The arc is maintained independently of the workpiece or parts being welded. The hydrogen gas is normally diatomic (H2), but where the temperatures are over 600 °C (1100 °F) near the arc, the hydrogen breaks down into its atomic form, simultaneously absorbing a large amount of heat from the arc. When the hydrogen strikes a relatively cold surface (i.e., the weld zone), it recombines into its diatomic form releasing the energy associated with the formation of that bond. The energy in AHW can be varied easily by changing the distance between the arc stream and the workpiece surface. This process is being replaced by gas metal-arc welding, mainly because of the availability of inexpensive inert gases.
In atomic hydrogen welding, filler metal may or may not be used. In this process, the arc is maintained entirely independent of the work or parts being welded. The work is a part of the electrical circuit only to the extent that a portion of the arc comes in contact with the work, at which time a voltage exists between the work and each electrode.