Introducing a new feature for Hymax Connect. Each week, a different staff member at Hymax USA will provide a Q&A addressing issues presented by customers. The first Q&A is by John Edwards who is Hymax’s customer applications manager extraordinaire. In his spare time, John enjoys running and spending time at the beach with his family.

Q: Why do you need to use an insert on HDPE pipe when using a restrained fitting?

A: HDPE has several properties that make it very different from other pipe materials like PVC or ductile iron. HDPE is not as rigid as other pipe materials and it has a low coefficient of friction, making it more slick. Fittings can easily slide along the pipe or rotate on it.

Proper restraint must be used when coupling pipe ends together to prevent pullout from hydraulic forces or temperature. With a much lower yield strength than ductile iron and even PVC, insert stiffeners must be used to strengthen the HDPE pipe wall and ensure a good connection between the fitting and the pipe.