Abstract: Cryogenic methane pump is important equipment in ethylene production plant using cryogenic separation technology. Taking frequent mechanical seal failure of cryogenic methane pump as the starting point, this paper expounds the sealing mechanism of cryogenic methane pump. Itdeterminedfrom the analysis of the sealing mechanism that there were two causes for the leakage of sealing fluid. First was the poor self-lubrication effect of theside sliding bearing of the pump impellerwhich could not form stable lubrication liquid film, resulting in dry friction between the bearing and the shaft sleeve. And this led to the vibration of the pump and intensified the separation of the rotor-stator ring. Second was the smallinner diameter pressureratio of the bellows ring surface and the insufficient pressure resistance of the static and dynamic ring, resulting in big sealing pressure difference of the sealing cavity. According to the analysis results, the optimized transformation scheme was adopted to reconstruct the bearing and improve the self-lubrication effect. The original L-shaped torus was replaced by a rectangular torus with a section to improve the pressure ratio of the inner diameter of the sealed bellows. More pressure-resistant PG rectangular section was used for the seal ring and the seal ring materialwas upgraded. Meanwhile, the pump operation monitoring means was optimized toprolong the pump operating life and reduce unnecessary maintenance work.

Key words: methane pump, mechanical seal, bearing, sealing pressure difference, pressure ratio, failure, optimization