Technical Blog

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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.

DI vs PVC: When “Strength” is a Weakness

Posted By John Houle on Feb 3, 2016

The Ductile Iron Pipe Research Association promotes ductile iron as “stronger” than PVC. While it is true that side-by-side laboratory testing would give the nod to DI, laboratory strength does not always transfer to real life.


A case in point is surge pressures. Ductile iron has a higher tensile modulus of elasticity than PVC, which means that any surges generated in DI pipe will be higher than in PVC pipe.

This tech brief uses the design example in the AWWA C900 PVC pipe standard to compare surges in DR18 PVC pipe and PC350 ductile iron pipe. As expected, the DI surges are much higher – so high that:

  • Total pressure in the DI pipe exceeds its allowable pressure capacity
  • System appurtenances might be at risk

Conventional wisdom is turned on its head: “strength” is sometimes a disadvantage.

Click here to read the Tech Brief.