Is ASTM A1043 on the AWS D1.1 prequalified base metal list?

Yes. ASTM A1043 is listed in AWS D1.1 Table 3.1 (prequalified base metals), which means a prequalified WPS is possible without running a PQR test weld—provided all other prequalified WPS conditions in Clause 5 are met, including joint geometry, filler metal, and preheat.

What makes A1043 different from A572 Grade 50 for welding purposes?

Both are 50 ksi minimum yield strength steels, but A1043 carries a guaranteed maximum yield-to-tensile ratio of 0.85 (Fy/Fu ≤ 0.85) and a minimum Charpy V-Notch requirement. A572 Grade 50 has no such Y/T cap or mandatory CVN. These properties make A1043 predictable in seismic plastic-hinging zones.

Can I use the same WPS for A1043 and A992 in a mixed-grade frame?

A WPS qualified (or prequalified) for the higher-strength member in the joint and the lower of the two base metals can typically cover dissimilar base-metal joints, but you must verify the filler metal matches both base metals' mechanical requirements and that the joint design is correct for each connection type. Review AWS D1.1 Clause 5.5 for dissimilar base metal provisions.

Does A1043 require the low-hydrogen mandatory rule that applies to A514?

No. A1043 Grade 50 has a carbon equivalent well below the threshold that triggers mandatory low-hydrogen procedures for high-strength steels. However, sound practice on seismic demand-critical CJP groove welds is to use low-hydrogen filler metals and storage practices regardless, since AWS D1.8 and AISC 341 may independently require it.

ASTM A1043 Low-Yield-Ratio Steel WPS Under AWS D1.1

WPS documentation for ASTM A1043 Grade 36 and Grade 50 low-yield-ratio structural steel under AWS D1.1:2025, including prequalification status, filler metal selection, and seismic application requirements.

ASTM A1043 is a structural steel grade that most fabricators encounter for the first time on a seismic project with AISC 341 protected-zone requirements. The structural engineer has specified it for moment-frame beam flanges or link plates, and the shop needs a welding procedure that covers it. Understanding what A1043 is, why it exists, and what it requires of the WPS program keeps the job moving without unnecessary procedure qualification testing.

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

Why A1043 Exists

Ordinary high-strength structural grades—A572 Grade 50 being the most common—carry a minimum yield strength requirement but no upper bound. Mill production routinely ships A572 Grade 50 plate and shapes with actual yield strengths well above 60 ksi, sometimes approaching 70 ksi or higher. That is fine for static loading, but it creates a problem in seismic moment frames where controlled plastic behavior is the design intent.

In a seismic special moment frame (SMF), the system is designed to absorb earthquake energy through ductile plastic hinging in beam flanges away from the column face (the protected zone). If the steel yields at a much higher force than the nominal design assumed, the plastic hinge may not form where the engineer expected, and the column or connection weld may see forces it was not designed to handle.

ASTM A1043 addresses this by guaranteeing a low yield-to-tensile ratio. A1043 Grade 36 and Grade 50 carry a contractual maximum Fy/Fu ratio of 0.85—the actual yield will not exceed 85% of the actual tensile strength. This cap provides assurance that the steel will exhibit significant plastic elongation before fracture, supporting the ductile behavior that seismic design relies on.

AISC 341, the seismic provisions for structural steel buildings, recognizes A1043 as an approved material for members where the protected-zone and plastic-hinge behavior requirements apply.

Prequalified Status Under AWS D1.1:2025

A1043 appears on the prequalified base metal list in AWS D1.1 Table 3.1, which means a prequalified WPS is viable for this grade without conducting a formal PQR test weld—provided all other prequalified WPS conditions are satisfied. This is a significant practical advantage for shops that do not already have A1043 in their PQR library.

The conditions for a valid prequalified WPS include:

Joint design: The joint geometry must be one of the prequalified designs listed in AWS D1.1 Annex B (or a prequalified variation thereof). Complete-joint-penetration (CJP) groove welds in moment-frame connections are typically prequalified designs if the bevel angles, root openings, and backing provisions conform.
Filler metal: The filler metal must be from the prequalified filler metals list for the applicable process (SMAW, GMAW, FCAW, SAW, GTAW), and it must have a minimum classification strength that matches or exceeds the base metal.
Preheat: Minimum preheat and interpass temperatures must comply with Table 3.2 of AWS D1.1.
Process limits: Certain welding processes and parameter ranges apply; review AWS D1.1 Clause 5.1 through 5.15 for process-specific prequalified WPS constraints.

If any one of those conditions is not met—most commonly when a non-standard joint geometry or a non-prequalified filler metal is used—the prequalified route is closed and a PQR-backed WPS is required.

For a refresher on when a prequalified WPS is valid versus when a PQR is needed, see prequalified WPS under AWS D1.1 Clause 5.

