ASME B31.3 Piping

[BPVN]

Hi,
Does ASME B31.3 allows to weld STD. 90 deg.elbow (Matl.-P8) to Slipon flange (SORF)-(Matl.-P8)?
Prompt reply will be highly appreciated!
Thanks in Advance!
BPVN

 

[ColonelSanders83]

Please perform an advanced search or even a google search before asking such questions.

See here

http://www.eng-tips.com/viewthread.cfm?qid=230173&page=9

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

 

[DSB123]

BPVN,
What you suggest is not a recommended combination. A bend welded to a weld neck flange is a better option.

 

[pennpiper]

BPVN,
1. The Code (ASME B31.3) does not state that you cannot weld a Slip-On flange to a 90 degree Elbow.

2. In my work history over more than 45 years I did it with no ill effects.

 

[DSB123]

Well pennpiper I bow to your experience but in my working life of 37 years I have never seen it done on this side of the pond because it is a very poor detail design since the flange is sat on the bend radius. The normal detail to use is a weld neck directly onto the bend - much better. I have heard that pipe-fitters like to use a SORF directly on a bend though.

 

[moltenmetal]

Pennpiper's suggestion in the original thread on the subject is to use a "long tangent" elbow in this case, which would work just fine. Just fine, that is, if you can GET such an animal from your piping supplier, and can ensure that it will be used in the correct location by whoever is doing the fitting. We tend to purge our pipe specs (and our pipe design software's fitting catalogs) of unusual fittings, as they're always a problem to source when we need them. I'd rather do an extra weld here and there than be waiting 6 weeks for odd components to arrive.

An ordinary long-radius elbow when inserted the proper distance into even 150# SO flanges gives you a very ugly and asymmetrical fillet weld between the hub of the SO and the OD of the elbow. It's a real mess when you go 300# or higher. The problem is even worse on the branch of a tee. You're going to be welding both front and back fillets on the SO, the front fillet is no problem and in category D piping you are permitted to weld only one of the two fillets. The practice of welding only one of the two welds on a SO is prohibited in normal fluid service in B31.3, so it stands to reason that both welds need to be sound and symmetrical when they're required.

We prohibit the practice on code piping purely on the basis that it looks bad, and we always do both welds on a SO, even for category D.

We prohibit the insertion of a fitting directly into a socket-welding flange entirely. In that case, I think there's sufficient justification to call that a bad practice from a strength and durability perspective rather than just on the basis of appearance.

As to whether there's a specific code prohibition against either practice, I've never seen one but that doesn't mean it isn't in there somewhere. I'll leave it to the people who have B31.3 tatooed to the back of their eyelids to answer the real question posed by the OP.

 

[DSB123]

moltenmetal,
You expanded my concern eloquently.

Regards