Creep crack growth behaviour of Type 316H steels and proposed modifications to standard testing and analysis methods

Tests have been performed on Type 316H stainless-steel compact tension specimens from four ex-service components and creep crack growth rates from these tests have been characterised using C*C*. Several modifications to standard creep crack growth testing and analysis methods have been proposed, including an improved approach for determining whether widespread creep conditions have been developed in the specimens. The observed behaviour has then been compared with existing creep crack growth rate data for this material. A change in cracking mode from ductile to brittle intergranular fracture was observed with increasing test duration. In addition, creep crack growth rates for several of the longest-term tests lie above an extrapolation of existing data from shorter-term tests. Models based on ductility exhaustion have been used to derive new equations for predicting creep crack growth rates in Type 316H steel at temperatures of 525 and 550 °C.