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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 1 Planktonic SRB growth in enriched artifcial seawater and full nutrient medium at different temperatures. grew well at one atmosphere and ployed to perform surface analyses. A 30,000 kPa in a laboratory.8 CHEMets† test kit was used to test the oxygen concentration in the experimental Experimental Methods vials. Anaerobic 125-mL vials flled with Desulfovibrio alaskensis (ATCC 14563) 100-mL liquid were used in the tests. A was used in this work as a laboratory glovebox deoxygenated with N2 gas pro- strain of SRB. Some experimental results vided an anaerobic environment. X65 as indicated were obtained by enriching carbon steel coupons were used. These artifcial seawater and natural seawater coupons had typical dimensions of 47.6 samples with 1 g/L yeast extract, 3.5 g/L by 10.9 by 1.6 mm. Prior to use, the sodium lactate, and 200 ppm Fe2+. coupon surfaces were polished succesFor bioflm observations under SEM, sively with 200 and 400 grit SiC abrasive unless mentioned specifcally, coupons papers, rinsed with alcohol, and then were pretreated according to the followsonicated in a beaker flled with alcohol. ing procedures: coupons were removed The ratio of coupon surface to liquid from vials and were immediately treated volume was close to that in 0.30-m (12-in) with 4% w/w glutaraldehyde for around inside diameter (ID) pipes. 1 h (to immobilize the bioflm), and then All liquids in the tests were de- were dehydrated with 30% (v/v), 50, 75, oxygenated using N2 sparging for at least and 100% alcohol in sequence. Before 30 min before use to refect oxygen scav- observing the bioflm, the coupons were enger use in the feld. Planktonic SRB frst treated using a Bal-Tec CPD 030† bacterial count was determined by critical point dryer and then coated with manual counting under an optical micro- a gold flm. scope at 400X using a hemacytometer. Only motile SRB were counted. If Results and Discussion needed, a Rodine hydrochloric acid (HCl) solution was applied to remove any Gulf of Mexico Seawater flms on the coupon surfaces. Scanning Table 1 shows that the Gulf of Mexico electron microscopy (SEM) and energy (GoM) seawater had a similar chemical dispersive spectrometry (EDS) were em- composition to that of typical natural † Trade name. 66 MATERIALS PERFORMANCE May 2013 (TOC) in the frst GoM sample was <1 ppm compared to <1 to 2 ppm TOC for typical seawater while the TOC of a second GoM sample was 4.6 ppm. The GoM seawater sample analyzed using polymerase chain reaction (PCR) was actually very clean. It had a total bacterial concentration of only 13.3 cells/mL, and its SRB cell count was below the detection limit of 1 to 3 SRB cells/L. The sample was taken from an offshore platform. When Hardy11 measured seven seawater samples from two similar locations of the North Sea, he obtained SRB numbers from 0 to 90 cells/mL, the average being 22 SRB/mL. Lee, et al.,12 using the most probable number enumeration method, detected ~10 and 100 SRB/mL in Persian Gulf and Florida Key West seawaters, respectively. These two water samples came from 1.2 to 1.5 m deep and near-shore (within 100 m) locations that could be contaminated by sewage, agricultural run-off, or other waste streams. Table 2 shows Na+, SO42–, and TOC in a comparison between typical natural seawater and Qurrayah seawater in Saudi Arabia. It is clear that Na+ and SO42– concentrations in Qurrayah seawater are ~1.6 times higher than in typical seawater, and the TOC concentration, which is very important for microbial growth, can be 500 times higher. Temperature Effect Figure 1 shows how temperature affected planktonic SRB growth, where 37 °C is the optimum growth temperature for the lab strain SRB. Compared to the full nutrient medium (ATCC 1250 modifed Baar's medium), the enriched artifcial seawater with limited nutrients is an acceptable environment for SRB growth, especially at 37 °C, and those added chemicals provided adequate nutrients for SRB growth. In general, mesophilic SRB grow well at 37 °C. Therseawater. The total organic carbon mophilic SRB prefer even a higher NACE International, Vol. 52, No. 5