某百万机组高温过热器在试运过程中,部分T92/Super 304H异种钢焊接接头开裂导致管道渗漏。通过对设备安装环境、焊接工艺、热处理工艺等分析,确认渗漏部位为异种钢焊接接头的热影响区低合金侧。焊接参数较大、焊后热处理不充分,导致焊接接头热影响区硬度较高,在机组试运过程中,管排震动触发该区域发生应力腐蚀开裂。为此,对所有焊口进行全面检测,并对泄漏焊口及硬度超标焊口进行重新焊接及焊后热处理(755~760 ℃回火),其他焊口追加同参数的焊后热处理工艺,用以降低焊接接头热影响区的残余应力,处理后接头的射线检测及硬度检测结果均符合规范要求。

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.