Technical Blog

Occasionally I hear a report about safety issues with air-testing of sewer pipes. The story usually starts with “An end-plug let go.” There was a sudden whoosh of air out of the manhole that had potential consequences for nearby personnel.

Engineers who are unfamiliar with PVC pressure pipe sometimes have a list of questions about the product. These questions, which often arise from misinformation propagated by competitive materials, usually have logical answers based on engineering principles.

The PVC Pipe Association has re-issued its “Tapping Guide.” The new guide includes additional diagrams and photos, as well as expanded text — all in a more logical, readable format.

Thrust forces are developed in a pressure pipe whenever there is a change in flow. When joint restraint is required to accommodate these forces, the most commonly used method is external joint-restraint devices. These devices have been used successfully on PVC pipe for more than 25 years.

Installation of PVC pipe into mechanical joint (MJ) appurtenances is a very common occurrence in North American municipal pressure pipelines. Problems with MJ connections can be minimized if proper installation techniques are used.

There are many different outside diameter (OD) types used for PVC pipe for various pressure and non-pressure applications. Not only are there several OD types, there are also associated abbreviations to add to the mix.

Uni-Bell has recently published a new document titled, Design and Installation Guide – PVC Fittings and Laterals for Solid-Wall PVC Sewer Pipe. The guide provides information on appropriate system design and proper installation of PVC fittings products where solid-wall PVC pipe is used in non-pressure applications.

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.

Water utilities have the choice of several materials for their pipe systems. For more than 70 years, PVC’s share of the municipal water market has increased steadily at the expense of iron and other pressure-pipe materials.

In piping systems, “permeation” is the movement of chemicals through a pipe wall or a gasketed joint. For potable water pipe, permeation is important because there may be adverse effects on the fluid inside the pipe.