Transient Loads – What You Need To Know

We’ve discussed the reason our lateral lining system is suitable for gravity sewer lines and not meant for pressure pipe nor potable water lines. We haven’t explored the reasons for not applying a gravity pipe to pressure systems, so I thought we’d explore the reasons today.

In pressure pipe systems, we’re looking at pumps that may stop and start. Additionally, the pipe may be drained or partially drained for various reasons including maintenance, leaks, or other reasons. When a pump starts in this environment a transient load which is a dynamic load is created and isn’t a good load when applied to a gravity sewer pipe. A transient load is the instantaneous initial pressure created when a pump starts. This load differs from a static load where pressure and velocity never change.

If, for example, a pressure system operates at 50 psi, the initial start of a pump to operate at the 50 psi may register up to 10 times or 500 psi pressure for an instant. Gravity sewer piping is designed to withstand a 5psi pressure test. If that gravity sewer pipe is subjected to a pressure in excess of the 5 psi, you may experience a failure.

Here’s where we run into issues with CIPP lining products designed for gravity piping but installed in a pressure pipe that is designed to carry that type of high-pressure loading. If the CIPP liner is not fully supported throughout the length of the liner you could run the risk of blowing a hole through the liner at the points not fully supported by the host pipe. Liner and resin may not fill in the entire gap where one section of the pipe is connected to another section. The liner may not fully expand to the outside radius of a turn in the pipe. Or in the case of a hole in the pipe, the hole, leaving the liner unsupported may be a point of future failure of the liner caused by the transient load.

Why, then, doesn’t coating have the same potential failure? The answer lies in the method of application. We are applying resin directly to the wall of the host pipe with a more flexible resin system. By applying the material directly to the wall of the pipe, the transient load is transferred to the pipe wall. The coating fills in the gaps, is pressed to the outside wall of the pipe during application and any holes in the pipe are filled with the material prior to applying the coating to the pipe.

If you are planning to rehabilitate a pressure pipe and want to talk specific applications call us at +1-888-354-6464 or write to

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