Vanguard Piping Systems: PEX Chlorine Resistance Listings

The recent addition of a new ‘minimum chlorine resistance requirement’ within ASTM F-876 is a positive step forward within the PEX community. However, some companies have misused and misrepresented the data developed through ASTM standard F-2023 (Standard Test Method for Evaluating and Oxidative Resistance of Crosslinked Polyethylene (PEX) Tubing and Systems to Hot Chlorinated Water).

In a nutshell, here’s how ASTM F 2023/F 876 and NSF P-171 differ: First, there are two chlorine resistance testing methods. NSF P-171 defines both the testing methodology and two distinct ‘end use’ conditions. ASTM standard F-2023 defines testing methodology but does not define any ‘end use’ conditions. The only ‘end use’ condition that has now been defined is in ASTM F-876. In P-171, tubing which receives a ‘domestic continuous recirculation’ listing has been thoroughly tested in chlorinated water and is projected to have a minimum chlorine resistance service lifetime of more than 40 years operating continuously in water temperatures of 140°F. Tubing which receives the ‘traditional domestic’ listing under P-171 is projected to have a chlorine resistance service lifetime of greater than 40 years, but with different operating temperature limitations. In the ‘traditional domestic’ application, end use conditions would include 75% usage at ambient temperature (73° F) and 25% usage at 140° F.

The only ASTM minimum ‘end use’ condition adopted into F-876 is identical to those of the ‘traditional domestic’ listing requirements of NSF P-171. Both pass/fail criteria are based on estimated ‘end use’ operating conditions of 75% usage at ambient temperature (73 degrees F) and 25% usage at 140 degrees F. The minimum chlorine resistance service life, according to F-876, shall be 50 years.

At first glance (50 years vs. 40 years), it would appear the ASTM minimum requirement is more stringent than P-171. Actually, the opposite is true. In NSF’s P-171, the minimum service lifetime is actually the extrapolated test lifetime (min. 80 years) multiplied by a design factor of 0.5 ! In ASTM F-876, the extrapolated test lifetime is equal to service lifetime. There is no safety factor applied.

In short, NSF protocol require 80 years, ASTM only 50 years. And, nothing is yet established in ASTM F-876 which even addresses the rigorous ‘end use’ conditions (100% @ 140°F) required to receive a ‘domestic continuous recirculation’ rating.

Vanguard supports the tougher NSF P-171 testing and pass/fail criteria because of the potential for water conditions or other external environmental factors which may present a significant risk in years ahead. PEX producers have no assurance that normal chlorine levels seen today will be the same 10 or 20 years from now.

Vanguard will support an NSF decision to withdraw its voluntary testing protocol (P-171) only when ASTM, through the consensus process, establishes both a reasonable safety factor for each ‘end use’ application and when equivalent pass/fail criteria are established for continuous high-temperature end use applications.

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