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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corrosion rates, and microbiological condi- tions over a period of time so any trends in the findings can be identified. Also, due to normal statistical variations associated with sample collection and microbio- logical testing, more reliable data typically result from performing tests on samples representing a time range rather than any single sample. Data collection and analysis should focus on differentiating the effects of biotic and abiotic factors on the likelihood, location, cause, and severity of internal corrosion. Samples of bulk fluids from pipelines are often collected to identify and quantify levels of planktonic (free floating) micro- organisms. To ensure that test results are relevant to MIC, data from bulk fluids should be correlated with other pipeline data, including liquid composition, operational conditions, sessile (attached) microbial abundance, and corrosion data. Since both corrosion and microbiological activity may occur directly on the internal surfaces of a pipeline, samples that are representative of these surfaces may provide significant infor- mation and should be collected, whenever possible, in conjunction with each liquid sample retrieved. Eckert notes that it can be very difficult to infer what is happen- ing on the pipeline's internal surface based solely on the composition of the bulk fluid because there isn't always a clear relation- ship between what is found on the surface and what comprises the bulk fluid phase. The microorganisms living in the bulk fluid (types and quantities of microbes), and even the chemical composition of the bulk fluid, can be far different than what is found on the internal pipe surface—that's been well established in research, he adds. Microbiological Testing Microorganisms are highly sensitive to environmental changes that affect nutri- ent availability, flow rates, temperature, salinity, the presence of dissolved gases, etc. Additionally, many chemicals produced by microbial metabolisms (e.g., organic acids and sulfide compounds) can be quickly oxidized or degraded by environmental changes. Because conditions can change The graph depicts data collected from a qPCR analysis. Image courtesy of Microbial Insights. rapidly once a sample is removed from the pipeline, certain tests relevant to MIC investigation or monitoring should be performed as soon as possible after a sample is collected to obtain results that accurately represent pipeline conditions. Historically, the ability to swiftly test samples has been one factor that has limited meaningful data collection for use in assessing pipelines for MIC, but improvements in detection technology have increased the availability of more types of tests and sophisticated The graph depicts data collected from a NGS analysis. Image courtesy of Microbial Insights. MATERIALS PERFORMANCE DECEMBER 2014 NACE INTERNATIONAL: VOL. 53, NO. 12 29 Diagnosing Microbiologically Influenced Corrosion in a Pipeline

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