Barlow's formula

Barlow's formula (called "Kesselformel"^[1] in German) relates the internal pressure that a pipe^[2] can withstand to its dimensions and the strength of its material. This approximate formula is named after Peter Barlow, an English mathematician.^[3]

${\displaystyle P={\frac {2\sigma _{\theta }s}{D}}}$

,

where

${\displaystyle P}$  : internal pressure,

${\displaystyle \sigma _{\theta }}$ : allowable stress,

${\displaystyle s}$   : wall thickness,

${\displaystyle D}$ : outside diameter.

This formula (DIN 2413) figures prominently in the design of autoclaves and other pressure vessels.