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M AT E R I A L S S E L E C T I O N & D E S I G N Investigation of Microbiologically Infuenced Corrosion in Pipeline Hydrotesting Using Seawater FIguRE 3 bioflm is present on an iron surface, causing the following reactions to go forward due to biocatalysis: Anodic: 4Fe → 4Fe2+ + 8e– (iron oxidation) (1) Cathodic: SO42– + 9H+ + 8e– → HS– + 4H2O (BCSR) SEM images (a) before acid cleaning, (b) after acid cleaning, and (c) EDS analysis before acid cleaning for a coupon after one-week exposure to the enriched Qurrayah seawater spiked with SRB at 37 °C. FIguRE 4 BCSR model prediction of two-week and one-month pit depths using bioflm aggressiveness calibrated from the one-week pit depth (18 μm). 68 MATERIALS PERFORMANCE May 2013 (2) By using charge transfer and mass transfer theories and electrochemical kinetics, a mechanistic model was developed and solved numerically. 14 The software based on the model is known as MICORP. It incorporates BCSR, proton reduction, and organic acid reduction to account for low pH at a pit bottom due to organic acids. Figure 4 shows the model prediction and experimental data obtained in this work. The model was calibrated with a single pit depth data to predict long-term pitting. Tetrakis hydroxymethyl phosphonium sulfate (THPS) is a biodegradable biocide that is most often proposed for hydrotest fuid treatment. A minimum dosage is needed to prevent bioflm establishment. Tests were carried out in anaerobic vials to evaluate the THPS degradation profles in artifcial seawater, GoM seawater, and Qurrayah seawater. A mechanistic model of THPS degradation under alkaline pH was obtained and reported elsewhere.15 Conclusions This work provided a framework for laboratory testing of MIC in hydrotesting. Arguments were made for laboratory testing at one atmosphere instead of a high pressure expected in a subsea pipeline during hydrotesting. Clean offshore seawater samples from the Gulf of Mexico and the Persian Gulf were found to lack native viable microbial activities. The seawater samples were enriched and spiked with a laboratory strain SRB to simulate contaminated seawater used in hydrotest. Bioflms and MIC pits were observed in the accelerated tests. A software package based on the BCSR theory was used to predict the pit growth. NACE International, Vol. 52, No. 5