Surprising Corrosion Failures of Standard and Special Stainless Steels and Nickel Base Alloys in Chemical Process Environments

Abstract

Stainless steels are well known for their corrosion resistance. Austenitic Stainless Steels of the ‘300’ series are known as Standard Austenitic Stainless Steels and are very much used for chemical process equipment utilizing their good corrosion resistance to most of the popular chemical environments with not very severe corrosive conditions. Unfortunately their corrosion resistance fails in severe corrosive situations such as high chlorides, high temperatures, highly reducing conditions, presence of residual stress, presence of microstructural inhomogeneities, etc. For such cases, special stainless steels such as Super Austenitic Stainless Steels and Duplex Stainless Steels and Nickel Base Alloys are developed. These are popularly known as CRAs (Corrosion Resistant Alloys). This paper deals with four real-time case studies of unusual surprising corrosion failures of standard stainless steel such as 316(L) SS, duplex stainless steel and a nickel base alloy, all analyzed by the author himself. The cases discussed involve the following types of corrosion: general high uniform corrosion by process impurities, stress corrosion cracking, crevice corrosion and improper weld corrosion. The environments involved are inorganic acid, waste streams, sea water, and marine atmosphere. Each case would be illustrated giving the process conditions, the circumstances which led to the failure, the mode of failure, and the recommendations for remedial measures.