Effect Of SRB Activity On Hydrogen Permeation Behavior And Embrittlement Of Hot-dip Galvanized Steel Immersed In Seawater

Structures made by galvanized steel were imperiled by the synergistic action of sulfate reducing bacteria (SRB), stress and hydrogen in marine environment. Self-hydrogen permeation curves of galvanized steels with perfect coating and with artificial defect on the coating in sterilized seawater, sterilized culture medium and culture medium inoculated with SRB were measured using Devanathan- Stachurski cell. The effect of coating defect, components of culture medium and SRB on hydrogen permeation behavior was discussed. Hydrogen permeation mechanism of galvanized steel was investigated after the corrosion mechanism of which was studied by electrochemical impedance spectroscopy method. The stress-strain curves of galvanized steel in different corrosive environments were obtained by slow strain rate tension test (SSRT), and the hydrogen embrittlement susceptibility of galvanized steel in sterilized seawater, sterilized culture medium and culture medium inoculated with SRB were estimated after comparing the mechanical properties and fractography in these different corrosive environments together with . It can be concluded from the results that:(1) Hydrogen permeation behavior of galvanized steel was promoted by the coating defect. The average hydrogen permeation current density of the sample with artificial coating defect in sterilized seawater and sterilized culture medium were 250.67%, 32.76% higher than which of the sample with perfect coating respectively; Hydrogen permeation behavior of galvanized steel was also promoted by some components of the culture medium. The average hydrogen permeation current density of sample with artificial coating defect and sample with perfect coating in sterilized culture medium 181.22%, 626.97% higher than which in sterilized seawater respectively; Hydrogen permeation behavior of galvanized steel was inhibit by SRB. The average hydrogen permeation current density of sample with artifical coating defect and sample with perfect coating in culture medium inoculated with SRB 90.84%, 77.14% lower than which in sterilized culture medium respectively.(2) Electrochemical experiments together with hydrogen permeation tests showed that corrosion ability of seawater can be enhanced by the components of the medium, resulting in the increasing of the self-hydrogen permeation ability of galvanized; Active SRB itself can promote the corrosion and hyrogen permeation of the galvanized steel, but the biofilm formed by SRB and its metabolites together with the film formed by corrosion products can inhibit the corrosion of and hydrogen entry of the galvanized steel; SEM results showed few products adhered on the sample immerged in sterilized culture medium, but compact film was formed on the sample immerged in culture medium inoculated with SRB.(3) Embrittlement of the galvanized steel was enhanced by the its hydrogen permeation promoted by the components of the culture medium. Percentage elongation after fracture and density energy of galvanized steel in sterilized medium were 4.97%,5.59% lower than which in sterilized seawater. On the contrary, Embrittlement of the galvanized steel was weakened resulted from the inhibition of its hydrogen permeation by the SRB, and Percentage elongation after fracture and density energy of galvanized steel increased 7.78%,8.44% respectively compared with which in sterilized culture medium.