An evaluation of high temperature hydrogen attack resistance and a possible new microstructure development based remnant life assessment method of a clean ASME Gr.91 thick section steel plate

Abstract

A thick section plate specimen of a completely refined Gr.91 steel plate met the requirements of ASME code concerning the toughness and creep strengths due to exact control of the chemical composition and lowering of impurities. Low impurities also resulted in almost the same HTHA (High Temperature Hydrogen Attack) resistance as that of 2.25Cr-1Mo steel at 500ºC at 20 MPa hydrogen pressure. The long-term creep strength of Gr.91 steel is reduced by the presence of weld heat-affected-zones. The weakening phenomenon is due to the formation of ‘Type IV damage’. In this study, a crystal misorientation diagram transition analysis method using electron-back-scattering-diffraction analysis, EBSD, is applied to predict the remnant creep life of the HAZ. The trial prediction agrees with the actual rupture time.

Keywords:

• Creep strength
• impurities
• toughness
• life assessment
• HTHA
• HAZ
• pressure vessel

Acknowledgement:

This study was initiated by Nippon Steel & Sumitomo Metal Corporation and the experimental results were constructed by an internal pressure creep test of heavy wall pipe with a circumferential weld in a project that was led by European Technology Development Consulting.