Corrosion in Evaporator Plants and Heavy Black Liquor Tanks

摘要

This study reports laboratory and field studies of the corrosion and stress corrosion cracking resistance of carbon steels and stainless steels in pulp mill evaporators, heavy black liquor tanks and piping. Increased sulfidity in pulping liquors and increased evaporation (higher solids) have increased both the corrosivity of liquors and their tendency to cause stress-corrosion cracking in Type 316 stainless steel. Welded U-bend coupons showed no stress corrosion cracking in one Swedish high solids concentrator whereas stress corrosion cracking was observed for stainless steel ASTM 316 at high dry solids content, high sulfidity and high temperature in another concentrator. Laboratory autoclave tests indicate that the susceptibility of austenitic stainless steels depends primarily on the sulfidity of caustic solutions.