Year

1997

Degree Name

Doctor of Philosophy

Department

Department of Materials Engineering

Abstract

The low alloy steels, 2.25Cr-lMo (CrMo) and 0.5Cr-0.5Mo-0.25V (CMV), are two of the most widely used creep resistant steels in the power generation and petroleum industries of Australia. This project involved the accelerated creep tests of repair welded CrMo steel which was aged at 190,000 hours at an operating temperature of 565°C and repair welded CMV steel which had been in service for 120,000 hours at an operating temperature of 538°C. Two welding procedures with varying heat inputs were used for the repair welding process: a high heat input (HHI) procedure and a low heat input (LHI) procedure. The results of creep tests of repair welded samples and detailed optical and scanning electron microscopy of failed cross-weld specimens are reported. Predictions of remaining life were made using 'temperature versus time' graphs, parametric extrapolation techniques (Larson-Miller Parameter), and the 'A' Parameter. In addition, microstructural analysis (Neubauer and Toft & Marsden Classifications), hardness testing and FEA models have been used as complementary indicators of remaining life. It was demonstrated that CrMo and CMV cross-weld samples had similar creep-rupture lives at the selected testing temperatures, with CrMo out-performing the CMV weldment in terms of microstructural damage and creep life. Also, the HHI cross-weld samples unexpectedly out-performed the LHI samples which were designed to be superior. The Larson-Miller parameter approach allowed predictions of remaining time in each weldment zone as did the 'A' parameter technique, but with less success.

Share

COinS