What Is ASTM A106 Gr.B Seamless Steel Pipe?
ASTM A106/A106M covers seamless carbon steel pipe for high-temperature service. Grade B is the workhorse of the specification and the grade most often ordered for pressure piping, steam lines, heat exchangers and boiler connections. It is a plain carbon-manganese steel with a minimum silicon content for deoxidation, supplied seamless so that the pipe wall is homogeneous and free of a longitudinal weld.
The ASME equivalent designation is SA106 Grade B, and pipe produced to either document is interchangeable for code work, since ASME adopts the ASTM specification with editorial only differences. Where the pipe will be welded pressure duty is specified, the pipe is marked with the specification and grade together with the hydrostatic or non-destructive test designation that applies.
Chemical and Mechanical Requirements
| Grade | C max | Mn | P max | S max | Si min | Tensile min | Yield min |
|---|---|---|---|---|---|---|---|
| A | 0.25% | 0.27 - 0.93% | 0.035% | 0.035% | 0.10% | 330 MPa | 205 MPa |
| B | 0.30% | 0.29 - 1.06% | 0.035% | 0.035% | 0.10% | 415 MPa | 240 MPa |
| C | 0.35% | 0.29 - 1.06% | 0.035% | 0.035% | 0.10% | 485 MPa | 275 MPa |
Grade B requires a minimum tensile strength of 415 MPa (60 ksi) and a minimum yield strength of 240 MPa (35 ksi), with elongation measured in accordance with the specification. Carbon, manganese, phosphorus and sulfur are held within the ranges above, and where the pipe is welded the carbon content is normally restricted further to keep weldability comfortable.
Size Range, Schedule and Lengths
Diameter: commonly NPS 1/2 through NPS 28, with larger sizes available on enquiry.
Wall thickness: schedule 10 through schedule 160, and additional heavier or lighter walls to the ordered average wall.
Lengths: single random of roughly 17 to 24 feet, double random of roughly 36 to 44 feet, or specified cut lengths.
Manufacturing route: NPS 1-1/2 and below may be hot finished or cold drawn; larger sizes are generally hot rolled or hot finished.
Ends: plain, bevelled, threaded or grooved as required for the welding or coupling method.
Applications
Grade B pipe is found in fossil fuel and biomass power plants as boiler tube connections, superheater support piping and main steam lines; in refineries and chemical plants as process and utility piping; in heat exchangers and condensers; in shipbuilding and offshore modules; and in general industrial steam, condensate, compressed air and process water systems. For long distance cross-country transmission, API 5L line pipe is normally the more economical choice, while A106 remains the reference material for plant piping and equipment connections.
Welding, Bending and Inspection Guidance
Grade B welds readily with shielded metal arc, gas tungsten arc, gas metal arc and submerged arc processes using matching carbon steel filler metals. Preheat is generally unnecessary on thin walls, but is applied as wall thickness, carbon equivalent and ambient conditions dictate, and post-weld heat treatment is usually limited to thick sections as required by the governing code. Cold bending and hot bending are both practical; hot formed bends are typically normalised afterwards to restore the mechanical properties of the parent pipe.
Inspection typically covers dimensional and wall thickness verification, hydrostatic or non-destructive testing of the pipe, and mechanical tests on the pipe body including tensile, flattening or bend tests on welded product where applicable. Order documents should state the grade, the outside diameter and wall, the length basis, the end finish, and whether hydrostatic, ultrasonic, eddy current or radiographic examination is required.
FAQ
Q: What is the difference between A106 Grade A and Grade B?
Grade B has higher carbon and manganese ranges and correspondingly higher tensile and yield strength, which makes it the standard choice for pressure and steam service, while Grade A is used for lighter duty.
Q: Is A106 Grade B seamless or welded?
The specification covers seamless pipe, and Grade B is most commonly supplied seamless; welded alternatives for similar service are covered by other specifications such as ASTM A53 or ASTM A672.
Q: What is the maximum service temperature for A106 Grade B?
The grade is intended for high-temperature service, with published application ranges extending to about 400 °C (750 °F); above that level, alloy steel specifications such as ASTM A335 are normally specified.
Q: What is the minimum yield strength of A106 Gr.B?
The specified minimum yield strength is 240 MPa (35 ksi) with a minimum tensile strength of 415 MPa (60 ksi) in the as-delivered condition.
Q: Can A106 Gr.B pipe be galvanised or coated?
Yes. The pipe is frequently hot-dip galvanised, epoxy coated or three-layer polyethylene coated for buried or corrosive service, provided the coating process does not exceed temperatures that would alter the specified mechanical properties.
