Formalisation of Wilshire–Scharning methodology to creep life prediction with application to 1Cr–1Mo–0·25V rotor steel

Abstract

Wilshire and Scharning have recently developed a new methodology that delivers accurate long term creep life predictions, and so offers the prospect of cost effective acquisition of long term creep design data. The present paper develops a procedure for formalising and estimating this Wilshire–Scharning model. Not only does this procedure provide the formalisation required for any acceptable international standard towards creep data acquisition, but it also allows for the construction of confidence limits around the Wilshire–Sharning predictions — something which until now has not been achievable. When applied to 1Cr–1Mo–0·25V steel, it was found that if this material was operated at a stress of 20 MPa, but a temperature of 873 K, there is only a 10% chance of failure at or before 157 702 h, and this could be stated with 95% certainty. The formalisation allows calculations to be carried out for any level of risk and for any material.

Keywords:

• CREEP
• LIFING
• CONFIDENCE LIMITS