A106 Gr.B Preheat for SMAW (non-low-hydrogen) — up to 3/4"
Minimum preheat and interpass temperature for A106 Gr.B welded with SMAW (non-low-hydrogen) at up to 3/4" thickness, per AWS D1.1:2025 Table 5.11.
Non-low-hydrogen SMAW process
SMAW (Non-Low-Hydrogen)
Non-low-hydrogen SMAW (E6010/E6011) uses cellulosic electrodes with higher hydrogen potential, assigned to Category A in Table 5.11.
On pipe joints, non-low-hydrogen SMAW root passes with E6010 use the keyhole technique to ensure complete penetration. Pipe rotation (roll welding) is preferred when practical; fixed-position welding requires 5G or 6G qualified procedures. The cellulosic coating generates significant spatter, so adjacent base metal should be protected with anti-spatter compound.
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
Seamless pipe rated for high-temperature service up to 750°F. At this thickness, SMAW with non-low-hydrogen electrodes places the joint in Category A of Table 5.11. The minimum preheat of 32°F compensates for the higher diffusible hydrogen from cellulosic electrode coatings. The thicker the material, the longer hydrogen takes to escape the heat-affected zone, which is why preheat rises with thickness even for this common grade.
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 up to 3/4"
Thin material sheds heat quickly, allowing hydrogen to escape the HAZ readily — lowest preheat tier in Table 5.11.
Why 32°F for A106 Gr.B?
A minimum preheat of 32°F (0°C) means no active preheating is needed above freezing conditions. Table 5.11 Category A at this thickness assigns the ambient minimum because A106 Gr.B with non-low-hydrogen SMAW has sufficient ductility and low enough carbon equivalent that hydrogen cracking risk is minimal at this section thickness. Per footnote (a), if working below 32°F, preheat the joint to at least 70°F (20°C) and maintain during welding.
Other Steels with SMAW (non-low-hydrogen) at up to 3/4"
| Steel | Category | Preheat |
|---|---|---|
| A36 | A | 32°F (0°C) |
| A53 Gr.B | A | 32°F (0°C) |
A106 Gr.B with SMAW (non-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
D1.1:2025 reference data. Not affiliated with AWS.