Technical Blog

PVC pipe has been used for force mains in North America since the 1970s, with more than 50,000 miles in service today. PVC force mains have demonstrated exceptional resistance to cyclic pressures – known as cyclic life – both in laboratory testing and in pressure sewer systems. Cyclic life is not an overall life expectancy. Rather, it is the amount of years PVC pipe will endure recurring surge pressures alone.

About twenty years ago, a new method for analyzing cyclic life of PVC pipe was developed at Utah State University. The method was significantly improved over what had been used previously, but it had its drawbacks: it was not “user friendly” and it did not allow for combining cyclic events of different magnitudes.

Utah State continued its research, improved upon the earlier method, and now offers a simplified process for cyclic analysis. The most recent iteration uses what is known as the “Folkman Equation” to calculate the expected cyclic life percentage of the pipe’s life consumed by each cyclic event. The advantages of the new equation include:

• Ease of use / streamlined process
• Ability to consider multiple surge events for a force main pipeline
• Ability to perform condition assessment and determine an in-service pipe’s remaining cyclic life

Using this new and improved analytical tool, the PVC Pipe Association has published a document titled, “Force Main Design Guide for PVC Pipe.” The guide discusses cyclic surges in general, introduces the Folkman method, and provides design examples for better understanding of the subject.

The user will find that using this guide and the new cyclic design procedure provides several benefits:

• Inherent conservatism in PVC pipe cyclic design
• A practical design example illustrating how different variables affect cyclic life
• Ability to consider single- or multiple-pump operations and different operating conditions such as high-flow events

To access the guide, click here.