Aluminium Condenser Header Pipe

What a header pipe does in a condenser

In a brazed aluminium condenser, flat microchannel tubes run in parallel between two header pipes. Hot refrigerant gas enters one header, is distributed across a group of tubes, condenses as it flows through them while air passes over the louvered fins, and is collected in the opposite header. Internal baffles divide the headers into passes, so the refrigerant may cross the core several times before it leaves as liquid.

The header therefore has to do several jobs at once. It must hold the system pressure, which in R134a, R1234yf and especially R410A or R32 systems can be high, with a large safety margin for burst testing. It must accept dozens of tube ends through accurately punched slots and form leak-tight brazed joints at every one of them. It must take baffles, end caps, connection blocks and sometimes an integrated receiver-drier. And it must survive years of road salt, coastal air or industrial pollution on the outside.

All of this is done in one controlled-atmosphere brazing (CAB) cycle at about 600 °C, where the Al-Si clad on the header melts and flows by capillary action into each joint. The header material is therefore a carefully engineered clad product, not a plain aluminium tube.

Core and cladding alloys

Header pipe is usually formed and welded from clad strip. The layers are chosen as a system: the core gives strength, the braze clad provides filler metal, and the optional zinc layer protects the core by corroding first.

Typical structures are described by their layer order, for example 4343/3003 (single-side clad), 4343/3003/4343 (double-side clad) or 4343/3003/7072. Extruded headers in 3003 or 6063 are also used in some designs; these are not clad and receive filler from clad tubes, fins or added braze rings and paste.

Some sources quote 237 W/m·K for aluminium. That is the value for pure aluminium; 3003 core alloy is closer to 160 – 190 W/m·K depending on temper. For headers, conductivity is secondary to pressure strength and brazeability.

Round, D-shape, square and pre-punched headers

Common round header pipe sizes and weights

Header diameter follows the width of the microchannel tube and the refrigerant flow. Common outside diameters are about 15 – 45 mm with walls of 1.0 – 2.0 mm; thicker walls are used for high-pressure refrigerants and large commercial units. The table lists frequently used round sizes with the calculated mass per metre at a density of 2.73 g/cm³ (3003).

D-shaped headers are specified by width × height × wall, for example 20 × 18 × 1.0 mm, 25.5 × 19 × 1.2 mm or 32 × 23 × 1.2 mm. Lengths are supplied from about 300 mm cut pieces up to straight lengths of several metres, or as coils for in-line cutting. Outside diameter tolerances on welded header tube are commonly about ±0.05 – 0.10 mm, tighter than general welded tube because slot positions and fit-up depend on them.

How header pipes are made

1. Clad stripBrazing sheet is roll-bonded with the core and clad layers, rolled to gauge and slit to a precise width for the tube circumference.
2. FormingA series of roll stands forms the strip into a round tube with the clad on the required side.
3. High-frequency weldingThe edges are heated by HF current and forged together; the outside bead is scarfed flush. Weld bead width and height are controlled so slots can be punched across or near the seam.
4. Sizing and shapingSizing rolls bring the tube to final diameter; D-shape and square forms are rolled or drawn from the round tube.
5. Cutting and end formingFlying saws or cut-off dies cut to length; ends are chamfered, flared or reduced.
6. SlottingTube slots and baffle slots are punched with progressive or rotary tooling, then the pipe is cleaned and inspected.

Typical quality limits on a good header line include a flush internal weld bead (often within about 0.1 mm), straightness of about 0.5 mm per 500 mm, square cut ends, and a clean, oil-free surface that will not upset flux application or brazing.

Brazing performance and leak prevention

Most field failures of condenser headers trace back to two sources: leaks at the weld seam, and poor tube-to-header joints. Both are controlled through material and process choices.

After brazing, condensers are leak-tested (helium or pressure decay) and samples are burst-tested. Corrosion performance is usually assessed with cyclic acidified salt spray testing such as SWAAT (ASTM G85 Annex A3) or neutral salt spray (ASTM B117); specify the test and duration your OEM requires rather than relying on a generic hours figure.

Where condenser header pipes are used

Compared with copper headers in round-tube plate-fin coils, all-aluminium microchannel designs avoid galvanic couples, reduce refrigerant charge and weigh considerably less, because aluminium has roughly one-third the density of copper.

How to specify and order header pipe

1. Profile and sizeRound, D-shape or square; OD or width × height, wall thickness and tolerances.
2. Clad structureCore alloy, clad alloys and side, clad ratio, and whether a zinc layer is required.
3. Length and featuresCut length or coil, end forms, slot and baffle drawings.
4. Quality requirementsWeld bead limits, straightness, cleanliness, eddy-current testing and post-braze strength.
5. Documents and termsEN 10204 3.1 certificate with chemistry, clad ratio and mechanical results; packing and delivery terms (EXW, FOB, CIF or DAP).

Metline supplies header pipe, brazing sheet, fin stock and microchannel tube as a matched material set, so clad ratios and alloys work together in one brazing cycle, and ships worldwide in clean, export-packed cartons or cases.

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Aluminium (aluminum) condenser header pipe: FAQ