Abstract:The butt-joint pipe was made of bars of 1Cr18Ni9Ti, weld with the same type pipe after machining,
then acid washing defects were found in the parts of suface. Through observation and analysis of suface morphology,
composition,metallography,microhardness and acid test, we can conclude that chromium depletion areas along the deformation
line was exist that cause the corrosion preventive becoming worse. In the machining process,the chromium
depletion areas expose to the surface or near the surface,corrosion first happened in the areas with the process of acid
washing,then macroscopic defects of pitting are formed. The chromium depletion phenomenon is the defects of raw material.
