Abstract
Corrosive gas such as H2S and CO2 makes for very severe environments for steel. It is well known that Hydrogen Induced Cracking (HIC) and Sulfide Stress Corrosion Cracking (SSCC) are major problems which occur under these corrosive environments. We have investigated the corrosion and cracking behavior of coated steel under a H2S and a H2S/CO2 environment. Panels of high tensile strength steel were U-bended in order to impart residual stress. After surface treatments, several epoxy coatings were applied for 50 to 400μm, then cured. Corrosion tests were conducted in autoclaves under increased pressure and the corrosive gas environments (H2S, H2S/CO2). The following results were obtained:
1. Corrosion rate of the steel panels increased parabolically.
2. Film appearance and adhesion to the substrate did not change if corrosion loss under the film has not reached 5mg/cm2.
3. For samples with thin coating thickness (e.g. 50μm), underfilm corrosion quickly propagated, blistering and peeling were observed, consequently HIC or SSCC was induced.
4. For samples with thick coating thickness (e.g. 200μm), permeation of the corrosive gas proceeded very slowly, and rates of the underfilm corrosion were considerably slow. In such cases, FeS layers were generated at film/steel interface. The FeS layers were fine enough to prevent further corrosion.
