# Pipe wall thickness, barlow equation problem

1. Apr 23, 2015

### rottweiler123

Hi guys
I am working on some project that involves pipe wall thickness calculation, and I have one problem.
here is the explanation of the example:

http://pokit.org/get/?24c6e34b...4662402372ce5fc7.jpg

Please, can some one tell me what means tf/m2 (ton force/square meter ???) and how to do conversion as shown on picture.

Thank you very much.

2. Apr 23, 2015

### SteamKing

Staff Emeritus
Fresh water has a density of 1000 kg / m3 (in round numbers) or a weight of 1000 kg-force for each cubic meter.

1 tonne-force = 1000 kg-force, therefore 1 m3 of fresh water weighs 1 tonne-force (tf).

Since the acceleration due to gravity is approximately 10 m/s2, 1 kg-f = 10 N approximately; thus 1 m3 of fresh water weighs 10 kN.

Each meter of depth of fresh water produces a pressure of 10 kN/m2,
so a head of 110.585 m = 110.585 tf/m2 = 110.585 tf/m2 × 10 kN/tf = 1105.85 kN/m2

1 m2 = 1,000,000 mm2, so a pressure of 1105.85 kN/m2 / 1,000,000 = 1.106 N/mm2

so it appears the value of 11.06 kN/mm2 is off by a few decimal places.

http://en.wikipedia.org/wiki/Ton-force

I'm not familiar with the equation shown for calculating the wall thickness of the pipe, but it is not the Barlow formula.

http://www.engineeringtoolbox.com/barlow-d_1003.html

3. Apr 23, 2015

### stewartcs

Can you describe the application a little bit? Are you using any particular codes (API, ASME, etc.)? Pipe burst pressures are determined using widely different safety factors depending on the code you're using and the application.

Regardless, I don't recommend copying an example to perform engineering calculations if you're not 100% sure of how it was derived! Start with stating the application, figure out your loading conditions (i.e., static internal pressure vs. cyclical, any external loading, etc.) then you can just pick one of the many industry standards/codes that cover your application.

CS