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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68 DECEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS SELECTION & DESIGN B Maintaining pipeline integrity is cru- cial, and when pipeline defects are detected or pipeline failures occur, understanding the cause of these events is of utmost importance. Inter- nal and external corrosion are key con- cerns when maintaining a pipeline to provide safe and reliable service. One cause of corrosion is microbiologically infuenced corrosion (MIC). This article covers sampling methods and testing procedures for MIC. B a c t eri a w ithin pip elin e s att a ch to internal surfaces and grow as biofilms. These biofilms can lead to microbiologi cally inf luenced corrosion (MIC), and as much as 40% of internal corrosion in the oil and gas industry may be caused by MIC. 1 The growth/maintenance of biofilms requires water, and even low concentra tions of water in crude oil pipelines or con densed water in gas pipelines can be suffi cient for patches of waterwet biofilms to grow. The preferred type of biofilm samples f or mi cro bi o l o g i c al t e sti n g a re th o s e obtained from weightloss corrosion cou pons present in a pipeline, and sidestream devices specifically designed for the collec tion of biofilm samples. 2 Also, the cleaning of pipelines, generally referred to as pigging a pipeline, produces a valuable source of samples for microbiological testing; but the heterogeneous nature of pig returns makes it challenging to collect representative data if not done properly. Obtaining and Preserving Samples Accurate detection and quantification of corrosionassociated microorganisms requires that samples be obtained and ana lyzed as quickly as possible when microbial growth tests are used. If samples are not analyzed promptly, erroneous data may result. Because MIC is not always consid ered when beginning an investigation of a pipe segment that is removed from service, it is not uncommon to have a pipe segment removed from service and sitting in a ware house for days or even months before the possible involvement of MIC is considered. Microbial growth tests are the most common way to test for corrosionassoci ated microorganisms, but fresh samples are required. Once a biofilm has been exposed to oxygen and dried out, microbial growth tests can't be performed. Genetic testing (quantitative polymerase chain reaction [qPCR]) may still be an option, however, particularly if underdeposit corrosion and/ or deep pits are present. 25 Sulfatereducing bacteria (SRB) are a particularly important group of microor ganisms because they convert sulfate into highly corrosive hydrogen sulfide (H 2 S). The effects of sample storage conditions on microbial growth tests for SRB are shown in Figure 1, where results are presented for samples that were stored at various tem Monitoring Pipelines for Microbiologically Infuenced Corrosion john j. KilBane, Intertek Westport Technology Center, Houston, Texas

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