Ductile Iron Pipe - Identification, Causes, and Alternative Solutions for Premature Corrosion Failure

摘要

The Tualatin Valley Water District located west of Portland, Oregon manages a system of nearly 800 miles (over 1200 km) of pipe comprised of approximately 95% iron pipe. 75% of iron pipe is ductile iron and 25% is cast iron. Iron pipe in its system is failing due to external corrosion in as little as 30 years. The district began investigating conditions, installation practices, or circumstances that lead to the corrosion. The district reviewed and evaluated various industry standards and recommendations related to corrosion protection for iron pipe. Based on its review and some of its own studies, the district is developing new installation standards that consider soil corrosivity and criticality of the pipeline. To help the district develop its new installation standards to address this problem, it is conducting a pilot study using ductile iron pipe with different types of protective measures including loose polyethylene bags and various tightly bonded coatings. it is also evaluating other noncorrosive pipe materials for smaller mains such as PVC pipe. As part of its pilot study work, the district is tracking cost of the installations; ease of construction, installation, and related issues; and overall effectiveness against corrosion.