Butt Weld Valve vs. Flanged Valve

Before looking at the possibility please explain why is there a need to consider it.

When designing or repairing a welded piping system, unless for some reason unique to that particular system, it is always better to weld the piping fittings and use flanged connections for valves and other critical components which might have to be removed from the system at a later time. Taking a flanged piece out of the piping is much easier and faster than cutting out a butt welded one.

A good pipe-fitter and a welder can install two flanges on the corresponding pipe ends faster than they can set-up and weld the component into the piping. This is particulary true if it involves out of position welding.

In some instances it is much faster to weld the flanges onto the pipes in the welding shop, level the flange holes in the field and weld the other pipe-ends in the field. For a component that has butt weld ends, weld-neck flanges can be welded on it in the shop and installed with the bolts in the field. Shop welding is usually faster and of higher quality than field welding. This is particulary true if it involves out of position, weather problems, access problems, flammable atmospheres or other field type problems.

For steam use you should use flange covers to prevent any leaks from injuring personnel.

Going from a 300# butt welded valve to a 600# flanged one only requires installing 2ea 600# flanges on the existing piping to accomodate it. Be sure pressure rating of the other components is not going to be exceeded if you are also going to raise the operating pressure above 300psi.

As per Engineering Practice we should prefare welded connection over flanged connection in following design condition-(for safety purpose mainly)

Design pressure is "50 barg and above" and or Design temperature is "400 deg celcius and above"