Electrochemical and Stress Corrosion Behaviors of Low-Alloy High-Strength Steel in the Soil Environment of Western China

The service safety of low-alloy high-strength steels (exemplified by X80 pipeline steel) in the soil environment of Western China is threatened by electrochemical and stress corrosion cracking (SCC) behavior beneath disbonded coatings, where the formation of microenvironments with pH gradients—alkaline near defects and acidic farther away—complicates mechanistic prediction and risk assessment. This study investigates the SCC behavior of X80 pipeline steel in simulated acidic (pH 5.1) and alkaline (pH 10.7) solutions representing typical conditions under a disbonded coating in Korle saline soil. Through an integrated approach combining electrochemical tests and slow strain rate testing (SSRT), the influence of applied cathodic potential on the SCC mechanism and susceptibility was elucidated. Results delineated a potential-dependent transition in SCC mechanisms, governed by the zero-current potential derived from fast-scan polarization curves. In the acidic environment, SCC susceptibility increased monotonically with cathodic polarization, whereas in the alkaline environment, susceptibility remained low until the potential exceeded a threshold near –900 mV SCE , attributable to the delayed contribution of hydrogen due to a more negative hydrogen evolution equilibrium potential. Based on non-steady electrochemical theory, two separate quantitative models were developed to evaluate SCC susceptibility for the acidic and alkaline environments, utilizing current densities from fast- and slow-scan polarization curves. The models demonstrated prediction errors of less than 10% and 20%, respectively. This work provides a mechanistic framework for understanding SCC in dual microenvironments and offers a rapid evaluation tool for guiding cathodic protection optimization and integrity management of in-service pipelines.