Review of the Bureau of Reclamation's Corrosion Prevention Standards for Ductile Iron Pipe (2009) / Chapter Skim
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1 Introduction
1 Introduction
Pages 10-21
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From page 10... ...
At that time, Reclamation's position from a corrosion standpoint was that ductile iron pipe would be treated the same as steel pipe, except that steel pipe could be coated with either cement mortar or a bonded dielectric coating (depending on soil conditions) , while [DIP]
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From page 11... ...
on a Reclamation designed project or on a project for which Reclamation has had an oversight responsibility. Reclamation indicated to the National Research Council's (NRC's) Committee on the Review of the Bureau of Reclamation's Corrosion Prevention Standards for Ductile Iron Pipe that since that statement in 2004, there have been corrosion leaks on Reclamation projects -- one failure of DIP with PE and CP on the Southwest Pipeline in North Dakota in October 2004 and two leaks on the Fountain Valley Project in Colorado in 2007. Reclamation's guidelines are updated occasionally to reflect the most current and applicable corrosion design parameters, and -- according to Reclamation's presentation to the committee -- in 2003 Congress prompted Reclamation to conduct an evaluation of the corrosion mitigation alternatives in Reclamation's April 23, 2003, table entitled "Corrosion Prevention Criteria and Requirements" and to recommend a more definitive standard.
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From page 12... ...
Following is a brief synopsis of the minimum corrosion requirements from TM 8140-CC-2004-1, "Corrosion Considerations for Buried Metallic Water Pipe." The current corrosion prevention strategy and required corrosion control methods of Reclamation are based in part on a 10 percent probability of encoun tering soils with a given resistivity. Soils with soil resistivity values below certain levels require more stringent corrosion protection methods; higher resistivity soils require less stringent levels of corrosion control.
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From page 13... ...
Monitoring Protection2 ≤2,000 ohm-cm Bonded dielectric3 YES YES Ductile Iron >2,000 ohm-cm <3,000 ohm-cm Polyethylene encasement YES YES ≥3,000 ohm-cm Polyethylene encasement YES NO <3,000 ohm-cm Mortar / coal-tar epoxy YES YES Pretensioned Concrete ≥3,000 ohm-cm Mortar YES NO <3,000 ohm-cm Concrete / coal-tar epoxy YES YES Reinforced Concrete ≥3,000 ohm-cm Concrete YES4 NO ≤2,000 ohm-cm Bonded dielectric3 YES YES Steel >2,000 ohm-cm <3,000 ohm-cm Mortar / coal-tar epoxy YES YES ≥3,000 ohm-cm Mortar YES NO 1This table [presents what] should be considered to be the minimum corrosion prevention requirements for a pipeline corrosion design.
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From page 14... ...
The soil resistivity values for the minimum corrosion protection measures required were revised in the July 2004 requirements to include the following: • For both steel and ductile iron, a bonded dielectric coating, corrosion monitoring, and CP are required for soil resistivities below 2,000 ohm-cm. The minimum corrosion control requirement for soil resistivities between 2,000 and 3,000 ohm-cm is an unbonded coating (PE for DIP and cement mortar with coal tar epoxy for steel pipe)
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From page 15... ...
This evaluation should include the differing costs for the CP systems needed because of the higher amount of CP current required for corrosion control options with different coating types and efficiencies. • More conservative corrosion control measures may be adopted in the pres ence of additional soil conditions and risk assessment factors on a case-by case basis for specific projects.
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From page 16... ...
In particular the report will address the following questions: -- oes polyethylene encasement with cathodic protection work on ductile iron pipe D installed in highly corrosive soils? -- ill polyethylene encasement and cathodic protection reliably provide a minimum W service life of 50 years?
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From page 17... ...
During that discussion, Reclamation stated that its view that for PE with CP to "work" on DIP installed in highly corrosive soils, it should deliver the project benefits for the design lifetime of 50 years without failure due to external corrosion. For the PE and CP to "reliably" provide a minimum service life of 50 years, Reclamation prescribed a system that would have no failures due to external corrosion that would cause the system to be out of service during the 50-year service life.
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From page 18... ...
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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From page 19... ...
Reclamation also sought data on such pipeline failure and found that the largest data set available on steel pipe, installed in severely corrosive soils with CP and bonded dielectric coating, was available through the Office of Pipeline Safety (OPS)
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From page 20... ...
However, the DOT database does not include information on the soil condi tions in which the pipelines are installed, so we are unable to further screen the data to include only pipe installed in severely corrosive soils. We are not able to quantify the impact this issue has on the calculated performance data noted above, but some adjustment to the computed failure rate may be warranted to compensate for this uncertainty in soil condi tions across the data set.14 Reclamation provided the committee with a simple analysis to determine the annual failure rate per mile of steel pipe with dielectric coating and CP.
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From page 21... ...
Thus, while much criticism over the appropriateness of bonded dielectric coatings on DIP centers on the relative expense of this corrosion control method as compared to that of PE with CP, the committee was not tasked to, nor did it, conduct an economic analysis. Rather, the committee regards cost as a question that must be considered by the Bureau of Reclamation and pipeline owners on the basis of the relative utility of each method and individual project needs.
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