Validation of improved methods for predicting long-term elastomeric seal lifetimes from compression stress-relaxation and oxygen consumption techniques

Conventional high-temperature compression stress-relaxation (CSR) experiments (e.g., using a Shawbury-Wallace relaxometer) measure the force periodically at room temperature. In this paper, we first describe modifications that allow the force measurements to be made isothermally and show that such measurements lead to more accurate estimates of sealing force decay. We then use conventional Arrhenius analysis and linear extrapolation of the high-temperature (80-110 degreesC) CSR results for two commercial butyl o-ring materials (Butyl-A and Butyl-B) to show that Butyl-B is predicted to have approximately three times longer lifetime at room temperature (23 degreesC). To test the linear extrapolation assumed by the Arrhenius approach, we conducted ultrasensitive oxygen consumption measurements from 110 degreesC to room temperature for the two butyl materials. The results indicated that linear extrapolation of the high temperature CSR results for Butyl-A was reasonable whereas a significant curvature to a lower activation energy was observed for Butyl-B below 80 degreesC. Using the oxygen consumption results to extrapolate the CSR results from 80 degreesC to 23 degreesC resulted in the conclusion that Butyl-B would actually degrade much faster than Butyl-A at 23 degreesC, the opposite of the earlier conclusion based solely on extrapolation of the high-temperature CSR results. Since samples of both materials that had aged in the field for similar to20 years at 23 degreesC were available, it was possible to check the predictions using compression set measurements made on the field materials. The comparisons were in accord with the extrapolated predictions made using the ultrasensitive oxygen consumption measurements, underscoring the power of this extrapolation approach. Published by Elsevier Ltd.