Why A36 and A992 structural steel fall in different preheat groups under AWS D1.1:2025 Table 5.11—and what that means for your WPS and CWI inspection plan.
Walk the shop floor of almost any structural steel fabricator and you will see A36 plate being cut next to A992 wide-flange sections. The two materials look identical, they are both prequalified under AWS D1.1:2025, and many shops use the same filler metal for both. Where they diverge—and where WPS errors occur—is preheat. A36 and A992 fall into different base-metal groups under Table 5.11, meaning the minimum preheat temperature before the arc strikes can be meaningfully different depending on joint thickness and welding process.
Understanding why the code treats them differently, and writing WPS documents that reflect that difference, is a core CWI and QC-manager competency.
Why Base-Metal Grouping Matters for Preheat
AWS D1.1:2025 Table 5.11 assigns minimum preheat and interpass temperatures based on three variables: the base-metal group, the thickness of the thicker part at the joint, and whether the welding process uses low-hydrogen consumables. The groups in Table 5.11 are defined primarily by minimum specified yield strength, which is a reasonable proxy for hardenability and cold-cracking susceptibility at the structural carbon ranges involved.
A36 carries a minimum yield of 36 ksi, placing it in the lower-yield group of common structural materials. A992 specifies a minimum yield of 50 ksi and a maximum of 65 ksi—the same as A572 Grade 50—which puts it in the next higher group. That one-group shift is enough to increase minimum preheat requirements for thicker joints or when non-low-hydrogen processes are specified on the WPS.
The practical result: a WPS written for A992 column-to-base-plate connections must specify higher preheat temperatures than an otherwise identical WPS written for A36 at the same thickness. If a shop uses a single preheat value that satisfies A36 but falls below the A992 requirement and both materials show up in the same project, an A992 joint is out of compliance the moment the welder sets up without reaching the higher temperature.
A36: Properties and Preheat Implications
ASTM A36 is one of the broadest structural steel designations in service. It applies to plates, bars, and shapes (though wide-flange sections in heavier sizes are rarely produced to A36 today—most mills roll them to A992 or A572). Key mechanical properties include:
Minimum yield strength: 36 ksi (250 MPa)
Tensile strength: 58–80 ksi (400–550 MPa)
Maximum carbon content: 0.26% for plate over 3/4 in; 0.25% for shapes
The relatively modest carbon ceiling and low yield strength keep A36 in a lower preheat group under Table 5.11. For thin plate (under 3/4 in) welded with low-hydrogen electrodes or wires, A36 can often be welded at ambient temperature, provided the ambient is above the minimum threshold and moisture is not a concern. For thicker joints or when non-low-hydrogen processes like SMAW E6010 are used as root-pass electrodes, preheat requirements increase but remain lower than those for A992 at the same dimensions.
This is worth noting on the WPS: if you are qualifying or writing a prequalified WPS for A36 and you plan to use a non-low-hydrogen root pass (a common practice for SMAW root/FCAW fill sequence), Table 5.11 specifies a significantly higher preheat than the low-hydrogen option. Many WPS documents set preheat based on the low-hydrogen column in Table 5.11 without flagging that the stated minimum does not apply if a non-low-hydrogen electrode is used for any pass. The CWI should verify that the process specified on the WPS matches the preheat shown.
A992: Properties and Preheat Implications
ASTM A992 was developed specifically for wide-flange shapes used in moment-frame and other seismic-designed construction, though it is now standard for all W-shapes regardless of seismic demand. Its property requirements are more tightly controlled than A36:
Minimum yield strength: 50 ksi (345 MPa)
Maximum yield strength: 65 ksi (450 MPa)—a cap that limits over-strength in seismic connections
Controlled manganese, silicon, and vanadium to limit hardenability
The 50 ksi yield threshold puts A992 in a higher group under Table 5.11 compared to A36. Even though A992's carbon ceiling is tighter than A36's (0.23% vs. 0.26%), the higher yield strength—which tracks with the material's alloying—drives a more conservative preheat requirement in the code's tabular approach.
For a typical W14 or W18 column-to-beam connection, the flange thickness of a heavy section can exceed 1 in. At that thickness, the difference between the A36 preheat and the A992 preheat in Table 5.11 can be substantial, particularly when a CWI reads the wrong row of the table. Verify which row applies before you sign off on the WPS preheat specification.
Rule library based on AWS D1.1:2025; verify against your governing edition.
Writing the WPS: What Must Be Specified
A conforming WPS for either material must state:
Minimum preheat temperature. Read from Table 5.11 for the actual base-metal group and the maximum thickness present in the joint (not an average). When the joint includes two different thicknesses (e.g., a 3/4-in plate welded to a 1-1/2-in flange), the thicker piece governs the preheat group determination.
Maximum interpass temperature. AWS D1.1:2025 Table 5.11 also establishes a maximum interpass temperature for some groups and thicknesses. This often goes unstated on WPS documents written to minimum requirements. Omitting the maximum can expose high-strength or toughness-critical welds to reduced impact values when interpass temperature runs hot.
