NSF Standards Require Stringent Testing for PEX Piping
NSF certifies potable water plastic piping to the American National Standard, NSF/ANSI Standard 14 - Plastic Piping System Components and Related Materials in addition to other required U.S. and Canadian standards. NSF/ANSI Standard 14 provides a significant benefit by combining the minimum physical, performance, health effects, product testing, long-term strength and quality control requirements that are key to ensuring proper product performance in the field.
The certification process involves several steps. This example is based on testing and certification of cross-linked polyethylene (PEX) pipe.
ApplicationManufacturers identify the products and production facilities to be certified, as well as provide a full formulation disclosure, including all materials, process aids and suppliers. NSF also requires ingredient level formulation information from ingredient suppliers.
Formulation ReviewNSF chemists and toxicologists conduct a formulation review to determine which analytical tests are needed to evaluate the health safety of the material. For decades, NSF’s certification policy has prohibited lead as an intentional ingredient in plastic pipe fittings and materials - with the exception of lead contained in brass, which meets the requirements of the U.S. Safe Drinking Water Act.
Production Facility InspectionNSF certification requires both initial and ongoing inspections to ensure compliance with applicable requirements. In fact, NSF’s policies require that certified potable water pipe facilities receive three unannounced inspections annually, the scope of which includes:
Health Effects TestingPlastic potable water products are required to meet NSF/ANSI Standard 61 – Drinking Water System Components – Health Effects by U.S. and Canadian drinking water standards. This standard establishes the requirements for chemical contaminants and impurities that are indirectly imparted to drinking water from products, components and materials used in drinking water systems.
Products are tested by exposing them to three different formulated exposure waters: pH 5, pH 8 and pH 10. The exposure waters are then analyzed for contaminants. The three formulated waters are each aggressive toward various contaminants of concern. Products are exposed to water at 73°F (23°C), 140°F (60°C), or 180°F (82°C), depending on the temperature and end use of the product.
Products are conditioned by exposure to the formulated waters for 14 days, and water is changed on 10 of the 14 days. Water collected from the final 16-hour exposure period is analyzed for contaminants. Any contaminants detected must be below EPA or Health Canada levels for regulated contaminants.
For non-regulated contaminants in the extraction water, NSF/ANSI Standard 61 sets health-based pass/fail levels based on review of available toxicity data using the risk assessment procedures in Annex A of the standard.
NSF/ANSI Standard 61 and the formulation review determine the specific chemical analysis for each product type. Common analytical tests include:
Performance TestingNSF/ANSI Standard 14 requires materials for pressure pipe applications to meet a minimum 50-year long-term strength requirement through establishment of a hydrostatic design stress in accordance with the Plastic Pipe Institute’s Technical Report Number 3. This includes testing pipes from at least three different lots of material and testing at two temperatures: 73°F and an elevated temperature, typically 180°F or 200°F.
To establish the hydrostatic design basis, products are repeatedly tested to failure to develop a stress time relationship. For PEX, two of the samples are tested at an elevated temperature for a minimum of 10,000 hours (over 400 days) and one sample is tested for a minimum of 16,000 hours (over 660 days).
Product Design StandardsProducts must also meet product design standards such as ASTM F876: Standard Specification for Crosslinked Polyethylene (PEX) Tubing and ASTM F877: Standard Specification for Crosslinked Polyethylene (PEX) Plastic Hot- and Cold-Water Distribution Systems, as well as CSA B 137.5 PEX tubing systems for pressure applications. Testing includes dimensions, density, 1,000-hour sustained pressure, hydrostatic burst, environmental stress cracking, degree of cross-linking, stabilizer functionality, chlorine resistance, thermocycling and excessive temperature sustained pressure. ASTM F876 requires all PEX pipes used in potable water to be evaluated against the chlorine resistance requirements using ASTM F2023: Standard Test Method for Evaluating the Oxidative Resistance of Crosslinked Polyethylene (PEX) Tubing and System to Hot Chlorinated Water and have a minimum extrapolated test lifetime of 50 years.
Quality ControlNSF/ANSI Standard 14 requires manufacturers to perform critical quality control testing at the production facility at specified frequencies. For example, PEX tubing manufacturers must perform dimensions on tubing at least every two hours, burst pressure testing every 24 hours and degree of crosslinking weekly. This quality control testing helps to ensure consistent quality.
UV ResistanceRecently there has been interest in the addition of the UV resistance testing, which will become an option for manufacturers whose products could potentially be exposed to sunlight.
While PEX tubing is not typically used in outdoor applications, tubing may become exposed to sunlight during storage. There is an ASTM task group proposal for testing involving exposing products to sunlight for a specified time period (as outlined in ASTM F2657, Standard Test Method for Outdoor Weathering Exposure of Crosslinked Polyethylene (PEX) Tubing), then evaluating the oxidative resistance of the product per proposed requirements in ASTM F876, Standard Specification for Crosslinked Polyethylene (PEX) Tubing, and according to the ASTM test method F2023 for evaluating the oxidative resistance of PEX tubing and systems to hot chlorinated water.
Once the product has gone through the applicable exposure period and has passed the UV resistance testing, the pipe material designation code will be updated to indicate that the material has met the requirements for UV resistance. The code will indicate the amount of exposure time that was used for the evaluation of the sample.