A106 Gr.B Preheat for SMAW (low-hydrogen) — over 2-1/2"

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 over 2-1/2"

Why SMAW (low-hydrogen) for A106 Gr.B at over 2-1/2"? SMAW (low-hydrogen) delivers 3-5 lb/hr deposition — compared to SAW 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 225°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 over 2-1/2"

The heaviest sections demand the highest preheat in Table 5.11. Multi-pass sequences require maintaining interpass temperature throughout.

Other Steels with SMAW (low-hydrogen) at over 2-1/2"

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