Welding Inspection & Metallurgy API ICP Self Study Notes

An important aspect of welding metallurgy is the gas metal reaction between
the molten weld metal and gases present during welding. Gas metal reactions
depend on the presence of oxygen, hydrogen, or nitrogen, individually or
combined in the shielding atmosphere. Oxygen can be drawn in from the
atmosphere or occur from the dissociation of water vapor, carbon dioxide, or
metal oxide. Air is the most common source of nitrogen, but it can also be
used a shielding gas for welding of austenitic or duplex stainless steels.
There are many sources of hydrogen. In SMAW or SAW, hydrogen may be
present as water in the electrode coating or loose flux. Hydrogen can also
come from lubricants, water on the workpiece, surface oxides, or humidity or
rain.