ABSTRACT
This paper will deal with zinc coated ductile iron pipe - its history and development, manufacture, and performance against corrosion. Test results from the Everglades will be presented showing various specimen combinations with emphasis on zinc coated ductile iron pipe with and without coating damage and enhanced polyethylene encasement with and without damage. The paper and presentation will also discuss a two-dimensional risk-based corrosion assessment and abatement model jointly developed by corrosion consultants and the Ductile Iron Pipe Research Association†.
The systematic approach to corrosion assessment and abatement within the model will be evident. The criteria used to assess risk of corrosion and consequence of corrosion in the two-dimensional analysis will be presented as well as the point value for each component of risk and consequence. Various Standards used in the water industry including installation practices will be included.
Zinc as a protective coating for iron pipe originated in Europe and has been used since 1958. It became so prevalent that an International Standards Organization‡ (ISO) protocol for it was developed in 1985.1 Every major world-wide producer of ductile iron pipe has the capability of applying zinc as a protective coating, and many offer it as standard in distribution-size diameters. The more recent embrace of zinc in the United States is related to the use of traditional polyethylene encasement as a preferred method of protection, and it has surely proven effective since 1958. But in fact, American producers of ductile iron pipe have supplied zinc coating for their export orders dating back to the early 1980s.2
The service record of iron pipe in the United States with more than 600 utilities having iron pipe in continuous service more than 100 years3 certainly supports the efficacy of those various decisions. The desire to make an excellent service record even better and to address the few remaining areas of application led to the introduction of zinc coatings on distribution diameters for domestic offerings.