Geometry Effects During Radiation Ageing of Elastomeric Seal Materials

Lifetime prediction models for elastomeric seals have been developed and validated for a range of elastomeric seal materials. At AEA Technology, a predictive model named SEALS has been developed using well-established time-temperature superposition methods (Burnay 1991) and the model has been validated using a long-term seals ageing programme. Recent work, however, has indicated that differences in compression set values can be obtained on O-rings of the same material but of different sizes, aged under the same environmental conditions. In nitrile O-rings which were exposed to thermal ageing only at 90°C, higher compression set values were observed in O-rings with the smallest cord diameter. This type of geometry effect tended to be smaller in O-rings which were radiation aged at ambient temperature than that seen in thermal ageing.