Review of the Bureau of Reclamation's Corrosion Prevention Standards for Ductile Iron Pipe (2009) / Chapter Skim
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, consisting of a sheet of polyethylene wrapped around the pipe or a tube of polyethylene sheeting slipped over the pipe at the time of installation. Another protective method is to use bonded dielectric coatings consisting of various polymers applied as coatings on prepared surfaces or to wrap tapes with adhesives on the same prepared surfaces.
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For highly corrosive soils, Reclamation specified that bonded dielectric coatings and CP were needed for adequate corrosion protection of DIP. It is this latter specification that Bureau of Reclamation, U.S.
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Specifically, the charge to the committee was that it provide advice to Reclamation concerning the following: • Does polyethylene encasement with cathodic protection work on ductile iron pipe installed in highly corrosive soils? • Will polyethylene encasement and cathodic protection reliably provide a minimum service life of 50 years?
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Project Scope Question B: Will polyethylene encasement and cathodic protection reliably provide a minimum service life of 50 years? Reclamation Clarification: This question is intended to seek the committee's technical assessment of the ability of DIP, installed in severely corrosive soils with CP and PE, to delay or reduce corrosion induced failures to a level that would allow the pipeline to pro vide reliable service for the minimum 50-year service life, which Reclamation requires.
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The committee finds that the limited data available and the scientific understanding of corrosion mechanisms show that ductile iron pipe with polyethylene encasement and cathodic protection is not likely to provide a reliable 50-year service life in highly corrosive soils (<2,000 ohm-cm)
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In doing so, it devoted considerable effort to analyzing the reliability experience for DIP with bonded dielectric coatings and CP in highly corrosive soils, since that system is the current stated specification of Reclamation. After considerable study and deliberation, the committee finds that using the performance of bonded dielectric coatings on steel pipe with cathodic pro tection as a benchmark for reliability, and based on available information, it is unable to identify any corrosion control method for DIP that would provide reliable 50-year service in highly corrosive soils. The committee considered other corrosion mitigation methods such as anti MIC (microbiologically influenced corrosion)
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Additionally, the nature of pipe section connections for DIP involves a bell on one end of the pipe, imparting significant diameter fluctuations along the pipeline not seen in the welded steel pipe used for natural gas pipelines. This diameter variability poses different challenges for a complete bonded dielectric coating on DIP because the spiral wrapping specified for tape is reportedly difficult to achieve on conically shaped objects, bends, and other irregular shapes. There is also a drawback to CP when it is used with coatings.
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The committee believes that the questions on adequate corrosion protection for DIP in highly corrosive soils and the appropriateness of Reclamation's specifi cations can be answered with greater certainty only after more data are generated. Greater experience is needed with the use of DIP in highly corrosive soils protected both by PE with CP and by bonded dielectric coatings with CP.
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While some users appear reluctant to use DIP with PE and CP in highly corrosive soils, others may find it difficult to obtain DIP with bonded dielectric coatings owing to its unavailability from U.S. manufacturers.
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