Einfluß sulfatreduzierender Bakterien auf den kathodischen Korrosionsschutz

Abstract

An Umhullungsfehlstellen von kathodisch geschutzten erdverlegten Rohrleitungen wird bei Korrosionsschaden haufig die Anwesenheit sulfatreduzierender Bakterien (SRB) festgestellt. In Laborversuchen wurde das Korrosionsverhalten von Stahl St 37 im Potentialbereich (-03 V > Uc,,cuso, > -l ,27 V) und beim Ruhepotential in Gegenwart einer SRB-haltigen Mischkultur untersucht. Zur Simulation realer Verhaltnisse wurden die Versuche an Stahlproben in sandgefiillten Saulen durchgefiihrt, die kontinuierlich mit einer glucosehaltigen Mineralsalzlosung durchstromt wurden.Aufgrund der ermittelten Abtragungsgeschwindigkeiten war fur die homogene Mischelektrode selbst bei freier Korrosion eine unmittelbare Korrosionsgefiihrdung durch SRB nicht abzuleiten. Es trat lediglich ein erhohter Schutzstrombedarf im Vergleich zu sterilen Bedingungen auf. Die Wasserstoffpermeation durch den niedriglegierten Stahl war in Gegenwart SRB-haltiger Mischkulturen gegenuber sterilen und H,S-freien Bedingungen leicht erhoht. Aus den ermittelten Permeationsstromdichten liel3 sich ableiten, da8 bei Potentialen Ucu,cuso, < -0,85 V unter sulfatreduzierenden Bedingungen nicht mit einer wasserstoffinduzierten Werkstoffschadigung zu rechnen ist.Sulfate-reducing bacteria (SRB) are frequently encountered at coating defects of cathodically protected pipes buried in soil. In laboratory experiments the corrosion behaviour of steel St 37 was studied at potentials in the range of -0.5 V > Uc,,cuso, >

Effects of cathodic protection potential on microbiologically induced corrosion behavior of X70 steel in a near-neutral pH solution

“…However, opposite results were obtained in our study because the high concentrations of HCO 3 and CO 2 in NS4 solution were hydrolyzed to produce a large quantity of H + [56]. H 2 S, HS -, and S 2produced in SRB metabolism acted as both catalysts for the reduction from H + to atomic H (reaction ( 9)) and toxic agents to hinder the reaction (12), thus increasing the hydrogen concentration on steel surface. Although SRB consumed some hydrogen through reactions (19) and (23), a large quantity of residual hydrogen exited on the surface of X70 steel under CP potential of −875 mV.…”

“…In the absence of CP potential, in NS4 solution containing SRB, in addition to electrochemical reactions (5)- (12), under the action of hydrogenase [37], the following cathode depolarization reactions also occurred on X70 steel, thus resulting in corrosion of X70 steel: In addition, SRB could directly utilize Fe 0 as an electron donor. In the MIC process of SRB, Fe 0 oxidation occurred outside of cells because Fe 0 could not enter cytoplasm.…”

“…Some researchers reported that the cathodic potential of −0.950 V (CSE) could not provide effective protection for steel pipelines [10] and some scholars even proposed that the CP potential of −1.35 V (CSE) achieved the ideal protection effect [11]. However, in some studies [12][13][14][15], the biofilm promoted hydrogen absorption in high-strength steel under the synergistic action of cathode polarization and SRB and greatly increased the The experimental solution was a near-neutral pH solution, NS4 solution composed of 0.137 g l −1 CaCl 2 , 0.122 g l −1 KCl, 0.131 g l −1 MgSO 4 •7H 2 O, and 0.483 g l −1 NaHCO 3 . Before the experiment, the solution was sterilized at 121 °C for 15 min in a pressurized steam sterilizer.…”

Effects of SRB on cathodic protection of Q235 steel in soils

“…Kajiyama et al demonstrated that SRB strived actively in clay when the cathodic polarization potential applied was more positively than À1100 mV (vs. Cu/CuSO4) [14]. Grobe et al found that compared to sterile conditions, there was an increase of protective current demand for steel St 37 in the soils containing SRB [15]. The present work was carried out in order to determine the effects of SRB on the CP of Q235 steel in the soils.…”