某电厂超临界火电锅炉的高温过热器管在服役约4×10⁴ h后，T91/TP347H异种钢焊接接头T91钢管侧出现环向断裂事故。通过宏观检查、结构分析、化学成分分析、金相检验及硬度测试等方法，对该焊接接头断裂失效的原因进行了分析。结果表明：焊接接头的T91钢管侧内壁车削后的厚度小于钢管的最小需要壁厚，该处钢管过量车削后的结构造成的工质流动变化引起了局部超温，材料加速老化，钢管强度下降；T91钢管侧热影响区由于强度不足而发生胀粗，产生蠕变裂纹，裂纹在轴向应力的作用下不断扩展，最终引起钢管环向断裂。

The welding joint of T91/TP347H dissimilar steels fractured circumferentially on the side of T91 steel pipe after the high temperature superheater of one supercritical thermal power boiler serviced for 4×10⁴ hours. Macroscopic inspection, structure analysis, chemical composition analysis, metallographic examination and hardness testing were carried out to analyze the fracture failure reasons for the welded joint. The results show that:the thickness of the T91 steel pipe was less than the required minimum thickness after the inner wall being over turned; the change of the fluid flow caused by the structure of the turned steel pipe led to the local overtemperature, accelerating ageing and decreasing the strength; due to the insufficient strength of the heat affected zone in the side of T91 steel pipe, the pipe swelled and creeping cracks occurred; the creeping cracks continuously expanded under the effect of axial stress, and eventually caused the circumferential fracture of the steel pipe.