External Pressure on a Pipe

[phllp581]

Can anyone refer me to a method or standard for calculating pipe stress when applying a external pressure to a pipe?

For example, I am installing a fully encompassing spherical fitting around a existing run to create a new branch. After welding the spherical onto the existing run I am suppose to pressure test it at 1.5xMAOP. So I would be putting a external pressure that on the existing pipe run that is 50% greater than the internal pressure and I am worried about the stress on the existing run and possibly collapsing the pipe.

Has anyone else dealt with something like this?

Thanks in advance for your help.

 

[bimr]

The Steel Tank Handbook has a method:

https://www.steeltank.com/Portals/0/pubs/Welded Steel Pipe 10.10.07.pdf

 

[jte]

A lot of folks would use an ASME Section VIII Div. 1 design check for this. B31.3 paragraph 304.1.3 sends the designer to VIII-1 with an exception for thick wall pipes.

 

[LittleInch]

Can you draw our sketch this thing. It sounds quite odd.

Small bits of pipe might need an FEA, or use a different fitting.

What pressure rating?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jte]

LittleInch

I imagine phllp is referring to something like these:

https://www.google.com/search?q=sph...-dI4TM:;Xrt4Za86dIT8YM:&imgrc=nZy9ZeBm-dI4TM:

 

[LittleInch]

Assuming that is correct, phlpp, you are right to be concerned. I had an article on exactly this sort of thing, but my current company machine is locked down tighter that a ducks ar*e so I can't attach it, but from memory the person needed to do an FEA analysis and could only pressurise to approx. 1.1 times whatever pressure was in the existing pipe at the time of the test.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.