FCAW-S vs FCAW-G: WPS Qualification Differences Under AWS D1.1

Flux-cored arc welding splits into two distinct processes: self-shielded (FCAW-S) and gas-shielded (FCAW-G). Most fabricators run both at some point — FCAW-G in the shop for productivity, FCAW-S in the field when shielding gas logistics become impractical. What catches QC managers off guard is that AWS D1.1 treats these as separate processes for qualification purposes. A WPS qualified on one cannot cross over to the other without requalification.

This article breaks down the technical distinctions, how each process maps to AWS D1.1:2025 essential variables, and what you need in your WPS documentation to cover both.

How the Shielding Mechanisms Differ

In FCAW-G, an external gas supply — typically 100% CO2, 75/25 Ar/CO2, or a tri-mix — flows through the nozzle to displace atmospheric oxygen and nitrogen from the arc zone. The flux core contributes slag coverage and deoxidizers, but the gas does the bulk of atmospheric protection.

FCAW-S electrodes are engineered to be self-contained. The flux core includes fluoride and carbonate compounds that decompose under arc heat, generating their own shielding atmosphere. No external gas cylinder is required. The trade-off is that self-shielded wires tend to produce more spatter, require tighter welder technique, and are generally restricted to lower-hydrogen designator classifications for structural applications.

Both processes produce sound welds when properly applied, but the weld metal composition, mechanical properties, and usable parameter windows differ enough that the two cannot be interchanged on a single WPS.

AWS D1.1:2025 Table 6.6 — Where the Line Gets Drawn

AWS D1.1:2025 Table 6.6 lists essential variables for SMAW, SAW, GMAW, FCAW, and GTAW. For flux-cored welding, several rows directly govern the FCAW-S/FCAW-G distinction:

• Shielding gas type and composition — Any change in the shielding gas mixture is an essential variable. The more fundamental change — adding gas to a self-shielded process or removing gas from a gas-shielded process — is an essential variable requiring full requalification of the WPS.
• Shielding gas flow rate range — A change outside the WPS-specified range is an essential variable. Self-shielded processes list no shielding gas entry; gas-shielded WPSs must document the flow rate and hold within that range.
• Electrode specification and classification — A change from one AWS classification to another is an essential variable. FCAW-S and FCAW-G wires carry different classification suffixes and cannot be interchanged.

Rule library based on AWS D1.1:2025; verify against your governing edition (the AHJ or contract may specify 2020 or earlier).

The consequence: if you qualify a WPS using E71T-1C-H4 (a CO2-shielded, low-hydrogen wire), that WPS is invalid for production welds run with E71T-8-S (a self-shielded wire). Two separate PQRs and two separate WPSs are required if the shop needs to use both.

Electrode Classification: A5.20 and A5.29

AWS A5.20 covers carbon steel FCAW electrodes; AWS A5.29 covers low-alloy steel FCAW electrodes. In both standards, the electrode designation encodes the shielding type:

For structural steel applications under AWS D1.1, the filler metal must be from a pre-approved list or qualified by test. Table 4.5 in D1.1:2025 (prequalified filler metals) specifies which classifications are acceptable for each base metal group without a PQR. Self-shielded wires for structural applications are typically limited to E71T-8-S and similar classifications that carry the -H16 or -H8 hydrogen designator.

This directly affects how you draft the filler metal section of your WPS. Don't write "FCAW per AWS A5.20" — specify the full classification (e.g., E71T-1C-H4 or E71T-8-S) and the shielding gas (or "self-shielded — no external gas") so that the essential variable row is unambiguous.

WPS Documentation Requirements for Each Process

A properly written FCAW-G WPS must document:

• Shielding gas composition (e.g., 75% Ar / 25% CO2) and flow rate range (typically 30–50 CFH)
• Wire classification with gas designator suffix
• Nozzle-to-work distance
• Contact-tip-to-work distance (CTWD) range

A properly written FCAW-S WPS documents:

• Electrode classification with -S suffix
• "No shielding gas" explicitly stated
• Stickout range (CTWD), which is typically wider than FCAW-G
• Any electrode extension limits specified by the manufacturer

Leaving the gas field blank on a FCAW-G WPS is a documentation deficiency that can cause an audit finding. Leaving it blank on a FCAW-S WPS, with no explicit note that the process is self-shielded, can create ambiguity during CWI inspection.

For a deeper look at how shielding-gas changes interact with other essential variable triggers, see WPS requalification triggers checklist for AWS D1.1.

Field vs. Shop Deployment

The more practical reason most shops run both processes is that FCAW-G is simply more productive and cleaner in controlled environments, while FCAW-S is more resilient outdoors.

AWS D1.1:2025 Clause 5.12 restricts welding in drafty or windy conditions when shielded processes are in use. A windscreen can resolve the issue for FCAW-G, but when work is at elevation or spread across an open site, FCAW-S becomes the pragmatic choice. The WPS must match the process being run in the field — if the erection crew is running self-shielded wire, the filed WPS needs to cover that, and if a different crew ran gas-shielded in the shop for fit-up welds, they need a separate WPS.

This also affects welder qualification. A welder qualified under a gas-shielded FCAW WPS is not automatically qualified for self-shielded FCAW. The process classification is different, so a separate performance qualification test is required.

For more on wind and draft restrictions and how to document field welding conditions in your WPS, see wind and draft welding conditions under AWS D1.1.

The Impact Testing Consideration

FCAW-S electrodes generally produce higher diffusible hydrogen and are more susceptible to weld metal toughness variability than their gas-shielded counterparts. If the contract or specification requires Charpy V-Notch (CVN) testing — common in seismic, bridge, or fracture-critical applications — the process choice matters significantly.

AWS D1.1:2025 Table 6.8 (CVN supplementary essential variables) adds additional requalification triggers when impact properties are required, including a change in heat input range and a change in filler metal classification. For applications with CVN requirements, the WPS must document the tested energy absorption values from the PQR and production welding must stay within the qualified heat input range.

Self-shielded wires in CVN-required joints require careful attention to heat input. The wider parameter tolerance that makes FCAW-S convenient in the field becomes a liability when you need to hold toughness values at −20°F or lower.

Keeping Your WPS Library Organized

Shops that run both FCAW processes should maintain separate WPS sets, clearly labeled, with no ambiguity about which process applies to which work order. A common failure in AISC fabrication audits is a single "FCAW" WPS that doesn't specify whether the process is self-shielded or gas-shielded — auditors flag this as a documentation deficiency because it cannot be verified that the actual production process matches the WPS.

A clean organizational approach: use a prefix in your WPS numbering scheme to distinguish processes (e.g., G-001 for GMAW, FC-001 for FCAW-G, FS-001 for FCAW-S). This makes it immediately clear which WPS governs which work, and it simplifies the welder qualification matrix.

For guidance on structuring a WPS library that holds up under audit, see WPS library management for multi-project shops under AWS D1.1 and wire feed speed vs. amperage in GMAW/FCAW WPS documentation.

If your shop needs to qualify both FCAW-G and FCAW-S and you want a system that tracks which WPSs cover which processes, positions, and base metals, see how the WPS generator handles multi-process qualification.