In-plant corrosion test on special stainless steels in bleach plant of paper industry

Bleach plant of paper industry is corrosion intensive. Recent changes brought about in bleaching practices are likely to enhance corrosivity thereby demanding the use of more resistant alloys. As such a mill test, the first ever of its type conducted on Indian bleach plant, was carried on special stainless steels namely 2205, 904L, 254SMO, and 654SMO including 316L type in chlorination and chlorine dioxide washers. The coupons were affected by uniform corrosion, pitting and crevice corrosion. The attack shows the gaseous phase of both washers as most corrosive followed by liquid and wet/dry phases. Overall, D-washer appears more corrosive than C-washer. The test clearly indicates the non-suitability of 316L type stainless steel, a conventional material hitherto. Avesta 654SMO remains unattacked. Avesta 254SMO, 904L and 2205 show varying degree of corrosion resistance which correlate well with the PRE number, CCT and CPT values. On the basis of corrosion resistance, mechanical properties, and material's cost, Avesta 254SMO has been suggested as an acceptable material for gaseous phase and 2205 for liquid and wet/dry phases of both the C- and D-washers.