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Steam Piping Union to Flange

Steam Piping Union to Flange

I am looking to replace 3/4" and 1" schedule 80 and schedule 40, in both sizes, and wanted to know if there is a definite standard as to when you can and cannot use unions on certain size pipe. Steam pressure can range from 60 - 100 psi.

RE: Steam Piping Union to Flange

What does the owner's engineer say? I really doubt that you'll find an American National standard on this. I avoid unions since they can vary a bit from manufacturer to manufacturer and so you will have to replace both sides if an issue occurs. But for small bore low pressure I would probably accept 'em. Are the other fittings threaded or welded? If you're already using SW elbows etc then I'd push for SW flanges.


RE: Steam Piping Union to Flange

In the Steam service you site (60 -100psi), I would recommend:

 - Socket-weld fittings (w/ SW unions for break-out) in all sizes 2" (DN 50) and smaller

 - Butt-weld fittings (w/ Weld-neck Flanges for break-out) in all sizes 3" (DN 80) and larger.

RE: Steam Piping Union to Flange

I second pennpiper's suggestion.....

The piping joints and size ranges are consistent with the power piping codes.

You ask:

"if there is a definite standard as to when you can and cannot use unions on certain size pipe"

Yes there is..... its in the  ASME B31.1 and.3 codes and the defined list of acceptable standards for piping fittings and joints


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