Understanding Barlow's Formula for Pipe Thickness

Understanding Barlow's Formula for Pipe Thickness

Are you trying to figure out how thick a pipe should be to handle a specific pressure? Look no further; Barlow's Formula is your answer. This essential formula in engineering helps calculate the wall thickness required for pipes subjected to internal pressure. Let's dive into what this all means, with a touch of narrative and some real world context to make it relatable.

What is Barlow's Formula?

Barlow's Formula is expressed as:

t = (P × D) / (2 × S)

Here, t represents the wall thickness of the pipe (in inches or millimeters), P stands for the internal pressure the pipe is subjected to (in pounds per square inch, or psi), D is the outside diameter of the pipe (in inches or millimeters), and S is the allowable stress of the pipe material (in psi).

Breaking Down the Variables

Internal Pressure (P)

The internal pressure (P) is the pressure exerted from the inside of the pipe outward. Think of a water pipe in your home. The pressure of the water within the pipe makes sure that the water flows to your faucets. If pressure increases, say, if you have a water pump, the stress on the pipe wall also increases.

Outside Diameter (D)

The outside diameter (D) tells you how wide the pipe is from one outside edge to the other. It's crucial because larger pipes will experience more stress on their walls for the same internal pressure than smaller pipes would.

Allowable Stress (S)

Allowable stress (S) is a material property that defines the maximum stress that the material can withstand without failing. Different materials have different allowable stress values, and these values are critical when deciding what material to use for a pipe that needs to withstand a certain internal pressure.

Wall Thickness (t)

Finally, wall thickness (t) is what you're solving for. It answers the question: How thick does the pipe wall need to be to safely contain the internal pressure given the pipe's size and material?

A Real Life Example

Suppose you are designing a pipeline that will transport natural gas under a pressure of 2,000 psi. The outside diameter of the pipe is 30 inches, and the allowable stress of the steel being used is 35,000 psi. Using Barlow's Formula:

t = (P × D) / (2 × S)

Plug in the numbers:

t = (2000 psi × 30 inches) / (2 × 35000 psi)

Calculating, you get:

t = 60000 / 70000

t ≈ 0.857 inches

So, the pipe should have a wall thickness of approximately 0.857 inches to safely carry the natural gas at 2,000 psi.

Table of Allowable Stresses

Here's a quick table of allowable stresses for different materials that can help you make an informed decision:

FAQs

Summary

Barlow's Formula is indispensable in the field of engineering for determining the required thickness of a pipe given its internal pressure, diameter, and material. By accurately calculating the required wall thickness, engineers ensure the safety and durability of piping systems, whether they're used for water supply, natural gas, or other applications.