Technical Blog

Welcome to John’s Blog. Answers to frequently asked questions are periodically posted here. The objective is to share information about PVC pipe with readers as well as with utilities, design engineers and pipe installers. The blog provides the latest information on PVC pipe design, installation, and application for water and wastewater infrastructure projects.

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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.

Pipe Stiffness Explained: PVC and Ductile Iron

Posted By John Houle on Jul 12, 2014

Pipe Stiffness Explained PVC and Ductile Iron

Some project specs require Ductile Iron (DI) pipe because of its supposed “strength” in resisting external loads. In the past it was true that iron pipe had plenty of pipe stiffness, but that was before the iron industry converted from thicker-walled Class pipe to thinner-walled Pressure Class pipe.


Conventional Wisdom Is Not Always True

This tech brief discusses how much a pipe can safely deflect – PVC is safer.

Pipe stiffness of two approximately equal pressure class pipes is compared – PVC is stiffer.

The facts:

  • DI pipe fails at a lower deflection than PVC pipe.
  • DI has a lower safety factor against failure.

Conventional wisdom is turned on its head: the stronger, safer pipe is PVC!

To find out more, click here for the Tech Brief.