ROLE OF CHLORIDES IN CORROSION AND STRESS CORROSION CRACKING OF STAINLESS STEELS IN PULPING LIQUOR ENVIRONMENTS, 2010 TAPPI PEERS Conference

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The high strength and corrosion resistance of select grades of duplex stainless steel (SS), containing 20 - 29% chromium (Cr), 1 -7% nickel (Ni), and 0.15 - 0.25% nitrogen (N), has been beneficial in many industrial processes that utilize alkaline environments such as the kraft process in pulp and paper manufacture, the esterification process of biodiesel conversion, the girdler sulfide process in heavy water treatment, and alumina extraction in the Bayer process, where resistance to localized corrosion or stress corrosion cracking (SCC) in the presence of stress are required. Catastrophic service failures have occurred due to SCC in many carbon steel and stainless steel structures, resulting in the loss of life and expensive repairs. Laboratory and field experience [1-19] have shown that duplex SSs are also susceptible to general corrosion and SCC at elevated temperatures in solutions containing Cl₂, H₂S, and/or Na₂S. SCC occurs in a wide range of environments containing more than one corrodent, namely chlorides, sulfides, or hydroxides. The combined effect of multiple corrodents can have an extraordinary effect on the SCC behavior. SCC behavior of carbon steel and austenitic SS in complex, multiple corrodent solutions has been well known for decades [20]. Much less is known about the SCC behavior of duplex SS in solutions containing multiple corrodents.