Corrosion and material selection
Pick materials for the site's exposure, and avoid metals that corrode each other.
REFCorrosion & Material Selection
Exposure categories and dissimilar-metal contact.
Exposure guidance — indicative; the project specification governs
| ISO 9223 | Corrosivity | Typical exterior environment | Material / finish guidance |
|---|---|---|---|
| C1 | Very low | Heated, dry interiors | Any; 430 stainless interior only |
| C2 | Low | Rural, low pollution; dry unheated interiors | 304 · anodise class 15 · polyester powder |
| C3 | Medium | Urban, moderate SO₂; low-salinity coast | 304 / 316 · anodise class 20 · · |
| C4 | High | Industrial; coastal, moderate salinity | 316L · anodise 20–25 · PVDF · HDG + paint |
| C5 | Very high | Humid industrial; high-salinity coast | 316L / 2205 · anodise 25 · PVDF 3-coat / |
| CX | Extreme | Offshore, splash zones, tropical extremes | 2205 or higher · specialist systems |
Dissimilar-metal contact
| Contact pair | Risk | Mitigation |
|---|---|---|
| Aluminium + SS fasteners | Low | Fine when fastener area is small; isolate in wet or coastal zones |
| Aluminium + copper / brass | High | Isolate fully; keep copper run-off off aluminium |
| Aluminium + carbon steel | High | Isolate; galvanise or paint the steel |
| Galvanised steel + copper | High | Isolate; prevent run-off onto zinc |
| Galvanised steel + stainless | Medium | Isolating washers and pads; keep stainless parts small |
| Carbon steel + stainless | Medium | Carbon steel corrodes — isolate and coat it |
Need help specifying?
Send us your drawing or specification and we will check the grade, finish and standard before quoting.
Polyvinylidene fluoride coating. A 70 % PVDF resin system is the standard high-durability façade coating.
Fluoro-ethylene vinyl ether. A fluoropolymer coating that allows high gloss and vivid colours.
Hot-dip galvanised: steel coated by immersion in molten zinc.