Optimal use of stainless steels in ClO2 bleaching service

The corrosion behavior of different grades of stainless steel has been inve stigated in order to find a basis for a technically and economically optima l selection of materials for use in D-filter washers and auxiliary equipmen t. A coupon-testing program has been carried out in three Swedish mills,wit h contemporaneous measurements of corrosion and redox potential and the cor rosion-affecting parameters: pH, Cl-, temperature and residual chlorine. Th e major conclusion is that the degree of corrosion in D-stage filter washer s varies amongst different mills and highly depends upon residual chlorine concentration. Test coupons of the superaustenitic material S31254 were res istant to crevice corrosion as long as the residual chlorine did not exceed 50-100 mg/L as active chlorine at 65 degrees C. Molybdenum-alloyed duplex stainless steels were superior not only to type 317n but also to the tested superaustenitic steels in terms of maximum depth of crevice corrosion.