A STUDY OF HYDROGEN EMBRITTLEMENT SUSCEPTIBILITY OF ADVANCED HYDROGENATION PRESSURE VESSEL STEELS

摘要

Nowadays, heavy oil refining processes require higher service temperatures and pressures in order for hydrogenation reactors to operate efficiently. To meet these demands, enhanced 2 1/4Cr-1Mo and 3Cr-1Mo-1/4V-Ti-B pressure vessel steels with higher tensile strength of 60kgf/mm~2 were certified in the ASME Code as designation No. of Code Case 1960 and 1961, respectively. In this study, the susceptibility to hydrogen embrittlement was evaluated for the newly developed steels with enhanced design stress intensity values at elevated temperatures. Threshold stress intensity factors under the hydrogen charged condition K_(IH) were measured in the wide ranges of tensile strength by a slow rate rising load test using CT specimens with thermally charged hydrogen. The 3Cr-1Mo-1/4V-Ti-B steel was confirmed to have lower susceptibility to hydrogen embrittlement compared with 2 1/4Cr-1Mo steels. As a result of metallurgical examination, the improved resistance was considered to be attained through the lower diffusibility of hydrogen due to the fine precipitations of vanadium carbides in the V-added Cr-Mo steel.