某电厂汽轮机二级抽汽疏水管在运行过程中于焊缝处发生开裂。采用宏观分析、化学成分分析、金相检验、扫描电镜分析等方法对疏水管焊缝开裂原因进行了分析。结果表明: 由于该疏水管直管和弯管对接焊后未进行去应力焊后热处理, 焊缝处残余应力较高; 在焊接残余应力、工作应力及氯离子的共同作用下, 疏水管焊缝内壁萌生裂纹, 裂纹由管内壁向外壁不断扩展, 最终导致疏水管发生应力腐蚀开裂。

Cracking leakage failure occurred at the welding seam of drain pipe of a steam turbine extraction in a power plant. By means of visual examination, chemical compositions analysis, metallographic examination and SEM analysis, the welding seam cracking reasons were analyzed. The result show that the welding seam contained high content of Cl and no post weld heat treatment implemented. By the combined action of Cl, residual stress and actual working stress, cracks emerged from inner wall of the drain pipe at the welding seam, and the cracks extended continuously from inner wall to outer wall which finally resulted in stress corrosion cracking of the drain pipe.