Evaluation of Stress Corrosion Cracking Susceptibility of the API 5L X70 Steel in Corn and Sugar Cane Ethanol Environments

Abstract

The interest in renewable and cleaner fuels has stimulated ethanol production in the last decades. Some of the drivers for that ever increasing production were the Brazilian Alcohol Program, Kyoto Protocol and the replacement in USA of the octane booster MBTE (methyl-tert-buthyl ether) for ethanol. The world’s largest producers of ethanol are The United States of America and Brazil, where the main sources are corn and sugar cane, respectively. Production flow via pipeline is the safest and most cost effective way to connect the producers, usually spread across the country, to the distribution terminals. However, in USA there are evidences that ethanol may have caused stress corrosion cracking (SCC) in pipelines and also in storage tanks. Controversially, in Brazil ethanol has been transported and stored since the 1970’s without any indication of SCC. The aim of this work is to evaluate the susceptibility of the steel API 5L X70 [1] to SCC in different ethanol (corn and sugar cane) using slow strain rate testing (SSRT). These tests were carried out on notched specimens according to NACE TM 0111 [2]. The SSRT results carried out in corn ethanol have shown a considerable reduction of plastic elongation and a mixed fracture micromechanism of quasi-cleavage and intergranular facets clearly indicating a susceptibility of the API 5L X70 steel to SCC. The SSRT also demonstrated that the carbon steel tested here is completely immune to SCC in sugar cane ethanol.