According to ASME B31.1, to execute a flanged connection using a socket weld flange, the pipe shall be at first inserted in the socket of the flange until it reaches the bottom of the flange, then it should be lifted by 1.6 mm and finally welded.
This gap shall be left to allow proper positioning of the pipe inside the flange socket after the solidification of the weld.
Socket Weld Flanges are used for small-size and high-pressure piping that do not transfer highly corrosive fluids.
This due to the fact that these flange types are subject to corrosion in the gap area between the end of the pipe and the shoulder of the socket.
Their static strength of socket weld flanges is similar to slip-on flanges’, but their fatigue strength is higher due to the presence of a single, instead of double, fillet weld.