Process and consumable classification. The preheat rows in Table 5.11 split between low-hydrogen processes/consumables and others. E7018 (H4 or H8 designator), ER70S-6, and E71T-1 are typically low-hydrogen. If your WPS lists SMAW E6010 for the root pass and E7018 for fill, the E6010 root is not low-hydrogen. Use the more conservative preheat column for the whole joint unless the WPS explicitly addresses the transition.
Base-metal group identification. The WPS should identify which ASTM designation(s) it covers, referenced to Table 5.11. If the WPS is intended to cover both A36 and A992 connections under a single document, the preheat must satisfy the A992 (higher group) requirement across the entire applicable thickness range.
Common Shop Errors CWIs Should Look For
Using A36 preheat values on A992 columns. This is the most common error when a shop transitions from A36 plate work to W-shape fabrication using an older WPS. The preheat specified on the WPS is correct for the steel it was written for, but it under-estimates what A992 requires.
Failure to segregate WPS documents by base-metal group. Some shops maintain a single "structural fillet weld" WPS used across every steel in the shop. If the preheat on that document was set for A36, it may not cover A992 at the thicknesses in use. The CWI should confirm that the applicable WPS preheat matches the base-metal group and thickness of the actual work, not just the process.
Ignoring the non-low-hydrogen column. When an E6010 root pass is used for access hole or fit-up reasons and the shop assumes the low-hydrogen column applies because E7018 is used for the fill passes, the preheat during the root pass is under-controlled. If the root pass cracks, no amount of subsequent E7018 fill will help.
Misidentifying material as A36 when it is A992. Wide-flange shapes purchased today are almost always A992. If the CMTR shows A992 and the WPS says A36, there is a base-metal mismatch that the inspector should flag before welding starts. See verifying base-metal CMTRs for structural welding for how to handle CMTR review systematically.
Combining A36 and A992 Under One WPS
It is entirely possible—and common—to write a single tested WPS that covers both A36 and A992. Under AWS D1.1:2025 Table 6.9, base metals are assigned to groups, and a PQR test on one material within a group qualifies the WPS for all materials in that group and in lower groups, subject to the essential variable rules in Table 6.6.
The key is to qualify the WPS at the A992 group preheat and thickness range, then confirm the base-metal group coverage extends down to include A36. The resulting WPS will specify the A992-level preheat throughout, which is conservative for A36 but always acceptable. Many shops find this approach simpler than maintaining separate WPS documents for each steel designation.
Knowing the correct preheat value on paper is not enough. The CWI's job is to confirm that the steel surface has actually reached that temperature before the first pass is deposited. Contact pyrometers, infrared thermometers, and tempilstik crayons all work, but each has application limits on rough mill scale, painted surfaces, or areas recently heated by adjacent work.
For a detailed breakdown of preheat measurement methods and their calibration requirements, see preheat verification methods for structural welding CWIs. Measurement should occur at least 3 in (75 mm) from the weld in the direction of heat travel, on the surface that will be in the arc zone, before any arc is struck.
Putting It on the WPS
Structural fab shops that work with both A36 and A992 benefit from clean, unambiguous WPS documents that identify the applicable ASTM designation(s), the Table 5.11 base-metal group, and a preheat minimum that is correct for the highest group covered. Ambiguous documents that simply say "50°F minimum" with no reference to the standard or the basis for that number create audit exposure and leave the welder without enough information to decide whether to reach for a propane torch before starting.
If your current WPS library has preheat values that were transcribed from a previous revision or copied from a competitor's document without reference to Table 5.11, now is the time to audit them. The WPS requalification triggers checklist can help you identify which documents may need revision before your next AISC audit.
Do A36 and A992 require the same preheat under AWS D1.1?
No. A992 carries a higher minimum yield strength (50 ksi) than A36 (36 ksi), which places the two materials in different base-metal groups under Table 5.11. A992 joints commonly require a higher minimum preheat, particularly at greater thicknesses and when using non-low-hydrogen processes.
Is A992 a prequalified base metal under AWS D1.1:2025?
Yes. ASTM A992 is listed in Table 5.6 as a prequalified base metal, allowing its use in a prequalified WPS without a PQR test—provided all other Clause 5 conditions are met.
Why does A992 sometimes need more preheat than A36 at the same thickness?
Because A992's minimum yield strength places it in a higher-preheat group in Table 5.11. Carbon equivalent also plays a role; A992 controls carbon (≤ 0.23%) and other elements tightly, but its 50 ksi strength level still triggers more conservative preheat requirements in the code.
Does a single WPS cover both A36 and A992 connections in a typical structural project?
Often yes, if qualified at the more restrictive group. A tested WPS qualified on A992 (Group II, using Table 6.9 coverage rules) can cover both materials. Confirm the base-metal group coverage with your welding engineer before combining them under one WPS.