Weld Repair for Pressure Vessels Made From Cr-Mo Steels

Pressure vessels made from Cr-Mo steels are utilized for high temperature and high pressure services including hot hydrogen services. After long term operation, there are several past experiences of damages and/or degradation of materials such as temper embrittlement, creep embrittlement, hydrogen attack and hydrogen embrittlement. This paper summarizes typical damages/degradation and examples of weld repairs including special attention to development of weld repair procedure. The subject equipments are heavy wall petroleum pressure vessels made from Cr-Mo steel with austenitic stainless steel overlay cladding. Cracking could be prevented by controlling the repair welding process to reduce the hydrogen content at the interface. After repair welding, adequate post weld heat treatment (PWHT) has to be executed. Recently, repair welding has become an important aspect as part of post construction codes for pressure equipment to keep safe and long term continuous operation of the process plants because many of the plants have been operated for more than thirty years in Japan. Responding to the needs of petroleum and chemical industries, The Chemical Plant Welding Research Committee (CPWRC) of The Japan Welding Engineering Society (JWES) established the Pressure Equipment Repair Welding Subcommittee (PERW S/C) [1]. The S/C has developed optimum repair welding methods and procedures in the guideline on November 2009, with reference to the above investigation results. This paper also introduces the repair welding guideline for the pressure vessels made from Cr-Mo steels.