- Primary Methods for Producing PEX Tubing
As Described by PPFA (Plastic Pipe and Fittings Association)
- The "Engel" or peroxide method employs a special extruder with a plunger action where peroxide is added to the base resin and through a combination of pressure and high temperature the cross-linking takes place as the tubing is produced.
- The "Silane" method of PEX production involves grafting a reactive silane molecule to the backbone of the polyethylene. The tubing is produced by blending this grafted compound with a catalyst which can be done using either the Sioplas method or by using a special extruder it can be done using the Monosil method. After extrusion the tubing is exposed to either steam or hot water to induce the final cross-linking reaction in the tubing.
- Electron Beam crosslinking takes place when very high energy radiation is used to initiate molecular cross-linking in high density polyethylene. This product is extruded like normal HDPE then taken to an E-beam facility and routed under a beam or ray in the accelerator where it is dosed with a specific amount of radiation to release the hydrogen atoms and cause polymer cahins to bond or link to the open carbon sites."
Click here for the History of PEX (PPFAhome.org)
- Based on European standards Method 1 is referred to as PEX-a, Method 2 is referred to as PEX-b, and Method 3 is referred to as PEX-c.
(As Described by the Agencies Themselves)
- ASTM F876
- "This specification covers crosslinked polyethylene (PEX) tubing that is outside diameter controlled, made in standard thermoplastic tubing dimension ratios, and pressure rated for water at three temperatures (see Appendix X1). Included are requirements and test methods for material, workmanship, dimensions, sustained pressure, burst pressure, environmental stress cracking, stabilizer migration resistance, and degree of crosslinking. Methods of marking are also given."
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- ASTM F877
- "This specification covers requirements, test methods, and methods of marking for crosslinked polyethylene plastic hot- and cold-water distribution systems components made in one standard dimension ratio and intended for 100 psi (0.69 MPa) water service up to and including a maximum working temperature of 180F (82C). Components are comprised of tubing and fittings. Requirements and test methods are included for materials, workmanship, dimensions and tolerances, burst pressure, sustained pressure, excessive temperature and pressure, temperature cycling tests, and bend strength. Also included are tests related to system malfunctions. The components covered by this specification are intended for use in residential and commercial, hot and cold, potable water distribution systems as well as sealed central heating, including under-floor heating systems."
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- Pressure Ratings by the Plastic Pipe Institute (PPI)
As Described by the PPI
- The Plastics Pipe Institute was conceived to broaden the market for, and accelerate the development of, plastic piping systems. PPI provided vision and leadership leading to the establishment of uniform test and design criteria for all current applications of plastics pipWorking closely with certification and standard-setting organizations for plastic pipe in its various industries, PPI has carried out extensive research on plastics in piping and conduit applications. The resulting research has been translated into accepted standards for quality and safety.
- PPI conceived the methodology for the rating of a material's long term strength, and the concepts of pipe pressure rating, standard dimension ratios, and the adoption of standard preferred numbers to state these properties. PPI also engineered the first code acceptances for plumbing, industrial, commercial, and gas distribution applications for plastics piping, and provided the first industry-wide statistics.
- PPI continues its research in support of industry standards for quality and safety, advancing the use of plastic pipe as an economical, safe, and environmentally friendly solution. See General Publications for a listing of PPI reports, technical notes, guidelines, recommendations, and statements form PPI's technical library for pipe quality and installation standards.
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As Described by the NSF
- NSF International, The Public Health and Safety Company™, a not-for-profit, non-governmental organization, is the world leader in standards development, product certification, education, and risk-management for public health and safety. For 60 years, NSF has been committed to public health, safety, and protection of the environment. While focusing on food, water, indoor air, and the environment, NSF develops national standards, provides learning opportunities through its Center for Public Health Education, and provides third-party conformity assessment services while representing the interests of all stakeholders. The primary stakeholder groups include industry, the regulatory community, and the public at large.
- Serving manufacturers operating in 80 countries, NSF was founded in 1944 and is headquartered in Ann Arbor, MI USA. The NSF Mark is recognized for its value in international trade around the world and is respected by regulatory agencies at the local, state, and federal levels.
- NSF is one of the most widely-respected and recognized global third-party certification providers. As such, NSF is uniquely qualified to evaluate your products and systems.
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