Aspects of intergranular corrosion of AISI 321 stainless steel in high-carbon-containing environments

Abstract

Purpose – The purpose of this paper is to present a case study of unexpected sensitization to intergranular corrosion of highly resistant AISI 321 steel in petrochemical conditions, where it was subjected to the simultaneous influence of elevated temperature of ∼250°C and vapors from the asphalt production process. Design/methodology/approach – Corrosion coupons were exposed in an installation carrying asphalt vapors. To identify the susceptibility to intergranular corrosion a standard Strauss test was performed. Scanning electron microscopy (SEM) micrographs show a degree of degradation as a result of local corrosion. Influence of the carburization process occurred during exposure and depletion of chromium in the passive layer and was evaluated using X-ray photoelectron spectroscopy (XPS) and X-ray spectroscopy (EDX) techniques. Findings – The paper provides information on origin of corrosion of AISI 321 steel in a high-carbon-containing environment. It was found out that long-term exposure can lead to intergranular corrosion in temperatures that are much lower than those that have been considered to be required for sensitization of austenitic steels. The high concentration of carbon introduced during the exposure is stated to be responsible for this effect. Practical implications – The formation of chromium carbides, leading to intergranular corrosion of the Type 321 stainless steel, is a major concern. The paper reports that in certain petrochemical environments, highly resistant stainless steels, such as AISI 321, can be susceptible to intergranular carbide degradation. Originality/value – The presence of titanium is not sufficient to increase resistance in multiple environments and sensitization can occur even at relatively low temperatures of ∼250°C.