Duplex Stainless Steel: An Effective Material for Use in Kraft Liquor Applications, 2001 Engineering / Finishing & Converting Conference Proceedings

J. -P. Audouard, J. Grocki--Carbon Steel is often used to handle Kraft liquors at temperatures between ambient and 80°C/176°F, but this material suffers from uniform thinning due to the high pH value of the liquors, combined with the presence of sulfide species and organic vapors.Expensive coatings must be applied to mitigate this problem.

Austenitic Stainless steels are known to be resistant to corrosion in caustic solutions like White, Black or Green liquors at moderate (<110°c 25°f)="" temperature.="" they="" are,="" however,="" more="" expensive="" than="" carbon="" steel.="" in="" addition="" they="" may="" also="" suffer="" from="" external="" chloride="" induced="" stress="" corrosion="" cracking="" (scc),="" especially="" under="" insulation,="" requiring="" the="" application="" of="" a="" protective="" paint="">

This paper discusses the superior corrosion performance of the Mo free duplex grade UNS S32304. Other attributes, such as higher mechanical strength, which make the alloy an excellent engineering design material, are discribed. Fabrication and welding characteristics are favorable when compared to the 300 series austenitic and other duplex stainless steels.

A comparison, including investment and life cycle costs, is presented for liquor tanks made of coated carbon steel, austenitic, and duplex stainless steels. It is demonstrated that S32304 grade is a competitive alternative.