Aluminized vs Galvanized Corrugated Steel Arch Pipes: Which Coating Lasts Longer?

Aohong Factory — Metal Structure Engineer Hu Bin

1. The Short Answer First

For corrugated steel arch pipes, also called galvanized corrugated steel arch culverts or metal corrugated arch pipes:

• Pure water, weak acid, high humidity → choose galvanized.

• Saline, alkaline, SO₂ fumes, high temperature → choose aluminized.

• Want both zinc’s sacrificial protection and aluminum’s barrier film? Use Zn-Al-Mg coating. Yes, it costs more upfront. But over 30 years of no maintenance, the annual cost ends up being lower.

2. What Are These Coatings?

Galvanized Coating

• Process: After annealing, immersion in molten zinc at 460 °C forms a pure zinc layer and Fe-Zn alloy layer. Typical thickness: 40–60 μm (Z600).

• Zinc has a lower electrochemical potential than steel. This means it corrodes first, acting as a “sacrificial anode.”

• Weakness: Poor alkaline resistance. At pH > 11, the corrosion rate triples. Above 60 °C in humid environments, white rust appears within a short period.

Aluminized (55% Al-Zn, known as “GL” coating)

• Process: A molten 55% Al-Zn bath at 600 °C creates Al-rich dendrites and Zn-rich cells. A dense Al₂O₃ passive film covers these.

• Mechanism: Aluminum builds a barrier oxide film, blocking oxygen, salt, and sulfur. The cells use zinc for backup protection. If the film gets scratched, the zinc helps prevent damage.

• Weakness: Vulnerable to chloride pitting. At tight bends, cracks form at the coating edge. Once exposed, red rust spreads quickly.

3. Real-World Case Comparisons

• Chenzhou, Hunan (Underground Drainage Arch, Φ3000 mm):

  • Groundwater pH: 6.8

  • Temperature: 18 °C

  • Installed: 2016

  • Materials: Galvanized (Z450) vs. Aluminized (GL150)

  By 2024:

  • Galvanized: 35% white rust, 2 perforations.

  • Aluminized: less than 5% rust, no penetration.

  → Winner: aluminized in neutral freshwater.

• Weifang, Shandong (Salt Yard Access Road, Φ2000 mm): Salt spray deposition is 3.2 mg/100cm² per day. In winter, we also use de-icing salt. Galvanized (Z275) had red rust bands within 3 years; aluminized (GL275) after 7 years had <1% rust. But bending edges had “black rust” pitting, requiring an epoxy seal to avoid breakout at year 10. → Winner: aluminized with edge sealing.

• Shanxi Power Plant (Flue Desulfurization Duct, Φ1500 mm): Flue gas 90–130 °C, SO₂ + NH₃, condensate pH 3–4. Galvanized lost its shine in 6 months and pitted after 1 year. Aluminized stayed shiny for 2 years, but the weld HAZ had pinholes. Final scheme: aluminized + sprayed zinc on weld + silicone seal. Ran for 6 years with no maintenance. → Winner: aluminized hybrid system.

• Tibet Plateau Tunnel (Φ3500 mm, drainage behind lining):

  • UV radiation is strong.

  • Temperature swings reach 35°C.

  • Drainage water has a pH of 12.

  Aluminized dissolved in alkaline water, blistered in 3 years. Galvanized had heavy white rust but only <0.1 mm penetration after 10 years. → Winner: galvanized in strong alkaline water.

4. Quick Selection Table (Print for Jobsite)

5. Installation & Construction Notes

• Seal cut edges with galvanized zinc-rich spray or Al-Zn epoxy. Make sure the width is at least 20 mm and the thickness is 40 μm or more.

• Bolt holes: pre-punched in the factory. Flame cutting removes 5 mm of coating; rust appears within two years.

• Lifting: use nylon straps, never bare steel wire — microcracks may form in the coating.

• Backfill: wash sea sand with Cl⁻ >0.05% to <0.02%, or aluminized pipes will fail.

• Grounding: Direct contact between aluminized pipes and copper bars leads to galvanic corrosion. Use a 304 stainless steel transition plate. Also, keep the potential difference under 50 mV to prevent this.

6. Cost Quick-Check (Sep 2025 Ex-works Prices)

Example: Φ2000 mm corrugated steel arch pipe, 180 kg/m. Aluminized costs +47 RMB/m. With 30 years maintenance-free, average is only 1.6 RMB/m/year, half the cost of painted systems.

7. Final Takeaway

“Match the environment, seal all cut edges, and use proper backfill.” Follow these three rules. Galvanized corrugated steel arch pipes last 20 years. Aluminized arches last 30 years. Ignore them, and no coating will save poor installation.