GTAW Root + FCAW Fill/Cap: Multi-Process WPS Under AWS D1.1:2025
How to qualify and document a multi-process WPS combining GTAW open-root with FCAW fill and cap passes for structural steel under AWS D1.1:2025. Covers essential variables, PQR scope, and production controls.
The combination of Gas Tungsten Arc Welding (GTAW, also called TIG) for the root pass and Flux Cored Arc Welding (FCAW) for fill and cap passes has become a reliable production strategy in structural steel fabrication. The driver is straightforward: GTAW produces a clean, fully fused root with tight heat control, while FCAW delivers high deposition rates on fill passes to keep cycle times competitive.
This multi-process approach is especially common on full-penetration groove welds in heavier wall HSS connections, moment frame beam-column joints requiring tight root quality, and critical bracing connections where internal root weld quality drives fitness for service. When AWS D1.1:2025 is the governing code, qualifying and documenting this combination correctly is a PQR-required exercise — there is no prequalified shortcut.
Clause 5 vs. Clause 6: Why GTAW+FCAW Always Requires a PQR
AWS D1.1:2025 Clause 5 lists the conditions under which a WPS can be used without a supporting Procedure Qualification Record (PQR). Prequalification is available for SMAW, SAW, GMAW, FCAW, and GTAW when those processes are used individually and when all joint, electrode, preheat, and base metal requirements within Clause 5 are met. Multi-process combinations — where two distinct welding processes are documented on a single WPS — are not eligible for prequalified status.
This means a combined GTAW/FCAW procedure requires qualification testing under Clause 6 before it can be used in production. The PQR documents the actual parameters used during the test weld, and the WPS is written from those parameters. Both sets of process-specific essential variables must be controlled and recorded on the PQR.
Rule library based on AWS D1.1:2025; verify against your governing edition.
Structuring the PQR Test Plate
For a combined GTAW + FCAW WPS, the PQR test coupon is welded exactly as you intend to weld in production: GTAW deposits the root pass (or root and hot pass), then FCAW deposits the fill and cap passes. The test plate must be welded at the parameters you intend to use, because the recorded values become the basis for the WPS ranges.
Practical notes when setting up the test:
Root pass parameters: Record shielding gas flow rate, back-purge gas flow rate and composition (if used), arc voltage, welding current, and travel speed. GTAW on structural steel commonly uses DCEN (direct current electrode negative), and the polarity is an essential variable.
Transition point: Clearly document at what pass the process transitions from GTAW to FCAW. Some shops run GTAW root and hot pass before switching; others use only a single GTAW root pass. Whatever is done during the PQR becomes the basis for the WPS.
FCAW parameters: Record wire diameter, electrode classification (e.g., E71T-1C or E71T-9C), shielding gas type and mixture, flow rate, voltage, wire feed speed (from which amperage is derived), and travel speed. If CVN testing is required, the FCAW electrode must meet the notch toughness requirements on its own, as the weld metal in the heat-affected critical zones will largely be FCAW deposit.
The test plate undergoes the standard Clause 6 mechanical test program: tensile (reduced section), guided bend tests (face, root, side depending on base metal thickness), and Charpy V-notch tests if required by supplementary essential variables.
Essential Variables: GTAW Portion (Table 6.6)
The GTAW rows in AWS D1.1:2025 Table 6.6 apply to the root pass portion of the WPS. Variables that trigger requalification if changed beyond the allowed range include:
Filler metal classification: The F-number and A-number of the GTAW filler wire (e.g., ER70S-2, ER70S-6 per AWS A5.18) are essential. Switching between these classifications requires requalification of the GTAW portion of the combined procedure.
Shielding gas: The composition and mixture percentage of the shielding gas (typically 100% Argon for GTAW on carbon steel, though some shops use Ar/He mixtures) is essential. Adding or removing a shielding gas constituent, or changing the mixture percentage beyond the allowed range, requires requalification.
Back-purge gas: When the joint design requires back purging (common for open-root GTAW on tubular or pipe-shaped HSS connections), the purge gas type and composition are essential variables.
Current type and polarity: DCEN is standard for GTAW on structural carbon steel. A change to DCEP or AC is an essential variable change requiring requalification.
Position: The test position bounds the production position per the qualified position ranges in AWS D1.1:2025.
Essential Variables: FCAW Portion (Table 6.6)
For the FCAW fill and cap passes, the FCAW-specific rows of Table 6.6 govern. Key essential variables include:
Electrode classification and F-number: E7xT-x type FCAW electrodes fall under a specific F-number. A change in F-number — for example, switching from an E71T-1 type to an E70T-4 self-shielded electrode — requires requalification. Note that AWS D1.1:2025 Table 6.6 Row 4 no longer includes A5.36 electrodes in the GMAW/FCAW prequalified group; FCAW electrodes designated per A5.36 require specific treatment as an essential variable.
