Prediction of service lifetimes of elastomeric seals during radiation ageing

Measurements have been made on fluoropolymer seals of leakage rates, sealing force and compression set over a limited range of temperature and irradiation conditions to compare these techniques for their effectiveness in determining seal lifetimes. The results obtained indicate that the use of compression set tests in the routine assessment of seal performance is justified. Compression set measurements have been made on a polyurethane and a fluoropolymer over a range of temperature and radiation dose rates. The time-temperature superposition principle has been used to determine the thermal and dose rate shift factors asub(T), asub(R) and activation energy Esub(a) for both materials. Determination of the functional dependence of asub(T), asub(R) and Esub(a) on the dose rate enables realistic lifetime predictions to be made even when dose rate effects and temperature-radiation synergism are present. (orig.)