Aluminium Compressed Air Piping Systems

Why plants are moving compressed air lines to aluminium

Compressed air is one of the most expensive utilities in a factory: most of the electrical energy a compressor uses becomes heat, and only a small fraction reaches the tools as useful work. Anything that wastes air or pressure between the compressor and the point of use, such as leaks, rough corroded pipe or undersized lines, adds directly to the electricity bill.

Traditional black or galvanised steel pipe corrodes internally because compressed air always carries some moisture. Rust scale roughens the bore, raises pressure drop, flakes off into filters and tools, and threaded joints loosen over time and leak. Copper avoids rust but is expensive and must be brazed. Plastic pipes are cheap but have limited temperature and pressure capability and some types are prohibited for compressed air because of brittle failure.

Aluminium tube solves most of these problems. Its natural oxide film, thickened by anodising or protected by powder coating, prevents rust inside and out, so the bore stays smooth and air quality remains high. The tube is light enough for one person to lift a 6 m length, and modular fittings let a line be built, extended or re-routed in hours without hot work. For these reasons aluminium has become the default for new compressed air, vacuum and inert gas networks in automotive plants, food and pharmaceutical factories, workshops and laboratories.

Components of an aluminium compressed air system

Each component must be rated for the same pressure, temperature and medium. Mixing fittings from one system with pipe from another is a common cause of leaks, because tube OD tolerance, ovality and surface finish all affect how well an O-ring and gripping ring seal.

Aluminium alloys and finishes for air pipe

Minimums shown for typical wall thicknesses; exact values depend on wall thickness band and are reported on the mill certificate. Seamless tube for pressure use is often ordered to ASTM B241 or EN 755.

Pipe is normally anodised (10 – 20 µm) or powder coated on the outside for colour coding and corrosion protection. The inside is left as extruded or anodised; a clean, smooth extruded bore has a very low roughness, which is why aluminium lines show lower friction loss than steel even when new, and much lower once steel has corroded.

Colour codes are not universal. Follow national standards and the plant's own identification scheme, and add labels with medium and flow direction.

Air quality is the other reason plants choose aluminium. ISO 8573-1 classifies compressed air by particles, water and oil content, and food, pharmaceutical, electronics and paint-shop users often need high purity classes at the point of use. A dryer and filters can deliver clean air to the main, but rusting steel pipe then adds particles back downstream. Corrosion-free aluminium preserves the quality created in the compressor room, so final filters at each drop last longer and need changing less often.

Typical pipe sizes, bore area and weight

Pipe for compressed air is usually specified by outside diameter in millimetres. The table gives common sizes with representative wall thicknesses; walls vary between systems, so confirm the exact dimensions with the fittings you will use. Weights are calculated from geometry at 2.70 g/cm³.

Nominal inch sizes are often quoted alongside: 20 mm is used for 1/2 in drops, 25 mm for 3/4 in, 40 mm for 1 1/4 in, 50 mm for 1 1/2 in, 63 mm for 2 in, 76 mm for 2 1/2 in, 100 – 110 mm for 4 in and 168 mm for 6 in mains. Larger diameters of 200 mm and above are available for high-flow distribution.

Pressure and temperature ratings

Complete aluminium air piping systems are commonly rated for maximum working pressures of 13 – 16 bar (about 190 – 230 psi) at ambient temperature in small and medium diameters, with lower ratings on the largest sizes. Ratings for vacuum service down to about −0.99 bar are also typical. Allowable pressure falls as temperature rises, mainly because the polymer seals and technopolymer fitting bodies lose strength, not because of the aluminium tube.

Piping is pressure equipment in many jurisdictions. In Europe, systems fall under the Pressure Equipment Directive 2014/68/EU; elsewhere, codes such as ASME B31.3 may be applied to plant air lines. Pressure-test the completed installation before commissioning, typically with air or nitrogen at a test pressure set by the applicable code, and record the result.

How to size aluminium compressed air pipe

1. Find the flowAdd the air consumption of all tools and machines (in m³/min or cfm of free air), apply a diversity factor for those that do not run together, and allow 20 – 30 % for future growth.
2. Set the pressure-drop budgetA good target is a total drop of no more than about 0.1 – 0.2 bar from the compressor room to the furthest drop, with most of that in filters and hoses rather than the main.
3. Choose a velocityKeep air velocity in mains to roughly 6 – 10 m/s and in drop legs to around 15 m/s or less; higher velocities raise pressure drop and carry water past drains.
4. Calculate the diameterUse the flow at line pressure, the pipe length plus equivalent length of fittings, and a pressure-drop chart or calculator for smooth tube.
5. Round upIf the result falls between sizes, take the larger pipe. The cost difference is small compared with the energy saved over the system's life.

A ring main (loop) feeds every drop from two directions and halves the effective flow path, which reduces pressure drop and evens out pressure across the plant. It is the preferred layout for larger shops, with isolation valves so sections can be maintained without shutting down production.

Installation best practice

• Thermal expansion: aluminium expands about 23.6 µm per metre per °C, so a 50 m run warming by 30 °C grows by about 35 mm; use expansion loops or flexible sections and sliding supports, with one fixed point per straight run
• Supports: space brackets according to pipe size and the system manufacturer's guidance, and add supports close to valves, tees and heavy drops
• Cut square and deburr: cut with a pipe cutter or saw, chamfer the outside edge and remove burrs so O-rings are not damaged
• Mark insertion depth: mark the pipe before pushing into fittings to confirm full engagement
• Slope and drains: slope mains slightly in the direction of flow towards drain points and take drops from the top of the main (gooseneck) so water does not reach tools
• Isolate dissimilar metals: avoid direct contact with copper or steel in wet locations; use insulated supports
• Test and tag: leak-test at the specified pressure, then label medium, pressure and flow direction

Aluminium compared with steel, copper and plastic air pipe

Steel remains appropriate for very high pressures, very large diameters and hot compressor discharge lines. For the main distribution network and drops in most factories, aluminium gives the lowest total cost once installation time, leakage and energy are counted.

Related aluminium tube and pipe pages

Aluminium (aluminum) compressed air piping: frequently asked questions