In the case of socket welding (SW) fittings, the referred standard is ASME B16.11. Here, a pipe could be inserted into a recessed area of the fitting. Both the fitting and the pipe shall be square cut and do not require any preparation or beveled end other than cleaning the outside. This will ease the installation and welding processes.

As for butt welding (BW) fittings, the referred standard is ASME B16.9. with their ends being welded on to the pipe end, the thickness would be the same as those of pipes. In this case, the end of the fittings could be beveled.

Application differences between Socket Welding (SW) Fittings and Butt Welding (BW) fittings

The socket welding fitting usually resists around half the strength of butt weld fittings. Hence, socket welding (SW) fittings are mainly used for small pipelines with diameters NPS 2 or even smaller.

On the other hand, butt weld (BW) fittings help to keep better strength. And better for high temperature or high-pressure pipelines. It also could be used when a welded joint with strength not greater than that of the base metal would be needed.

Considering the above reasons, butt welding is better than socket welding on providing higher strength and higher pressure resistance.