FCAW (Flux Cored Arc Welding) is two distinct procedures sharing a process name. FCAW-G uses external gas shielding. FCAW-S is self-shielded. They use different wires, qualify under different essential variables, and have different audit gotchas.
FCAW-G (gas-shielded)
Wire: A5.20 E71T-1C (CO2 shielded) or E71T-1M (Ar/CO2 mix shielded) — the suffix matters.
Shielding: 100% CO2 for T-1C; 75/25 Ar/CO2 for T-1M.
Where used: indoor shop production, especially structural beam-to-column work.
Strengths: smooth bead profile, low spatter, faster deposition than SMAW, all-position with appropriate wire.
Limitations: wind sensitivity — anything over ~5 mph blows shielding away and causes porosity.
FCAW-S (self-shielded)
Wire: A5.20 E71T-8 (multi-pass) or E70T-4 (single-pass).
Shielding: none external — flux generates its own atmosphere.
Where used: field erection, outdoor work, structural steel in the wind.
Strengths: wind-tolerant, no gas cylinders required, fast all-position with T-8.
Limitations: higher fume, more spatter than FCAW-G, generally slightly lower toughness on thick sections.
What this means for the WPS
Two separate WPSs in most shops:
- One FCAW-G WPS for indoor production
- One FCAW-S WPS for field erection
The WPS must declare both the wire classification and the shielding strategy. A WPS that says "FCAW" without disambiguating is ambiguous.
Wire classification mismatches — the #1 audit finding
The single most common FCAW audit finding: a T-1C wire (designed for CO2) used with an Ar/CO2 mix, or vice versa. Wire and gas must match. The classification suffix is the giveaway:
- E71T-1C → 100% CO2 only
- E71T-1M → Ar/CO2 mix only
- E71T-8 → no gas (self-shielded)
- E70T-4 → no gas (self-shielded, single-pass)
If the WPS lists E71T-1C and 75/25 Ar/CO2 in the gas block, the WPS contradicts itself. Auditor flag.
Position rules
- FCAW-G with E71T-1 (C or M): all positions, vertical progression UP. Down-progression NOT prequalified.
- FCAW-S with E71T-8: all positions, vertical UP or DOWN depending on classification suffix.
- FCAW-S with E70T-4: flat and horizontal only — single-pass.
Position progression is essential under Table 6.6. Switching vertical-up to vertical-down in production requires a separate qualification.
Hydrogen designator
FCAW classifications include H designators just like SMAW:
- E71T-1C-H4 = gas shielded, low hydrogen (under 4 mL/100 g deposited)
- E71T-8-H4 = self-shielded, low hydrogen
For AISC seismic demand-critical work, H4 is standard. For ordinary structural, H8 is sufficient.
Storage and moisture
FCAW wires are more humidity-tolerant than SMAW low-hydrogen electrodes, but not bulletproof:
- Sealed plastic spools
- After opening, store in a low-humidity environment (or with desiccant)
- Replace wire that shows surface rust or flux discoloration
- For demand-critical work, document opening date and limit ambient exposure
CVN supplementary (Table 6.8)
For AISC 341 demand-critical welds, FCAW-G is the standard. The supporting PQR must include CVN data and the WPS must invoke Table 6.8 supplementary. FCAW-S is acceptable for some demand-critical applications but the qualifying T-8 classification must be the CVN-certified variant (consult the wire manufacturer's certification).
Common pitfalls on FCAW WPSs
- Wire / gas mismatch (T-1C with Ar/CO2 or T-1M with CO2)
- Vertical-down position claimed prequalified with E71T-1
- Hydrogen designator omitted on AISC seismic work
- CVN scope claimed without supporting PQR essential-variable data
- Single WPS for FCAW-G and FCAW-S — they are different essentials
A rule engine that cross-references wire classification suffix, shielding gas, and position progression catches all five at draft time.