UV resistance may not be a top-of-mind factor in selecting PEX tubing. However, for construction applications that have a long schedule or may be prone to delays, a high UV resistance provides peace of mind in the stability and quality of the product when installed.
The last two digits of the PEX material designation code represent the Plastic Pipe Institute’s (PPI) recommended hydrostatic design stress (HDS) at 73.4 degrees Fahrenheit. HDS is determined based on a material-specific design factor applied to the hydrostatic design basis or HDB. The HDB offers values specific to each plastic material type that the Hydrostatic Stress Board has determined, with a high degree of certainty, will not fail within standard operating parameters. For PEX tubing, the HDS can fall within the following range:
- An “06” designation indicates a 630psi HDS.
- An “08” designation indicates an 800psi HDS.
The value, entered in the following formula provided by ASTM F876, determines the maximum operating pressure the tubing is approved to:
P=2*HDS/(SDR-1) or P=2*630/(9-1); P=157.5 which gets rounded up to 160 psi
For “06” this relates to a 160psi @ 73.4F rating
Designation codes are limited in providing information on tubing performance in that they only indicate if the product meets a standard, not if it exceeds the standard, or by how much. For example, some manufacturers, like Viega, manufacture their PEX tubing to exceed standard requirements by a sizable margin. Through better design, manufacturers can provide superior protection and density to deliver greater quality assurance and performance. Reviewing manufacturer information can provide additional knowledge on product performance and testing to enable the best product selection.
How do various manufacturers compare?