Quick Summary
ASTM A179 is the standard specification for seamless cold-drawn low-carbon steel tubes primarily used in heat exchangers, condensers, and other similar heat transfer applications. Its key characteristics are excellent surface finish, dimensional accuracy, and high thermal conductivity, making it ideal for transferring heat efficiently.
1. Key Features and Characteristics
Manufacturing Process: Seamless and Cold-Drawn. The "cold-drawn" process involves pulling the steel through a die at room temperature. This work-hardens the steel, resulting in:
Smoother inner and outer surface finish.
Excellent dimensional accuracy and tighter tolerances.
Increased strength and hardness compared to hot-finished tubes.
Material: Low-Carbon Steel. Typically, the carbon content is very low (see chemical composition below). This gives the tubes:
Excellent Thermal Conductivity: The primary reason for its use in heat exchangers.
Good Ductility and Formability: Easy to bend and shape without cracking.
Good Weldability: Can be easily welded using common methods.
Primary Application: Heat Transfer. Designed for services where heat needs to be transferred through the tube wall, such as in shells and tube heat exchangers, condensers, and other similar pressure vessels.
2. Chemical Composition
The chemical composition (by heat analysis) is a key factor in its performance. The following table outlines the maximum percentages:
| Element | Composition (% Max) |
|---|---|
| Carbon (C) | 0.06 - 0.18 % |
| Manganese (Mn) | 0.27 - 0.63 % |
| Phosphorus (P) | 0.048 % max |
| Sulfur (S) | 0.058 % max |
| Copper (Cu) * | 0.20 % min (when specified) |
| Silicon (Si) * | 0.10 % max |
Note: Copper is often specified for improved corrosion resistance in certain environments. Silicon is a residual element.
3. Mechanical Properties
The cold-drawing process imparts specific mechanical properties. The requirements are for the finished tube:
| Property | Requirement |
|---|---|
| Tensile Strength | Minimum 47 ksi (325 MPa) |
| Yield Strength | Minimum 26 ksi (180 MPa) |
| Elongation | Minimum 35% (in 2 inches) |
4. Standard Dimensions and Sizes
ASTM A179 tubes are available in a range of standard sizes, governed by specifications like ASME B36.10M.
Outside Diameter (OD): Typically from 1/8 inch (3.2 mm) up to 3 inches (76.2 mm).
Wall Thickness: Defined by a nominal or average wall. Common thicknesses are specified in the BWG (Birmingham Wire Gauge) or fractional inches. Standard walls range from 0.035 inches (0.9 mm) to 0.165 inches (4.2 mm).
A very common size for heat exchangers is 3/4" OD x 16 BWG (0.065" wall).
Length: Typically supplied in random lengths from 12 to 22 feet, or cut-to-length.
5. Common Applications
The primary use is in heat transfer equipment where the tube is surrounded by a medium (like water) and another fluid flows inside the tube (or vice-versa).
Shell and Tube Heat Exchangers
Condensers (in power plants, refrigeration systems)
Feedwater Heaters
Evaporators
Other similar heat transfer apparatus in chemical, petrochemical, and power generation industries.
6. Advantages and Disadvantages
Advantages:
High Thermal Conductivity: Superior heat transfer efficiency.
Cost-Effective: Generally less expensive than alloy steels like ASTM A213 T5/T11 or stainless steels like A213 TP304/TP316.
Smooth Surface: The cold-drawn finish minimizes fouling (build-up of deposits).
Easy to Fabricate: Can be bent, flared, and welded with ease.
Disadvantages:
Low Corrosion Resistance: Not suitable for corrosive environments (acids, chlorides, etc.). It is susceptible to rust.
Lower Strength: Compared to medium-carbon or alloy steels.
Temperature Limitation: Generally recommended for service up to ~750°F (400°C). Beyond this, its strength decreases significantly.
7. Comparison with Similar Grades
It's often compared to ASTM A214, which covers ERW (Electric Resistance Welded) carbon steel tubes for the same applications. The key difference is that A179 is seamless, while A214 has a weld seam.
| Feature | ASTM A179 | ASTM A214 |
|---|---|---|
| Manufacturing | Seamless & Cold-Drawn | ERW (Welded) & Cold-Drawn |
| Consistency | No seam, uniform structure | Has a weld seam which can be a potential weak point |
| Cost | Generally higher | More economical |
| Application | Critical services, high pressure | Less critical services, lower pressure |
Conclusion
ASTM A179 is the go-to material for efficient and cost-effective heat transfer in non-corrosive environments. Its seamless, cold-drawn nature provides the reliability, surface quality, and dimensional precision required for high-performance heat exchangers and condensers in industries like power generation and petrochemicals. When corrosion is a concern, engineers typically look to stainless steel (A213 TP304/316) or other alloy grades.
