Socket Weld (SW) fittings are defined in the ASME B16.11. As with socket weld, a pipe is inserted into a recessed area of the fitting. Both the pipe and the fitting are square cut, with no need for beveled end or preparation other than cleaning the outside, which allows easy welding and installation.
Socket weld is easy to install. But it requires approx. 1/16″ of gap at the bottom of the pipe to socket into, to allow thermal expansion. This gap can lead to over stress problem that cracks the fillet weld of the fitting. Socket weld is troublesome in corrosive fluid service due to crevice corrosion. And it is easy to corrode due to the discontinuity of the smooth pipe internals.
Butt weld is the “best” in terms of strength, fatigue, and corrosion resistance, and temperatures compliance. However, it is more difficult to fit-up and weld properly, needing skilled welder and much time.
Normally, the price of Socket weld fittings is higher than Butt weld fittings in similar size. But the extra cost of butt weld is higher for installation, considering labor cost and skilled welder.
