text: Barlow's formula (called "Kesselformel" in German) relates the internal pressure that a pipe can withstand to its dimensions and the strength of its material.
  This approximate formula is named after Peter Barlow, an English mathematician.
  where
  :  : internal pressure,
  : : allowable stress,
  :   : wall thickness,
  : : outside diameter.
  This formula (DIN 2413) figures prominently in the design of autoclaves and other pressure vessels.