Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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69 NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS PERFORMANCE DECEMBER 2014 peratures and then tested after one, two, and seven days. Significant changes in the quantif ication of micro organi sms can occur from storage conditions if a sample is n ot an aly z ed imm edi at ely. Stora ge of microbiological samples on ice (4 °C) yields the best results, but storage at 4 °C for only one day can lead to underestimates of the true microbial population (results may be only 10% of the true concentration). Stor age of samples at higher temperatures can yield values that are 100 times higher than the results obtained with fresh samples. Coupons and Sidestream Devices Obtaining biofilm samples from pipe lines can be challenging. Possible methods include weightloss corrosion coupons, sidestream devices, and pigging returns. Biofilms can be collected from weightloss corrosion coupons (Figure 2) using a sterile cotton swab. This procedure takes less than a minute and doesn't interfere with the col lection of weightloss data for calculating corrosion rates. Sidestream devices (Figure 3) are sometimes installed in pipelines, particularly water pipelines, to provide specific sampling locations for biofilms that can be used in microbiological testing. Frequently, weightloss coupons and side stream devices are not available for a given pipeline. In this event, the only source of biofilm samples are pigging solids resulting from pipeline cleaning. Pigging Returns The solids obtained from a pipeline pig ging operation are very heterogeneous. The data graphed in Figure 4 were derived from six different samples from the pig returns shown in Figure 5. The solids obtained from pigging this crude oil pipeline were oil coated and they all looked the same, yet Fig ure 4 illustrates that some samples con tained large amounts of microorganisms and others did not. While the amount and the appearance of the solids recovered from pigging of different oil, water, and gas pipe lines are different, pigging solids from all these sources show similar variability in microbiological testing. The recommended protocol for sampling pig returns involves FIGURE 1 Effect of storage conditions on the accurate quantifcation of SRB. FIGURE 2 Example of a weight-loss corrosion coupon. FIGURE 3 Example of a sidestream device for the cultivation of bioflms for microbiological testing. collecting a minimum of two composited samples from the pigging solids and from three different locations on the body of the pigging tool. These two composited sam ples can then be used to inoculate microbial growth tests, perform testing to quantify adenosine triphosphate (ATP), or perform genetic testing. Obtaining composited sam ples increases the likelihood that any micro organisms present will be detected, but data interpretation is also important. Bio films grow on pipe surfaces, but they do not generally coat all pipe surfaces uniformly. Rather, biofilms may be present only in cer

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