Schedule 40 vs Schedule 80

Quick Answer

Schedule 80 pipe has a thicker wall than Schedule 40 for the same NPS, resulting in higher pressure ratings, higher weight, smaller bore, and higher cost. SCH 40 is the default for most process piping; SCH 80 is specified when higher pressure, corrosion allowance, or threading is required.

Both schedules share the same outside diameter for a given NPS. The difference is entirely in wall thickness, which determines the internal diameter, pressure capacity, and weight per meter.

Side-by-Side Comparison

NPS	OD (mm)	SCH 40 Wall (mm)	SCH 80 Wall (mm)	SCH 40 ID (mm)	SCH 80 ID (mm)	SCH 40 Weight (kg/m)	SCH 80 Weight (kg/m)
1	33.4	3.38	4.55	26.6	24.3	2.50	3.24
2	60.3	3.91	5.54	52.5	49.2	5.44	7.48
3	88.9	5.49	7.62	77.9	73.7	11.29	15.27
4	114.3	6.02	8.56	102.3	97.2	16.07	22.32
6	168.3	7.11	10.97	154.1	146.4	28.26	42.56
8	219.1	8.18	12.70	202.7	193.7	42.55	64.64
10	273.1	9.27	15.09	254.5	242.9	60.31	96.01
12	323.9	10.31	17.48	303.2	288.9	79.73	132.08

Pressure Rating Impact

The allowable internal pressure depends on wall thickness, pipe material, design temperature, and the applicable code (ASME B31.3, B31.1). For ASTM A106 Grade B at ambient temperature:

NPS	SCH 40 Approx. Pressure (bar)	SCH 80 Approx. Pressure (bar)
2	159	227
4	128	184
6	103	160
8	91	142

Values are approximate, based on ASME B31.3 at 38°C, E=1.0 (seamless), no corrosion allowance.

When to Use Schedule 40

• General process piping at moderate pressures and temperatures
• Utility services (water, air, nitrogen)
• Most pipe class specifications for Class 150 service
• Fire water systems (commonly specified per NFPA)

When to Use Schedule 80

• Higher design pressures requiring additional wall thickness
• Services with significant corrosion or erosion allowance (1.5-3 mm added)
• Threaded connections (NPT threads cut into the pipe wall reduce effective thickness)
• Small-bore piping (NPS 1.5 and below) where SCH 80 or XS is standard practice in many EPC project specifications
• Socket-weld connections per ASME B16.11

Common Mistake

Using SCH 80 everywhere “just to be safe” increases material cost by 30-60%, adds weight to pipe supports, and wastes procurement budget. The correct approach is to calculate required wall thickness per ASME B31.3 Section 304.1.2 and select the minimum schedule that meets the requirement, including corrosion allowance and mill tolerance.

For detailed wall thickness charts across all schedules and NPS values, see the ASME pipe wall thickness reference.

Read the full guide to pipe types