Does AWS D1.1 treat tandem SAW as a separate process from single-wire SAW?

No. AWS D1.1 classifies tandem (twin-wire) SAW as SAW. However, the number of electrodes, their spacing, and the polarity and current type of each electrode are essential variables under Table 6.6, so a PQR run with single-wire SAW does not cover tandem SAW production without requalification.

What are the critical essential variables when changing from single-wire to tandem SAW?

Under AWS D1.1:2025 Table 6.6, changes to number of electrodes, electrode spacing beyond the qualified range, and polarity or current type of either electrode each require requalification. Flux-wire combination classification changes are also essential. Rule library based on AWS D1.1:2025; verify against your governing edition.

Do I need CVN impact testing on a tandem SAW PQR?

CVN testing is required when the contract, specification, or engineer of record invokes the supplementary essential variables in AWS D1.1:2025 Table 6.8. The very high heat input typical of tandem SAW makes CVN testing especially important on applications where notch toughness matters, such as AISC 341 demand-critical welds or fracture-critical bridge members.

Can tandem SAW be used on prequalified WPS under AWS D1.1?

No. Prequalified WPS status is only available for single-wire SAW meeting all requirements of AWS D1.1 Clause 4. Tandem SAW requires qualification by testing with a PQR per Clause 6.

Oct 20, 20266 min read

Tandem SAW WPS Qualification Under AWS D1.1

Tandem submerged arc welding runs two wires simultaneously. Learn the AWS D1.1 essential variables, PQR test requirements, and CVN considerations unique to this high-deposition process.

WPS SAW AWS D1.1 PQR Submerged Arc Welding Fabrication

Heavy fabricators running plate girders, box columns, and bridge superstructures often turn to tandem submerged arc welding (SAW) to push deposition rates well above what single-wire SAW can achieve. Running two electrodes through the same weld pool — or in close leading-trailing sequence — can triple deposition rates and cut longitudinal seam welding time dramatically. But tandem SAW introduces its own WPS qualification requirements under AWS D1.1 that catch shops off guard, particularly those who assume their single-wire SAW PQR covers all SAW production.

This article walks through what AWS D1.1:2025 actually requires for tandem SAW WPS qualification, the essential variables that change when you add a second wire, and the heat-input and toughness considerations that matter on structural applications.

What Tandem SAW Is — and How AWS D1.1 Classifies It

Tandem SAW (also called twin-wire SAW or dual-wire SAW) places two electrodes in the same joint in close proximity, typically with the lead wire on DCEP and the trailing wire on AC to reduce arc blow and magnetic interaction. Both wires may share a single flux layer, or the setup may use discrete flux nozzles. High-current versions run leads at 1,000–1,200 A, producing deposition rates that can exceed 30 lb/hr.

AWS D1.1 does not define "tandem SAW" as a separate welding process — it is SAW. The process classification on the WPS and PQR should read "SAW." However, that does not mean a single-wire SAW qualification covers tandem production. The essential variables table specifically calls out characteristics that differ between single-wire and tandem setups.

Key Essential Variables Under AWS D1.1:2025 Table 6.6

Rule library based on AWS D1.1:2025; verify against your governing edition.

For SAW, Table 6.6 identifies the following items that are directly affected when moving to or between tandem configurations:

Number of electrodes (Table 6.6, SAW row). Adding a second electrode is a change in the number of wires, which requires a new PQR. A PQR run with one wire does not qualify two-wire production.

Electrode spacing. For tandem setups, the center-to-center spacing between the lead and trail electrodes — and their relationship to the weld joint — affects arc interaction, bead profile, and heat distribution. The qualified spacing range must be documented on the WPS and matched in production within the tested range.

Polarity and current type of each electrode. Lead wire typically runs DCEP; trailing wire commonly runs AC. These are separate essential variables. Changing the polarity of either wire requires requalification.

Flux-wire combination classification. The flux classification and wire classification together constitute the filler metal essential variable. If either changes beyond the qualified range, a new PQR is required. See also our discussion of SAW flux classification as an essential variable for single-wire SAW.

Wire diameter. Diameter of each electrode is an essential variable. Qualifying with 5/32 in. lead and 3/16 in. trail does not cover reversing those diameters or using 1/4 in. lead.

Supplemental filler metal. If cold-wire or metal powder addition is used to boost deposition further, it becomes part of the essential variable record per Table 6.6, row 7 (A5.36 requirements and ±10% electrode-to-supplemental-filler ratio threshold — a 2025 edition change).

PQR Test Plate Requirements for Tandem SAW

Because prequalified WPS status is not available for tandem SAW, every tandem SAW WPS must be supported by a PQR developed under AWS D1.1 Clause 6.

The test plate should be representative of the thickest production base metal. For a CJP groove weld qualification, a 1 in. (25 mm) test plate qualifies unlimited maximum thickness in the same groove configuration when all essential variables are within range. For production joints thicker than tested, the deposited weld metal thickness on the PQR governs the qualified filler metal thickness range per Clause 6 provisions.

