Hydrogen Evolution and Absorption in an API X100 Line Pipe Steel Exposed to Near-Neutral pH Solutions

Hydrogen evolution kinetics and hydrogen absorption in an API X100 line pipe steel exposed to near-neutral pH solutions is studied in this work. At the corrosion potential, dissolved CO2 in the solution accelerates the hydrogen evolution kinetics through the carbonic acid discharge reaction. At potentials more negative than the corrosion potential, hydrogen evolution due to bicarbonate discharge dominates the other cathodic reactions occurring at the ocp. The hydrogen diffusivity in the API X100 steel is found to be approximately 4.4 × 10−7 cm2/s. A measurable amount of diffusible hydrogen of approximately 1 appm is detected in the steel at the freely corroding condition using an electrochemical hydrogen permeation technique. Higher concentration of diffusible hydrogen is observed at more negative applied potentials as well as at higher CO2 partial pressures. The results in this paper support the attribution of stress corrosion cracking of pipelines in near-neutral pH trapped water environments to hydrogen embrittlement.