A516 Gr.55/60 Preheat for GMAW — 3/4" to 1-1/2"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A516 Gr.55/60 welded with GMAW at 3/4" to 1-1/2" is 50°F (10°C), Category B. Preheat below this raises hydrogen-cracking risk in the heat-affected zone; the same temperature is the minimum interpass limit maintained through the weld.
Built on AWS D1.1:2025 Table 5.11 — every value traced to the clause.
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GMAW (Gas Metal Arc Welding)
GMAW (MIG) feeds continuous solid wire with shielding gas — an inherently low-hydrogen process assigned to Category B in Table 5.11.
For pressure vessel work, GMAW with ER70S-6 provides excellent deposition rates on long seam welds. Gas backing with argon on back-purged root passes produces a smooth internal weld profile that satisfies radiographic acceptance criteria. Shielding gas purity is critical for vessel code quality; dew point must be below -40°F.
Why GMAW for A516 Gr.55/60 at 3/4" to 1-1/2"
Why GMAW for A516 Gr.55/60 at 3/4" to 1-1/2"? GMAW delivers 8-12 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a516-5560/saw/3-4-to-1-1-2-inch/">SAW</a> at 15-40 lb/hr. Position capability: all positions (not GMAW-S). Suitability: primarily shop.
Filler Metal for GMAW
Common wire: ER70S-6 (AWS A5.18). Diameter: 0.035" for thin sections and out-of-position, 0.045" for production flat/horizontal. Shielding gas: 75/25 Ar/CO2 (standard), 90/10 Ar/CO2 (less spatter, better profile), or 100% CO2 (deeper penetration, more spatter). Contact-tip-to-work distance: 1/2" to 3/4".
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
A516 Gr.55/60
ASTM A516 Grades 55 and 60 are carbon steel plates designed for moderate and lower temperature pressure vessel service. Grade 55 (55 ksi tensile, 30 ksi yield) and Grade 60 (60 ksi tensile, 32 ksi yield) are widely used in storage tanks, heat exchangers, and process drums. Chemistry limits (0.24% max carbon for Gr.55, 0.27% max carbon for Gr.60 on thicker plate) and typical carbon equivalent of 0.38-0.44 qualify them for both Category A (non-low-hydrogen) and Category B preheat in Table 5.11. A516 is produced in plate thicknesses from 1/4" through 12". Grades 55 and 60 may be ordered as-rolled, normalized, or stress-relieved depending on the ASME Code requirements for the specific vessel design temperature and thickness.
Why This Preheat for A516 Gr.55/60 with GMAW
Pressure vessel plate for storage tanks and heat exchangers at moderate strength. With low-hydrogen GMAW, this combination falls under Category B rather than Category A — the continuous solid wire and gas shielding in GMAW produce inherently low hydrogen levels, typically 2-4 mL/100g. The 50°F minimum preheat is lower than what non-low-hydrogen SMAW would require at the same thickness because GMAW significantly reduces the driving force for hydrogen-induced cracking in the heat-affected zone.
Typical Applications for A516 Gr.55/60
Specified for atmospheric storage tank shells per API 650, heat exchanger tube sheets, air receiver vessels, condensate drums, deaerator shells, and low-pressure separator vessels. A516 Gr.60 is the workhorse for ASME VIII Division 1 vessels under 650°F design temperature. Shell-to-head circumferential seams and nozzle reinforcement pads are the primary weld details. Plate thicknesses for API 650 tank shells typically range from 5/16" at the top course to 1" or more at the bottom course depending on tank diameter and liquid specific gravity. Vertical seam welds carry the full hydrostatic head and require complete joint penetration with radiographic examination. Tank diameters range from 15 feet for small day tanks to over 300 feet for crude oil terminal storage. Shop-welded vessel shells are rolled from flat plate with longitudinal seams welded first, then circumferential seams joining shell courses together on the vessel rotator.
Why Preheat Matters at 3/4" to 1-1/2"
Preheat climbs at this range as thicker material slows heat dissipation, trapping hydrogen at crack-susceptible grain boundaries.
Other Steels with GMAW at 3/4" to 1-1/2"
| Steel | Category | Preheat |
|---|---|---|
| A516 Gr.65/70 | B | 50°F (10°C) |
| A633 Gr.E | C | 150°F (65°C) |
| A709 HPS70W | C | 150°F (65°C) |
| A710 Gr.A | C | 150°F (65°C) |
A516 Gr.55/60 with GMAW
Try Different Combinations
Use the interactive preheat calculator to look up any steel, process, and thickness combination from D1.1:2025 Table 5.11.
A516 Gr.55/60 Welding Guides
Primary sources
D1.1:2025 reference data. Not affiliated with AWS.
Application context
A516 Grade 55/60 plate in the 3/4 to 1-1/2 inch range with GMAW shows up in heavier pressure-vessel-adjacent structural fabrication — vessel skid frames carrying large vessels, support saddles for high-volume tanks, and structural connections to PV-grade plate where the welding falls under D1.1 (structural) rather than ASME Section IX (pressure boundary). The gas-shielded process suits shop conditions where stable gas integrity is achievable.
Pre-weld notes
Same scope question as every A516 weld: D1.1 vs ASME Section IX. For D1.1 structural work at this thickness, three constraints layer in. First, the 50°F preheat floor needs active verification per Clause 7.6 — the heated zone must extend at least twice the base-metal thickness from the welding point. Second, shielding-gas integrity per Table 5.10 (Ar/CO₂ 75–90 / 10–25, Ar/O₂ 95–98 / 2–5, or 100% CO₂ for ER70S-X / E70C-X electrodes per A5.18/A5.18M). Third, matching-strength filler from Table 5.7 Group I.
What a CWI verifies
A CWI on A516 Gr.55/60 GMAW mid-thickness structural work first verifies the WPS scope — D1.1 structural vs ASME Section IX pressure-boundary. For D1.1 structural work, the inspection covers (1) preheat through-thickness verification with a contact pyrometer after the first pass group, (2) shielding gas conforms to Table 5.10 with flow-rate sampled at the torch (not the regulator), (3) the matching-strength filler classification against Table 5.7 Group I, and (4) the prequalified GMAW limits in Table 5.3. Pressure-boundary welds get bumped to ASME Section IX-qualified procedures.