A106 Gr.B Preheat for FCAW — 3/4" to 1-1/2"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A106 Gr.B welded with FCAW 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.
Have a preheat question? Ask Flux
FCAW (Flux Cored Arc Welding)
FCAW uses tubular flux-cored wire, available gas-shielded (E71T-1) or self-shielded (E71T-8) for field work. Category B in Table 5.11.
FCAW on pipe butt joints uses gas-shielded wire for root passes with backing rings or ceramic backup. Self-shielded FCAW excels on pipeline tie-in welds in windy field conditions where gas cups cannot maintain a stable envelope. Typical wire diameter for pipe work is 0.045" for root and 0.052" for fill passes.
Why FCAW for A106 Gr.B at 3/4" to 1-1/2"
Why FCAW for A106 Gr.B at 3/4" to 1-1/2"? FCAW delivers 8-12 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.
Filler Metal for FCAW
Gas-shielded: E71T-1C (AWS A5.20, requires 100% CO2) or E71T-1M (requires 75/25 Ar/CO2 mixed gas) — the C/M suffix designates the required shielding gas. Self-shielded: E71T-8 (no external gas, field-ready). Diameter: 0.045" standard, 1/16" for high-deposition. Stick-out: 3/4" to 1-1/4" (longer than GMAW due to resistive heating of flux core).
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
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 FCAW
Seamless pipe rated for high-temperature service up to 750°F. With low-hydrogen FCAW, this combination falls under Category B rather than Category A — flux-cored wire in FCAW provides a combination of deoxidizers and low-moisture flux formulations that control hydrogen. The 50°F minimum preheat is lower than what non-low-hydrogen SMAW would require at the same thickness because FCAW 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 FCAW 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 FCAW
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 FCAW 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, FCAW classification on the spool against the WPS-cited variant — self-shielded vs gas-shielded is an essential variable per Table 6.6, and FCAW-S is the practical choice for outdoor field welds on pipe supports where wind disrupts gas-shielded variants. Third, axial heat conduction along the pipe and the heat-sink effect of the wall make through-wall preheat lag larger than on plate.
What a CWI verifies
A CWI on A106-B FCAW 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, (2) the FCAW classification on the spool against the WPS-cited variant, (3) inter-pass slag removal across the joint sequence, and (4) amperage/voltage against Table 5.4 prequalified limits. The 50°F floor is binding at this wall thickness.