What Is ASTM A106 Grade B?
ASTM A106 is the American Society for Testing and Materials specification for seamless carbon steel pipe for high-temperature service, formally designated A106/A106M. Grade B is the most widely used grade of the specification, covering a seamless carbon steel with a minimum yield strength of 240 MPa and a minimum tensile strength of 415 MPa. It is produced only as seamless pipe, by hot finishing or cold drawing, and is the default material for many power, refining and chemical process piping systems.
The material is a plain carbon steel made to tight compositional limits. A distinctive feature of A106 is the requirement for a minimum silicon content, which indicates fully killed steel and contributes to sound, weldable pipe with stable high-temperature properties.
Chemical Composition
The chemical composition of A106 Grade B is controlled within the limits below, which balance strength, weldability and resistance to elevated-temperature service.
| Element | Limit, % |
|---|---|
| Carbon C | 0.30 max |
| Manganese Mn | 0.29 - 1.06 |
| Phosphorus P | 0.025 max |
| Sulphur S | 0.025 max |
| Silicon Si | 0.10 min |
| Chromium Cr | 0.40 max |
| Nickel Ni | 0.40 max |
| Copper Cu | 0.40 max |
| Molybdenum Mo | 0.15 max |
| Vanadium V | 0.08 max |
The residual limits on chromium, nickel, copper, molybdenum and vanadium ensure that the material remains a true carbon steel without unintended alloying, which keeps welding procedures simple and predictable.
Mechanical Properties
| Property | Requirement |
|---|---|
| Tensile strength, min | 415 MPa |
| Yield strength, min | 240 MPa |
| Elongation | Per the table in ASTM A106, based on wall thickness and test gauge length |
These values are specified at room temperature; at elevated service temperature the allowable stress is derived from the code stress tables, which account for the reduction of strength with temperature.
Size Range and Manufacturing
A106 Grade B seamless pipe is available in a broad size range, typically from 21.3 mm up to 762 mm outer diameter, with wall thickness from 2.0 mm up to 140 mm. Larger seamless sizes are produced by hot finishing, while smaller diameters and tighter tolerances are produced by cold drawing.
The pipe is normally supplied with plain ends or beveled ends for welding, and in single random, double random or fixed lengths. Hydrostatic testing is performed on each pipe unless a non-destructive electric test is agreed instead, and tensile testing and flattening or bending tests are carried out per the specification.
Typical Applications
Power generation: boiler and superheater piping, steam lines and feedwater systems.
Petrochemical and refining: process piping, furnace transfer lines and utility systems handling high-temperature fluids.
Construction and industrial plants: high-temperature and high-pressure carbon steel piping where seamless construction is required.
Grades A, B and C and Material Comparisons
A106 defines three grades. Grade A has the lowest carbon and strength, Grade B is the standard choice for general high-temperature service, and Grade C offers the highest tensile strength of the three.
In Chinese practice, A106 Grade B is frequently mapped to GB/T 8163 grade 20, and Grade A to grade 10. Such comparisons are convenient for reference, but the governing specification for procurement, testing and design must always be the contractually applicable standard, because heat treatment, test scope and tolerances can differ.
Selection and Inspection Points
Select Grade B unless the design temperature or pressure requires the higher strength of Grade C, and confirm the required wall thickness schedule before ordering.
Verify on receipt that the mill test certificate shows the heat number, chemical analysis and tensile results, and that the hydrostatic test and any agreed non-destructive examination have been carried out.
During welding, follow qualified procedures for carbon steel pipe and confirm that filler metal matches the base material strength.
Frequently Asked Questions
Is A106 Grade B carbon steel?
Yes, it is a carbon steel with a carbon limit of 0.30 percent maximum and only residual amounts of other elements. It is not an alloy steel.
Can A106 Grade B be welded?
Yes, it is one of the most weldable pipe materials in service. Standard carbon steel welding procedures with E70-series filler metal are used, and preheat is generally not required for thin and medium walls.
What is the difference between A106 Grade A, B and C?
The grades differ mainly in carbon content and strength. Grade B is the most common balance of strength and weldability, while Grade C provides higher tensile strength and Grade A lower strength with slightly better formability.
Is A106 Grade B the same as API 5L Grade B?
They have similar strength levels, but A106 Grade B is a seamless pipe for high-temperature service with a silicon requirement, while API 5L Grade B is a line pipe grade covering both seamless and welded product. They should not be substituted without code approval.
What does the material 20 in GB/T 8163 mean in comparison?
GB/T 8163 grade 20 is a Chinese seamless steel pipe material with carbon content around 0.20 percent and strength close to A106 Grade B. It is a rough equivalent used in Chinese practice, but full compliance with A106 should be verified by testing and documentation when required.
What size range does A106 Grade B cover?
The specification covers seamless pipe from small diameters of about 21.3 mm up to 762 mm outer diameter, with wall thickness from 2.0 mm to 140 mm, and corresponding larger sizes can be produced to order.