Cause Analysis and Reform of Leakage of High Speed ​​Pump Mechanical Seal
The ethylene unit propylene delivery pump (position E-GA301A/B) supplies the raw material for the downstream polypropylene unit. This pump is extremely important for the entire polypropylene unit. The liquid propylene used for the reaction is supplied by it, so once If there is a problem with the pump, it will cause the entire ethylene and polypropylene unit to stop. Since the pump was put into use in April 2001, the two pumps have repeatedly experienced lubricant, sealant and propylene leakage failures. Although it has been repaired many times, new mechanical seal parts have been replaced, but the effect is minimal. The pump frequently fails, which not only consumes a lot of propylene, increases the maintenance cost, but also brings great hidden troubles to the stable production of the whole polypropylene device. By analyzing the causes of the leaks, we have carried out comprehensive transformations in a targeted manner and have achieved good results.
First, the basic situation
The E-GA301 pump is a vertical high-speed pump of the type GSB, manufactured by the 11th Research Institute of the Aerospace Industry Corporation. It consists of a motor, a speed increaser, a pump body, a forced lubrication system, and a sealing fluid circulation system. The speed increaser is the secondary gear speed increase, the input shaft speed is the motor speed is 2950r/m, the output shaft speed is 10275r/m, and the two shaft seals adopt different forms. The upper shaft seal (ie the input shaft shaft seal) is a lip seal (rubber skeleton lip seal), and the lower shaft seal (ie the output shaft shaft seal) is a mechanical seal, the code number is: 60C, the speed increaser is filled with lubricating oil, The forced lubrication system is circulated to lubricate and cool the lower machine seal.
The shaft seal of the pump body part is two sets of mechanical seals in series, the upper mechanical seal code is 60B, and the lower mechanical seal code is 60A. The sealed chamber between the two sets of mechanical seals is filled with sealing oil and circulated in the seal liquid replenishing 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 ring, snap ring and so on. The ring, the spring, the spring seat and the snap ring, the auxiliary seal has an "O" rubber ring and a PTFE wedge ring, and the static ring material is graphite (M106K). The moving ring material is different. The moving rings of 60A and 60C are made of cemented carbide YG6, and the moving ring of 60B is made of oCrl8N112M02Ti. The thickness of the sealing end face is 1.5mm. Carbide.
Second, mechanical seal leakage analysis
There is a cavity between the high-speed pump speed increaser and the pump body, and the leaked lubricating oil and the sealing oil are accumulated here, and are led to the oil cup outside the pump body through the oil drain hole. After the pump is put into use, oil leaks out into the oil cup, and the pump speeder tank needs to be supplemented with oil every 3-5 days. After 1-2 months of operation, the mechanical seal sealing performance began to deteriorate, the sealing oil leaked outward, the color of the oil in the oil cup and the sealed oil tank turned black, and the propylene enamel began to enter the sealed chamber into the sealed oil tank and oil. In the cup, the vibration of the pump body is increased, and finally a large amount of propylene leaks, causing the high pressure of the sealed tank to alarm and stop. The high-speed pump was disassembled and found that the static seal end face of the mechanical seal 60B was damaged, and a black graphite powder was stuck on the end face of the moving ring. The 60A wear was serious, and the 60C had only slight wear marks.
Third, the transformation plan:
1. Reconstruction of 60A static ring and auxiliary sealing ring
The static ring of the 60A friction pair is impregnated with graphite. When the medium is light hydrocarbons and high speed, the resin impregnated graphite material has better working performance. However, during the working process of the impregnated graphite ring, if the wear powder gathers at the auxiliary sealing ring, especially the Teflon blade seal, the sealing edge will be indented and even hinder the compensation of the compensation ring. . In the transformation, a silver-impregnated graphite ring with high strength, good friction performance and good temperature resistance was selected. Maintain system operation stability. To ensure sealing performance, the auxiliary seal should have good elasticity. Based on the failure analysis of the above auxiliary sealing ring, the auxiliary sealing ring is changed from the Teflon wedge ring to the fluoro rubber O-ring, and a rectangular cross-section filled PTFE gasket is installed. The inner diameter of the gasket is closely related to the sealing body. Fit to prevent solid particles from entering the sealing surface of the seal. In addition, the gasket can also prevent the rubber ring from being extruded due to the high medium pressure. In addition, the 0-shaped sealing ring adopts an axial floating mounting structure, and the spring force acts directly on the compensation ring through the rectangular push ring. When the compensation ring compensates for movement, there are two moving points on the 0-shaped ring. This not only ensures the compensation effect of the compensation ring, but also ensures the sealing effect of the auxiliary 0-ring, thereby improving the reliability of the seal. Due to the large friction of the rubber sealing ring, the damping effect of the compensation ring during abnormal operation can also be increased to protect the friction end surface.
2, 60B dynamic ring transformation
Although the end face of the speed increaser side mechanical seal 60B is smaller than the pressure value, the pressure on both sides of the seal end face is zero, and the pump rotation speed is high. Therefore, the use of a large end face ratio pressure value may intensify the wear. Therefore, the material and structure of the moving ring are changed without changing the specific pressure of the end face, and the original moving ring is redesigned. The modified seal has been in operation since it was put into operation in November 2001. The operation is in good condition. The accumulated normal operation time has exceeded 2 years. No leakage has occurred so far, and the sealing effect is very good. The economics of fittings and installations alone are very high.
Fourth, the conclusion
Aiming at the cause of high-speed pump mechanical seal leakage, the comprehensive maintenance has extended the maintenance cycle of the high-speed pump, completely eliminating this unsafe hidden danger and solving the problem well. This method has certain reference value for solving the problem of equipment leakage with similar working conditions. (Source: Hebei Innovation Sealing Material Co., Ltd.)
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