Scope of ASTM A179
ASTM A179/A179M is the standard specification for seamless cold-drawn low-carbon steel heat exchanger and condenser tubes. It covers tubes with an outside diameter from 3.2 mm to 76.2 mm, supplied in straight lengths or as U-bent tubes, and it is selected wherever a low-carbon tube with good formability and dependable thermal performance is required. The document is written as a product specification, so the general requirements for delivery, tolerances, testing and marking are taken from ASTM A450/A450M for carbon and low-alloy steel tubes and, in metric practice, from the corresponding general requirement standard. A complete order therefore has to reference both the product specification and the general requirement specification.
Chemical Composition
Percent by mass, heat and product analysis.
| Element | Requirement |
|---|---|
| Carbon | 0.06 to 0.18 |
| Manganese | 0.27 to 0.63 |
| Phosphorus | 0.035 maximum |
| Sulphur | 0.035 maximum |
The narrow carbon range is deliberate. The lower limit guards against a steel too soft to hold a finished surface after rolling and expanding, while the upper limit keeps the material readily cold drawable and weldable without building excessive hardness into the finished tube. The manganese range supplies the required strength without impairing ductility, so the tube can be expanded into a tube sheet or rolled into a tube-to-tubesheet joint without cracking.
Mechanical Properties and Heat Treatment
| Property | Requirement |
|---|---|
| Tensile strength | 325 MPa (47 000 psi) minimum |
| Yield strength | 180 MPa (26 000 psi) minimum |
| Elongation | 35 percent minimum in 50 mm |
| Hardness | 72 HRB maximum |
| Heat treatment | After the final cold-drawing pass, treated at 650 degrees C or higher |
The mandatory post-drawing heat treatment is not a normalising treatment for grain refinement. Its purpose is to relieve the cold work introduced by the final drawing pass, restore elongation and bring the tube within the hardness limit. Tubes that are bent after delivery, such as U-bends in a heat exchanger bundle, are bent in the annealed condition and stress relieved afterwards where the application requires it.
Testing, Dimensions and Delivery Condition
Each lot is subjected to a tension test, a flattening test and a hardness test, and the tubes are either hydrostatically tested or examined by a nondestructive electric test such as eddy current inspection, as agreed in the order. Dimensions, wall thickness tolerances, length tolerances, straightness and surface condition are controlled by the general requirement specification, and the surface is normally supplied clean and free of scale. Tubes are ordered by outside diameter and minimum wall thickness, with the wall tolerance applied to minimum wall unless an average wall is specified.
Common finishes: as-drawn pickled, or bright annealed where contamination of the process fluid must be avoided
Straight lengths or U-bent, with the bend radius and leg length stated on the order
Marking, bundling and protective end caps governed by the general requirement standard
Test report type and any third-party inspection stated before the heat is rolled
Comparison with Related Grades
ASTM A179 is a lower strength grade than ASTM A106/A106M Grade B, which has a minimum tensile strength of 415 MPa and a minimum yield strength of 240 MPa and is used for pressure piping rather than for heat transfer surfaces. The low carbon content and soft condition of A179 make it easier to bend, expand into a tube sheet and roll into a tube-to-tubesheet joint, and its thermal conductivity is not reduced by alloying additions. Where higher temperature strength is needed, a low-alloy grade such as ASTM A213 T11 or T22 is selected instead, and where a welded tube is acceptable an electric resistance welded heat exchanger tube specification, such as ASME SA214, is used. The choice among these options follows from the design metal temperature, the tube side fluid chemistry and the tube-to-tubesheet jointing method.
FAQ
Q: What is ASTM A179 tube used for?
It is used for heat exchanger tubes, condenser tubes, feedwater heater tubes and similar heat transfer surfaces, typically in the chemical, petrochemical and power industries where a low-carbon, readily formed tube is required.
Q: What is the difference between ASTM A179 and ASTM A106 Grade B?
A179 is a heat exchanger tube specification with a minimum tensile strength of 325 MPa and a minimum yield strength of 180 MPa, while A106 Grade B is a pressure pipe specification with minimum values of 415 MPa and 240 MPa. A179 is produced cold drawn and heat treated for formability, and A106 is produced hot finished or cold drawn for pressure containment.
Q: Why must A179 tube be heat treated after the final cold drawing?
The final cold-drawing pass raises strength and lowers ductility. Treatment at 650 degrees C or higher relieves that cold work, restores elongation and brings the tube within the 72 HRB hardness limit so that it can be rolled, bent and expanded.
Q: Is a hydrostatic test always required?
The specification permits either a hydrostatic test or a nondestructive electric test such as eddy current inspection, depending on the order, so the choice has to be stated when the tube is ordered.
Q: What is the maximum hardness allowed?
72 HRB. This limit is one of the acceptance criteria of the specification and is checked on the finished tube after heat treatment.
Q: Which dimensions are available?
Outside diameters from 3.2 mm to 76.2 mm, with wall thickness, length and tolerance in accordance with the general requirement specification referenced in the order.
Q: Can A179 tube be supplied as U-bent bundles?
Yes. U-bent tubes are formed from annealed straight tube, and the bend radius, leg length and any post-bend stress relief requirement are stated in the order along with the general requirement specification.