Introduction to pipes and the schedule terminology
For pipes of all dimensions the outside diameter (O.D.) remains relatively constant. The variation in wall thickness affects only the inside diameters (I.D.).
A schedule number indicates the approximate value of
Sch = 1000 P / S
Sch = schedule
P = service pressure (psi)
S = allowable stress (psi)
The higher the schedule number is, the thicker the pipe is. Since the outside diameter of each pipe size is standardized, a particular nominal pipe size will have different inside pipe diameter depending on the schedule specified.
Welded and Seamless Wrought Steel Pipes
To distinguish different weights of pipe it is common to use the Schedule terminology from ANSI/ASME B36.10 Welded and Seamless Wrought Steel Pipe:
- Light Wall
- Schedule 10 (Sch/10, S/10)
- Schedule 20 (Sch/20, S/20)
- Schedule 30 (Sch/30, S/30)
- Schedule 40 (Sch/40, S/40)
- Standard Weight (ST, Std, STD)
- Schedule 60 (Sch/60, S/60)
- Extra Strong (Extra Heavy, EH, XH, XS)
- Schedule 80 (Sch/80, S/80)
- Schedule 100 (Sch/100, S/100)
- Schedule 120 (Sch/120, S/120)
- Schedule 140 (Sch/140, S/140)
- Schedule 160 (Sch/160, S/160)
- Double Extra Strong (Double extra heavy, XXH, XXS)
Note that many of the schedules are identical in certain sizes.
Stainless Steel Pipes
For stainless steel pipes thru 12-inch schedule numbers from Schedule 5S to schedule 80S are used as published in ANSI/ASME 36.19M Stainless Steel Pipe.
- Schedule 5S (Sch/5S, S/5S)
- Schedule 10S (Sch/10S, S/10S)
- Schedule 40S (Sch/40S, S/40S)
- Schedule 80S (Sch/80S, S/80S)