Do elbows provide vacuum support

[KevinNZ]

I am designing a DN1050 pipe run for vacuum conditions. Calculations per ASME VII-1 UG28.

The question is. Do elbows count as support points and the length between support Ls can start at elbows? Or do support rings have to be added to elbows?

Also how to calculated the external pressure rating of an elbow?

 

[jte]

Interesting question... My approach would likely be to run an FEA. But perhaps a simpler way to look at it is that your length to diameter ratio is likely not going to matter. If you look at II-D Figure G for determining the A factor, you'll note that with a Do/T value of 50, the L/D has no impact on the A factor if it is higher than about 10. So the question is, is it worth evaluating the elbows as a point of support (external pressure wise), or do you just go with L/D is infinite, grab the A factor, and move on?

 

[KevinNZ]

Thanks jte

L is important if the pipe is not thick enough and support rings are required. I have worked back from value A where the pipe is thick enough to get a required L.

 

[pennpiper]

1. What is the nominal size of the elbow/piping system?
2. what is the wall thickness?

Sometimes its possible to do all the right things and still get bad results

 

[KevinNZ]

Pipe is DN900, Std weight with 3mm CA. external pressure 0.801 bar.

 

[Compositepro]

If you are asking about a welded elbow that is the same wall thickness as the pipe, I would think that it would just as likely introduce wall buckling stresses into the pipe as it would to resist them.