Practical application of an ultra-miniature creep test to the remaining creep-rupture life prediction using an iso–stress approach for in-service boiler piping of modified 9Cr-1Mo steel

ABSTRACT

A practical procedure for predicting the remaining creep-rupture life of in-service boiler pipes under their operating conditions is proposed and discussed in this study. Tests were conducted on a coupon obtained using electric discharge sampling equipment from the outer surface of an in-service boiler pipe of modified 9Cr-1Mo steel. An ultra-miniature creep (UMC) specimen machined from the coupon was employed for the tensile creep test. Focusing on an iso–stress approach that has potential for the remaining life prediction using a limited test data, its suitability has been discussed. Test results indicate that the iso–stress approach can be applied to predict the remaining creep-rupture life using the UMC testing method with high accuracy. Furthermore, an examination of the high-temperature oxidation resistance of the UMC specimen indicated that oxidation had little influence on the rupture time.

KEYWORDS:

• In-service piping
• modified 9Cr-1Mo steel
• remaining creep life prediction
• ultra-miniature specimen
• iso–stress approach
• Larson–Miller parameter
• Monkman–Grant relationship
• high-temperature oxidation

Disclosure statement

No potential conflict of interest was reported by the author(s).