What is the difference between a Butt weld and a socket weld?

Answer 1

A butt weld is where the diameter of the pipes welded together are the same, a socket weld is where a larger diameter pipe is fitted into a smaller one. In making a butt weld, the pipes (or pipe and fitting) usually have an angle machined or ground into the outside corner, so when they are placed together face-face, there is a circumferential V shaped gap serving as the weld prep. In a socket weld, the pipe is inserted into the socket, backed off slightly to make a gap between the end of the pipe and the bottom of the socket, and the weld is made around the outside diameter of the socket to the outside diameter of the pipe. The gap at the bottom of the pipe prevents thermal expansion from stressing the joint during or after welding.