External Pressure Testing

[RPl1989]

Could anyone help me with this one? Looking to test an assembly with stopper fitting that will be welded to existing pipeline. Pipeline is running at 475 psig and looking at testing the stopper fitting at 1080 psig up against the pipe. Any concerns for pipe collapsing? Pipe specs are 12”, OD 12.75”, x46, .250” wall and exposed. Could someone do the pipe collapse calculation with test pressure and system pressure on the pipe and explain the steps for me?

Thank you!

 

[RPl1989]

Just to clarify, 475 psig on inside of pipe and 1080 psig on outside of pipe when stopper fitting welded on outside of pipe and tested against pipeline.

Thanks.

 

[LittleInch]

Yes the are concerns.

Not sure what this mysterious "assembly" is but I think the only way you will get an answer for what is really a point load is a FEA.

When people look at testing tees and weldolet before cutting a hole the guide is no more than 10% above the internal pressure at the time of testing.

Do a bit of searching on this site. This issue has come up before.

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

 

[mk3223]

More info is needed, such as material, branch type and size, operation temperature during welding, etc.
You need to check first the maximum internal pressure of the main pipe during welding based on the main pipe thickness. Consider to reduce the operator pressure during the welding for safety operation.
The external testing pressure is based on the local pipe thickness, branch connection type and ID, and main pipe pressure.

 

[LittleInch]

Have a look at this thread.

http://www.eng-tips.com/viewthread.cfm?qid=288974

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

 

[RPl1989]

Existing pipe is APL-5L, x46. The fitting would be a split tee and no outlet hot tap. The plan would be to weld on the fitting to pipe, then pressure test the fitting at 1080 psig. The pipe that the stopper fitting is welded to is at 475 psig.

So basically we will have an internal pressure of the pipe at 475 psig, with 1080 psig on external.

 

[LittleInch]

Then you will deform the header pipe or severely over stress it.

Who is approving this design?

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