Union vs. Coupling

A union is used in situations where both ends of the piping system is permanently fixed. This will facilitate removing and replacing to fix a leaking pipe or joint without disturbing the system.

A coupling like a socket (screw or press in) cannot be removed and replaced.

There are however other couplings (Johnston or flanged) which will give the same functionality as a union. (but there may be restrictions caused by the fluid or pressure.

A coupling like a socket (screw or press in) cannot be removed and replaced.

.......unless they are Quick connect/ release couplings of course.

Thanks for giving me valuable info. Actually the purpose of question is to know the situations in a plant where we can use union & coupling with example & logic behind.

Regards

sachin

Equipment that may need to be removed for repair or replacement. Places where access maybe needed. Easier to remove a length of pipe with unions on it then to unscrew all the lengths need to get back to it.

Local codes may restrict use of unions. for example in NYC unions are not allowed in natural gas lines. A reverse thread coupling is required.

Generally couplings are used to join pipes in long runs when no equipment is connected. Unions are used at points where equipment is connected into the pipework so that the equipment can be dissconnected for service repair.

Couplings are much cheaper than unions,so use unions only where needed to remove a valve, or other equipment is required, as previously stated, so it is a matter of economics.It would be nice to have nothing but unions, for convenience, but prohibitive in cost.

Grooved fittings are allowed in fire protection systems, and these allow removing at every pipe length.

Application and local codes also dictate in certain situations.

Dear Mr. sachin rastogi

Where the pipe is to be isolated union is fixed. If coupling is fitted, isolation is not possible.

DHAYANADHAN.S