# Min Vacuum Pressure in Pipe

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1. Dec 8, 2016

### Bryan Sutter

I have a length of pipe where air is being pulled through by a high powered fan at one end. The pipe is stainless steel, outer diameter is 100 inches. the thickness is 0.125 inches. I need to know what is the minimum vacuum pressure inside the pipe can be before the atmospheric pressure will collapse the steel?

2. Dec 8, 2016

### Mech_Engineer

Have you done a pipe buckling calculation to determine its critical buckling pressure?

3. Dec 8, 2016

### Staff: Mentor

Welcome to the PF.

Can you add a fan at the input to the pipe to minimize the gauge pressure on the pipe wall? How long is the pipe?

4. Dec 9, 2016

### Bryan Sutter

Can you elaborate on this? You aren't referring to Euler's column buckling formula are you?

5. Dec 9, 2016

### Bryan Sutter

The input of the pipe is inside a tank, so I do not believe adding a fan at this location is possible. As to the length it is ductwork going through a large plant, so I do not have length on hand, but it is quite long.

6. Dec 9, 2016

### JBA

For a reference on your problem got to: http://web.ornl.gov/info/reports/1962/3445605700239.pdf [Broken]

And for something that might help review the set of tables starting on pg 439 of: http://ijiset.com/vol2/v2s12/IJISET_V2_I12_50.pdf

These and a list of other pertinent items will be found with a web search under the title "external pressure buckling of pipes or tubes"

Last edited by a moderator: May 8, 2017
7. Dec 10, 2016

### Mech_Engineer

This http://web.ornl.gov/info/reports/1962/3445605700239.pdf [Broken].

Roark's Formulas for Stress and Strain also includes a section titled "Thin Tube Under Uniform lateral External Pressure; Very Long Tube with Free Ends", which is a set of equations for calculating buckling strength of pipes. You may be limited based on your wall thickness to diameter ratio, so pay close attention to the stated limits of any formulas you might find.

Last edited by a moderator: May 8, 2017