Influence of Tube Metallurgy on Liquor Heater Corrosion Resistance, 1990 Engineering Conference Proceedings

Liquor heaters and in particular liquor heater tubes in kraft pulp mills are today mainly manufactured from the grades ASTM Tp304, duplex stainless steels and Alloy 600. The use of these grades should be seen in light of general corrosion and fatigue failure faced with ferritic 13% chromium steel tubes which dominated in the 1930’s to the 1950’s. To overcome the problems, austenitic stainless steels of the type AISI 304 were installed. The previous problems with the 13% chromium steel tubes were solved but instead another unexpected failure, stress corrosion cracking, occurred.

Duplex stainless steel and Alloy 600 tubes are used for best resistance against stress corrosion cracking. Furthermore modern duplex stainless steels and Alloy 600 also have more suitable mechanical and physical properties for liquor heater tubes than an AISI 304 stainless steel. Finally cleaning of liquor heater tubes with hydrochloric acid must be carried out with precaution.