Prediction of Long Term Creep Curve and Rupture Life of 2.25Cr-1Mo Steel

Abstract

This paper aims at predicting long term creep curves and rupture lives of 2.25Cr-1Mo steel on the basis of the following creep equation:
ε=ε₀+A{1–exp(–αt)}+B{exp(αt)–1},
where, ε₀, A, B, α: parameters to be determined by curve fitting to a measured creep curve.
The parameters are expressed as simple functions of stress and temperature, and can easily be extrapolated to a lower stress or a lower temperature, i.e., to a long term creep condition. Inserting the extrapolated values into the creep equation, one can draw a long term creep curve up to the tertiary creep stage.
Rupture life is linearly related to the following rupture parameter P derived from the creep equation:
P=(1/α)ln{(ε_r–ε₀–A)/B}, where, ε_r: the strain to rupture.
By the aid of this parameter long term rupture lives can be predicted.
The predicted creep curves and rupture lives were confirmed by long term creep tests up to about 400 Ms (13 years).