Study of the effect of tensile stresses on hydrogen absorption upon cathodic protection of steel in sea water

Abstract

When using cathodic protection of steel in sea water, hydrogen can be accumulated on the cathode surface and penetrate deep into the metal. This rather dangerous phenomenon of hydrogen corrosion can lead to hydrogen embrittlement, i.e., to destruction of the metal. We present the results of studying the impact of the temperature and external tensile stresses on the hydrogenation of cathodically protected steel in calm and mobile Baltic sea water. Dependence of the inhibitory hydrogenation on the temperature and applied load under the action of benzenesulfapyridine chloride as an inhibitor was analyzed. An MIP-102 machine (wire samples) and special equipment (half-ring and plate lamellar samples) were used to provide smooth control of the applied load set by the deflection and controlled by dynamometers (lamellar samples were tested under constant deformation). When studying the effect of temperature on steel hydrogenation, the working cell was thermostatically controlled. The wire and plate samples were polarized for 96 h, and half-ring samples for 1 h. The potential was measured with respect to the silver chloride reference electrode. The layered distribution of absorbed hydrogen in the metal was determined using anodic dissolution. It is shown that external tensile stresses increase the hydrogen content in the surface layers of steel. Hydrogen absorbed by a metal changes the potential of the steel surface (the more absorbed hydrogen, the stronger change). It is also shown that hydrogen is absorbed by the metal more actively in moving seawater than in calm water, and an increase in the load contributes to an increase in hydrogen content in the metal both in calm and mobile seawater. However, the load did not affect the hydrogen absorption with the inhibitor present, thus providing reduction of the hydrogen content in the metal under loading.