A588 Preheat for SMAW (low-hydrogen) — 3/4" to 1-1/2"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A588 welded with SMAW (low-hydrogen) 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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SMAW (Low-Hydrogen)
Low-hydrogen SMAW (E7018/E7016) uses basic-coated electrodes requiring rod oven storage, assigned to Category B in Table 5.11.
E7018 is the default electrode for structural fillet and groove welds on common building steels. Rod ovens should hold at a minimum of 250°F per D1.1 Clause 7.3.2.1; exposure time out of the oven is limited to 4 hours maximum per Table 7.1. For overhead position, use 3/32" diameter rods to control puddle size. Vertical-up stringer beads provide the best fusion on thicker members.
SMAW-LH Tips for Common Structural Steels
For A588 weathering steel (50 ksi yield, Category B), E7018 is acceptable for interior or unexposed joints but exposed weld faces on unpainted bridges and architectural weathering steel require E8018-W2 or other weathering-type low-hydrogen electrode to develop matching atmospheric corrosion resistance. Weld joint Color mismatch on exposed A588 joints using standard E7018 — the carbon steel deposit does not form.
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
Why SMAW (low-hydrogen) for A588 at 3/4" to 1-1/2"
Why SMAW (low-hydrogen) for A588 at 3/4" to 1-1/2"? SMAW (low-hydrogen) delivers 3-5 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a588/saw/3-4-to-1-1-2-inch/">SAW</a> at 15-40 lb/hr. Position capability: all positions. Suitability: field and shop.
A588
ASTM A588 is a weathering steel specification (50 ksi minimum yield, 70 ksi minimum tensile) that forms a protective iron oxide patina when exposed to atmospheric wet-dry cycling. The copper (0.25-0.40%), chromium (0.40-0.65%), and nickel (0.25-0.40%) alloying creates a dense, adherent rust layer that stabilizes after 2-5 years of exposure. Used in unpainted bridges and exposed structural members, it requires low-hydrogen processes (Category B) per Table 5.11 due to its higher alloy content pushing CE-IIW to 0.45-0.52. Weld filler metal must be a matching weathering composition (e.g., E8018-W2) to achieve corrosion-matching at exposed joints. A588 is produced as plate up to 8" thick and is available in structural shapes, though A709 Gr.50W is more commonly specified for bridge applications.
Why This Preheat for A588 with SMAW-LH
Weathering steel forming protective patina for unpainted bridge applications. This steel is prequalified only with low-hydrogen processes under Table 5.11. With SMAW-LH, E7018 low-hydrogen electrodes produce typically 4-8 mL/100g diffusible hydrogen under proper rod oven conditions. The 50°F minimum preheat balances the steel’s strength level and carbon equivalent against the hydrogen control provided by SMAW-LH. Non-low-hydrogen SMAW is not an option for this grade under D1.1 prequalified WPS.
Typical Applications for A588
Used in unpainted highway bridge girders, exposed pedestrian bridges, architectural weathering facades, transmission tower legs, rail bridge stringers, and marine navigation light structures. A588 welds must use compatible weathering-type filler metals (e.g., E8018-W2 or ER80S-G) to achieve matching corrosion resistance in the exposed weld face. Girder flange splices and stiffener fillet welds are primary fabrication joints. The distinctive brown-orange patina develops over 2-5 years of atmospheric exposure to form a stable, adherent oxide layer that does not require repainting. In coastal locations with salt spray or in areas where the surface stays wet for extended periods, the protective oxide layer may not form properly, limiting A588 to inland applications with reliable wet-dry cycling. Bolt holes and copes must be deburred to prevent corrosion concentration. Drainage details in the steel design prevent water traps that would undermine the patina formation process.
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 SMAW (low-hydrogen) at 3/4" to 1-1/2"
| Steel | Category | Preheat |
|---|---|---|
| A36 | 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) |
A588 with SMAW (low-hydrogen)
Try Different Combinations
Use the interactive preheat calculator to look up any steel, process, and thickness combination from D1.1:2025 Table 5.11.
A588 Welding Guides
Primary sources
D1.1:2025 reference data. Not affiliated with AWS.
Application context
A588 plate in the 3/4 to 1-1/2 inch range with SMAW low-hydrogen is the bare-finish weathering combination for bridge primary connection plates, transmission-tower main-leg gussets, and exposed-architectural primary members — sections heavy enough that the 50°F preheat floor is binding and the LH consumable selection drives the inspection effort.
Pre-weld notes
Three constraints layer at this combination. 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 in all directions (1.5 to 3 inches at this band). Second, Clause 7.3.2.1 LH electrode storage — 250°F holding oven, no rebake more than once, no use after wetting — and Clause 7.3.2.2 atmospheric-exposure clock per Table 7.1 column A. Third, for exposed unpainted applications the electrode must conform to Table 5.9 per Clause 5.6.3 (B2L, C1, C1L, C2, C2L, C3, or WX analysis under A5.5/A5.5M).
What a CWI verifies
A CWI on bare A588 SMAW-LH mid-thickness work verifies (1) preheat at perimeter and samples mid-joint with a contact pyrometer after the first pass group, (2) electrode classification matches Table 5.9 for exposed weathering applications, (3) holding-oven temperature and the contractor's rebake log, and (4) atmospheric-exposure tag on the working can against Table 7.1 column A. The 50°F floor is closer to binding at this thickness than at thin section — winter shop conditions or large-section heat-sink effects can put base metal below the floor without obvious signal.