Abstract
Prior research has confirmed the occurrence of SCC of X60 and X65 pipeline steels in simulated fuel grade ethanol (SFGE) environments, and has shown that this SCC is exacerbated by the presence of chloride ions, dissolved oxygen, and organic acids. These constituents also contribute to SCC in commercial fuel grade ethanol (FGE). Prior research has shown that the SCC of c-steel in SFGE involves film induced cracking mechanism. This research seeks to characterize the effects of chloride ions, dissolved oxygen, and pHe changes on the composition and protective properties of the passive film, film breakdown with applied stress, and repassivation kinetics of X65 carbon steel in FGE and SFGE. Environmental effects on film breakdown and crack initiation were studied using constant load tapered tensile sample tests (TTT). Passivation kinetics were investigated in-situ via the scratching-electrode method. Composition of the passive film was studied ex-situ with X-ray photoelectron spectroscopy (XPS). Results indicate that Cl− ions slow repassivation, and the presence of chloride or organic acids significantly enhances dissolution of steel where the film has been compromised.
