Effect of Oxygen on Ethanol Stress Corrosion Cracking Susceptibility: Part 2—Dissolution-Based Cracking Mechanism Available to Purchase

The mechanism of stress corrosion cracking (SCC) of carbon steel in fuel-grade ethanol was investigated. Repeated potentiodynamic polarization measurements were made during slow strain rate (SSR) tests. Current difference curves were determined from measurements made in the plastic and elastic regions. Peaks in the current difference curves were observed in the same potential region where SCC was found previously with potentiostatic SSR tests, which reveals the relation of cracking susceptibility and slip-enhanced anodic dissolution. Notched bar SSR tests exhibited consistent evolution of measured current vs. strain at constant applied potentials. A high R-ratio and low cyclic frequency crack growth rate (CGR) test was intended to simulate the real service condition of pipelines. The CGR at different applied anodic potentials was higher in the same SCC-susceptible potential range determined by the other approaches. The results support a slip-enhanced dissolution-based mechanism of ethanol SCC.