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Microbiologically-influenced corrosion of on- and offshore pipelines

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Corrosion is one of the leading causes of failures in on- and offshore transmission pipelines, threatening pipeline integrity internally and externally

Of all the different origins of corrosion, microbiologically-influenced corrosion (MIC) has been identified as one of the major causes of corrosion failures1, 2. MIC is the term used for the phenomenon in which corrosion is initiated or accelerated by the activities of microorganisms. Microorganisms may adhere to metal surfaces forming biofilms (complex microbial ecosystems) that can alter the electrochemical conditions at the metal surface in such a way that corrosion can be induced locally; most commonly occurring as pitting.

Despite advances in the understanding of MIC, it remains difficult to accurately predict where it will occur, in combination with high metal loss rates. These characteristics present challenges to implementing effective corrosion management of engineered systems in which MIC is an applicable threat.

Since MIC is an interdisciplinary science, it is especially important to combine various areas of expertise to tackle the phenomenon.  DNV GL has established a MIC Technical Exchange Group to help broaden the industry’s understanding of microbiologically-influenced corrosion and encourage solutions to combat the issue.

External MIC

In 2011, DNV GL’s teams of pipeline specialists in the Netherlands, launched an ambitious research programme in close cooperation with Deltares3. A unique MIC probe was developed, based on an electrical resistance (ER) probe. On the metal plate of the ER probe a biofilm can be grown artificially under laboratory conditions.

The probe is then inserted in soils close to underground pipelines susceptible to external MIC. Corrosion rates can be instantaneously measured with the ER probe, making it possible to study the development of external MIC of buried pipelines under realistic field conditions. We are able to prioritise, therefore, which groundwater and soil conditions are conductive to MIC, and the effectiveness of mitigating measures can be monitored online.

DNV GL’s next goal will be to set up a joint industry project (JIP) that will see the company developing a recommended practice on the prediction and mitigation of external MIC on onshore pipelines alongside a number of industry partners.

The JIP will assist pipeline operators to better understand and manage external MIC,  enabling owners to take precautionary measures to ensure safety and reduce maintenance costs. In particular, the JIP will focus on preventing or mitigating MIC by specifying cathodic protection criteria and by taking into account coating condition. Measurement techniques to determine MIC rates will also be considered, in addition to a decision support tool on MIC threat and mitigation options.

DNV GL has started to establish the JIP with interested partners, aiming to kick-off in 2015. 

Internal MIC

DNV GL’s pipeline specialists in Dublin (Ohio, US), Bergen and Oslo (Norway), have established a number of initiatives and projects to help the oil and gas industry manage internal corrosion of pipelines and topside facilities.

Examples of internal MIC management, supported by DNV GL, were shared in two technical papers at the NACE International Annual Conference in March 2014. The first paper4 discussed the use of molecular microbiological methods (MMM) as a tool for determining the role of microorganisms in internal corrosion and identifying appropriate corrosion management strategies.

Since microorganisms can influence corrosion in different ways, MIC diagnostics must be undertaken in consideration of other factors that support corrosion. These include a pipeline’s operating history, fluid composition  and mitigation history. The paper presented field case studies for a subsea water injection pipeline, a subsea multiphase pipeline and an oil export pipeline.

A second NACE paper5 discussed internal corrosion assessment and mitigation based on the results from extended analysis of corrosion coupons in an offshore oil and gas gathering system. DNV GL’s laboratory in Dublin, Ohio, has supported this unique type of analysis for over ten years in addition to performing forensic corrosion investigation of pipeline failures caused by MIC.

More than 2,000 extended coupon analyses are performed each year to support several US oil and gas pipeline operators in assessing and mitigating internal corrosion and MIC. The use of extended analysis of corrosion coupons is now described in two NACE international Standards6, 7.


References
1 GH Koch, MPH Brongers, NG Thompson, YP Virmani, JH Payer, Corrosion Cost and Prevention Strategies in the United States, FHWA-RD-01-156, Office of Infrastructure Research and Development, Federals Highway Administration (2002)
2 TR Jack, MJ Wilmott, RL Sutherby, RG Worthingham, External Corrosion of  Line pipe- A Summary of Research Activities, MP35, 3 (1996)
3 Deltares is an independent knowledge institute working in the area of soil, water and infrastructure, see http://www.deltares.nl/eng
4 TL Skovhus, RB Eckert, Practical Aspects of MIC Detection, Monitoring and Management in the Oil and Gas Industry Corrosion Management of MIC, Paper 3920, NACE International Corrosion, Houston, TX (2014)
5 TL Skovhus, RB Eckert, A Fundamental Approach to Selecting Internal Corrosion Mitigation Measures for Offshore Wet Gas Gathering and Liquid Transmission Pipeline Systems, Paper 3908, NACE International Corrosion, Houston, TX (2014)
6 Detection, Testing and Evaluation of Microbiologically Influenced Corrosion on Internal Surfaces of Pipelines, NACE TM0212-2012 (2012)
7 Techniques for Monitoring Corrosion and Related Parameters in Field Applications, NACE 3T199 (2013)8: SPE International Oilfield Corrosion Conference and Exhibition 2014
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