High-temperature oxidation and the prediction of creep life for 0.5Cr-0.5Mo-025V steel

Abstract

Creep life assessment of thick-sectioned components such as steam pipes and headers have traditionally been made from uniaxial creep tests conducted in air on specimens of relatively small diameter. As a consequence of oxidation, such creep life assessments although safe are likely to underestimate the available life of such components. Owing to economic pressures there is currently a great need to quantify the size of this conservatism so that such components can be safely operated beyond their original design life. Yet there are few inert atmosphere data available from which this can be directly achieved. This paper suggests a way of incorporating oxidation data into the 0 projection method so as to enable life predictions of thick-sectioned pipes (where the effects of oxidation can be ignored) to be made from short-term tests conducted in air on small-diameter specimens. The paper shows that the resulting model is capable of analysing results from tests conducted in air under test conditions that give a life of up to 100 h and from this accurately predicting the life of thick-sectioned specimens (oxide free) operating under stress-temperature conditions that give a creep life of up to 60000 h. The proposed method for adjusting these predictions to produce estimates of the life of small-diameter specimens operating in air at test conditions giving a life of up to 60000 h is also shown to work well.