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Economic considerations in the building industry as well as variables related to the characteristics of our water supply have made crosslinked polyethylene (PEX) an increasingly attractive plumbing pipe alternative compared with copper, CPVC and other materials. With the increase in PEX use, it is important to understand how PEX plumbing systems differ from other types and what to look for when inspecting these systems.
The PE in PEX refers to polyethylene, the raw material used to make PEX. The X refers to the crosslinking of the polyethylene across its molecular chains. Currently, three methods exist to crosslink PEX. However, all three methods of manufacturing PEX are subject to the same ASTM standards for use in domestic water systems.
The tables shown display the manufacturing standards and subsequent pipe markings you may see on PEX pipe when performing an inspection.
PEX Pipe Markings
It is a requirement that certain information be legibly printed on PEX piping. The print stream on PEX provides several different types of information and identifiers. The table shown gives an example of the markings on Uponor AquaPEX pipe.
Material designation codes
Material designation codes are four-digit, numerical codes that are located after the brand name on the print stream (i.e., PEX XXXX). The codes are tested in accordance with and defined by ASTM F876. Each digit in the code is further explained below.
The first digit in the material designation code is for chlorine resistance tested in accordance with ASTM F2023. A digit 5 indicates the PEX piping has been tested and meets the requirements for minimum chlorine resistance at end-use conditions 100 percent of the time at 140°F (60°C). A digit 5 is the highest classification for chlorine resistance. A digit 3 indicates end-use condition of 50 percent at 140°F and 50 percent at 73°F. A digit 1 indicates an end use condition of 25 percent at 140°F (60°C) and 75 percent at 73°F (23°C). A digit of 0 indicates the pipe has not been tested or rated.
The second digit is for demonstrated ultraviolet (UV) resistance of PEX material when tested in accordance with ASTM F2657. A digit of 1 indicates the PEX piping has a UV resistance of 30 days. A digit of 2 means the pipe has a UV resistance of 90 days. A digit of 3 indicates a UV resistance of 180 days.A digit of 0 means the pipe has not been tested or rated.
The third and fourth digits are for hydrostatic design stress (HDS) as tested in accordance with the Plastics Pipe Institute (PPI) Technical Report TR-4. A digit of 06 indicates the PEX piping has an HDS of 73°F (23°C) at 630 psi. A digit of 08 indicates the PEX piping has an HDS of 73°F (23°C) at 800 psi.
A firestop is a passive fire protection system comprised of various components used to seal openings and joints in fire-resistance-rated wall and/or floor assemblies. Numerous firestop manufacturers have tested their products with PEX pipe to establish the procedures for installing firestop around PEX at the penetration. The type of penetration (e.g., wall, floor or ceiling) determines how these test assembly sections are divided.
Not all caulks are approved for all penetrations. Make sure the penetration is sealed in accordance with the appropriate test assembly, using the type of firestop material recommended by the manufacturer. Larger penetrations may not allow the use of some caulk type of firestop -- a wrap or collar assembly may be required. Refer to the respective firestop manufacturer for more information on appropriate applications of their products.
Ensure the system uses plastic or metal supports designed for use with copper tube size (CTS) plastic pipe. PEX pipe has the same outside diameter as similar nominal diameter copper pipe. Thus, a reference to CTS is applicable to PEX as well as copper. Inspect metal supports for sharp edges and ensure supports allow for linear expansion of the pipe — approximately 1.1 inches (27.9mm) per 10°F (5.6°C) temperature change for every 100 feet of piping.
When installing piping runs, thermal expansion calls for an extra 1/8 to 3⁄16 inches of longitudinal clearance per foot of pipe in the piping run. The piping should not dip excessively between supports. There should be adequate clearance between the PEX and the structure (bored holes or sleeves) to allow the pipe to move freely due to thermal expansion and contraction. Grommets are required when passing through steel framing, and sleeving is required when passing through masonry construction.
