The Corrosion And Hydrogen Damage Behaviour Of 10CrSiNiCu Steel In The Simulated Deep Sea Environment

With the exploitation of resource in the deep ocean, more and more engineering structures need to work safely for a long time in the deep sea environment. The environment of deep sea has a distinctively different from the shallow water. As a result, it makes the corrosion behaviour and mechanical property change apparently.In this work, the effect of hydrostatic pressure and synthetic effect of hydrostatic pressure and uniaxial tensile stress on the hydrogen permeation of 10CrSiNiCu low alloy high strength steel in 3.5 % NaCl acidic solution has been studied by a modified Devanathan-Stachurski double-cell. A series of experiments has been conducted, such as electrochemical permeation measurement, weight loss measurement,surface morphology observation, fracture mechanics properties analysis and so on. The aim of this work is to understand the hydrogen permeation and corrosion behaviour performance of a high-strength:steel under the hydrostatic pressure and the combined effect of hydrostatic pressure and applied tensile stress, making sense of the mechanism that the hydrogen atoms absorption,diffusion and finally desorbed from the surface. Besides, it has also been found that the inductive loop at low frequencies of EIS can be used to assess the hydrogen permeation behavior by evaluate the capacity of H+ adsorb on the surface. The results indicate that:The sub-surface hydrogen concentration and the corrosion rate were inhibited by the hydrostatic pressure. With the increasing of hydrostatic pressure, the surface diffusion of H adatoms and H2 molecules was markedly inhibited. And a majority of H adatoms and H2 molecules were fixed at the cathodic active positions. Subsequently, the whole cathodic reaction was retarded by the hydrostatic pressure, leading to a lower sub-surface hydrogen concentration and corrosion rate.The applied tensile stress under hydrostatic pressure can promote the hydrogen permeation behavior of 10CrSiNiCu low alloy high strength steel by means of increasing the sub-surface hydrogen concentration and hydrogen diffusivity. The increasing hydrogen diffusivity is caused by the transformed shape of defects, such as inclusion and vacancy. But the increasing sub-surface hydrogen concentration was not totally controlled by the electrochemical corrosion rate. Both of the surface morphology observation and EIS measurement dates led us to the conclusion that the change of the surface state caused by the tensile stress increased the surface energy of metal and led to a higher hydrogen concentration on the surface.Compared with the results of hydrogen permeation, contact angle and EIS measurement,it has been found that the inductive loop at low frequencies of EIS can be used to assess the hydrogen permeation behavior by evaluate the capacity of H+ adsorb on the surface. This provides a technical foundation for the further study of hydrogen damage behavior in the deep sea environment.