The contruction of the Boiler usually consists of:
Boiler tubes, GTAW root, SMAW fill and cover pass. Howver, Diametrics are being used more and more as boilers are being designed with this process in mind.
Water Wall Membrane, SMAW, GMAW
Piping GTAW root, SMAW fill and cover passes. Common SMAW rods being 5P, ER7018, ER308, ER309, ER316, and ER80S for GTAW.
Condenser, GMAW, SMAW, SAW, and GTAW.
There are many others, but like in China, GTAW and SMAW are the most common.
Hope this helps.
Mike