Ultrasonic Velocity Ratio Method for Detecting and Evaluating Hydrogen Attack in Steels

An ultrasonic attenuation technique has been employed in practice to detect hydrogen attack nondestructively. However, it is difficult to evaluate hydrogen attack quantitatively by this technique, because ultrasonic attenuation is influenced by the test conditions and the material itself.

In this paper, a new approach to a quantitative evaluation of hydrogen attack with an ultrasonic velocity technique is described. The longitudinal and shear wave velocities were observed to decrease more than 10% and 7%, respectively, in a steel fully attacked by hydrogen as compared with those in sound steel. This large change in velocity is sufficient to enable the thickness attacked by hydrogen to be predicted, if the wall thickness of material concerned is known.

Moreover, the ratio of shear wave velocity to longitudinal wave velocity is quite promising as a factor for evaluating the thickness attacked by hydrogen, without measuring the thickness of material tested.