Hydrogen attack is produced in steels from the seepage of hydrogen that reacts with carbides to form methane gas. This gas decarburizes the steel, produces microcracks, and lowers the toughness of the steel without necessarily a loss of thickness. Detection of hydrogen attack is important to assure safe operation of pressure vessels and piping susceptible to such damage. To nondestructively detect hydrogen attack, three ultrasonic techniques based on velocity, attenuation, and back-scatter, respectively, were investigated. Specifically, velocity decreased while attenuation and back-scattering increased. In samples with hydrogen attack, the experiments showed all three parameters were affected to a certain degree.
Based on this study, recommendations are that both velocity and back-scattering be used to detect hydrogen attack in steels. The study also determined that an inspection based only on velocity measurements may not detect earlier stages of hydrogen attack.
