Nominal Pipe Sizes & Schedules vs. PEX Tubing
Comparing 2 standards across 14 specifications. 14 key differences identified.
Nominal Pipe Size (NPS) and Schedule designations under ASME B36.10M standardize the outer diameter, wall thickness, and pressure capabilities of forged steel, wrought iron, and stainless pipe. For NPS 1/8 to NPS 12, the nominal number represents approximate inside diameter, while maintaining a standardized fixed outer diameter across Schedule 40 (Standard) and Schedule 80 (Extra Strong) walls.
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.
Specification Comparison Table
14 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standard
|
ASME B36.10M / ASTM A53 / ASTM A106 | — |
|
Metric Equivalent
|
DN (Diamètre Nominal) in millimeters (e.g., NPS 1/2 = DN 15) | — |
|
NPS 1/2" Dimensions
|
OD: 0.840" (21.3 mm) | Sch 40 Wall: 0.109" (2.77 mm) | Sch 80 Wall: 0.147" (3.73 mm) | — |
|
NPS 3/4" Dimensions
|
OD: 1.050" (26.7 mm) | Sch 40 Wall: 0.113" (2.87 mm) | Sch 80 Wall: 0.154" (3.91 mm) | — |
|
NPS 1" Dimensions
|
OD: 1.315" (33.4 mm) | Sch 40 Wall: 0.133" (3.38 mm) | Sch 80 Wall: 0.179" (4.55 mm) | — |
|
NPS 2" Dimensions
|
OD: 2.375" (60.3 mm) | Sch 40 Wall: 0.154" (3.91 mm) | Sch 80 Wall: 0.218" (5.54 mm) | — |
|
Schedule Transition Boundary
|
For NPS ≥ 14, Nominal Pipe Size equals the exact Outer Diameter in inches | — |
|
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) |