Flat-oval radiator tube is the thin, welded aluminium tube that carries coolant through a brazed radiator core. It is roll-formed from brazing-clad strip, high-frequency welded and sized to a precise width, height and wall, so it joins to fins and headers in a single brazing cycle. This guide explains profiles, clad constructions, sizes, quality checks and how to specify tube for a new core or a replacement supply.
A modern aluminium radiator is a brazed sandwich of three parts: rows of flat tubes that carry coolant, corrugated louvred fins between them that shed heat to the air, and headers (tube plates) that receive the tube ends and connect to the tanks. The tube is the pressure-retaining part, so its profile, wall and weld decide how much heat the core can move and how long it survives.
A flat-oval section has two long parallel faces joined by rounded ends. The flat faces give a large contact area with the fins and a thin coolant channel, which raises the heat-transfer coefficient on the liquid side; the low height keeps the air-side pressure drop down so more air passes through the core. Compared with the round tubes used in older copper-brass radiators, a flat tube of the same cross-sectional area puts far more of its surface against the fins.
Most radiator tube is made by roll-forming brazing-clad aluminium strip into a closed shape and joining the seam by high-frequency (HF) induction welding. The outside clad layer melts during furnace brazing and becomes the filler metal that bonds tube to fin and tube to header. Other tube families, such as folded B-type tube and extruded multi-port microchannel tube, compete for the same job and are compared later in this guide.
Tube is described as width × height × wall (W × H × T) in millimetres. Width matches the core depth or one row of a multi-row core; height is the minor dimension that sets coolant channel size; wall is the strip gauge. The ranges below cover passenger-car, commercial-vehicle and off-highway radiators.
| Common section (W × H, mm) | Typical wall range (mm) | Typical use |
|---|---|---|
| 12 × 1.7 | 0.20 – 0.26 | Compact cores, heater-type cores |
| 14 × 1.6 | 0.20 – 0.26 | Small passenger-car radiators |
| 14.55 × 1.45 / 1.5 | 0.20 – 0.25 | Thin-core car radiators |
| 16 × 1.5 | 0.20 – 0.28 | Passenger-car radiators |
| 16 × 1.8 / 16 × 2.0 | 0.20 – 0.40 | Car and light-truck radiators |
| 18 × 2.0 | 0.26 – 0.35 | Light commercial vehicles |
| 20 × 1.5 / 20 × 2.0 | 0.25 – 0.30 | Single-row deeper cores |
| 22 × 1.8 / 22 × 2.0 | 0.24 – 0.40 | SUV, pick-up and van radiators |
| 23.5 × 2.0 / 26 × 2.0 | 0.25 – 0.40 | Heavier-duty single-row cores |
| 32 × 2.0 / 34 × 1.8 | 0.30 – 0.32 | Truck and bus radiators |
| 36 × 1.6 / 40 × 2.0 | 0.30 – 0.40 | Off-highway and industrial radiators |
Sections are examples of profiles commonly specified by radiator makers. Any section inside the range can be developed from a drawing or a sample tube.
Radiator tube strip is a roll-bonded composite. Each layer is a different alloy with a specific job, and the combination is chosen to suit the brazing process and the coolant and road environment the radiator will see.
Aluminium-silicon alloys that melt below the core. 4343 contains about 6.8 – 8.2 % Si and 4045 about 9.0 – 11.0 % Si; the higher silicon of 4045 gives more fluid filler and larger fillets. The clad is on the outside, where it bonds to fins and header.
The structural layer. 3003 (Al-Mn-Cu) is the standard core. 3005 adds a little magnesium for more strength after brazing, but magnesium must be kept low for flux brazing because it reacts with the fluoride flux.
An Al-Zn alloy (about 0.8 – 1.3 % Zn) on the inside of the tube. It is electrochemically more active than the core, so it corrodes preferentially and spreads attack sideways instead of letting a pit run through the wall.
| Construction (outside / core / inside) | Layer arrangement | Where it is used |
|---|---|---|
| 4343 / 3003 / 7072 | Braze clad, 3003 core, sacrificial liner | Standard automotive radiator tube |
| 4343 / 3005 / 7072 | Braze clad, stronger 3005 core, sacrificial liner | Thinner walls or higher pressure duty |
| 4045 / 3005 / 7072 | High-Si braze clad, 3005 core, sacrificial liner | Cores that need generous fillets plus internal protection |
| 4343 / 3003 / 4343 | Braze clad on both sides | Tubes with internal inserts or turbulators that must be brazed inside |
| 4343 / 3005 / 4343 | Double-sided braze clad, 3005 core | Heavy-duty and off-highway tube profiles |
| 4045 / 3003, 4045 / 3005 | Single-sided braze clad, no liner | Cores where internal corrosion is controlled by coolant chemistry |
Clad thickness is usually expressed as a percentage of total strip thickness per side, commonly in the range of about 5 – 15 %. Too little braze clad leaves weak fillets; too much causes erosion of the thin core during brazing. Your brazing furnace profile and fin design should be considered together with the clad ratio. Metline also supplies the strip itself: see brazing clad strip and coil.
