Welds are made simultaneously along both flange-web joints in the horizontal fillet position. Two 1000 AMP twin arcs, in tandem, are used to make each weld, and into both arc areas are fed two relatively small diameter wires, electrically in parallel. The two wires are close enough that they operate under a common molten pool of flux, yet far enough apart that the metal from the first arc has frozen before the metal from the second arc is deposited on top. This technique has several benefits:
The first bead can be designed to give deep penetration, while the second can be designed to build up throat thickness and desired surface profile
The resultant weld cross-section is such that relatively high amperages can be used without throat cracking, which is occasionally encountered with deep penetration welds.
It is possible to make the full range of weld sizes required without changing wire diameter by simply altering the relative positions of the parallel electrodes, and speed of travel
Full penetration welds can be accommodated up to a maximum web thickness of 5/8″