A titanium-aluminium composite tube is a bimetallic heat-exchanger tube with a titanium inner tube and a continuous aluminium outer layer. The titanium resists seawater, brine and other corrosive media flowing inside the tube, while the aluminium spreads heat and can be rolled into integral fins on the outside. This guide explains how the tube is built, where it makes sense, where it does not, and how the aluminium side should be specified. Metline supplies the aluminium materials used for the outer layer and fins, and all-aluminium tube alternatives; we do not supply titanium.
The tube is two separate metals, not an alloy. A thin-walled titanium tube (usually commercially pure Grade 1 or Grade 2) forms the bore and touches the tube-side fluid. Around it, a layer of soft, high-conductivity aluminium is pressed or drawn on so tightly that the two act as one tube for heat transfer. The outer aluminium can stay plain or be cold-rolled into helical fins.
The idea is to put each metal where it does best. Titanium is almost immune to chloride corrosion and erosion in seawater, but it conducts heat poorly, is expensive and is hard to form into fins. Aluminium conducts heat about ten times better than titanium, is light, inexpensive and very easy to form, but it would corrode quickly in seawater or brine. A composite tube keeps the corrosive fluid on the titanium and gives the outside of the tube an aluminium surface.
| Heat path | Material | Role |
|---|---|---|
| 1. Tube-side fluid | Seawater, brine, cooling water | Corrosive medium that must stay inside |
| 2. Inner tube | Titanium Grade 1 / 2 | Corrosion barrier and pressure boundary |
| 3. Interface | Mechanical or metallurgical bond | Must stay tight for good heat transfer |
| 4. Outer layer | Aluminium 1050 / 1060 / 1070 | Spreads heat, forms fins, reduces weight |
| 5. Shell-side medium | Air, refrigerant, mild process fluid | Must be compatible with aluminium |
Do not confuse this product with "titanium aluminide" (TiAl) or titanium alloys containing aluminium such as Ti-6Al-4V. Those are single alloys; a composite tube is a layered bimetal.
The aluminium layer is left smooth. Used where the outside is a condensing or boiling refrigerant, or where the tube is later formed, bent or assembled with separate fins. The aluminium gives a surface that is easier to join and expand than titanium.
A thick aluminium sleeve is cold-rolled into helical fins, in the same way as the bimetallic extruded-fin tubes long used in air-cooled heat exchangers with steel or copper liners. The fins are part of the sleeve, so there is no fin-to-tube gap to loosen or corrode.
A bare titanium tube with wound, L-foot, embedded or plate fins attached afterwards. A mature alternative, but the fin root contact is less intimate than an integral fin.
Typical finished outside diameters for composite tubes are around 19.5 – 40 mm, with titanium walls in the region of 0.8 – 1.2 mm. The aluminium layer thickness depends on finished OD and on how much metal is needed to roll the fins. Fin height, pitch (fins per inch), fin OD, effective finned length and the length of plain ends are set by the heat-exchanger design.
The aluminium side is where Metline is involved. It is normally a 1xxx commercially pure grade because these combine the highest thermal conductivity with the ductility needed to roll deep fins without cracking.
| Grade | Aluminium content | Typical thermal conductivity (O temper) | Why it is used |
|---|---|---|---|
| 1050 / EN AW-1050A | 99.5 % min | About 230 W/m·K | Widely available, good fin-forming |
| 1060 | 99.6 % min | About 234 W/m·K | Common fin and sleeve grade, slightly higher conductivity |
| 1070 / EN AW-1070A | 99.7 % min | About 230 W/m·K | Highest purity of the three, very ductile |
| 3003 (for comparison) | Al-Mn | About 190 W/m·K | Stronger fins, used where fin damage is a concern; harder to roll deep fins |
| Titanium Grade 2 (for comparison) | — | About 16 – 22 W/m·K | Shows why titanium alone makes a poor fin |
| Option | Outside surface | External corrosion resistance | Fin forming | Relative titanium use |
|---|---|---|---|---|
| Titanium-aluminium composite | Aluminium, plain or integral fins | Depends on the aluminium-side environment | Easy (rolled from aluminium) | Liner only |
| Solid titanium plain tube | Titanium | Excellent | None | Whole tube |
| Solid titanium integral-fin tube | Titanium fins | Excellent | Difficult, low fins only | Whole tube |
| Titanium tube + attached aluminium fins | Aluminium fins | Depends on aluminium side | Mature processes | Base tube |
| All-aluminium tube | Aluminium | Good in air and refrigerants | Easy | None |
Aluminium expands about 23 µm/m·K and titanium about 9 µm/m·K. When the tube heats up, the aluminium grows away from the titanium and contact pressure falls. Manufacturers of bimetallic finned tubes therefore state a maximum operating temperature for each construction; confirm it before design.
Heat transfer depends on intimate contact at the interface. Ask how bond integrity is checked, for example by sectioning samples, push-out tests or thermal performance tests.
Where the tube enters the tube sheet, the aluminium is usually removed to expose titanium for expansion or welding. The bare transition must be sealed or kept out of the corrosive fluid.
Titanium is far more noble than aluminium. If both metals are wetted by the same electrolyte, for example at a damaged tube end or by salty condensate, the aluminium will corrode rapidly. Keep the aluminium side dry or in a non-conducting medium and protect transitions.
U-bending finned tubes requires plain sections at the bend. The aluminium layer can be expanded and bent easily, but the titanium liner sets the minimum bend radius.
Titanium heat-exchanger tube standards such as ASTM B338 (plain) and ASTM B891 (integral-fin) cover the titanium tube only. Define the complete composite tube by a project specification that references them for the liner and an aluminium standard for the sleeve.
A typical example is a seawater-source heat pump evaporator. A copper-nickel tube would be cheaper but can suffer erosion and sulphide attack in polluted harbour water; a solid titanium finned tube would be expensive and has only low fins. A titanium liner with a rolled aluminium fin sleeve gives the corrosion resistance of titanium on the water side with the large external surface of aluminium on the refrigerant side.
Where the tube-side fluid is not chloride-rich, an all-aluminium tube is lighter and much cheaper than any titanium construction. Common choices include 3003 and 1xxx seamless tube for refrigerant circuits, inner-grooved tube for evaporators and condensers, microchannel flat tube for compact coils and aluminium finned tube for air coolers. These are aluminium products Metline supplies directly, with mill certificates and export packing.
No. It is two separate layers, titanium inside and aluminium outside, bonded mechanically or metallurgically. Alloys such as Ti-6Al-4V or titanium aluminide are single materials with completely different uses.
Inside. The titanium bore is the corrosion-resistant surface. The aluminium outside suits air, refrigerants and other mild media; seawater, salt spray or chloride-rich condensate on the outside will attack the aluminium.
Aluminium conducts heat roughly ten times better than titanium, is far easier to roll into tall fins and costs much less. Titanium fins are possible but limited to low fin heights and are expensive.
Mainly differential thermal expansion. Aluminium expands about two and a half times as much as titanium, so at high temperatures the outer layer loosens and heat transfer falls. Each manufacturer qualifies a maximum temperature for its construction.
Only to the titanium liner. The complete tube needs a project specification covering the aluminium layer, the bond, dimensions, fin geometry and inspection.
Metline supplies aluminium only. We provide the aluminium side, such as 1050, 1060 or 1070 sleeve tube and fin strip, and all-aluminium heat-exchanger tubes. The titanium liner and composite manufacture are sourced by the tube maker.
Tell us the grade, form and size of aluminium sleeve, fin strip or heat-exchanger tube you need. We reply with availability, certification and a delivered price.
