What ASTM A106 Covers
ASTM A106/A106M is the standard specification for seamless carbon steel pipe for high-temperature service. It covers nominal pipe sizes from NPS 1/8 to NPS 48, with wall thicknesses normally ordered to the schedules of ASME B36.10M. The specification fixes chemical composition, tensile and yield strength minima, elongation, permissible variations, workmanship, marking and the alternative acceptance of a hydrostatic test or non-destructive electric examination.
Only seamless pipe is included. Welded pipe for comparable duties is covered by other specifications such as ASTM A53, ASTM A671 or ASTM A672. In ASME construction the same material is adopted as SA106 in ASME Boiler and Pressure Vessel Code Section II, and allowable stresses are listed in ASME B31.1 and B31.3.
Chemical Composition of Grades A, B and C
| 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 |
Carbon and manganese rise in step with the grade, and that is what produces the strength difference. Grade A is the lowest-carbon, most formable grade; Grade C carries the highest carbon and therefore the highest strength and the lowest weldability margin.
Mechanical Properties
| Grade | Tensile strength, min | Yield strength, min | Typical role |
|---|---|---|---|
| A | 330 MPa | 205 MPa | Low-pressure and low-temperature piping, bending and forming |
| B | 415 MPa | 240 MPa | General high-temperature and high-pressure piping, the most widely used grade |
| C | 485 MPa | 275 MPa | Higher-strength service where the design stress governs |
Minimum elongation is specified grade by grade and by specimen type in the standard, so the tensile test certificate should always be reviewed against the ordered grade rather than assumed.
Grade Selection and Temperature Limits
Grade B is the default choice in petroleum, chemical and power projects because it balances strength, weldability and cost, and it is the most readily available grade on the market.
Grade A suits low-temperature, low-pressure duties and parts that are cold bent or formed, where extra ductility helps.
Grade C is selected only when the additional strength is needed, and welding procedures must be qualified accordingly because higher carbon raises hardness and cracking risk.
ASTM A106 pipe may be used down to about -29 degrees C. Below that temperature, impact testing is required and a low-temperature specification such as ASTM A333 should be considered.
At elevated temperature, allowable stress falls with temperature and design must follow the applicable code; the oxidation resistance of plain carbon steel limits long-term service at the top of the range.
Heat Treatment, Testing and Ordering
Pipe may be furnished hot finished or cold drawn. Cold-drawn pipe is heat treated, and normalising, annealing or quenching and tempering may be specified for particular duties; normalising refines the grain structure and improves toughness, while annealing is used mainly to relieve residual stress after cold working.
Tests: tensile test, flattening test, bend test where applicable, and either a hydrostatic test or non-destructive electric examination.
Supplementary requirements: impact testing, grain size, hardness limits, or ultrasonic examination can be added at the order stage.
Ordering information: grade, NPS, schedule or wall thickness, length, end finish, test requirements, coating or galvanizing, and marking requirements.
Surface protection: bare pipe is normally supplied with a protective varnish or with external coating such as 3PE, and hot-dip galvanizing is available for atmospheric service.
FAQ
Q: What grades does ASTM A106 include?
There are three grades, A, B and C. Grade B is the most commonly used, Grade A has the lowest carbon content and Grade C the highest carbon and manganese contents.
Q: What is the difference between ASTM A106 Grade B and Grade C?
Grade B has a carbon maximum of 0.30 % and a minimum tensile strength of 415 MPa, while Grade C allows up to 0.35 % carbon and requires 485 MPa minimum tensile strength. Grade C is stronger but harder to weld, so Grade B remains the practical default.
Q: Why is ASTM A106 Grade B so widely used?
It gives the best balance of strength, weldability and cost for high-temperature and high-pressure piping, it is available in a wide size range, and its properties cover most petroleum, chemical and power applications.
Q: Can ASTM A106 pipe be heat treated?
Yes. Normalising, annealing or quenching and tempering can be specified. Cold-drawn pipe is heat treated as part of normal production, and normalising is used to refine grain structure and improve toughness.
Q: Is ASTM A106 suitable for low-temperature service?
It is normally accepted down to about -29 degrees C. For lower temperatures, Charpy impact testing is required and a low-temperature grade such as ASTM A333 is the correct choice.
Q: Is ASTM A106 pipe seamless or welded?
The specification covers seamless pipe only. Where welded pipe is acceptable, ASTM A53, ASTM A671 or ASTM A672 apply instead.
