Abstract
Microalloyed steels are subject to stress corrosion cracking in fuel-grade ethanol according to studies carried out in this last decade. This work identifies the key agents that cause stress corrosion cracking on API 5L X70 steel in anhydrous fuel ethanol by statistical analysis of chemical analyses data of anhydrous-ethanol samples and data from stress corrosion cracking tests previously achieved. For validation of the statistical analysis, slow-strain rate tests were carried out with API 5L X70 steel in analytical-grade anhydrous ethanol contaminated with the compounds identified in the statistical analysis. Tests were also conducted in a simulated solution of anhydrous ethanol, prepared according to ASTM D 4806 standard by replacing the gasoline used as a denaturing agent for aliphatic n-hexane hydrocarbon. The tests were performed under super-dry synthetic air and ultrapure nitrogen atmosphere. The most aggressive medium was the simulated solution with gasoline followed by the simulated solution containing n-hexane, both under a nitrogen atmosphere. The solutions of analytical-grade ethanol contaminated with n-hexane and contaminated with chloride ions were equally aggressive and the solution of analytical-grade ethanol contaminated with acetic acid was the less aggressive one. The nitrogen atmosphere made the analytical-grade ethanol with n-hexane more aggressive when compared with the synthetic-air atmosphere. The presence of n-hexane was as aggressive as the presence of chloride ions.
