechanical seal 60B seal ring seal surface has been damaged, moving ring end surface stuck with a circle of black graphite powder, 60A wear more serious, 60C only a slight wear marks. Third, the transformation program: 1,60A static ring and auxiliary seal transformation 60A friction pair static resin impregnated resin graphite, the medium is light hydrocarbons, high speed, impregnated resin graphite material performance is better. However, impregnating the resin graphite ring during operation, wear powder if gathered in the auxiliary seal ring, especially polytetrafluoroethylene blade seal, will make the seal edge indentation, and even hinder the compensation ring compensation . In the transformation, the selection of high strength, good friction properties and temperature resistance impregnated graphite ring. Maintain the stability of the system operation. To ensure the sealing performance, auxiliary seal should have good flexibility. Based on the failure analysis of the above auxiliary seal, the auxiliary seal was changed from Teflon wedge ring to Viton 0 ring, and a rectangular cross-section filled Teflon washer was installed. The inner diameter of washer was close to the seal body Fit to prevent solid particles into the sealing ring sealing surface. In addition, due to the medium pressure is high, the gasket can also play a role in preventing the rubber ring is squeezed out. In addition, the 0-ring with axial floating mounting structure, the spring force through the rectangular ring directly on the compensation ring, when the compensation ring compensation movement, the O-ring has two moving points. This will not only ensure the compensation of the compensation ring, but also ensure the sealing effect of the auxiliary 0-ring, thus improving the reliability of the sealing. Due to the large friction of the rubber seal ring, it is also possible to increase the cushioning effect of the compensation ring during abnormal operation and protect the friction end face. 2,60B dynamic ring transformation gearbox side mechanical seal 60B end surface pressure ratio is small, but the pressure on both sides of the sealed end face is zero, the pump speed is very high, so the use of large end surface pressure value but will exacerbate its Wear and tear Therefore, taking the pressure does not change the end face, only changing the material of the moving ring, structure, the original moving ring redesign. After the transformation of the seal, put into operation since November 2001 after operation so far, running in good condition, the cumulative normal operation of more than 2 years, so far no leak, the sealing effect is very good. Only the economic benefits of accessories and installation are significant. Fourth, concluding remark: In view of the reason of the high-speed pump mechanical seal leakage, through the comprehensive transformation of 3 sets of seals, extended the high-speed pump maintenance cycle, completely eliminate this unsafe hidden trouble, a good solution to the problem. This method has the certain reference value for solving the equipment leakage problem with similar working conditions.