Abstract
Cold cracking sometimes occurred in long-term operated petroleum pressure vessels due to hydrogen embrittlement by thermal stress and diffusible hydrogen after repair welding. The cracking was caused by the hydrogen concentration at the base metal of 2. 25Cr-1Mo steel⁄overlaying metal of austenitic stainless steels during the service with high temperature and hydrogen partial pressure. Such tendency was accelerated by carbides precipitation at the interface due to the post weld heat treatment and the operation with high temperature. That is, the crack susceptibility at the interface became markedly higher owing to the hydrogen embrittlement with metallurgical degradation by thermal embrittlement. In this study, the crack susceptibility was evaluated by y-groove weld cracking test varying residual overlay thickness and hydrogen exposure conditions. On the other hand, hydrogen content at the interface was calculated by the theoretical analysis using the diffusion equation based on activity. The cracking test reveals that the crack susceptibility was raised with increase in hydrogen content at the interface. In addition, the theoretical analysis results indicate that the cracking could be prevented by reduction of hydrogen content at the interface to control the repair welding thermal cycles.
