Determination of creep and damage properties for P92 at 675 °C

In order to predict the service life of components that operate at high temperatures, such as steam carrying pipes in conventional power plants, the material creep behaviour needs to be determined. There are little creep data available on grade P92 (9Cr2W) steel (a potential successor to P91) as it is a relatively new material; therefore a testing programme has been undertaken. This paper presents the results of uniaxial and notched bar creep tests on P92 parent material (PM) and P92 weld metal (WM) at 675 °C. The PM had higher failure times and lower minimum creep strain rates for tests in the same stress range (80–100 MPa) as the WM, but the PM and WM values tend to converge at high stress, with a significant difference between the failure times as applied stress decreases. The notch strengthening effect was found to decrease as the applied stress decreased. Processing of the test data including the calculation of the minimum creep strain rates has been performed to determine the material constants required for Norton’s steady state creep and both the Kachanov and the Liu and Murakami creep damage models. Material constant sets for creep of P92 PM and WM at 675 °C, including a parameter to describe the effect of a multiaxial stress state, have been obtained that give a good fit to the test data. Validation was achieved using finite element analysis.