Repassivation behavior of X65 pipeline steel in fuel grade ethanol and its implications for the stress corrosion cracking mechanism

Common fuel grade ethanol (FGE) constituents affect SCC susceptibility of pipeline steels. Scratch testing employed to study effects of chloride, oxygen, water, and pHe on repassivation kinetics of X65 steel in simulated FGE and FGE revealed increased current density and decreased current decay rate from the bared steel as Cl− concentration increased, and incomplete current decay in deaerated environments. Using an Avrami kinetics-based film growth model, current was deconvoluted into dissolution and film formation components. The relationship between repassivation kinetics SCC of the pipeline steel/FGE system is discussed in terms of the previously proposed film rupture/anodic dissolution SCC mechanism.

► Investigated repassivation kinetics of carbon steel in ethanol fuel via scratched electrode test.
► Presence of chloride increases current from bare X65 steel surface.
► Oxygen removal prevents complete current decay from the scratch.
► Specific levels of Cl− and water produce localized corrosion within the scratched area.
► Modeling current transients indicates significant dissolution in some environments.