Abstract: Addressing the surface pitting corrosion of the S30408 seamless stainless steel tube，relevant inspections are conducted to the said tube in terms of surface morphology，chemical composition，metallographic structure near the corrosion pit and the corrosion products as well as intergranular corrosion performance，etc. And the occurrence mechanism of and reasons for the pitting corrosion are also analyzed. As a result，it is revealed that occurrence of pitting corrosion is mainly due to the contact friction between the baffle and the steel pipe during operation，which causes damage to the surface passivation film of the pipe and gets its base metal exposed，and then with the induction of the relatively high concentrations of Cl^- in water，the base metal combines with the metal cations to form small corrosion points which then develop into pitting corrosion core，and continuously develop into corrosion holes. The medium inside the hole is in a stagnant state relative to the medium outside the hole，resulting in a continuous increase of the Cl^- concentration. With the passage of time，the pits continue to develop deeper and deeper，and inevitably become corrosion pits.