Abstract: The paper discusses that a large number of spot corrosion hole and a little cracks were found in the inner surfaces of stainless steel welding seams and overlay cladding of a lean- rich amine heat exchanger tube tank in use; analyses the causes and processes the defects. The example indicated that it is essential to carry out penetrant testing on the key parts of stainless steel equipment where may be have defects so as to guarantee the safety while in use.