Butt and Socket Weld Fitting Difference

Exactly what the names state.

Butt weld fittings are designed to butt up to a pipe & often have a bevelled weld face (depending on the size & schedule) & require a root opening for proper penetration. when you weld these you are making a butt joint & have to control the weld puddle for full penetration without blowing through.

Socket weld fittings are designed to have the pipe slide into the fitting, somewhat similar to a copper or plastic pipe fitting. These are welded on the outside perimeter of the pipe where it enters the fitting, & sometimes on the inside where it ends to seal the cavity around the pipe & inside the fitting. It requires less skil to make a fillet joint around the pipe, but is not as suitable for sanitary purposes unless the inside is sealed.

I was about to comment on the simplicity of this question. Then I went looking for a simple explanation on the web to post. (to demonstrate how simple it would have been to find the answer)

Guess what? I could not find a simple explanation of these two terms.

Although it may seem simple to English speakers, there isn't a clear, simple explanation of these terms, that I could find.

Nice job.

I Browse various sites and found this which looks simple to me

"

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."

Note that butt weld fittings are almost never actually butted up face to face (except tube regardless of whether or not they have a bevelled edge, a root opening is almost always required. They also generally require jigging as there is little or no mechanical contact of the two parts prior to welding.

Socket welds are NOT normally used to join different sized pipe (in my experience- anyone have experience otherwise please say so!) in the manner described from any code standpoints- I have done it myself for other applications. This would require a socket coupler for proper joining. You are correct regarding the expansion gap for higher temperature cycling, but I have seen some very nice (non-code) work for 304 SS flanges on DI water sytems where the operator simply tacked the pipe & then ran a TIG fillet on the inside edge of the pipe. Very easy & clean, more expensive fittings but the reduced labour & ability to do the welds without backgassing was considered worth it. That's a bit more than your OP asked for though!

If I am going to use EBW process (Electron beam welding), then root opening is required or not?

EBW & other orbital tube welding processes that do not use a filler metal generally do not require a root opening, but your equipment manufacturer is the one to give you a specific answer.

Web searching the two terms will turn up some vendor literature with pictures.