Observation of corrosion behavior of stainless steels in a salt manufacturing plant environment using the multichannel electrode method

Crevice corrosion of four kinds of stainless steel, SUS316L, NAS64, NAS185N and NAS254N, in saturated NaCl solution at temperatures up to 100 °C was investigated using the multichannel electrode method. In this method, a pile of five individual working electrodes (WEs) of stainless steel sheet were embedded in epoxy resin and a small hole penetrating through the five WEs was treated as an artificial crevice. Time transition and distribution of the coupling current between the five WEs were measured as a function of crevice depth, kind of stainless steel, temperature and concentration of dissolved oxygen (DO). Anodic or cathodic coupling current on the five WEs of SUS316L changed depending on their corroding state. On the other hand, NAS64, NAS185N and NAS254N showed that the WE outside the crevice contributed as a cathode and that WEs inside the crevice contributed as an anode. The coupling current on SUS316L was strongly affected by concentration of DO, while the coupling current on NAS64, NAS185N and NAS254N was not affected by DO, probably due to the establishment of a passive state inside the crevice.