What Is ASTM A106 Grade B?
ASTM A106 Grade B is the most widely specified seamless carbon steel pipe for high-temperature service in the oil and gas, petrochemical, and power generation industries. It covers seamless pipe for service at temperatures from ambient to approximately 425°C (800°F), making it the workhorse specification for process piping in refineries, chemical plants, and steam systems.
Grade B is one of three grades under ASTM A106 (A, B, and C), with Grade B being the dominant grade due to its balance of strength, weldability, and availability. Over 90% of all A106 pipe ordered globally is Grade B.
| Property | ASTM A106 Grade B |
|---|---|
| Manufacturing | Seamless (hot-finished or cold-drawn) |
| Material | Carbon steel (killed or semi-killed) |
| Yield strength (min) | 240 MPa (35 ksi) |
| Tensile strength (min) | 415 MPa (60 ksi) |
| Elongation (min) | 30% (in 50 mm gauge, longitudinal) |
| Hardness (max) | 197 HBW |
| Max carbon | 0.30% |
| Temperature range | -29°C to 425°C |
| Size range | NPS 1/8 to NPS 26 (seamless capability) |
| Dimensions | Per ASME B36.10 |
| Design code | ASME B31.3, B31.1 |
Chemical Composition
| Element | Grade A | Grade B | Grade C |
|---|---|---|---|
| Carbon (max) | 0.25 | 0.30 | 0.35 |
| Manganese | 0.27-0.93 | 0.29-1.06 | 0.29-1.06 |
| Phosphorus (max) | 0.035 | 0.035 | 0.035 |
| Sulfur (max) | 0.035 | 0.035 | 0.035 |
| Silicon (min) | 0.10 | 0.10 | 0.10 |
| Chrome (max) | 0.40 | 0.40 | 0.40 |
| Copper (max) | 0.40 | 0.40 | 0.40 |
| Molybdenum (max) | 0.15 | 0.15 | 0.15 |
| Nickel (max) | 0.40 | 0.40 | 0.40 |
Allowable Stress (ASME B31.3)
The allowable stress decreases with increasing temperature, which directly affects the required wall thickness.
| Temperature | Allowable Stress (MPa) |
|---|---|
| -29°C to 38°C | 138 |
| 100°C | 138 |
| 200°C | 134 |
| 300°C | 118 |
| 350°C | 110 |
| 400°C | 96 |
| 425°C | 82 |
Above 425°C, the allowable stress drops sharply and chrome-moly alloy steels (ASTM A335 P11, P22, P91) are required for creep resistance.
A106 Grade B vs. A vs. C
| Property | Grade A | Grade B | Grade C |
|---|---|---|---|
| Yield (min) | 205 MPa | 240 MPa | 275 MPa |
| Tensile (min) | 330 MPa | 415 MPa | 485 MPa |
| Carbon (max) | 0.25% | 0.30% | 0.35% |
| Weldability | Excellent | Good | Fair |
| Application | Low-pressure, high-weldability | General-purpose | High-pressure, limited welding |
Grade A has better weldability (lower carbon) but lower strength. Grade C has higher strength but is harder to weld. Grade B sits in the optimal middle ground for most applications.
Applications
- Refinery process piping (crude units, vacuum units, FCC units)
- Power plant steam and feedwater piping (below 425°C)
- Chemical plant process lines
- Boiler external piping per ASME B31.1
- General-purpose high-temperature piping in EPC projects
For a comparison with ASTM A53, the other common carbon steel pipe spec, see the A106 vs A53 article.
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