Influence of Macro- and Microfouling on Corrosion of Steel Bridge Piles Submerged in Natural Waters.

Anomalous localized corrosion of submerged steel H-piles was detected in a Florida bridge. Microbiological analysis at the site indicated a high population of sulfate-reducing bacteria (SRB). The steel piles coincidently also had heavy marine growth, which can affect the corrosion process. As part of research to identify the role of macrofoulers on the aggravation of microbiologically-influenced corrosion (MIC), the objective of the work was to identify the influence of crevices created by the macrofoulers to facilitate proliferation of SRB and development of MIC. Steel coupons were immersed at three Florida bridge sites. Localized corrosion developed under the marine fouling coinciding with high sessile SRB populations. Crevice conditions with different interactions with the bulk solution can develop. Crevice environments associated with well-adhered barnacles would have less interaction with the bulk solution than that of the poorly-adhered and interlayered barnacles or marine flora. Aeration levels would be similarly affected. Laboratory experiments were made in solutions inoculated with SRB and with idealized crevices. The lab testing provided verification that sequential injections of nutrients and viable SRB allowed for SRB populations to be sustained. MIC developed in the environments representative of the occluded regions under fouling organisms. [ABSTRACT FROM AUTHOR]