| Check | Method | What it shows |
|---|---|---|
| Section dimensions | Profile projector, micrometers | Width, height and wall within the drawing tolerance |
| Weld integrity | Online eddy-current testing | Pinholes, lack of fusion and cold welds along the full length |
| Burst pressure | Hydraulic burst test on samples | Pressure margin over the radiator design pressure |
| Weld structure | Metallographic cross-section | Weld line shape, clad continuity and absence of oxide inclusions |
| Clad ratio | Metallography of the strip | Braze clad and liner thickness as specified |
| Straightness and length | Gauge and length check | Suitability for automated core stacking |
| Brazeability | Trial brazing of mini-cores (on request) | Fillet formation and erosion under your furnace profile |
A useful habit is to agree lot traceability from strip coil to finished bundle. If a core fails in the field, the coil number lets both parties check the clad ratio and chemistry of that exact batch. Every Metline delivery carries a mill test certificate to EN 10204 3.1 for the strip material.
| Feature | HF-welded flat-oval | Folded B-type | Extruded microchannel |
|---|---|---|---|
| How it is made | Roll-formed and welded from clad strip | Folded from clad strip with a central web, no weld | Extruded multi-port section, clad by zinc spray or separate filler |
| Internal web | None (plain bore) unless an insert is added | Yes, folded centre web adds pressure strength | Many small ports |
| Typical use | Engine radiators, heater cores | Thin-wall radiators and heater cores | Condensers, evaporators, high-pressure refrigerant circuits |
| Pressure capability | Suited to coolant system pressures | Higher for the same wall | Highest; handles refrigerant pressures |
| Strip / material | 3-layer clad strip | 3-layer clad strip, often thinner | Extrusion alloys such as 1xxx or 3xxx |
For water-glycol radiators running at modest pressures, welded flat-oval tube is usually the most economical choice. Where the design pushes wall thickness down to save weight, a folded B-type tube with its internal web keeps pressure strength. For refrigerant circuits, extruded microchannel tube is standard. See the B-type tube guide and the microchannel tube guide for detail.
Single-row radiators with 16 – 26 mm tubes, thin walls and 4343/3003/7072 construction. Weight and core depth are tightly constrained.
Wider 32 – 40 mm sections and heavier walls resist pressure cycling, vibration and longer service intervals.
Cores face dust, debris and high ambient temperatures. Thicker walls and double-sided clad sections are common.
Narrow 12 – 16 mm tubes in compact cabin heaters, often with the same clad system as the main radiator.
Stationary radiators for engines, compressors and hydraulic systems, built to custom sizes.
Replacement radiator makers match OE tube sections from samples so cores fit existing tanks and headers.
If you are switching supply for an existing radiator, send two or three sample tubes. Cross-sections reveal the clad layers and their thickness, which removes most of the guesswork in matching the original.
Each layer has a job. The 4343 outer clad melts during brazing and bonds the tube to the fins and header; the 3003 core carries the pressure; the 7072 inner liner corrodes sacrificially so coolant-side pits spread sideways rather than perforating the thin wall.
Yes. A sample tube is cross-sectioned to measure width, height, wall and clad layers, and a matching section is developed. A drawing with tolerances speeds this up.
Most passenger-car tubes run 0.20 – 0.28 mm. Trucks, buses and off-highway radiators usually use 0.30 – 0.40 mm for higher pressure-cycle and erosion margin. The right figure depends on design pressure, coolant flow velocity and expected service life.
4045 has more silicon (about 9 – 11 % against 6.8 – 8.2 %), so it melts at a slightly lower temperature range and flows more freely, giving larger fillets. 4343 gives less erosion of thin cores. The choice depends on fin design and furnace profile.
Vacuum brazing normally uses magnesium-bearing filler alloys such as 4004 or 4104 rather than 4343. Tell us which brazing route you use so the clad system matches it.
Tubes are bundled by count, protected against crushing and moisture, and packed in wooden cases or crates for sea or air freight, with the mill test certificate and packing list.
Send the section, clad construction, volumes and destination, or a sample tube. We will confirm material, testing and delivery terms.
