Pipe Stress Budget

The Pipe Stress Budget calculator computes the pressure that a pipe can withstand based on the allowable stress, wall thickness and outside diameter.

INSTRUCTION: Choose units and enter the following:

• (S) Allowable Stress
• (t) Wall Thickness
• (D) Outside Diameter of Pipe

Pressure Budget (P): The calculator returns the pressure in pounds per square inch (psi).  However, this can be automatically converted to compatible units (e.g., pascals) via the pull-down menu.

The Math / Science

The most common diameters of gas pipes, typically measured in inches, vary based on the application (residential, commercial, or industrial) and the type of gas system. For residential natural gas supply systems, the following diameters are common:

1. ½ inch
2. ¾ inch
3. 1 inch

For larger commercial or industrial applications, pipes with diameters of 1¼ inch, 1½ inch, and 2 inches or more might be used. The size needed depends on the volume of gas required, the length of the pipe run, and local building codes. 

The thickness of a 1-inch pipe depends on its schedule, which indicates the wall thickness. Pipe schedules vary based on the pipe's application and material. Below are common schedules and corresponding wall thicknesses for a 1-inch pipe:

1. Schedule 40 (Standard):
   • Wall thickness: 0.133 inches (3.38 mm)
2. Schedule 80 (Extra strong):
   • Wall thickness: 0.179 inches (4.55 mm)
3. Schedule 160 (High pressure):
   • Wall thickness: 0.250 inches (6.35 mm)

The thicker the pipe (higher schedule), the higher its pressure rating, but this also decreases the inner diameter.

This calculator is based on Barlow's formula which relates the internal pressure that a pipe can withstand to its dimensions and the strength of its material.

The Barlow formula is:

P=(2•S•t)/D

where: 

• P = pressure based on Barlow's formula
• S = allowable stress
• t = wall thickness
• D = outside diameter

This formula figures prominently in the design of autoclaves and other pressure vessels. 

References

Wikipedia (https://en.wikipedia.org/wiki/Barlow%27s_formula)