The presence of solids with nutrients that can support the growth of microbial communities may lead to microbially influenced corrosion (MIC) in carbon steel pipelines. Many factors affect MIC rates, for example, biofilms in pipeline sludges can produce corrosive chemicals that can attack metals, alter local acidity, and create differential aeration and galvanic cells. This paper examined the microbial diversity of sludges obtained from four (4) different locations of a crude oil transmission system. Bacterial activity reaction tests (BARTTM) and molecular microbiological methods (MMM) were used to determine microbial numbers (cells/g of sludge). X-ray diffraction (XRD) and Energy-dispersive X-ray spectroscopy (EDX) analyses were also performed on the sludge to identify key corrosion indicators. Furthermore, pipeline mitigation history along with the operating conditions of the pipelines were collected from the operators to better understand the corrosion mechanisms and help the operators with pipeline integrity management practices. Generally, some degree of correlation in microbial numbers between BARTs and MMM was observed for the pipeline sludges analyzed; i.e. for both test methods, the microbial numbers was higher in sample B followed by sample C. Microbial numbers were higher when MMM was used as compared to BARTs indicating the later may underestimate microbial count. In general bio-treatment reduced microbial numbers with corresponding before and after treatment values of >104 cells/g and 10 cells/g for pipeline A and >106 cells/g and 103 cells/g for pipeline B. When MMM was used all the sludges analyzed presented the six (6) groups of microorganisms believed to pose MIC threat, including archaea and bacteria. Hence while BARTs can be used to assess the diversity of microbial communities already known by the corrosion industry, MMM is recommended to comprehensively assess the susceptibility of pipelines to MIC, i.e. characterize sludges for bacteria, archaea and emerging microbes that may contribute to corrosion.

Subject
X-ray diffraction, Piping, Pipelines, Iron, Minerals, Biofilms, Sludge, Bacteria, Carbon, Pigging, Microorganisms, Microbiologically influenced corrosion, Samples
Keywords:
MIC, MI-UDC, MMM, Biofilms, Transmission pipeline, Corrosion
© 2017 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2017
Association for Materials Protection and Performance (AMPP)
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