“Valve end” refers to the way a valve is connected to a pipe. The most common valve end connections for pipelines above 2 inches in diameter are the flanged and the butt weld types. Smaller diameter valves are connected to pipes with threaded (NPT, BSP, ISO) or socket weld end connections (pipe is screwed on the valve or connected with a fillet weld).
Valves should be tightly connected to pipes to ensure a good sealing and no leakages. The three most used types of valve ends are:
FLANGED END CONNECTION
A flanged connection is made by using two flanges and an appropriate number of stud bolts and nuts. Flanged connections very common types of joints used for high-pressure pipelines and are also a cheap solution to connect pipes to valves.
SOCKET-WELD END CONNECTION
Socket weld valve (left) and butt weld valve (right)
A welded connection is in place when the valve (or the fitting) is welded directly onto the pipe. Welded connections are more expensive than flanged joints but ensure tight and leakage-free joints between pipes, fittings and, valves. This type of joining is used for high-pressure pipelines are of two main types: butt weld and socket weld (the latter is used for small sized pipeworks, generally below 2 inches). Butt weld connections require a full welding of the beveled ends of the two parts to be joined, whereas socket weld connections are made by fillet welds.
THREADED END CONNECTION
In this case, the valve is connected to the pipe by a thread (tapered thread). This type of connection is used for low-pressure pipelines with bore size below 2 inches, not subject to mechanical forces as vibration and elongation.
Threaded connections are quicker to execute and cheaper, as the pipe is simply screwed onto the valve, without the need for flanges, stud bolts or welding operations. In case of leakage, however, threaded connections need to be changed and can’t be repaired (which is instead possible for the two previous types of pipe to end connections).
Types of threaded connections
Male to female, male to male, female to female
Threading type (tapered and parallel)