TECHNICAL TOOLS
Wall Tickness
Barlow's Formula is useful in determining the wall thickness required for a piping system. To illustrate, assume a piping system has been designed with the following criteria:
1. A working pressure of 2000 psig (P)
2. The pipe to be used is 8 5/8" OD (D) specified to ASTM A53 grade B (SMYS = 35,000 psi)
Rearranging Barlow's Formula to solve for wall thickness gives:
| t = |
PD |
= |
(2000) (8.625) |
= 0.246" wall |
| 2S |
(2) (35,000) |
Wall thickness does not affect the outside diameter-only the inside diameter is affected. For example, the outside diameter of a one-inch extra-strong piece of pipe compared with a one-inch standard weight piece of pipe is identical; however, the inside diameter of the extra strong is smaller than the inside diameter of the standard weight because the wall thickness is greater in the extra-strong pipe.
The American National Standards Institute (ANSI) assigns "schedule numbers" to classify wall thicknesses for different pressure uses. ANSI schedule numbers cover all pipe sizes from NPS 1/8" through NPS 36".
In pipe sizes NPS 1/8"-10", ANSI Schedule 40 thicknesses are identical to standard weight pipe; Schedule 80 (NPS 1/8" through 8") is identical to extra-strong pipe; and, Schedule 160 falls between extra-strong and double extra-strong pipe.
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