PEX Tubing Standards (ASTM F876 / F877)
Direct Answer
Cross-linked Polyethylene (PEX) is flexible plastic potable water and radiant heating tubing standardized under ASTM F876 and F877. Classified by cross-linking manufacturing chemistry into PEX-A (Engel cold expansion), PEX-B (Silane crimp/clamp), and PEX-C (Radiation), PEX adheres to Copper Tube Size (CTS) outer dimensions with SDR-9 pressure ratings.
Source: ASTM F876-20 / ASTM F877-20
Specs
| Governing Standards | ASTM F876 / ASTM F877 / CSA B137.5 / NSF 61 / NSF 14 |
| Standard Dimension Ratio | SDR-9 (OD to wall thickness ratio = 9:1) |
| PEX-A (Engel Method) | >85% cross-linking | Extreme flexibility & thermal shape memory (ASTM F1960) |
| PEX-B (Silane Method) | 65–70% cross-linking | High chlorine resistance (ASTM F1807 / F2159) |
| PEX-C (Electron Beam) | 60–65% cross-linking | Eco-friendly manufacturing process |
| Pressure Ratings | 160 PSI @ 73.4°F (23°C) | 100 PSI @ 180°F (82°C) | 80 PSI @ 200°F (93°C) |
| Bend Radius Minimum | 6× outer diameter (PEX-A can bend tighter to 5× OD) |
PEX-A vs PEX-B vs PEX-C Manufacturing and Properties
The letter designations denote the chemical cross-linking method, not quality grades:
- PEX-A (Peroxide / Engel Method): Polymers are cross-linked above the crystal melting point ($>85\%$ cross-linking). Features thermal shape memory; if kinked, applying heat with a hot air gun returns the tube to its original molecular form. Exclusively supports ASTM F1960 ProPEX cold expansion fittings that do not restrict water flow.
- PEX-B (Silane / Moisture-Cure Method): Cross-linked after extrusion using silane chemistry ($65\text{–}70\%$). Stiffer with slightly higher burst strength and chlorine oxidation resistance. Joins via ASTM F1807 copper crimp rings or stainless steel cinch clamps.
- PEX-C (Radiation / E-Beam Method): Cross-linked via physical electron beam bombardment ($60\text{–}65\%$). Contains no chemical additives, commonly used in radiant in-floor heating.
F1960 Cold Expansion vs F1807 Insert Crimp Flow Dynamics
A key hydraulic difference lies in fitting design:
- ASTM F1960 Expansion (PEX-A): An expander tool enlarges the PEX-A pipe and an outer PEX collar; a full-port brass/polyphenylene fitting is inserted, and the tube contracts tightly over the fitting. There is zero internal diameter restriction.
- ASTM F1807 / F2159 Crimp (PEX-B/C): An insert fitting sits inside the tube and is compressed externally by a copper ring. The fitting wall reduces the internal cross-sectional area by $20\text{–}30\%$, increasing friction loss in high-demand domestic plumbing loops.