1. Base Tube Material: SA209
Composition:
Carbon (C) 0.10–0.20%
Manganese (Mn) 0.30–0.80%
Phosphorus (P) ≤ 0.025%
Sulfur (S) ≤ 0.025%
Silicon (Si) 0.10–0.50%
Molybdenum (Mo) 0.44–0.65%
Copper (Cu) ≤ 0.25% (if present)
Chromium (Cr) ≤ 0.30%
Nickel (Ni) ≤ 0.40%
Vanadium (V) ≤ 0.03%
Properties:
- Good high-temperature strength and creep resistance.
- Improved resistance to oxidation and corrosion compared to plain carbon steels at elevated temperatures.
- Good weldability.
2. Fin Material: AL1060
Properties:
Excellent Thermal Conductivity: (~230 W/m·K) - The primary reason for using aluminum fins.
Good Corrosion Resistance: Forms a protective oxide layer.
High Formability/Ductility: Easily shaped during manufacturing.
Low Density: Lightweight.
Low Strength: Softer than alloyed aluminums, but sufficient for many fin applications.
High Electrical Conductivity.
3. Fin Type: Embedded (G-Fin)
Manufacturing Process:
- A groove is machined (often by knurling) into the outer surface of the steel base tube.
- A strip of aluminum fin stock (AL1060) is fed into the groove.
- High-pressure rollers or dies force the tube wall material over the edges of the aluminum strip, cold-working and mechanically locking the fin base securely into the groove. This creates a continuous, tight, mechanical bond along the entire length of the fin.
Key Features:
- Strong Mechanical Bond: The fin is physically locked into the tube wall, offering excellent resistance to fin loosening due to thermal cycling or vibration.
- No Solder/Braze: Eliminates issues like flux corrosion, braze alloy melting point limitations, or potential voids in the bond line.
- Direct Metal-to-Metal Contact: Provides low interfacial thermal resistance (good heat transfer efficiency).
- Fin Integrity: The AL1060 fin material itself remains unaltered (not melted), retaining its full thermal conductivity and corrosion resistance.
- Fin Density: Allows for relatively high fins per inch (FPI).
- Appearance: Typically has a clean, metallic look with a visible seam where the tube metal is rolled over the fin base.
Key Advantages:
- High heat transfer efficiency.
- Excellent fin bond strength and durability under thermal cycling.
- Good high-temperature capability of the base tube.
- Corrosion resistance of fins (AL1060) and base tube (SA209).
- No low-melting-point braze alloys to limit operating temperature.
4. Application
- Marine & Offshore Systems
- Desalination Plant Heat Exchangers
- Sulfuric Acid (H₂SO₄) Coolers
- Sour Gas (H₂S) Reboilers
- Steam Condensers in Geothermal Plants
- Flue Gas Waste Heat Recovery
- Ammonia (NH₃) Evaporators
- Heat Recovery Ventilators (HRVs)
5.Typical Applications:
- Heat Recovery Steam Generators (HRSGs): Economizer and evaporator sections.
- Boiler Economizers: Recovering heat from flue gases.
- Air Heaters (Ljungström type or tubular): Preheating combustion air.
- Process Gas Heaters/Coolers: In refineries, petrochemical, and chemical plants.
- High-Temperature Finned Tube Bundles: Where both elevated temperature resistance and efficient extended surface are required.
