Study of Reasons for Pitting Corrosion Occurred on Flange Made of 1Cr18Ni9Ti Stainless Steel

Abstract

Abstract When pickling the stainless steel flange made of 1Cr18Ni9Ti after welding process, rough pits were observed on the surface of the part. An investigation of occurrence mechanism and chemical composition of these pits has been carried out, which involved scanning electron microscope (SEM) and Energy Dispersive Spectroscopy (EDS). It was found that the flange suffering local corrosion called pitting corrosion during the pickling process, for the reason of that cavities occurred between the outer sleeve nut and the weld joint area blocked the movement of cations, mostly Fe3+ and Cr3+. These cations hydrolyzed to H+ absorbing Cl− outside the cavity in the pickling acid causing corrosion on the part surface. Adjusting purity of pickling acid and shafting the part during pickling process can obviously reduce the potential of occurrence of pitting corrosion.