The hydrostatic stress rupture test has conventionally been conducted as a useful method of lifetime evaluation. The hot water circulation test which is reflected to the actual operating condition is also useful method. The correlations and differences between the two tests were examined. Compared with the hydrostatic stress rupture test, it was found that the antioxidant in the resin was eluded into the circulating water and was consumed rapidly in the hot water circulation test. The lifetime of the pipe became shorter in the hot water circulation test. In addition, it was also found that when using the brass fittings, copper ions eluded from the joint accelerated degradation of a resin, a crack initiation at the pipe inner surface and a slow crack growth through the pipe thickness due to the hoop stress.
This paper describes comparison of test results between the conventional hydrostatic stress rupture test and various accelerated durability tests considering the actual using condition using polyethylene pipes for heating and hot water supply containing a relative small amount of antioxidants which have low mobility in a resin. It was found that the dissolved oxygen in hot water and the diffusion factor of oxygen in a resin affect the degradation of a pipe. It was also clarified to the temperature dependence of oxidative degradation by the hot water circulation test and copper ion aqueous solution circulation test and to the mechanism of generation of thermal degradation by copper.