Pipe Schedules

Reference data and engineering information about pipe schedules for fluid mechanics applications.

pipeschedules

Overview

Pipe schedule numbers are a standardized way to specify pipe wall thickness. The outside diameter (O.D.) of a given nominal pipe size is fixed regardless of schedule, so increasing the schedule number only increases wall thickness and therefore decreases inside diameter (I.D.).

The schedule number is approximately:

$S = \frac{1000 \times P}{S_a}$

where P is the internal working pressure and S_a is the allowable stress at the service temperature. This means higher schedule numbers correspond to thicker walls suitable for higher pressures.

Two primary ANSI/ASME standards govern pipe schedules:

ANSI/ASME B36.10M — Welded and Seamless Wrought Steel Pipe (Sch 10 through Sch 160, plus STD, XS, XXS)
ANSI/ASME B36.19M — Stainless Steel Pipe (Sch 5S through Sch 80S)

The S-suffix schedules (5S, 10S, 40S, 80S) have thinner walls than their carbon-steel counterparts for the same nominal size.

Key Formulas

The inside diameter of a pipe is calculated from the outside diameter and wall thickness:

$D_i = D_o - 2 \times t$

The schedule number relationship to working pressure and allowable stress:

$P = \frac{S \times S_a}{1000}$

Variables

Symbol	Description	Typical Unit
D_i	Inside diameter	mm, in
D_o	Outside diameter	mm, in
t	Wall thickness	mm, in
P	Internal working pressure	psi, MPa
S_a	Allowable stress at temperature	psi, MPa
S	Schedule number	dimensionless

Schedule Designations

12 rows

Common ASME pipe schedule designations for carbon and stainless steel
Schedule	Designation	Wall	Typical Use
5S	—	Very thin	Low-pressure stainless
10S	—	Thin	Low-pressure stainless
10	—	Thin	Low pressure, gravity
20	—	Medium-thin	General service
30	—	Medium	Moderate pressure
40S / STD	Standard Weight	Standard	Most common general service
60	—	Medium-heavy	Higher pressure
80S / XS	Extra Strong	Heavy	High pressure, steam
100	—	Heavy	High pressure
120	—	Extra heavy	Very high pressure
160	—	Very heavy	Very high pressure
XXS	Double Extra Strong	Extra heavy	Extreme pressure

Source: engineeringtoolbox.com

Calculator — Inside Diameter

Pipe Inside Diameter

Outside Diameter(mm)

Wall Thickness(mm)

Unit Converter

Pipe Schedule Unit Converter

Diameter or wall thickness(mm)

Pipe weight(kg/m)

Pressure(psi)

Allowable stress(psi)

Example Dimensions — NPS 4 in. (D_o = 114.3 mm)

7 rows

Typical dimensions for NPS 4 in. steel pipe across schedules
Schedule	Wall Thickness(mm)	Inside Diameter(mm)	Weight(kg/m)
5S	2.77	108.76	7.58
10S	3.05	108.2	8.37
40 / STD	6.02	102.26	16.07
80 / XS	8.56	97.18	22.32
120	11.13	92.04	28.32
160	13.49	87.32	33.54
XXS	17.12	80.06	41.03

Source: engineeringtoolbox.com

Engineering Notes

O.D. is constant for a given nominal pipe size — only the I.D. changes with schedule.
Schedules 5S, 10S, 40S, 80S are specific to stainless steel (B36.19M) and are not interchangeable with carbon-steel schedules of the same number.
Schedule 40 is identical to Standard Weight (STD) for NPS 10" and smaller; for larger sizes STD has its own wall thickness.
Schedule 80 is identical to Extra Strong (XS) for NPS 8" and smaller.
Double Extra Strong (XXS) has no fixed schedule number; its wall thickness is defined independently.
Always confirm dimensions against the applicable ASME standard for critical or high-pressure service.

References

Original Source — Engineering ToolBox

Source: engineeringtoolbox.com