Preheat and Interpass Temperature

A1043 Grade 50 has a carbon equivalent similar to A572 Grade 50 (generally in the 0.40–0.45 PCE range depending on chemistry), which places it in the same preheat tier as A572 Grade 50 under AWS D1.1 Table 3.2. For typical section thicknesses used in moment-frame connections (1 in to 2.5 in plate, or comparable flange thicknesses on W-shapes), minimum preheat is commonly in the 150°F (65°C) range for low-hydrogen processes — but confirm against the specific chemistry from the MTR and the thickness in question, using Table 3.2 in your governing edition.

There is no maximum interpass temperature constraint for A1043 in AWS D1.1 that is analogous to the 400°F cap on A514/A517 high-strength steels. A1043 is not a quenched-and-tempered grade; it does not depend on a heat treatment for its yield strength, so elevated interpass temperatures do not soften a hardened microstructure in the same way. The standard interpass upper limits in the WPS apply.

However, if the project also invokes AWS D1.8 (Seismic Supplement) for demand-critical welds in the SMF, D1.8 may impose additional heat-input management requirements on the WPS. Coordinate between AWS D1.1 and D1.8 at the WPS development stage, not after the PQR is qualified.

Filler Metal Selection

For most A1043 structural applications, matching filler metals are used. For Grade 36, an E70XX or ER70S-X filler provides strength match. For Grade 50, an E70XX filler also typically provides a strength match; the 70 ksi minimum tensile strength of the filler exceeds the 65 ksi minimum tensile of A1043 Grade 50. Confirm the specific matching requirements from AWS D1.1 Table 3.1 and the applicable filler metal table for the process.

On seismic demand-critical joints, AWS D1.8 imposes supplementary CVN requirements on the filler metal as well. The deposited weld metal must demonstrate minimum CVN toughness at the specified test temperature. Only filler metals with the appropriate CVN classification suffix (typically the "-J" or similar CVN designation depending on the AWS filler metal standard) qualify for demand-critical use under D1.8. Verify the filler metal classification against AWS D1.8 Table 4.1 or 4.2 (depending on edition) for the applicable process.

For a breakdown of CVN filler metal requirements on demand-critical welds, see CVN filler metal selection for demand-critical welds.

CVN Testing on the A1043 Base Metal

Unlike A572 Grade 50 — which does not include CVN testing by default — ASTM A1043 includes mandatory Charpy V-Notch testing as part of its base specification. A1043 requires minimum 40 ft-lbf (54 J) at 70°F (21°C) for all thicknesses and grades. This is built into the ASTM standard; you do not need to specify a supplementary requirement to get CVN data on an A1043 MTR.

This is one of the reasons A1043 is well-suited for seismic applications: the base metal toughness is guaranteed by the grade itself, not by a purchase order supplement that could be missed. When the CWI reviews the incoming MTR for A1043 material, the CVN column should always be populated with measured values. An MTR showing no CVN data for A1043 is a noncompliant material certificate that needs to be resolved before the material enters production.

A1043 vs. A992: Choosing Between Two Low-Y/T Options

Fabricators sometimes ask when to use A1043 plate versus A992 shapes (both are low-yield-ratio grades acceptable for seismic protected zones). The practical answer is determined by the product form:

A992 is a W-shape (wide flange) specification — it applies to hot-rolled I-sections used as columns and beams. It includes both a Y/T cap (Fy/Fu ≤ 0.85) and a maximum yield strength ceiling (65 ksi for Grade 50), plus mandatory CVN.
A1043 is a plate and bar specification — it applies when cut plates, flat bars, or plates are fabricated into built-up members, link plates, or connection components in the protected zone.

When a connection requires a cope cut, added doubler plate, or link plate component that must satisfy Y/T requirements, A1043 plate is the specified grade. The WPS for that plate-to-W-shape joint needs to cover both A1043 (the plate) and A992 or A572 (the shape), which means the prequalified base metal list entry for each grade must be confirmed for the joint in question.

WPS Submittal and Project-Specific Documentation

On seismic projects with AISC 341 requirements, the structural engineer or special inspector may request documentation confirming that the WPS covers A1043 and that it meets any supplementary D1.8 requirements. The WPS submittal package should include:

The WPS itself, showing A1043 as the base metal (or range of base metals covered).
The PQR, if a tested WPS is required — or a statement confirming prequalified status with the applicable table and clause citations.
Filler metal certification, including CVN test reports where the D1.8 demand-critical CVN requirement applies.
Base metal MTRs showing A1043 CVN results for the heat(s) assigned to the protected-zone members.

Getting this package organized before the first weld is made is far easier than reconstructing it during a special inspection hold point or owner audit. If your shop manages WPS packages, PQR records, and base metal MTR traceability in one place, the WPS management workflow at wpswelding.com/pricing is built for exactly this kind of multi-document seismic project package.

For more on the seismic WPS requirements that apply alongside A1043, see AWS D1.8 seismic supplement WPS requirements and AISC 341 seismic provisions WPS and PQR requirements.