Pex (Cross-Linked Polyethylene) Specifications

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Pex (Cross-Linked Polyethylene) Specifications

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Pex (Cross-Linked Polyethylene) Specifications, design use and installation and sizes.

Pex (Cross-Linked Polyethylene): PEX was first used for hot-water radiant heating in the early 1970's, and today is a reliable solution around the world for hot- and cold water plumbing, radiant heating and cooling, outdoor snow and ice melting, residential fire protection, hydronic (hot-water) building services piping, and other demanding applications such as natural gas piping (outside of North America).

PEX is a polymeric material formed by the chemical joining of individual polyethylene molecules in a process called cross-linking. Cross-linking alters the performance of the original polyethylene polymer improving several key properties. The primary reason for cross-linking polyethylene (PE) is to increase the material's elevated temperature performance under load. In addition, cross-linking substantially improves the pipe's environmental stress crack resistance (ESCR), resistance to slow crack growth, chemical resistance, toughness and abrasion resistance.

Uses of Cross-Linked Polyethylene (PEX) Tubing

Residential and commercial potable cold- and hot-water distribution systems
Residential fire protection systems
Hydronic radiant heating and cooling, using warm or chilled fluids
Outdoor snow and ice melting
Outdoor turf conditioning
Ice surface piping
Hot-water distribution piping
Hot-water baseboard piping
Warm- and hot-water radiator connection piping
Potable water service pipes
Geothermal ground loop heat exchangers
Chilled water piping
Specialized industrial and mining applications PEX is typically not used for refrigerant line piping or medical gas applications
Pex tubing is available in a variety of colors

Standard Pex Size Dimensions:

Nominal PEX Size inch	Outside Diameter inch	Inside Diameter inch	Wall Thickness, inch
3/8	0.500	0.350	0.070
1/2	0.625	0.475	0.070
5/8	0.750	0.574	0.083
3/4	0.875	0.677	0.097
1	1.125	0.863	0.125

Bend Radius Design PEX

PEX Size inch	Outside Diameter inch	Minimum Inside Bend Radius inch
3/8	0.500	4
1/2	0.625	5
5/8	0.750	6
3/4	0.875	7
1	1.125	9

Fluid Performance PEX (Approximate)

PEX Size inch	Volume Gal/100 ft	Weight lbs / 100 ft
3/8	0.500	4.50
1/2	0.920	5.80
5/8	1.340	8.38
3/4	1.830	11.00
1	3.030	17.06

PEX Pressure Drop Table (psi per 100ft of tubing length)

Flow Rate GPM	Pex Tubing Size
Flow Rate GPM	3/8"	1/2"	5/8"	3/4"	1"
0.5	2.50	0.51	0.21	0.05	0.02
1.0	7.50	1.70	0.71	0.34	0.10
2.0	26.1	5.30	2.12	1.02	0.35
3.0	54.1	11.0	4.36	2.10	0.63
4.0	-	18.4	7.36	3.53	1.06
5.0	-	27.4	11.0	5.26	1.58
6.0	-	38.1	15.3	7.30	2.19
7.0	-	-	20.1	9.63	2.89
8.0	-	-	25.6	12.3	3.68
9.0	-	-	31.7	15.1	4.55
10.0	-	-	-	18.3	5.50
11.0	-	-	-	21.7	6.52
12.0	-	-	-	25.4	7.63
13.0	-	-	-	-	8.81
14.0	-	-	-	-	10.1
15.0	-	-	-	-	11.4

1 psi = 2.3 ft of head (for fresh water), or 1 ft of head = 0.434 psi

Pressure Ratings: Pressure rating of plastic pipe is highly dependent on material, as well as wall thickness. Most commercially available plastic pipe will be rated by the manufacturer.
PEX pressure ratings are 160 psi at 74°F and 100 psi at 180°F.

Elongation (linear expansion): Typical elongation is anywhere from 1" to 2.5" for every 100ft of PEX pipe at a 10°F temperature rise. Since PEX expands and contracts with temperature changes, it should be secured so as to provide sufficient space for expansion to occur.

PEX pipe is typically connected using either a copper crimp ring or expansion fittings with outer expansion rings. In the crimping method, a copper crimp ring is put over the pipe near the end, a copper fitting is inserted into the pipe end, and a crimping tool is used to crimp the ring over the pipe and fitting. In the expansion fitting method, an expansion tool is used to open the diameter of the pipe, into which an expansion fitting is inserted.

Specifications and Standards

ASTM F876: Standard Specification for Crosslinked Polyethylene (PEX) Tubing.
ASTM F877: Standard Specification for Crosslinked Polyethylene (PEX) Plastic Hot and Cold Water Distribution Systems.
ASTM F1807 – Standard Specification for Metal Insert Fittings Utilizing a Copper Crimp Ring for SDR 9 Cross-linked Polyethylene (PEX) Tubing and SDR 9 Polyethylene of Raised Temperature (PE-RT) Tubing
ASTM F1960 – Standard Specification for Cold Expansion Fittings with PEX Reinforcing Rings for use with Cross-linked Polyethylene (PEX) Tubing
ASTM F2159 – Standard Specification for Plastic Insert Fittings Utilizing a Copper Crimp Ring for SDR9 Cross-linked Polyethylene (PEX) Tubing and SDR 9 Polyethylene of Raised Temperature (PE-RT) Tubing
ASTM F2080 – Standard Specification for Cold-Expansion Fittings With Metal Compression-Sleeves for Cross-Linked Polyethylene (PEX) Pipe
ASTM F2098 – Standard Specification for Stainless Steel Clamps for Securing SDR9 Cross-linked polyethylene (PEX) Tubing to Metal Insert Insert and Plastic Insert Fittings
CSA B137.5 – Cross-linked Polyethylene (PEX) Tubing Systems for Pressure Applications
ANSI/AWWA C904-06 – AWWA Standard for Cross-Linked Polyethylene (PEX) Pressure Pipes 1/2 inch (12 mm) through 3 inch (76 mm) for Water Service
ASTM F2023: Oxidative resistance of PEX to Hot Chlorinated Water per NSF protocol P171 (Non-Barrier PEX Tubing).
CSA B137.5: Crosslinked Polyethylene (PEX) Tubing Systems for Pressure Applications.
NSF/ANSI 14, nsf-rfh: Evaluated for use in Radiant Floor Heating (NSF-rfh) Applications (Oxygen Barrier PEX tubing).
NSF/ANSI 61-G, NSF/ANSI 372, nsf-pw-g: Complies with NSF/ANSI standard 61-G for Lead-Free Drinking Water System Components (Non-Barrier PEX Tubing).
UPC listed by IAPMO (International Association of Plumbing and Mechanical Officials).

Specification example:

ASTM F876 “Standard Specification for Crosslinked Polyethylene Tubing”

Pipes are CTS, SDR9, with tight tolerances on dimensions
Minimum Quick Burst Capability:
- 475 psi @ 73.4°F, 210 psi @ 180°F, 180 psi @ 200°F
Long-term Pressure Ratings:
- 160 psi @ 73.4°F, 100 psi @ 180°F, 80 psi @ 200°F
Sustained Pressure Tests
- Up to 16,000 hours accelerated laboratory hydrostatic testing is required for PPI “Standard Grade” listings
ASTM F876 has categories for performance in three key properties*
*PEX pipes have no “cell classification” •
Performance categories are defined in the “Material Designation Code”
- Example shown from ASTM F876

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