A computational procedure for life assessment of UHP reciprocating seals with reference to fatigue and leakage

A calculation procedure is shown for assessing the working life of reciprocating plastic seals for Ultra High Pressure (UHP) applications. Two main damage phenomena are considered, low cycle fatigue and wear, associated with structural failure or leakage respectively. An integrated approach, based on a finite element analysis of the seal, is proposed to evaluate both fatigue failure and leakage occurrence. The model takes into account non-linear effects due to seal contact interactions, material cyclic behaviour and its dependence on hydrostatic pressure. Fatigue life is predicted by combining equivalent strain range calculated in the critical points with life curve of the material. Leakage prediction is made by calculating a leakage index, based on instroke and outstroke pressure gradients and related to contact pressure profile change due to wear. Seal design can be optimised by choosing seal material and geometry so to delay fatigue failure and leakage, scheduling their occurrence at the same time.