Study of the effect of static stresses on the hydrogen content and electrochemical characteristics of steels of different types

Abstract

When cathodic protection is applied in places where paint films are damaged, an intense release of hydrogen occurs, which is removed both through diffusion and by transition from the adsorbed state on the metal surface to the subsurface layers thus leading to static hydrogen fatigue of steels, i.e., a brittle fracture occurs suddenly under static loading conditions at stress values significantly lower than the strength limit and even below the plasticity limit. We present the results of studying the impact of static tensile stresses on the hydrogen absorption by a metal during its cathodic polarization and the distribution of hydrogen over the cross-section of the metal surface. Three types of metal samples were used: wire samples made of U8A steel, plate samples made of 10KhSND steel, and semicircular samples made of Kh18N9T stainless steel with a stress concentrator. Tests of wire and semi-ring samples were carried out under a constant load and plate samples were tested under constant deformation. Polarization of wire and plate samples was carried out at different current densities for 4 days and semi-ring samples for 1 hour. At the end of polarization, the layer-by-layer distribution of hydrogen absorbed by the metal was determined by the anodic dissolution method. It is shown that with increasing deformation, the hydrogen content of the surface layers of the metal increases. Moreover, application of tensile loads and deformation of the metal by bending contribute to an increase in the amount of absorbed hydrogen and affect hydrogen distribution over the metal cross section. The thickness of the layer containing the maximum amount of hydrogen differs in steels of different compositions and structures. The results obtained can be used to protect structural steels against corrosion in sea water.