Corrosion Problems in Kraft Liquor Systems

Abstract The results of a 1978 survey of corrosion problems in the kraft linerboard industry are described. The major problems were erosioncorrosion by pulp/liquor slurries in digester transport systems; caustic attack and cracking of mild steel in white liquor (transport and clarification); localized corrosion by deposit attack and differential aeration cells in green and weak liquor processing; stress corrosion of liquor heater tubing; and hot corrosion attack by vaporcondensate-liquor environments in heavy black liquor storage. Liquor corrosivity is assessed by chemical analyses and corrosion rates of mild steel, via, pipeline probes (linear polarization technique). All uniform corrosion rates on mild steel were low, measuring,.2 -.7(8-30), .07-.5(3-20) and <.05(2) mm/y(mpy) in white, green and weak black liquor, respectively. The current materials of construction for equipment used in kraft liquor processing are presented; most mills replace mild steel with Types 304 and 316 stainless steel in white and heavy black liquor processing equipment.