What Is ASTM A210?
ASTM A210/A210M is the standard specification for seamless medium-carbon steel boiler and superheater tubes. It is applied to boiler tubes and boiler flue tubes, including safety ends, domes and support tubes, and to superheater tubes that operate in the high temperature, high pressure environment of a steam generator. The specification is issued in two grades, Grade A-1 and Grade C, and it relies on the seamless process so that the tube wall is uniform and free of a welded seam in the most highly stressed part of the boiler circuit.
Size Range Covered
Outside diameter: 1/2 inch to 5 inches, that is 12.7 mm to 127 mm
Minimum wall thickness: 0.035 inch to 0.500 inch, that is 0.9 mm to 12.7 mm
Other sizes may be supplied provided they meet all other requirements of the specification
For tubes with an inside diameter below 1/8 inch (3.2 mm), or a wall below 0.015 inch (0.4 mm), the mechanical property requirements do not apply
Length, straightness and end finish are agreed at the ordering stage, and the tube may be supplied with plain ends or prepared for welding into the boiler header.
Chemical Composition of Grade A-1 and Grade C
Percent by mass, heat and product analysis.
| Element | Grade A-1 | Grade C |
|---|---|---|
| Carbon, max | 0.27 | 0.35 |
| Manganese | 0.93 max | 0.29 to 1.06 |
| Silicon, min | 0.10 | 0.10 |
| Phosphorus, max | 0.035 | 0.035 |
| Sulphur, max | 0.035 | 0.035 |
Grade C carries the higher carbon and the wider manganese range, which is what allows it to reach a higher tensile strength than Grade A-1. The minimum silicon content in both grades supports the deoxidation practice needed for tube steel that will see sustained elevated temperature service.
Mechanical Properties
| Property | Grade A-1 | Grade C |
|---|---|---|
| Tensile strength, min | 415 MPa (60 000 psi) | 485 MPa (70 000 psi) |
| Yield strength, min | 255 MPa (37 000 psi) | 275 MPa (40 000 psi) |
| Elongation, min in 50 mm | 30 percent | 30 percent |
Both grades share the same minimum elongation, so the higher strength of Grade C is obtained through composition rather than through a loss of ductility. Appropriate heat treatment during manufacture is permitted and its type is decided by the grade and the final service condition, since the tube has to remain sound through rolling, bending and welding operations in the boiler shop.
Inspection and Testing Requirements
Tensile test: one test per lot of not more than 50 tubes, and two tests per lot of more than 50 tubes
Flattening test: one finished tube per lot, samples taken from each end; for Grade C with an outside diameter of 2.375 inch (60.3 mm) or less, tears or breaks at the 12 o'clock and 6 o'clock positions are not a cause for rejection
Expansion test: one finished tube per lot, different from the tube used for the flattening test, with samples taken from each end
Hardness test: two tubes per lot, tested by the Brinell or Rockwell method
Hydrostatic or nondestructive test: every tube is pressure tested, and a nondestructive test may be substituted when the purchaser specifies it
Identification: the standard number, grade, size, heat number and other required data are marked on the tube for traceability
The lot definition and the sampling rules matter in practice, because a change of heat or of finishing operation resets the lot and triggers a fresh set of tests.
FAQ
Q: What is ASTM A210 used for?
Seamless medium-carbon steel boiler and superheater tubes, including boiler flue tubes, safety ends, domes and support tubes in power station boilers, industrial boilers and superheaters.
Q: What is the difference between Grade A-1 and Grade C?
Grade C has a higher maximum carbon and a wider manganese range, giving minimum tensile strength of 485 MPa and yield strength of 275 MPa, against 415 MPa and 255 MPa for Grade A-1.
Q: Why must A210 tube be seamless?
The seamless process removes the weld seam from a component that works at high temperature and pressure, so the wall is uniform and better able to resist creep and internal pressure.
Q: Can a nondestructive test replace the hydrostatic test?
Yes. Every tube is pressure tested in principle, but a nondestructive electric test may be substituted when the purchaser designates it in the order.
Q: What is the minimum elongation for A210 tube?
30 percent in 50 mm for both Grade A-1 and Grade C, which is why the higher strength of Grade C does not come at the cost of ductility.
Q: How many tensile tests are required per lot?
One test for a lot of up to 50 tubes and two tests for a lot of more than 50 tubes, with the lot set by heat and by finishing operation.
Q: When is an alloy grade chosen instead of A210?
When the design metal temperature or the creep duty exceeds what a medium-carbon steel can sustain, an alloy boiler tube grade with better elevated temperature strength is specified.