Specifying the test weld parameters. The PQR must record:

Lead wire: classification, diameter, amperage, voltage, polarity
Trail wire: classification, diameter, amperage, voltage, polarity
Travel speed
Electrode spacing (center-to-center and lead/trail orientation)
Flux classification and lot (AWS A5.17/A5.23)
Preheat and interpass temperature — particularly important for tandem SAW

Because tandem SAW heat input is substantially higher than single-wire SAW at equivalent travel speed, the PQR should also record the arc energy per Clause 6. This value will gate CVN testing decisions.

Heat Input and CVN Toughness Considerations

Tandem SAW concentrates significant thermal energy in a narrow pass. High heat input coarsens the heat-affected zone (HAZ) grain structure and can degrade Charpy V-notch toughness in the HAZ — the same effect that makes heat input control a central concern in SAW on CVN-qualified structural applications.

When the contract or specification invokes AWS D1.1:2025 Table 6.8 supplementary essential variables for CVN testing, any increase in heat input beyond the qualified range is an essential variable change. Tandem SAW PQRs that will be used on CVN-sensitive applications (AISC 341 seismic demand-critical welds, fracture-critical bridge members, or contract-specified impact-tested joints) must include CVN specimens in the PQR testing program.

CVN specimens from a tandem SAW PQR test plate should sample both the weld metal centerline and the HAZ at 1 mm, 3 mm, and 5 mm from the fusion line, at the temperatures specified by the contract. If HAZ toughness is marginal with the tested heat input, reducing interpass temperature or increasing travel speed (both of which reduce heat input per linear inch) may improve results — but either change constitutes a new essential variable and requires a revised PQR.

See the detailed treatment of CVN testing under Table 6.8 for specimen location requirements and cooling requirements before testing.

Documenting the WPS for Tandem SAW Production

The WPS derived from the tandem SAW PQR must include all variables tested and their qualified ranges. Because two electrodes are involved, some WPS forms designed for single-wire SAW do not have dedicated fields for lead and trail wire parameters. The simplest solution is to add a table or supplemental page that captures:

Parameter	Lead Wire	Trail Wire
Classification
Diameter (in.)
Current type / polarity
Amperage range (A)
Voltage range (V)

Travel speed, flux classification, electrode spacing range, preheat minimum, and interpass maximum should appear in the standard WPS body.

Fabricators using digital WPS management can add custom fields to capture tandem-specific parameters without modifying a preprinted AWS Annex M form — a practical advantage when the same WPS template is used for both single-wire and tandem SAW.

Production Controls for Tandem SAW

Beyond WPS documentation, tandem SAW production requires operator vigilance on three fronts:

Arc interaction monitoring. The lead and trail arcs must not interact destructively. Proper spacing and polarity selection (DCEP lead, AC trail) stabilize the process, but changes in contact-tip-to-work distance, wire alignment, or current imbalance can degrade bead quality. Weld monitors or data loggers that capture per-wire amperage and voltage are valuable quality records.

Interpass temperature. With high heat input, interpass temperature can spike rapidly in multi-pass thick-plate work. Verify with a calibrated contact pyrometer before each pass. The WPS interpass maximum must not be exceeded; if production conditions push toward the limit, pausing between passes or reducing lead wire current resolves the issue without requalification.

Flux coverage and recovery. At high travel speeds, maintaining consistent flux depth ahead of the weld can be challenging. Inadequate flux coverage causes arc exposure, porosity, and slag entrapment. Periodic flux depth checks and recovery system maintenance are part of a complete tandem SAW quality plan.

Bottom Line for Fab Shop QC Managers

Tandem SAW offers compelling productivity gains on thick structural plate, but it requires its own PQR — your single-wire SAW record does not cover it. Document all per-wire parameters, perform heat input calculations and CVN testing when applicable, and ensure the WPS captures the qualified electrode spacing range. A well-supported tandem SAW WPS positions your shop for AISC certification audits and owner-supplied QC plan reviews without scrambling to requalify mid-project.

FAQ

Frequently asked.

Does AWS D1.1 treat tandem SAW as a separate process from single-wire SAW?: No. AWS D1.1 classifies tandem (twin-wire) SAW as SAW. However, the number of electrodes, their spacing, and the polarity and current type of each electrode are essential variables under Table 6.6, so a PQR run with single-wire SAW does not cover tandem SAW production without requalification.
What are the critical essential variables when changing from single-wire to tandem SAW?: Under AWS D1.1:2025 Table 6.6, changes to number of electrodes, electrode spacing beyond the qualified range, and polarity or current type of either electrode each require requalification. Flux-wire combination classification changes are also essential. Rule library based on AWS D1.1:2025; verify against your governing edition.
Do I need CVN impact testing on a tandem SAW PQR?: CVN testing is required when the contract, specification, or engineer of record invokes the supplementary essential variables in AWS D1.1:2025 Table 6.8. The very high heat input typical of tandem SAW makes CVN testing especially important on applications where notch toughness matters, such as AISC 341 demand-critical welds or fracture-critical bridge members.
Can tandem SAW be used on prequalified WPS under AWS D1.1?: No. Prequalified WPS status is only available for single-wire SAW meeting all requirements of AWS D1.1 Clause 4. Tandem SAW requires qualification by testing with a PQR per Clause 6.