Flux Cored Arc Welding
FCAW (flux cored arc welding) is a variation of the GMAW process which uses flux-cored wire instead of solid bare wire. Among other things, the flux forms a slag which helps hold the molten metal in place so the process can be used for all positions.
FCAW processes are used primarily in the spray transfer mode, but globular transfer is not uncommon. The processes are noted for high deposition rates. Applications include nozzle welds and welds to vessel attachments such as stiffening rings, insulation support rings, internals, and supports.
FCAW processes can be either gas-shielded or self-shielded (with or without inert shielding gas). (See Figures 600-16 and 600-17.) The gas-shielded FCAW process (FCAW-G), like the GMAW process, is much better suited for shop fabrication than field fabrication since air movement must be less than 5 mph to maintain the inert gas blanket. The self-shielded FCAW process (FCAW-SS) is equally suited for either shop or field fabrication.
The FCAW-SS process should not be accepted for pressure vessel fabrication without special review by a materials or welding specialist, on a case-by-case basis. This precaution should be taken because of the need for careful consumable selection and the significant training and supervision required to obtain reliable welds with this process. Furthermore, the FCAW-G process is acceptable for pressure vessel fabrication only if special low-hydrogen flux-cored wire is used (See Section 662 below).
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