MIC Considerations for Cathodically Protected Encased Ductile Iron Pipelines: A Case Study
- Jeffry B. Giddings (HDR) | Mersedeh Akhoondan (HDR) | Graham Bell (HDR)
- Document ID
- NACE International
- CORROSION 2018, 15-19 April, Phoenix, Arizona, USA
- Publication Date
- Document Type
- Conference Paper
- 2018. NACE International
- bacteria, microbiological influenced, polyethylene encasement, Corrosion, ductile iron, cathodic polarization
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There is a wide range of opinions about the proper method of corrosion control, including the need for cathodic protection, tight bonded coating and polyethylene encasement for ductile iron pipe. While polyethylene encasements are commonly used for protection of ductile iron pipe, there is a concern about microbiological influenced (MIC) corrosion mechanism beneath loosely-bonded polyethylene in certain environment. This paper presents a case study where MIC was recognized as primary cause of failure for an encased ductile iron water pipeline. The cathodically protected pipe was located within the proximity a creek crossing and had suffered from multiple failures. An investigation initiated to determine the root cause of failures and make recommendations to mitigate future problems. The field inspection included cathodic protection surveys, soil corrosivity survey and evaluation of suspect joints, polyethylene encasement and joint bonds. Samples were collected and sent to a laboratory in for further testing. A gray fused “cemented” sand was observed near the failure zones. Traces of black granular solids adhered to the pipe near joints. Gray paste and black tuberculation were found on the surfaces of the pipe beneath the polyethylene. The field and laboratory investigations indicated significant bacteria activities and MIC. Presence of high concentration of sulfate in the soil likely contributed to the bacteria growth. The preliminary results of this investigation is presented in this paper. The authors believe that presenting this investigation in the form of a case study will instigate further interest and research in this area.
Microorganisms are widely distributed in natural and industrial environments and according to their special characteristics they can be harmful to buried pipe.1 Microbiologically influenced corrosion (MIC) refers to indirect and direct effects that a biological agent may have on the corrosion of materials. In this case, biological organisms can alter the corrosion reaction kinetics at the surface of the material to either enhance or inhibit corrosion. These organisms may adhere to the surface creating a biofilm layer that can significantly change the characteristics of the material/solution interface and the corrosion performance of the material.
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