scope:

INTRODUCTION

Crosslinked polyethylene (PEX) is a polyethylene material which has undergone a change in molecular structure whereby the majority of polymer chains are chemically linked. This crosslinking of the polymer chains results in improved performance properties such as elevated temperature strength, chemical resistance, environmental stress crack resistance (ESCR), resistance to slow crack growth (SCG), toughness, and abrasion resistance.

These properties are described in great detail in other PPI publications.

The inherent flexibility of crosslinked polyethylene also results in excellent freeze-break resistance properties. This means that if water- or fluid-filled PEX pipe or tubing freezes, the elasticity of the material typically allows it to expand without cracking or splitting, and then to return to its original diameter upon thawing. However, there are installation variables that can cause PEX to fail in certain situations, as described within this Report, and the freezing of fluid within any type of pipe should be prevented for multiple practical reasons.

This Technical Report will explain how proper installation and protection can prevent freezing of water or other fluids inside PEX, how the inherent material properties of PEX can delay freezing of water, and how PEX can resist breaking if the fluid inside does freeze.

Topics discussed in this document include:

• Section 2.0: PEX material properties

• Section 3.0 Published research

• Section 4.0: Code requirements for piping insulation & protection

• Section 5.0: PPI recommendations

• Section 6.0: Summary

This Technical Report is not an installation guide. Installers, builders, inspectors, engineers, and designers should refer to local regulations to determine the requirements for protecting PEX pipe and tubing against freezing.

Note 1: Although fittings and connections are part of every PEX system, fittings are not specifically addressed within this Report. Various fitting types constructed of materials such as brass and polymer are described within the research reports referenced in Section 3.