| Abstract: | A number of techniques have been developed in the past for the prediction of the dependence of the creep rupture life of polyethylene pipe on applied stress and temperature. It is now proposed that, using a modified form of the activated rate procss equation in which the activation volume varies predictably with temperature, a generalized equation may be derived which describes the “brittle” creep rupture curve over a range of temperatures, and also allows the use of a Larson-Miller type equation. Since the known “ductile” creep rupture curve at 20°C can be extrapolated from measurements carried out over a short period at room temperature in the laboratory, the intersection point between the extrapolated “ductile” curve and the calculated “brittle” curve can easily be calculated. If the proposed method is applied to creep rupture data obtained from Hoechst AG (GM5010, HDPE pipe) as an example, a transition at about 11 years is predicted. |
