Leakage analysis of B shape ring self-energized seal in high pressure polythene polymerizer due to the aging of its nonmetallic ring

Abstract B shape ring with metal and nonmetallic materials is often used in the high-pressure polythene polymerizer for the self-energized seal. However, many factories reported that leakages often occurred when pressure is lower than 30 MPa, especially during the shutdown after a long period of operation. In this paper, the nonmetallic material Valqua 6502 were aged at 270 °C for 60 days, which is close to the working conditions of polymerizer. The compression and resilience abilities were tested and compared with those before aging. It reveals that the temperature aging reduces both compression and resilience abilities of the nonmetallic materials. FEM model was worked out for the simulation of sealing performance, which includes working conditions such as the assembly of the self-energized structure, the start up with temperature and pressure rise and the shutdown with temperature and pressure drop. It reveals that the sealing performance is not only influenced by the aging of nonmetallic ring, but also related with the interference fit to nonmetallic ring and clearance fit to the metal ring. Another kind of nonmetallic material XX300 was also aged as comparison, which performed better than the currently used one. With parameter studies, optimal interference and clearance fit were worked out for XX300 but failed for 6502. Therefore, when B shape ring with nonmetallic and metal materials works under high temperature and high pressure, the aging of the nonmetallic material should be considered to avoid decreasing its deformation and resilience ability and harming the sealing performance.