Corrosion never touches the base tube. That is the whole promise of the extruded bimetallic construction: an aluminum outer tube is swaged over the working tube, then its wall is extruded upward into tall helical fins, leaving the pressure-carrying tube sheathed in aluminum from end to end with full metal contact at every fin root. USA Piping Solution supplies extruded aluminum fin tubes on carbon steel, stainless, and copper base tube for coastal, offshore, and chemically aggressive atmospheres where wound fins corrode at the root. The rest of the fin family is compared on our Finned Tubes page.
The Anti-Corrosive Mechanism, Spelled Out
Every wound fin, however tight, leaves a line where fin meets tube, and in salt or chemical air that line is where attack starts: moisture wicks into the root gap, corrodes the interface, and the fin's thermal contact dies before the fin does. Extruded construction has no such line. The fins and the sheath are one piece of aluminum, formed from a muff mechanically bonded to the base tube over its full length, so the atmosphere only ever sees continuous aluminum, an alloy that defends itself with its own oxide. This is why specifications for coastal and offshore air coolers call for extruded fin by name, sometimes written as helically wound anti-corrosive high fin tube, and why it outlasts L-wrapped equivalents in the same salt air by years.
Specifications
| Specification | Details |
|---|---|
| Construction | Bimetallic: aluminum muff swaged over the base tube, fins extruded from the muff wall |
| Base Tube | Carbon steel, stainless steel, or copper; the fluid side picks it |
| Fin / Sheath Material | Aluminum (1060-type typical) |
| Service Temperature | To approximately 280°C, the bimetallic bond's working ceiling |
| Base Tube OD | Typically 16 – 51 mm |
| Fin Geometry | High fin, commonly 9 – 16 mm height, 7 – 11 fins per inch |
Applications
- Coastal & Offshore Air Coolers: fin-fan exchangers in marine salt air, the construction's defining call.
- Chemical Plant Atmospheres: acid-bearing or humid industrial air that eats wound fin roots.
- Air-Cooled Condensers: power and process condensing in aggressive outdoor air.
- Refrigeration & Gas Coolers: long-life coils where recoiling cost dominates.
In benign inland air, L and LL wrapped fin delivers similar thermal performance for less; LL's overlapped feet are the budget version of this page's full sheath. Extruded fins on copper base tube, raised from the tube's own wall rather than a muff, are covered on the Copper Finned Tubes page.
Coastal Duty? Send Location and Gas Conditions →
Testing, Certification & Availability
Base tube ships certified to its ASTM standard; sheath integrity, fin geometry, and bond are inspected on the finished product; our Quality Policy page covers the program. Send base tube material and size, fin geometry, and length for lead time.
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Frequently Asked Questions
What does “bimetallic” mean on an extruded fin tube datasheet?
Two metals doing two jobs: the inner base tube carries the process fluid and pressure, the outer aluminum muff carries the fins and faces the atmosphere. The muff is swaged on mechanically over the full length, so heat crosses a continuous metal-to-metal interface.
Is “helically wound anti-corrosive high fin tube” the same product?
In practice, yes: that phrase describes exactly what extruded bimetallic fin delivers, tall helical fins with a fully sheathed, corrosion-protected base tube. Quotes written either way land on this construction.
Why is the temperature ceiling around 280°C?
The mechanical bond between muff and base tube relies on the swage fit, and aluminum's expansion outpaces steel's as temperature climbs, gradually easing that fit. Above the ceiling, welded fin constructions take over; see the hub's fin-type table.