A588 Preheat for SMAW (low-hydrogen) — up to 3/4"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A588 welded with SMAW (low-hydrogen) at up to 3/4" is 32°F (0°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 up to 3/4"
Why SMAW (low-hydrogen) for A588 at up to 3/4"? SMAW (low-hydrogen) delivers 3-5 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a588/saw/up-to-3-4-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 32°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 up to 3/4"
Thin material sheds heat quickly, allowing hydrogen to escape the HAZ readily — lowest preheat tier in Table 5.11.
Other Steels with SMAW (low-hydrogen) at up to 3/4"
| Steel | Category | Preheat |
|---|---|---|
| A36 | B | 32°F (0°C) |
| A633 Gr.E | C | 50°F (10°C) |
| A709 HPS70W | C | 50°F (10°C) |
| A710 Gr.A | C | 50°F (10°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 at or below 3/4 inch with SMAW low-hydrogen is the bare-finish weathering-steel combination — bridge stringers, transmission-tower lattice, sunshade fins, and architectural members where the developing rust patina is the design intent rather than a corrosion concern.
Pre-weld notes
Two binding constraints stack at this thickness, neither of which is the preheat floor. First, Clause 7.3 low-hydrogen electrode storage holds — the electrode pulls moisture from shop-floor humidity in hours, and field rework on weathering steel often happens after consumables sit on a service truck. Second, for exposed unpainted applications the electrode classification 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) — the Table 5.7 matching-strength list alone does not cover atmospheric-corrosion match.
What a CWI verifies
A CWI on bare A588 verifies (1) holding-oven temperature at or above 250°F per Clause 7.3, (2) atmospheric exposure within Table 7.1 column A for the specific electrode classification, and (3) electrode classification matches Table 5.9 for exposed weathering applications. The 32°F preheat floor rarely binds at this thickness; consumable selection and storage dominate the inspection effort.