What Is ASTM A106 Grade B?
ASTM A106 is the standard specification for seamless carbon steel pipe intended for high-temperature service. The specification covers three grades, A, B and C, and Grade B is by far the most commonly ordered because it balances strength, ductility and weldability for elevated-temperature piping. A106 pipe is supplied as seamless only; the specification does not cover welded product.
The minimum yield strength of Grade B is 35,000 psi (240 MPa), and the minimum tensile strength is 60,000 psi (415 MPa). The steel is fully killed, with a minimum silicon content of 0.10%, which guarantees complete deoxidation and predictable behavior during welding and hot bending.
Chemical Composition Requirements
The chemistry below is controlled so that the pipe keeps useful strength up to about 750 degrees F (399 degrees C) continuous service while remaining weldable in the field. Residual elements are limited to avoid unpredictable high-temperature behavior.
| Element | Grade B (max %) | Grade A (max %) | Grade C (max %) |
|---|---|---|---|
| Carbon | 0.30 | 0.25 | 0.35 |
| Manganese | 0.29-1.06 | 0.27-0.93 | 0.29-1.06 |
| Phosphorus | 0.035 | 0.035 | 0.035 |
| Sulfur | 0.035 | 0.035 | 0.035 |
| Silicon | 0.10 min | 0.10 min | 0.10 min |
| Chromium, Copper, Molybdenum, Nickel | 0.40 / 0.40 / 0.15 / 0.40 | 0.40 / 0.40 / 0.15 / 0.40 | 0.40 / 0.40 / 0.15 / 0.40 |
| Vanadium | 0.08 | 0.08 | 0.08 |
The silicon minimum is the key marker of killed steel. It is also what separates A106 from general-purpose A53 pipe, where no silicon minimum is specified.
Mechanical Properties
| Property | Grade B | Grade A | Grade C |
|---|---|---|---|
| Tensile strength (min) | 60,000 psi / 415 MPa | 48,000 psi / 330 MPa | 70,000 psi / 485 MPa |
| Yield strength (min) | 35,000 psi / 240 MPa | 30,000 psi / 205 MPa | 40,000 psi / 275 MPa |
| Elongation in 2 in. (min) | 30% | 35% | 25% |
No maximum yield or tensile values are specified, so heat treatment and chemistry are the practical controls. Where low-temperature notch toughness is required, Charpy impact testing can be added by agreement, although A106 is not a low-temperature specification.
How A106 Pipe Is Manufactured
Almost all A106 Grade B is produced by rotary piercing, also called the Mannesmann process. A solid round billet is heated to roughly 2,200-2,400 degrees F (1,200-1,315 degrees C) and rotated between angled rolls while a piercing plug forms a hollow shell. The shell is then rolled on a mandrel or plug mill, sized, and straightened. Extrusion is used less often and mainly for specialized shapes.
Delivery conditions include hot finished (as-rolled), normalized, normalized and tempered, annealed, and cold drawn with stress relief. For service above about 500 degrees F, normalized pipe is usually preferred because the refined grain structure holds its high-temperature properties longer.
Size Range and Schedules
A106 pipe is normally furnished in nominal sizes from 1/8 in. to 26 in. NPS, with wall thicknesses matching Schedules 10, 20, STD, 40, 80, 120, 160 and XXS. Standard lengths are single random (16-22 ft), double random (35-45 ft), or cut to exact length. Outside diameters follow ASME B36.10 for carbon steel pipe.
Temperature and Pressure Ratings
Design work for A106 piping is done to ASME B31.1 (power piping) or ASME B31.3 (process piping). The basic pressure thickness formula is t = P D / 2 (S E + P Y), where S is the allowable stress from ASME Section II Part D, E is the weld joint efficiency (1.0 for seamless), and Y is a temperature-dependent coefficient.
As a working example, a 6 in. Schedule 40 A106 Grade B line at 500 degrees F has an allowable stress of about 18,900 psi, a wall of 0.280 in. and an OD of 6.625 in., which gives a design pressure in the region of 1,600 psi. Allowable stress falls steadily above 500 degrees F, so the practical continuous-service ceiling is 750 degrees F.
Testing and Certification
Every heat is verified with a tensile test, and each pipe is hydrostatically tested to a pressure based on 60% of the specified minimum yield strength, with a minimum of 1,000 psi, held for at least 10 seconds. Eddy current or ultrasonic testing may be substituted by agreement. Bend and flattening tests check ductility on sizes up to 8-5/8 in. OD.
For code projects the mill certificate (MTC) must show full chemistry, mechanical results, heat number, hydrostatic pressure and any heat treatment records. Marking includes the manufacturer, specification, grade, size, heat number and test pressure.
A106 Grade B vs A53 Grade B vs API 5L Grade B
| Parameter | A106 Grade B | A53 Grade B | API 5L Grade B |
|---|---|---|---|
| Primary service | High-temperature process | General purpose | Line pipe for oil and gas |
| Continuous temperature limit | 750 degrees F | ~400 degrees F | Ambient to moderate |
| Silicon minimum | 0.10% | Not specified | Not required |
| Killed steel | Required | Typical only | Not required |
| Manufacturing | Seamless only | Seamless, ERW, furnace | Seamless and welded |
Many mills dual-certify pipe to both A106 Grade B and A53 Grade B, and some to API 5L Grade B as well, which gives buyers flexibility when a project requires more than one designation.
Typical Applications
A106 Grade B is standard in power plant main steam and feedwater lines, refinery process piping, heater transfer lines, boiler piping, and industrial steam distribution. It is also accepted by ASME Boiler and Pressure Vessel Code Sections I and VIII and by NFPA fire protection systems.
Ordering Checklist
When requesting a quotation, specify the standard and grade, size (NPS and schedule or OD x WT), length, end preparation (plain, beveled, threaded), heat treatment, additional testing, marking and packaging. A typical purchase description reads: ASTM A106 Grade B, 12.75 in. OD x 0.375 in. WT x 40 ft, beveled ends, normalized, hydrostatic tested, MTC required.
FAQ
Can ASTM A106 Grade B be used below 400 degrees F?
Yes, and it is frequently used at ambient temperature. The premium over A53 is only justified when elevated temperature, code requirements or long service life matter, but nothing prevents using A106 at lower temperatures.
Is A106 pipe galvanized?
Galvanizing A106 is possible but uncommon. The zinc coating is normally applied to A53 pipe, and A106 is usually specified bare or with a shop primer because galvanized coatings are not intended for sustained high-temperature service.
Does A106 Grade B require preheating before welding?
Preheat is generally required when the wall exceeds about 3/4 in. or when the ambient temperature is below 50 degrees F, to avoid hydrogen cracking. Filler metals such as E7018 or ER70S-6 are typical for matching strength.
What is the difference between A106 Grade B and Grade C?
Grade C has a higher carbon limit (0.35%) and higher strength minima, with tensile at least 70,000 psi and yield at least 40,000 psi. It is used less often because weldability and toughness are traded for strength.
Can A106 Grade B be used for low-temperature service?
Not as a default. A106 has no specified minimum service temperature, and the material can lose toughness at low temperature. For service below about -20 degrees F, ASTM A333 is the usual choice.
What documentation should the buyer request?
At minimum, a mill test certificate with full chemical analysis, tensile results, heat number, hydrostatic test pressure and heat treatment records. For ASME code work, positive material identification and third-party inspection are often added.
