High-temperature oxidation and the prediction of creep life for 0.5Cr-0.5Mo-0.25V steel

Creep life assessment of thick-sectioned components such as steam pipes and headers have traditionally been made from uniaxial creep tests conducted i n air on specimens of relatively small diameter. As a consequence of oxidat ion, 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 s uch components can be safely operated beyond their original design life. Ye t there are few inert atmosphere data available from which this can be dire ctly achieved. This paper suggests a way of incorporating oxidation data in to the theta projection method so as to enable life predictions of thick-se ctioned pipes (where the effects of oxidation can be ignored) to be made fr om 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 (oxid e free) operating under stress-temperature conditions that give a creep lif e of up to 60 000 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 60 000 h is also shown to work w ell.