Cracking Causes and Treatment Measures of T92/Super 304H Dissimilar Steel Welded Joint

During the trial operation of the high-temperature superheater of a million unit, some T92/Super 304H dissimilar steel welded joints cracked, resulting in pipeline leakage. Through the analysis of the installation environment, welding process and heat-treatment process, it was confirmed that the leaky part was the heat-affected zone on low alloy side of the dissimilar steel welded joint. Large welding parameters and insufficiency of post-welded heat-treatment led to high hardness of the heat-affected zone in the welded joint. During the trial operation of the unit, the vibration of tube row triggered the stress corrosion cracking in this area. So a comprehensive inspection was carried out for all welded joints, re-welding and post-welded heat-treatment (tempering at 755 ℃ to 760 ℃) for leaky welded joints and welded joints with excessive hardness, additional post-welded heat-treatment process with the same parameters for other welds were conducted to reduce the residual stress in the heat-affected zone of the welded joints. The radiographic and hardness test results of the treated joints met the requirements of the specification.