A36 Preheat for SMAW (low-hydrogen) — 1-1/2" to 2-1/2"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A36 welded with SMAW (low-hydrogen) at 1-1/2" to 2-1/2" is 150°F (65°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 A36 structural steel (36 ksi yield), E7018 is the universal choice for field repair welds, overhead clip angle fillet welds, and out-of-position groove welds where wire feed processes cannot reach. Use 1/8" diameter at 120–150 A for overhead and vertical-up; 5/32" at 150–175 A for flat/horizontal production work. Rod oven at 250°F minimum per Clause 7.3.2.1; re-bake at 500–800°F.
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
Filler Metal for SMAW-LH
Electrode: E7018 (AWS A5.1) — the universal low-hydrogen structural rod. 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.
A36
ASTM A36 is the most commonly specified structural steel in North America, with a minimum yield strength of 36 ksi and 58-80 ksi tensile range. It appears in both Category A (non-low-hydrogen SMAW) and Category B (low-hydrogen processes) of Table 5.11. A36 is available as plate (up to 8" thick), W-shapes, channels, angles, and bars from virtually every domestic mill. Its moderate carbon content (0.26% max for shapes, 0.25% max for plate up to 3/4") and typical carbon equivalent of 0.35-0.42 give it good weldability across all prequalified processes. A36 plate thicker than 1-1/2" carries a slightly higher carbon limit of 0.29%, while plate from 3/4" to 1-1/2" stays at 0.25% max.
Why This Preheat for A36 with SMAW-LH
Widely used structural carbon steel with 36 ksi yield and 0.26% max carbon. With low-hydrogen SMAW-LH, this combination falls under Category B rather than Category A — E7018 low-hydrogen electrodes produce typically 4-8 mL/100g diffusible hydrogen under proper rod oven conditions. The 150°F minimum preheat is lower than what non-low-hydrogen SMAW would require at the same thickness because SMAW-LH significantly reduces the driving force for hydrogen-induced cracking in the heat-affected zone.
Typical Applications for A36
Common in angle-to-gusset fillet welds, beam web clip angles, stiffener plates, base plate bearing connections, light bracing members, stair stringers, handrail posts, and miscellaneous steel fabrication. A36 plate is the default choice for connection elements such as shear tabs, moment end plates under 36 ksi demand, and simple beam-to-column seated connections. In retrofit and renovation, A36 angles and channels are standard for reinforcement brackets and framing infill. Typical shop drawing callouts include 3/8" and 1/2" A36 plate for gussets, 5/16" fillet welds on clip angles, and partial joint penetration groove welds on base plate stiffeners. A36 is so ubiquitous that most structural steel shops maintain permanent inventory in multiple thicknesses from 1/4" through 2" plate. Fillet weld sizes on A36 connections typically range from 3/16" minimum to 5/8" for heavy gusset-to-column welds, with E70XX electrodes providing significant overmatching strength.
Why Preheat Matters at 1-1/2" to 2-1/2"
Heavy plate with significant restraint and thermal mass — preheat is critical to maintain slow cooling for hydrogen escape.
Other Steels with SMAW (low-hydrogen) at 1-1/2" to 2-1/2"
| Steel | Category | Preheat |
|---|---|---|
| A53 Gr.B | B | 150°F (65°C) |
| A633 Gr.E | C | 225°F (110°C) |
| A709 HPS70W | C | 225°F (110°C) |
| A710 Gr.A | C | 225°F (110°C) |
A36 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.
A36 Welding Guides
Primary sources
D1.1:2025 reference data. Not affiliated with AWS.
Application context
A36 plate in the 1-1/2 to 2-1/2 inch range with SMAW low-hydrogen is the heavy-section repair and field-rework combination — fit-up correction welds on heavy A36 connection plates, walkway-bracket retrofits on existing structures, and field repair of heavy A36 members where stick welding's portability matters more than the deposition rate of FCAW or SAW. The 150°F minimum is the heavy-section preheat — not a token requirement.
Pre-weld notes
Crossing the 1-1/2 inch threshold changes the preheat-extent rule. Per Clause 7.6, for base metal 1-1/2 inch [38 mm] and greater, the heated zone shall extend at least equal to the base metal thickness, but not less than 3 inches [75 mm] — the rule shifts from twice-thickness (sub-1.5 inch) to once-thickness with a 3-inch floor. The 150°F minimum is interpass too, not just preheat. SMAW-LH at heavy section runs slower than thin section, which means longer atmospheric exposure on the working can — Table 7.1 column A still gates exposure time, and the 250°F holding-oven discipline of Clause 7.3.2.1 holds firmly.
What a CWI verifies
A CWI on A36 SMAW-LH heavy-section work verifies (1) preheat through-thickness, not just surface — typical method is sampling 3-6 inches from the arc on the back side, where surface temperature lags through-thickness by the longest interval, (2) the heated-zone extent against Clause 7.6 (at least equal to base-metal thickness, not less than 3 inches), (3) interpass temperature held above 150°F with a contact pyrometer between pass groups, and (4) LH electrode handling discipline. The 150°F floor is a real constraint at this thickness, not a paper requirement.