A709 HPS50W Preheat for SMAW (low-hydrogen) — 3/4" to 1-1/2"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A709 HPS50W 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.
Why SMAW (low-hydrogen) for A709 HPS50W at 3/4" to 1-1/2"
Why SMAW (low-hydrogen) for A709 HPS50W at 3/4" to 1-1/2"? SMAW (low-hydrogen) delivers 3-5 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a709-hps50w/saw/3-4-to-1-1-2-inch/">SAW</a> at 15-40 lb/hr. Position capability: all positions. Suitability: field and shop.
Filler Metal for SMAW-LH
Electrode: E7018 (AWS A5.1). Table 5.7 lists it for Group I and Group II base metals only; Groups III, IV and V take AWS A5.5 low-alloy electrodes from Table 5.7. Diameter: 1/8" (general/out-of-position), 5/32" (production), 3/16" (heavy plate flat only). Storage: 250°F rod oven minimum per D1.1 §7.3.2.1. Exposure limit: 4 hours out of oven per Table 7.1, then re-bake at 500-800°F for minimum 2 hours per §7.3.2.4 (A5.1 classification).
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
A709 HPS50W
ASTM A709 HPS50W is a high-performance weathering steel (50 ksi yield, 70 ksi minimum tensile) developed specifically for unpainted bridge construction. The HPS designation indicates enhanced weldability through lower carbon (0.11% max), controlled sulfur (0.006% max with calcium treatment), and copper-nickel-chromium alloying for atmospheric corrosion resistance. These chemistry controls reduce the CE-IIW to approximately 0.38-0.42, well below conventional weathering steels. It falls under Category B in Table 5.11. The FHWA-funded development program that created HPS grades (starting in the 1990s) aimed to eliminate the weldability problems, lamellar tearing, and inconsistent toughness that plagued earlier weathering steel bridge designs. HPS50W has largely replaced conventional A709 Gr.50W in new unpainted bridge designs.
Why This Preheat for A709 HPS50W with SMAW-LH
High-performance weathering bridge steel with enhanced weldability at 50 ksi. 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 A709 HPS50W
Deployed in unpainted bridge plate girders across humid or coastal environments, curved girders on interchange ramps, signature pedestrian bridges in architectural applications, and rural highway bridges where lifecycle paint costs exceed the HPS premium. The enhanced weldability of HPS50W reduces fabrication risk at flange splices and allows wider groove angles with reduced risk of lamellar tearing in thick flange plates through controlled sulfur and inclusion shape control via calcium treatment. The chemistry control (0.11% max carbon, controlled sulfur at 0.006% max) differentiates HPS from conventional weathering grades. Material cost premium over standard A709 Gr.50W is typically 15-25% per ton but eliminates lifetime repainting cycles estimated at $15-25 per square foot every 20-25 years. The lower CE-IIW of HPS50W compared to conventional weathering grades means it welds with less preheat sensitivity, reducing reject rates on thick flange CJP splices during cold-weather bridge fabrication.
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 |
|---|---|---|
| A913 Gr.50/60/65 | B | 50°F (10°C) |
| A709 HPS70W | C | 150°F (65°C) |
| A710 Gr.A | C | 150°F (65°C) |
| A913 Gr.70 | C | 150°F (65°C) |
A709 HPS50W 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.
A709 HPS50W Welding Guides
Primary sources
D1.1:2025 reference data. Not affiliated with AWS.
Application context
A709 HPS50W in the 3/4 to 1-1/2 inch range with SMAW low-hydrogen sits at the modern-bridge primary-member end of weathering-steel work — high-performance steel splice plates, gusset plates, and connection plates on AASHTO LRFD-designed bridges where fracture-critical member status drives consumable selection and the section thickness pushes the 50°F preheat floor into the binding-constraint position.
Pre-weld notes
Four discipline layers stack 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 from the welding point. 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 bare HPS50W 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). Fourth, bridge-owner CVN testing on HPS members commonly elevates the WPS to qualified-rather-than-prequalified.
What a CWI verifies
A CWI on A709 HPS50W 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-lot traceability to the WPS-cited heat lot, (3) electrode classification matches Table 5.9 for exposed bare applications and any project-specific CVN deposit requirements, and (4) holding-oven temperature with the contractor's rebake log walked. Where CVN is specified, the inspection covers Clause 6 essential-variable controls (Table 6.6 + Table 6.8) on top of the prequalified gate.