A new method for assessing high temperature crack growth

Experimental creep crack growth (CCG) test data are obtained by following standards that characterize CCG rates using the C* parameter. Such data are then used in high-temperature failure assessment procedures. An alternative approach to defect assessment at high-temperature failure is an extension of the R6 failure assessment diagram (FAD). At high temperature, creep toughness, Kcmat, can be estimated from CCG tests and replaces low-temperature toughness in R6. This approach has the advantage that it is not necessary to establish a creep fracture regime, such as small-scale, primary or widespread creep. Also, a new strain-based FAD has been developed, potentially allowing variations of stress and temperature to be accommodated. In this paper, the results of a series of crack growth tests performed on ex-service 316H stainless steel at 550 °C are examined in the light of the limitations imposed by ASTM for CCG testing. The results are then explored in terms of toughness and presented in FADs.