Fundamental Studies on the Corrosion Behavior of Weldments in Marine Microbial Environments

• Main Authors: Buchanan, R A, Lundin, C D, Angell, P, Kovacs, A, Khan, K K
• Format: Report
• Language: English
• Subjects: 304L STAINLESS STEEL; 308L FILLER METAL; ATTACK; BACTERIA; CELLS; CORROSION; Couplers, Fasteners, and Joints; CREVICE SITES; FIELD CONDITIONS; LABORATORY TESTS; Marine Engineering; MEASUREMENT; MIC(MICROBIALLY INFLUENCED CORROSION); MICROBIOLOGICAL TESTS; OCEAN ENVIRONMENTS; PITTING; Properties of Metals and Alloys; PROTOTYPES; STAINLESS STEEL; SURFACE ANALYSIS; TEST AND EVALUATION; WELD METAL; WELDMENTS

During the first year of this project, comprehensive literature reviews were completed in the areas of (1) weldments employed in marine applications, (2) microbially influenced corrosion (MIC) in marine environments, and (3) MIC of weldments in marine environments. Specific weldment types covering a wide range of materials were selected for MIC evaluation. Laboratory MIC evaluations were initiated on a prototype weldment (as-welded 304L stainless steel base metal, 308L filler metal) in the crevice condition. Combinations of variables were employed to enhance MIC attack of the weldment during bacterial exposures, as compared to the corrosion observed during sterile control exposures. The variables included three different consortia of marine bacteria, different degrees of solution aeration, and different solution replacement rates (dilution rates) during continuous low-flow conditions. Unfortunately, little differentiation between the bacterial and sterile-control results have been obtained to date. When corrosion occurred, either in the bacterial or control experiments, it always occurred as general or pitting-type corrosion at crevice sites within the weld-modified (weld-metal/HAZ) surface area, never within the unaffected base-metal area. Corrosion potential and solution-redox-potential measurements suggested that oxygen concentration cells contributed to the sterile-control results, but due to the uniform and highly-deaerated condition at the bacterial specimen surfaces, did not contribute to the bacterial results.