Flow Test Results for Ductile Iron and PVC Pipes in the Same Water System

The water industry always benefits from the testing of pipelines that have been in service for several years. Many of the recommended design parameters are based on laboratory testing, but those tests can only provide approximate predictions for headloss, for example. As an example, for potable water transmission and distribution pipelines, the design calculations may use nominal pipe sizes and assumed values for “roughness” of the inside pipe surface. Conducting field tests enhances laboratory values and provides insights into the actual performance of a pipeline after years of service. This paper reports the results of flow testing of ductile iron and PVC pipelines, both in service in single utilities. These tests provide insight into the sensitivity of the variables in the Hazen-Williams equation, such as the inside diameter and the recommended values for the C coefficient. In these tests, the headloss between two points on isolated pipeline sections was measured in order to calculate the relative values for the Hazen-Williams C. The results help us to appreciate which of the variables in Hazen-Williams equation control the headloss calculations and provide guidance on ways to improve headloss predictions for new pipelines.