Along horizontal runs, install supports every 32 inches (some local codes allow 48 inch for 1¼-inch and larger PEX pipe). If horizontal runs are continuously supported with Uponor’s PEX-a Pipe Support or equivalent pipe-support channel, support spacing intervals can be increased to every 6 feet for ½- to ¾-inch pipe and 8 feet for 1-inch and larger PEX pipe.
Along vertical risers, install riser clamps at the base of each floor and provide a mid-story guide. Vertical runs within a stud cavity should be supported every five feet. To alleviate stress on connections and fittings, bend supports or elbows should be installed when minimum distances from a PEX connection cannot be achieved. (Refer to manufacturer installation instructions for minimum distances.)
Ensure fittings and connections comply with manufacturer installation instructions and that transition joints comply with manufacturer-approved fittings. Engineered polymer (EP) and lead-free (LF) brass fittings are all suitable for direct burial.
• Cold-expansion fittings should be listed to ASTM F1960 and CSA B137.5.
• Compression sleeve fittings should be listed to ASTM F2080.
• Crimp fittings should be listed to ASTM F1807 (brass) or ASTM F2159 (EP).
All lead free brass products shall comply with NSF/ANSI 61 Annex G, NSF/ANSI 372 and conform to the lead-content requirements for lead free plumbing as defined by the Federal Reduction of Lead in Drinking Water Act, effective January 4. Note that per NSF/ANSI 61 Annex G, lead-free products contain no more than 0.25 percent weighted average lead content on wetted surfaces.
Termiticide or pesticide treatment
Generally, PEX is approved for installation directly within or below concrete slabs including where soil termiticide or pesticide treatment is required (be sure to check with the manufacturer for installation limitations). PEX is not required to be sleeved within or below concrete slabs. However, it is recommended to use either a flexible polyethylene (PE) protection sleeve or rigid polyvinyl chloride (PVC) bend guides at all slab penetrations to protect the PEX from abrasion at the pass-through point.
When using a protection sleeve, it is necessary to fill the annular gap between the protection device and the PEX at the exposed ends to help prevent pathways for pests or accidental application of harmful chemicals into the annular space between the PEX pipe and the protection device.
Use only the following sealants that are compatible for external contact on PEX when sealing between PEX and slab-penetration protection devices.
• Latex caulk
• Latex foam
• Silicone sealant
• Polyurethane expanding foam
Note: The application of pesticides or termiticides between PEX pipe and slab penetration protection devices is strictly prohibited.
Pressure test a PEX plumbing system with potable water, air or a mixture of both in accordance with local code requirements. The recommended test pressure is at either 100 psi or at least 25 psi above working pressure. Slight fluctuations in pressure are normal due to ambient temperature changes.
Note: Due to ambient temperature changes, test pressures above 100 psi will cause a slight radial expansion of the pipe and a subsequent relaxation of the material, resulting in a reduction of test pressure. This is normal and does not indicate a leak. Larger-volume PEX systems may require conditioning of the system prior to the test. Refer to manufacturer installation instructions for proper conditioning procedures.
Note: When using valved manifolds, open the valves on the manifold prior to pressure testing. Ensure the valves remain open until the pressure test is complete.
As with all plumbing system inspections, local codes and requirements take precedence. If you have any questions relating to design or installation practices with PEX pipe, contact the PEX manufacturer or you can also contact the Plastics Pipe Institute at www.plasticpipe.org or the Plastic Pipe and Fittings Association at www.ppfahome.org.
Mike Rivers is a product manager for Plumbing at Uponor North America. He has more than 13 years of experience in the industry with an emphasis in plumbing system installation, application and design as well as new product development and product management for the commercial market. Rivers holds a certification in plumbing design (CPD) from the American Society of Plumbing Engineers (ASPE). He is a professional member of ASPE and the Plastics Pipe Institute (PPI) and holds a Bachelor of Science degree in construction management and a Bachelor of Arts degree in business administration from Minnesota State University at Mankato.