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Corrosion and hydrogen damage of steel in contact with soil bacteria and micromices. Preventive ability of organic inhibitors

Beloglazov S.M.

Advances in Materials Science

2007

Vol. 7, nr 2(12)

202-209

The martensitic stainless steel (ca. 13%Cr, 2%Ni and 0.25%C) corrodes in anaerobic aqueous salt medium deteriorated with H2S, as metabolic product of sulfate reducing bacteria, with small rate, but absorb a high quantity of hydrogen, that formed a very thin subsurface hydrogen rich layer. It can be explained by existence of collectors in the subsurface of metal, filled withmolecular hydrogen, which prevent the deeper penetration of H while diffusing in steel. Molecularization process of H on the internal collector surface results in growth of partial H2 pressure in collectors. The further diffusion of H into the metal depth then bas to take place through the already stressed and strained metal around the collectors. The stress field prevent the hydrogen diffusion into the depth of steel. The earlier elaborated special steel anodic dissolution technique (step-strip technique) bas been successfully applied for hydrogen analyzing in austenitic steel. The hydrogen concentration profiles gained from these tests may be very useful in the explanation of the hydrogen embrittlement of high-strength Cr-Ni-steels. The H2S-content - time curves in media with SRB have the similar character and sequence as one s SRB cells number (bacterial liter) - time. The OC being studied can act as satisfactory inhibitors of SRB-induced corrosion of martensitic stainless steel in aqueous salt medium. The corrosion inhibiting of OC under study is in a good agreement between their molecular structure and inhibiting efficiency. The increase of electron density on the functional groups provide the made strong adsorption of organic molecules on the steel surface. The bactericidal action of OC on SRB corresponds essentially to their steel corrosion inhibiting effi-ciency in aqueous salt medium. Mould fungi (Aspergillus niger, Penicillium chrysogenum, Penicillium charlissii and Phialophora fastigiata) isolated from soil exhibits stimulating action on steel corrosion visible already after two days of exposure. N-containing OC having linear molecules showed significantly greater inhibiting corrosion action in media with Phialophora fastigiata and Pen. charlissii in comparison with Asp. niger and Pen. chrysogenum.