Hydrogen attack on steel was investigated in a dynamic exposure environment under hydrogen pressures from 650 to 1400 psig at 950 to 1150 F (510 - 621 C). A hydrogen concentration gradient was maintained in the specimen wall during exposure by pressurizing the interior of tubular Ferrovac 1020 specimens while maintaining the exterior at one atmosphere hydrogen pressure. This environment simulates exposure conditions experienced in the hydrogen attack of steel pressure vessels and differs from the hydrostatic exposure environment used during earlier investigations of the phenomenon, in which the hydrogen concentration was maintained constant throughout the exposed specimen.
A gas chromatograph analysis of effluent gases showed only methane and hydrogen as reaction products. Gas analysis and metallographic examination of the attacked specimens showed that fissures in the steels’ microstructure do not link up to release the entrapped methane. Analysis also revealed the extent and depth of fissuring.
Thermodynamics of the attack reaction are discussed and applied in establishing a mechanism and predicting maximum depth of attack (fissuring) observed as a function of pressure and temperature. Agreement between theory and experimental data was good.
