Branch Connections 2

[AllHandlesTaken]

Hi,

Please describe the benefits/drawbacks for "stub-in" versus "stub-on" branch connections.

 

[Gator]

Agreed. This is fascinating.

If there is any thermal cycling, the weldolet will take longer to heat up, and hold the heat for a longer time...

That reminded my of my cold box (low pressure, really low temp) days where we'd use Sch. 10s, stub-ins and slip-on flanges (flanges only where absolutely necessary) for just that reason. I always wondered why sweepolet-type branches weren't preferred for LOX service as that would avoid the eventual hydrocarbon collection in stub-in "sharp" edges, crevices and snag points. Perhaps the additional welding/fitting hassle outweighed the risk after considering the typical strict maintenance requirements for liquid oxygen service.

<a href="

http://www.pipingdesign.com">Paul</a>

 

[BillyS]

We have a piping design which has weld'o'let located onto eccentric and concentric reducung butt weld fittings. As this is not sound engineering practice,and B31.3 has no referenct to this type of design has anyone found any written document which does not allow.

 

[pennpiper]

Think of a Reducer as just a piece of pipe that changes size from one end to the other.
If you can weld an "O-Let" fitting to a piece of straight pipe then you can also weld it to a Reducer.

 

[JohnBreen]

Hello,

Actually, the reducer is a fitting. The reducer is not designed for pressure the same way as a piece of pipe (wall thickness per paragraph 304). Fittings do not have a wall thickness specified in B16.9 - they are required to pass a pressure test or be shown to be able to pass a pressure test. So you cannot do "area replacement" calculations for a branch connection. If you take a B16.9 fitting (a piping "component") and alter its design (punch a hole in it for a branch attachment) you have created an "unlisted component" and you must then follow the rules of paragraph 304.7.2 (Unlisted Components).

So, BillyS, the component that you describe is an "unlisted component" and I would suggest reading ALL of paragraph 304.7 and its sub-paragraphs.

Regards, John.