Effect of cathodic protection on the activity of microbial biofilms
Impressed current or sacrificial anode systems are used to protect the subsea structures of offshore oil platforms and rigs. The steel is considered protected when a potential of -850 mV(Cu:CuSO/sub 4/) is achieved, in many cases, the potential is further reduced to -950 mV to protect the steel from corrosion caused by the activity of sulfate-reducing bacteria (SRB). Therefore, some operators have questioned the presence of sulfide-containing deposits under marine macrofouling, indicating that SRB are active on structures protected to -950 mV. The decreased potential, however, is not applied to prevent the activity of SRB, but is based on a theoretical level which will allow passivity of steel in sulfide environments. This study was performed to determine the effect of a -950 mV cathodic potential on the activity of the biofilm formed, and the production of sulfide within that biofilm. 50D mild steel (BS 4360 Grade5D)/sup (1)/ corrosion coupons, both unprotected and protected with a sacrificial anode, were exposed in the estuarine waters of Aberdeen Harbor. The activities of the bacterial biofilms were determined using radiorespirometric methods. Biofilms were shown to develop on both substrata. The activity of the aerobic and anaerobic bacteria and SRB populations, however, were significantly greater on the unprotected coupons. Furthermore, sulfide could only be detected in the biofilm formed on the unprotected coupons. The results show that a potential of -950 mV does not prevent an active population of SRB developing on the metal surface. It is suggested that the lower activity of the biofilm on the protected coupon is not directly caused by any inhibitory effect of the cathodic potential; but that the greater activity on the unprotected coupon may be the result of the production of an extensive corrosion film that offers more favorable conditions for the activity of anaerobic bacteria.
- Research Organization:
- Corrosion Specialists (North Sea) Ltd., Devanha House, Riverside Drive, Aberdeen
- OSTI ID:
- 6961743
- Journal Information:
- Mater. Performance; (United States), Journal Name: Mater. Performance; (United States) Vol. 25:11; ISSN MTPFB
- Country of Publication:
- United States
- Language:
- English
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020300* -- Petroleum-- Drilling & Production
42 ENGINEERING
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423000 -- Engineering-- Marine Engineering-- (1980-)
550700 -- Microbiology
59 BASIC BIOLOGICAL SCIENCES
AEROBIC CONDITIONS
ALLOYS
ANAEROBIC CONDITIONS
ANODES
ANTIFOULANTS
BACTERIA
BIOLOGICAL FOULING
CATHODIC PROTECTION
CHALCOGENIDES
CORROSION PROTECTION
CORROSIVE EFFECTS
DRILLING RIGS
ELECTRIC POTENTIAL
ELECTRODES
EUROPE
FILMS
FOULING
IRON ALLOYS
IRON BASE ALLOYS
MATERIALS TESTING
MICROORGANISMS
OFFSHORE PLATFORMS
OIL WELLS
STEELS
SULFATE-REDUCING BACTERIA
SULFIDES
SULFUR COMPOUNDS
TESTING
UNITED KINGDOM
WELLS
WESTERN EUROPE