Shielding gas: For FCAW-G (gas-shielded), the shielding gas composition is essential. For FCAW-S (self-shielded), there is no external shielding gas, and any addition of a shielding gas is a process change that requires requalification.
Current type and polarity: Most FCAW-G electrodes use DCEP. A change in polarity is essential.
Wire diameter: A change in wire diameter outside the allowed range under Table 6.6 is essential. Shops commonly qualify with a single diameter and note the range on the WPS.
Writing the Multi-Process WPS
The WPS for a GTAW+FCAW procedure explicitly lists both processes. AWS D1.1:2025 Clause 6 does not specify a required WPS format, but the information documented must fully define the welding condition for each process. Annex J Form J-1 is the reference WPS form in AWS D1.1:2025; it accommodates multi-process documentation by providing rows for each process.
Practical WPS documentation tips:
List the processes in order: Process 1 = GTAW (root/hot pass), Process 2 = FCAW (fill/cap).
For each process, document: electrode/filler classification, shielding gas type and flow, current and polarity, voltage range, amperage range, wire feed speed (FCAW), travel speed range, and position.
Preheat and interpass temperature apply across both processes — use a single preheat/interpass requirement that covers the entire weld joint regardless of process.
Heat input: if heat input limits apply (e.g., due to CVN supplementary essential variables under Table 6.8), document the maximum heat input separately for the GTAW root and FCAW fill passes. GTAW root passes are typically low heat input; FCAW fill passes drive the overall heat input for thick-section work.
Welder Qualification Considerations
A welder qualified to perform GTAW root passes and FCAW fill passes on structural steel under AWS D1.1:2025 Clause 6.4 must demonstrate proficiency in both processes. The welder performance qualification test (WPQ) for a combined procedure should reflect the actual production sequence: the welder deposits the GTAW root before transitioning to FCAW.
Some shops qualify welders on the two processes separately (one WPQ for GTAW, one for FCAW) and assign two welders per joint in production — a GTAW-qualified welder for the root and an FCAW-qualified welder for fill and cap. This is permissible under AWS D1.1:2025 as long as the WPS identifies both processes and the production sequence is controlled.
Production Controls and Inspection Checkpoints
The CWI inspection scope for a GTAW+FCAW procedure is more involved than single-process work:
Root pass VT: Inspect the GTAW root pass before transitioning to FCAW fill. Look for fusion at the root opening, root suck-back, or burn-through. This is the best opportunity to identify and repair a root deficiency before it is buried under fill passes.
Back-gouge and re-weld (if used): Some procedure qualification tests back-gouge the GTAW root from the backing side before applying FCAW fill. If back-gouging is part of the WPS, it is an essential variable to document and control.
Interpass temperature: Verify that the weld joint does not exceed the maximum interpass temperature listed on the WPS when transitioning between processes or between FCAW passes. GTAW root passes are relatively slow and may not preheat the joint as effectively as the FCAW fill passes — verify temperatures at the start of each FCAW pass.
Shielding gas flow: GTAW and FCAW-G both require shielding gas, but at different flow rates and with different nozzle designs. Verify gas flow for each process during the welding sequence.
Does combining GTAW and FCAW on one WPS require separate PQRs for each process?
No. A single PQR test plate that uses both processes — GTAW for the root and FCAW for the fill and cap — qualifies a combined WPS. Each process must be run under the conditions that bound the combined WPS, and each set of process-specific essential variables is evaluated independently within the same coupon.
Can a FCAW-S electrode be used for the fill passes on a WPS qualified with GTAW root?
Only if the PQR was made with FCAW-S (self-shielded) fill passes. FCAW-G (gas-shielded) and FCAW-S electrodes fall under different F-number groups and flux/shielding class essential variable requirements under AWS D1.1:2025 Table 6.6; you cannot substitute one for the other without requalification.
Is GTAW root + FCAW fill allowed on prequalified WPS under AWS D1.1:2025 Clause 5?
No. Prequalified WPS status under Clause 5 applies to single-process procedures using the prequalified processes (SMAW, SAW, GMAW, FCAW, GTAW) individually. A multi-process combination always requires a supporting PQR per Clause 6 — there is no prequalified multi-process option.
What essential variables apply to the GTAW root portion of the combined WPS?
The GTAW portion is governed by the GTAW rows in AWS D1.1:2025 Table 6.6. Key essential variables include filler metal F-number and A-number, shielding gas composition and flow rate, back-purge gas, electrical characteristics (DCEN vs. DCEP vs. AC), and current/voltage range. A change to any of these that exceeds the listed limits requires requalification of the GTAW portion of the combined procedure.