Electroslag Welding:

Electroslag Welding (ESW) deposits the weld metal into the weld cavity among the two plates to be connected. This space is together with this by water cooled copper dams or shoes to prevent melt slag from running off. The weld metal is created from a filler wire so as to forms an first arc with the work piece until a enough pool of liquid metal is created to use the electrical resistance of the melt slag.

This procedure needs particular equipment used mainly for horizontal
welds of very big plates up to 36 inches or additional by welding them in one pass as in big equipment and nuclear reactor vessels.

There are in addition differences of ESW where shielding is provided by a suitable gas and a nonstop arc is used to give weld metal. These are termed Electro gas Welding or EGW machines.