Aluminum vs Steel Compressed Air Piping – Air Compressor Manufacturers

Carbon steel rusts, aluminum alloy doesn't. Compressed air pipe material selection, core issue is just this.

Infrastructure

Compressed Air Distribution Network

Compressed air has water in it. Compressor draws from environment, water vapor in the air goes in too, compression process raises temperature, water vapor stays gaseous, gets to receiver and piping where temperature drops, water condenses out. Install a refrigerated dryer and it removes most, but not all. Pipe ends where temp is low and flow is slow, water vapor keeps condensing; low spots accumulate water that won't drain; long-unused branch pipes are damp inside. Carbon steel plus water equals rust, no exceptions.

Once rust starts it doesn't stop. Rust layer is loose and porous, moisture seeps in and corrodes metal underneath, new rust layer is also loose, keeps rotting inward. Cut open carbon steel pipe used six or seven years and look, inner wall has rust nodules in clumps, some spots have lost a third of wall thickness. Rust scale breaks off and runs downstream with airflow, filters clog faster, cylinder seals wear, solenoid valves stick, paint job surfaces show particles. Troubleshooting this stuff is tedious, maintenance people usually replace parts first, replace valves, replace filters, go around in circles still not fixed, finally think to check the pipes. There was an auto parts plant, pneumatic equipment kept failing every few days, fixed for over half a year couldn't get it right, later cut open a section of main pipe, inside was rusted beyond recognition, replaced a batch of pipes and then things settled down.

Aluminum alloy is completely different situation. Aluminum surface contacts air and oxidizes forming aluminum oxide film, this film is very thin, a few microns, invisible to naked eye, but very dense, isolates the metal underneath from environment, oxidation process stops there. Film gets damaged it self-repairs. Aluminum alloy pipe installed for ten or twenty years, inner wall not much different from new. Outer wall too, carbon steel pipe outside needs anti-corrosion paint, touch up every few years, aluminum alloy pipe needs no treatment inside or out.

0.05mm

Steel Roughness

0.002mm

Aluminum Roughness

40%+

Pressure Drop Increase

$5-7K

Annual Energy Diff

Pipe inner wall roughness directly affects pressure drop. New carbon steel pipe inner wall roughness about 0.05mm, aluminum alloy pipe 0.002mm. When pipes are new this gap isn't too extreme, problem is carbon steel pipe roughness increases. Rust accumulates, inner wall gets rougher, 0.1mm, 0.15mm all possible. Roughness and pressure drop aren't linear relationship, roughness doubles and pressure drop increases even more. Measured some old pipes, used seven or eight years, pressure drop over 40% higher than design value. End equipment needs 6 bar working pressure, pipe pressure drop is high, compressor has to push higher. 1 bar pressure difference corresponds to about 7% energy consumption difference, 75kW compressor over a year that's $5,000-7,000 difference in electricity. Aluminum alloy pipe inner wall roughness basically doesn't change, pressure drop maintains initial level.

Steel Installation

Welding Required

Aluminum Installation

Quick-Connect Fittings

Installation differences are big. Carbon steel pipe main lines mostly welded, welding needs welder cert, needs hot work permit, needs gas bottles and welding machine, after welding need to clean slag, some projects also require X-ray testing. Thread connections need threading machine, large diameter flange connections need rigging coordination. This whole process takes time. Aluminum alloy pipe uses quick-connect fittings, cut the pipe, insert, tighten, O-ring seal, no welding no hot work, regular maintenance worker reads the instructions and can install. Weight is also way different, same spec pipe carbon steel weighs about three times aluminum alloy. 6-meter length DN100 pipe, carbon steel two people carrying up scaffolding is quite a job, aluminum alloy one person shoulders it up no problem. Support spacing can stretch out, fewer hanging points to install. Project timeline can differ by half to two-thirds.

Future pipe modifications is something lots of people don't consider during selection. Production line adjustments, equipment adds and removes, process changes, pipes get modified all the time. Carbon steel pipe modifications need to shut off air and depressurize, get hot work permits, wait for welder availability, after modifications need pressure test and leak check, sometimes a small change drags one to two weeks. Aluminum alloy pipe disconnect fittings and reconfigure, some situations can even do it under pressure, finish same day. R&D companies, contract manufacturers with fluctuating orders, modifying pipes several times a year is normal, each time stopping production waiting for welder, lost money is more than the pipes themselves cost.

Material purchase price for aluminum alloy pipe is higher, 50% to double more expensive. Compare only material cost and carbon steel is definitely cheaper. Add installation cost and it's a different story. Welder labor is expensive, welding consumables cost money, hot work approval has hidden costs, long project timeline with other trades waiting is also cost. Aluminum alloy pipe installation is just regular worker labor plus pipe cutter wear. Bigger the project, higher percentage installation cost is of total, for projects with kilometers of pipe, two approaches total price is similar or aluminum alloy might even be lower.

Long-term operations carbon steel pipe has lots of money pits: outer wall anti-corrosion touch-ups every few years, wall thickness testing to assess remaining life, pressure drop increases meaning electricity bill increases, rust scale causing downstream equipment failures and repairs, rusted-through pipe sections needing partial replacement. Aluminum alloy pipe basically has none of these expenses, just fitting O-rings might need replacing after ten-plus years.

When to choose carbon steel pipe? Budget only looks at first cost, leased facility not sure about renewal, temporary use for a few years then dismantling, environment is very dry with little condensate, need non-standard specs custom fabricated on-site, have your own welding crew so installation cost is low. Other than that, aluminum alloy pipe is the better deal in most cases. Food, pharma, electronics industries with high air cleanliness requirements, aluminum alloy pipe is almost mandatory.

Industry

Pharmaceutical

Industry

Food Processing

Industry

Electronics

Other pipe materials have narrow selection. Stainless steel pipe is most corrosion resistant, also most expensive, pharma clean areas, semiconductor fabs will use it, regular industrial doesn't need it. Galvanized steel pipe used to be common, not recommended now, galvanizing layer flakes off, zinc flakes are harder to deal with than rust. Copper pipe suits small diameter instrument air and control air lines, large diameter cost is too high. PPR pipe has limited pressure and temp ratings, can't use for main systems.

Retrofit projects note one thing: partial pipe replacement try to match original system material. Aluminum alloy and carbon steel in direct contact will have galvanic corrosion, rusts faster than single material, if connecting put insulating piece in between to isolate. Complete system replacement is another matter, original carbon steel pipe used eight or ten years with pile of problems, switching to aluminum alloy is an option.