Thread Branch Connection for B31.3 Piping

[SG12345]

Just wondering if anyone is aware of a clause in B31.3 that specifically disallows the use of threaded branch connections. I've had a read through and I can't find a specific paragraph that explicitly disallows it though my instincts say that threaded branch connections should not be permitted.

Any thoughts on this subject would be most appreciated.

 

[moltenmetal]

Threaded branches are permitted where threads are permitted. Threaded branches attached by partial penetration welds (i.e. half couplings set on and fillet welded) are not permitted. Branches beyond a certain size need to use either self-reinforcing fittings (thread-o-lets etc.) or for the conditions of the area replacement calc to be satisified.

Be aware that some people (properly in my view) distinguish between a piping branch and an instrument branch. Piping can put a lot more stress on such a branch than you'd get from installing a pressure gauge, as an example.

 

[SG12345]

Thank you MoltenMetal. I may not have been clear so I will clarify. Per B31.3, would it be permitted to tap a female NPT hole in a pipe and as an example, install a threaded NPT Swagelok fitting into it?

 

[SG12345]

I should say Male threaded NPT Swagelok fitting....

 

[moltenmetal]

Per B31.3 304.3.2 you are permitted to attach branches by three methods:

1) fittings (i.e. tees),
2) unlisted fittings under 3" attached by welding, or
3) welded stub-in connections

Sorry, but drilling/tapping the wall isn't permitted even in Category D services (ie. nonhazardous fluids), unless those services are exempted from compliance with the code in your jurisdiction. An example would be potable water (which may be subject to other codes), or in some jurisdictions, air piping 3/4" NPS and smaller attached entirely by means other than welding.

 

[SG12345]

Thanks moltenmetal. Much appreciated. This confirms my feelings as well.