Comparison of applicability of different nondestructive testing methods for assessing hydrogen concentration in carbon steel

The change in the parameters values of different physical nondestructive testing methods (surface acoustic waves, magnetic structuroscopy, and electrochemical potential) was studied depending on the hydrogen concentration in carbon steel in the range of 0.4–8.5 ppm. The most sensitive are the coercive force values, which changed by more than 25%. The values of the residual magnetic induction and the electrochemical potential of the metal surface changed by 23 and 20%, respectively, making them also applicable for assessing the hydrogen content in this steel. Other investigated parameters showed lower efficiency and their change were: for the magnetic hysteresis loop area of about 10%, and the maximum magnetic permeability and the relative change of the surface acoustic wave propagation velocity—approximately 2%.