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John Houle: Senior Technical Consultant, PVC Pipe Industry
John Houle holds a Master’s Degree in Civil Engineering from the University of Missouri and an MBA from the University of Oregon. He has more than 25 years of experience in the plastic pipe industry in applications engineering, market development, forensic analysis, technical writing, and standards development.
This document compares two pipe materials for response to “occasional surge,” a term that might not be well understood. AWWA standards define “occasional surge” as:
Occasional (emergency or transient) surge pressure: Surge pressures caused by emergency operations, usually the result of malfunction (such as power failure, sudden valve closure, or system component failure).
The design assumption is that an emergency event would occur at most only a few times in the life of the pipeline. For this reason, occasional surge is analyzed differently from “recurring surge” (also known as “cyclic surge”), which is a design condition for sewer forcemains. The ductile iron (DI) industry promotes their material as superior to PVC for surge pressures. The attached comparison uses the same set of design conditions to compare PVC and DI for occasional surge pressure. See for yourself – both products are suitable for the static pressure, but the total pressure (including surge) in the DI pipe is 495 psi compared to 282 psi in the PVC pipe. For ductile iron the total pressure is at 110% of the allowable pressure – redesign would be required. Meanwhile, for PVC the total pressure is only 75% of allowable. Furthermore, the 495 psi pressure in the DI pipe might damage non-pipe components such as valves, fittings, and service lines.
Click here to read.
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