As-Manufactured DIP with Cathodic Protection

Since bonded coatings on DIP are not available in the United States, several utilities and corrosion engineers have elected to install bare DIP with CP instead of with PE to minimize the problems with electrical shielding. The city of Seattle, Washington, installed a 40,000-foot section of bare DIP with an impressed current CP system next to a transit authority.78 Russell Corrosion Consultants reported that it is installing more than 15 miles of bare ductile iron pipeline with CP on 18 different projects in the northeastern United States.79 The Washington Suburban Sanitary Commission in the Washington, D.C., area has reported that, because of concerns about shielding from PE, it is installing several thousand feet of bare (as-manufactured) DIP with CP.80

Other Methods of Corrosion Control

Other corrosion control methods that may be considered include but are not limited to specifying additional pipe wall thickness in the design of the pipe system to account for a calculated corrosion rate for the life of the system, soil enhancements (e.g., controlled low-strength material), anti-MIC PE, microperforated PE with CP, use of resistance probes or perforated plastic monitoring pipes, and pipeline monitoring and repair. These are discussed in more detail in Appendix D of this report.

Selection of a Corrosion Control Method

In selecting a method for corrosion control for DIP, the designer and owner should consider all factors, including soil condition, capital costs of construction, operation and maintenance of the CP system, consequences of failure, and cost of repair.

78

Les Nelson, Seattle Public Utilities, Seattle, Washington, communication with the committee, September 2008.

79

Michael Szeliga, Russell Corrosion Consultants, communication with the committee, September 2008.

80

Dick Newell, Washington Suburban Sanitary Commission, communication with the committee, September 2008.



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