The mechanical properties of elastomers in high-pressure CO2

Elastomer seals are widely used to contain high-pressure gases and can suff er from decompression damage when the contained gas is depressurized. The g enerally accepted mechanism for the damage is that there is a considerable degree of dissolution of the gas into the elastomer which cannot diffuse ou t quickly enough when the contained pressure is reduced; hence bubbles and fissures occur in the bulk of the elastomer. Attempts to model this behavio ur typically assume the elastomer material properties are measured in the a bsence of the dissolved gas. In this study, a standard dumb-bell test piece tensometer has been developed which allows the elastomer material properti es to be measured while saturated with CO2 and N-2 (two gases with markedly different solubilities) at pressures of up to 4 MPa. The equipment was sho wn to be capable of providing accurate measurements under these conditions and various fluorocarbon, nitrile and silicone elastomers were tested. Thes e tests showed that the high-pressure CO2 induced a slight reduction in ini tial modulus compared to tests in air, accompanied by a more significant lo ss in both strength and ultimate extension. The reduction was greater than 50% in some cases. Electron micrographs of the samples showed that the frac ture surfaces were of a smoother nature for the samples tested in CO2, sugg esting a mechanism of disruption of interchain forces. The implications of these results for models of decompression damage are noted. (C) 1999 Kluwer Academic Publishers.