Reasons Analysis on Cracking of Welding Seam of Drain Pipe of Stem Turbine Extraction

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.