Gas Nozzles- GTAW
Water cooled metal nozzles are generally preferred over ceramic nozzles, particularly when higher welding currents are used. The ceramic nozzles are not as durable at higher temperatures and are more easily broken. However, the smaller ceramic nozzles may be preferred for welding certain joints, such as 45° intersectional welds where the clearances are small. Small diameter, extra long ceramic nozzles, or coated metal nozzles, are often used to avoid short circuiting of the nozzle when welding such joints. Nozzle sizes are shown in tables 3-11 of D10.7.
Tungsten Electrodes.
As discussed previously, pure tungsten or zirconiated tungsten electrodes are used for a-c gas tungsten arc welding. One or two percent thoriated tungsten or 1.5 or 2 percent lanthanated tungsten arc welding. Electrode sizes are listed in tables 3-11 of D10.7.
Filler Metals
Filler metal selection can be made from table 2 of D10.7 for the various pipe alloys and combination of alloys.
Inert Gas
Arcon (AWS classification SG-A, AWS A5.32/A5.32M, Specification for Welding Shielding Gases) is the preferred gas for most gas shielded arc welding. A mixture of helium an argon (SG-heA-X) is sometimes employed for gas metal arc welding with 5XXX filler alloys and for greater penetration in a-c GTAW. Helium is necessary for DCEN welding with the GTAW process. Welding grade gases are required.
Jorge T. Reyna´s Blog (NDT, Welding, Concrete & Coatings)