PIPE ENGINEERING GUIDE · 8 MIN READ
SCH 40 vs SCH 80 Pipe
Understand the practical difference in wall thickness, bore, weight, flow and selection—before you release your next piping RFQ.
What does pipe schedule mean?
Pipe schedule is a dimensional designation associated with pipe wall thickness. Common designations include SCH 10, 20, 40, 80, 120 and 160. The schedule number is not a direct wall-thickness measurement; the actual thickness depends on the nominal pipe size and dimensional standard.
ASME B36.10M is commonly referenced for welded and seamless wrought steel pipe, while ASME B36.19M is commonly referenced for stainless steel pipe. Always verify the current project specification.
SCH 40 and SCH 80 compared
| Parameter | SCH 40 | SCH 80 |
|---|---|---|
| Wall thickness | Comparatively thinner | Comparatively thicker |
| Internal diameter | Comparatively larger | Comparatively smaller |
| Outside diameter | Same for the same NPS | Same for the same NPS |
| Weight per metre | Lower | Higher |
| Flow area | Comparatively larger | Comparatively smaller |
| Typical use | General industrial services | More demanding services |
Pressure capability cannot be determined from schedule alone. Grade, temperature, corrosion allowance, tolerance, joint efficiency and the governing design code must also be considered.
Common SCH 40 vs SCH 80 dimensions and weights
Nominal ASME-series dimensions, cross-checked against the supplier references in our pipe-size guide. Calculated plain-end weights use carbon-steel density 7,850 kg/m³.
| NB | NPS | OD mm | 40 wall mm | 40 kg/m | 80 wall mm | 80 kg/m |
|---|---|---|---|---|---|---|
| 15 | 1/2 | 21.3 | 2.77 | 1.27 | 3.73 | 1.62 |
| 20 | 3/4 | 26.7 | 2.87 | 1.69 | 3.91 | 2.20 |
| 25 | 1 | 33.4 | 3.38 | 2.50 | 4.55 | 3.24 |
| 32 | 1 1/4 | 42.2 | 3.56 | 3.39 | 4.85 | 4.47 |
| 40 | 1 1/2 | 48.3 | 3.68 | 4.05 | 5.08 | 5.41 |
| 50 | 2 | 60.3 | 3.91 | 5.44 | 5.54 | 7.48 |
| 65 | 2 1/2 | 73 | 5.16 | 8.63 | 7.01 | 11.41 |
| 80 | 3 | 88.9 | 5.49 | 11.29 | 7.62 | 15.27 |
| 90 | 3 1/2 | 101.6 | 5.74 | 13.57 | 8.08 | 18.64 |
| 100 | 4 | 114.3 | 6.02 | 16.08 | 8.56 | 22.32 |
| 125 | 5 | 141.3 | 6.55 | 21.77 | 9.53 | 30.97 |
| 150 | 6 | 168.3 | 7.11 | 28.26 | 10.97 | 42.56 |
| 200 | 8 | 219.1 | 8.18 | 42.55 | 12.70 | 64.64 |
| 250 | 10 | 273.1 | 9.27 | 60.31 | 15.09 | 96.02 |
| 300 | 12 | 323.9 | 10.31 | 79.73 | 17.48 | 132.09 |
Full NB-to-inch chart, stainless schedules, formula and downloadable reference →
Example: NPS 2 carbon-steel pipe
In this common example, the outside diameter remains approximately 60.3 mm. The thicker SCH 80 wall reduces the bore and increases the theoretical weight. Confirm dimensions against the applicable standard before procurement or fabrication.
When SCH 40 may be suitable
- Utility and cooling-water systems
- Compressed-air services
- General plant piping
- Fire-water networks
- Low-to-moderate design conditions
When SCH 80 may be specified
- Higher-pressure process piping
- Steam and condensate systems
- Elevated-temperature services
- Lines needing added corrosion allowance
- Heavy-duty industrial applications
Does SCH 80 always have a higher pressure rating?
A greater wall thickness generally provides greater pressure capability when all other variables are equal. But schedule alone does not establish the allowable pressure. Engineers must consider material grade, design temperature, corrosion or erosion allowance, manufacturing tolerance, weld quality, service fluid and the applicable piping code.
How schedule affects flow
SCH 80 has a smaller internal diameter than SCH 40 for the same NPS. This can change flow capacity, velocity, friction loss, pressure drop and pumping requirements. Hydraulic calculations should therefore use the actual internal diameter—not only the nominal pipe size.
Materials and grades commonly supplied
Information required before ordering
- Material specification and grade
- Seamless, ERW, EFW, SAW or spiral construction
- Nominal pipe size and required schedule
- Length, quantity and end condition
- Dimensional and material standards
- MTC, testing and inspection requirements
- IBR, NACE or TPI requirements, when applicable
- Delivery location and required delivery period
SELECTION SUMMARY
Choose from engineering data—not schedule number alone
Select SCH 40 when it satisfies the approved design conditions and required service economically. Select SCH 80 when the engineering design requires greater wall thickness, pressure capability, corrosion allowance or mechanical strength.
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Engineering reference guidance only. Final material selection, pressure-temperature suitability and dimensions must be verified against the latest applicable standard, design code and approved project specification.