Microbiological Corrosion: Hydrogen Permeation and Sulfate-Reducing Bacteria

Abstract

This study was undertaken to evaluate cathodic depolarization as the action mechanism triggered by sulfate-reducing bacteria (SRB) in microbiologically induced corrosion (MIC), using an inert substrate such as a 1-mm thick Pd foil with and without cathodic polarization, a H 0 permeation conventional Devanathan-type cell, and the bacteria Desulfovibrio desulfuricans subsp. desulfuricans ATCC 7757. The permeation tests were run using a deaerated sterile culture medium inoculated or not with 10% D. desulfuricans at 10 8 cell/mL. Serial dilution was used to evaluate the bacterial growth, and scanning electron microscopy (SEM) was used to analyze the characteristics of the biofilm and products formed on the Pd foil. Results indicated bacterial growth on the order of 4 ¥ 10 10 CFU/mL at 24 h in both polarization and nonpolarization tests, and hydrogen permeation tests without cathodic polarization determined that there were no conditions for the reduction of the H + generated by hydrogen sulfide (H 2 S) dissociation. These results show that these bacteria develop similarly, whether or not they are on a polarized surface as a source of H 0 , generating H 2 S as a product of sulfate-dissimilating activity. Furthermore, hydrogen permeation tests with cathodic polarization determined an increase in the permeation current, which was associated with the maximum enzymatic activity phase of the bacteria. This good SRB development with cathodic polarization could be an indication that cathodic protection does not control MIC problems.

Hydrogen uptake by structural steels at cathodic protection in sea water inoculated with sulfate reducing bacteria

“…Since the bacteria metabolism has been found to produce OH À ions [4,9], the increase in the pH should have been expected. However, the slightly lower pH was measured in inoculated than in sterile water.…”

“…The action of bacteria, present in any natural environment, especially the sulfate reducing ones (SRB) modifies the conditions at the metal surface, and thus can affect the hydrogen evolution and hydrogen uptake by the metal [1][2][3][4][5][6][7][8][9][10]. This is especially important in the case of the installations subjected to cathodic protection.…”

“…In the course of the sulfite breathing, SRB consume the hydrogen evolved from the organic species present in water [4], in corrosion processes [4,8] and at cathodic polarization [2,6,7,10] of steels. The products of the bacteria metabolism are H 2 S and OH À [4,9]. H 2 S has been known as the hydrogen entry promoter [11], whereas increase in pH inhibits hydrogen evolution [12] and thus, inhibits hydrogen charging of the metal.…”

A Study of Microbiologically Induced Corrosion by Sulfate-Reducing Bacteria on Carbon Steel Using Hydrogen Permeation

“…Nevertheless, when it is polarized cathodically, the hydrogen does diffuse through the material, as was observed in the previously cited studies using a palladium strip. 10 These results are of great importance in discussions reported about the apparent hydrogen embrittlement or blistering to which CS is susceptible in the presence of SRB. According to several researchers, [15][16] hydrogen embrittlement can occur because of biogenic H 2 S, which reduces the fracture toughness of steel by more than half and produces failure in several ways because of the development of cracks.…”

“…[8][9] Recently, an article was published utilizing 69 these techniques on a noncorrodible substrate, palladium, both with and without cathodic polarization, in which the main conclusions were the following: 10 -D. desulfuricans subs. desulfuricans grows similarly regardless of whether or not a cathodically polarized metal surface charged with H o exists, because it can generate the H o needed to reduce sulfates to sulfi des at the cell level, with no net H o production.…”