A106 Gr.B Preheat for SMAW (low-hydrogen) — 3/4" to 1-1/2"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A106 Gr.B 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.
For pipe butt joints, E7018 fill and cap passes follow the E6010 root. Vertical-down technique is not permitted with low-hydrogen electrodes. Interpass cleaning requires chipping and wire brushing between every pass to remove slag inclusions. Restart craters should be ground to sound metal before striking a new arc.
SMAW-LH Tips for Pipe and Tube Steels
For A106 Grade B seamless pipe (35 ksi yield, high-temperature service), E7018 fill and cap passes follow E6010 root on process piping butt welds per ASME B31.1/B31.3. On thick-wall Schedule 160 and XXH A106 pipe (wall thickness over 1/2"), preheat to 150°F minimum for Category B at the 3/4"–1-1/2" tier. E7018 at 130–160 A (1/8" rod) in vertical-up position handles.
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
Why SMAW (low-hydrogen) for A106 Gr.B at 3/4" to 1-1/2"
Why SMAW (low-hydrogen) for A106 Gr.B at 3/4" to 1-1/2"? SMAW (low-hydrogen) delivers 3-5 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a106-b/saw/3-4-to-1-1-2-inch/">SAW</a> at 15-40 lb/hr. Position capability: all positions. Suitability: field and shop.
A106 Gr.B
ASTM A106 Grade B covers seamless carbon steel pipe for high-temperature service up to about 750°F, with 35 ksi minimum yield and 60 ksi minimum tensile strength. Produced in sizes from 1/4" through 30" NPS, it is the standard pipe material for power plants, refineries, and process piping where elevated temperature and pressure coexist. Chemistry limits (0.30% max carbon, 0.29-1.06% manganese) give it a weldability profile that matches common structural grades with Category A and B preheat requirements. A106 is exclusively seamless, which eliminates the ERW seam concern present in A53. Grade C (40 ksi yield) exists but Grade B handles the vast majority of process piping service.
Why This Preheat for A106 Gr.B with SMAW-LH
Seamless pipe rated for high-temperature service up to 750°F. 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 50°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 A106 Gr.B
Used in boiler steam headers, refinery piping racks, process plant branch connections, heat exchanger nozzle welds, power plant main steam lines, petrochemical reactor feed piping, and high-temperature manifolds. A106 Gr.B butt welds in process piping require joint preparation to B31.1 (power piping) or B31.3 (process piping) depending on service classification. Socket welds on small-bore A106 drain lines and instrument take-offs are common in utility stations, typically 1/2" to 2" NPS. Typical wall thicknesses range from Schedule 40 (0.237" wall on 2" NPS) to Schedule 160 (0.500" wall on 4" NPS) in critical high-energy service. Weld procedure qualification often includes side bend tests and tensile tests specific to the pipe diameter and wall thickness being joined. Field welds at pipe-to-flange connections and valve set-on joints require portable preheating equipment when wall thickness exceeds 1/2".
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) |
A106 Gr.B 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.
A106 Gr.B Welding Guides
Primary sources
D1.1:2025 reference data. Not affiliated with AWS.
Application context
A106 Grade B seamless pipe in the 3/4 to 1-1/2 inch wall range with SMAW low-hydrogen is the heavier structural-pipe combination — refinery and industrial pipe-support brackets on larger-diameter lines, primary pipe-to-plate connections on industrial structures, and structural-pipe field welds where the welding falls under D1.1 (structural) rather than ASME B31.1/B31.3 (process piping) and the wall thickness pushes the 50°F preheat floor into the binding-constraint position.
Pre-weld notes
Same scope question on every A106 weld: D1.1 vs ASME B31.x. For D1.1 structural work at this wall 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 wall thickness from the welding point. Second, the LH electrode storage and atmospheric-exposure discipline of Clause 7.3.2.1 and Clause 7.3.2.2 holds. Third, axial heat conduction along the pipe and the heat-sink effect of the wall thickness make through-wall preheat lag larger than on plate at the same nominal thickness — surface readings on one side of a heavy-walled pipe overstate the through-wall reading.
What a CWI verifies
A CWI on A106-B SMAW-LH mid-wall structural work first verifies the WPS scope by reading the WPS title block — D1.1 structural vs ASME B31.x pressure piping. For D1.1 structural work, the inspection covers (1) preheat at multiple positions around the circumference with a contact pyrometer after the first pass group — uneven preheat is more common on pipe than plate, (2) the LH electrode storage and atmospheric-exposure discipline per Clause 7.3, (3) the matching-strength filler classification against Table 5.7 Group I, and (4) the welder qualification for tubular position welding under Clause 6.11. The 50°F floor is binding at this wall thickness.