Half coupling vs Stub in or Set in branch

[Xk333]

Hi,

What is a stronger connection between Half Coupling and a Stub in for branching of a pipe?
For Stub in we get a butt weld connection which is stronger in branch as opposed to 2 welds in half coupling? Why do we still use half coupling as we have to anyways make a hole in the run pipe in both cases?

 

[Abloom]

Watch some YouTube videos about hot tapping bro.

 

[LittleInch]

Half coupling confused me for a while, but this is maybe what you mean?

https://www.youtube.com/watch?v=Kht4L-C7-kw

Stub in you only get a full pen weld if you allow for it and there are many bad examples of stab in branching.
There is a big stress concentration on both of them and hence you either need reinforcing plates or most people just use a weldolet....

some half couplings go through the header pipe, some don't

People use half couplings because they are lazy and just want something cheap to weld on.

You're asking a lot of basic questions here about pipe connections etc. Can you expand on what your role is and why the sudden interest in finding cheap ways to do things?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[david339933]

putting a half coupling and stub in is basically the same thing. Use a proper branch connection such as a weldolet. Not sure what hot tapping has to do with any of this.

 

[MJCronin]

What is the code of record and what does it say about this ? ... What are the sizes of your piping ?

What, exactly do YOU mean by "stronger" ? .... Please describe this in more complete and cogent terms

ASME B31.1/B31.3 has lots to say about this....

There are many dangers in not having a "code of record" and relying on "Whatdoyathink" engineering ..... IMHO

MJCronin
Sr. Process Engineer

 

[Abloom]

A stub-in is pipe into pipe. Use a reinforcement pad (repad) around the stub, where it meets the run pipe.

A coupling is a double female joint fitting. Threaded or socketweld, depending on everything.

A half coupling is a single female joint with a plain end, and is shorter.

Common standard install for branching off a main or header is close on stub-in (or half coupling & nipple) then a blinded isolation valve. The idea is to have the branch valve os as close to the header as possible, so it's durable. Schedule or material thicknesses & welding details are influential.

Studying hot tap videos might pique your curiosity regarding fundamental piping principles & the why's driving a specific arrangement, perhaps.

 

[mk3223]

There are the stub-in pipe Code,

 

[mk3223]

The half coupling fitting on the branch connection is similar to the sockolet fitting which is integrally reinforced for good branch connection strength. Even the only pipe branch connection without the reinforced pad is accepted by the Code, the Company has replaced this connection in the plant as the result of cracking or leaking on the branch connection in the past.

 

[r6155]

I don't think installers machine the coupling fitting to fit the inside surface of the pipe.

Regards

 

[LittleInch]

A 1" or 1/2" connection into a 24" or 30" line you won't notice the lack of machining, but a 4" you would.

From what I can see, people still use half couplings to make it easier to either screw in a valve or a pipe or socket weld something.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

@ LittleInch
If exact machining is not performed on the inner surface, then air is trapped during hydrostatic pressure testing in a horizontal pipe, which is not permitted.

Regards

 

[KevinNZ]

Piping codes cover Half Coupling (Bosses). e,g B31.1 has welding details and limitations

There are two points to consider the SIF in the stress model. The Coupling to header weld and the pipe to coupling. Usually the later is higher but depends on the header wall thickness.

A stab in weld is an unreinforced tee and will have a high SIF. You can add a pad but the SIF may still be high.

 

[GD2]

OP,
ASME B31.3 limits use of half-couplings, regardless of stub-on or stub-in. It’s not allowed in severe cyclic service, high pressure system ( Chapter IX) and Category M fluid service. Instead, use WOL.

GDD
Canada