Industrial Atmospheres (SO₂, NOx, Chlorides)
How pollution attacks coils
Sulphur dioxide dissolves in the moisture film on fins and tubes and forms sulphurous and sulphuric acids. Nitrogen oxides form nitric acid in the same way. The acidic film attacks both aluminium and copper, and the corrosion products absorb more moisture, which keeps the surface wet.
ISO 9223 uses sulphur dioxide deposition, together with chloride deposition, temperature and humidity, to estimate a site’s category.
Where to move up to a chemical-resistant film
A thin film protects well against general industrial air. Where the site has measurable acid gases, ammonia, or splash from process chemicals, the thicker air-dry chemical-resistant system is the safer choice, accepting its higher film build.
ISO 9223 corrosivity category
Typical category for this environment: C3–C5.
- C1Very low
- C2Low
- C3Medium
- C4High
- C5Very high
- CXExtreme
Recommended protection by site
| Condition | ISO 9223 | Recommended system | Note |
|---|---|---|---|
| Urban and light industrial | C3 | PG-W Waterborne 2K | |
| Industrial estate, heavy traffic | C4 | PG-S1 Polysiloxane sol-gel | Thin film applied by dip before installation. |
| Port or coastal industrial zone | C5 | PG-S1 Polysiloxane sol-gel | PG-C where acid gases are measured on site. |
| Refinery, chemical plant, acid gases or splash | C5 | PG-C Air-dry 2K | Thicker chemical-resistant film. |
Not sure which category your site falls into?
Enter distance from the sea, humidity and nearby industry to get an estimated ISO 9223 category.
Related
- CoatingsAir-Dry Two-Component Chemical-Resistant Coating
- EquipmentCopper Tube, Aluminium Fin Coil Protection
- EnvironmentsWastewater Treatment Plants (H₂S)
- MarketsCoil Coating for HVAC Projects in the Middle East and Gulf
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- GuidesCan One Coating Handle Salt and Industrial Pollution Together?
Also see
- CoatingsWaterborne Polysiloxane (Sol-Gel) Coil Coating
- EquipmentCondenser Coil Anti-Corrosion Coating
- EnvironmentsCoastal HVAC Corrosion by Distance from the Sea
- MarketsCoil Coating for HVAC Projects in Central Asia
- ComparisonsPhenolic vs Epoxy Coatings
- GuidesHow to Select a Coil Coating for Your Project
- CoatingsWaterborne Two-Component Coil Coatings
- EquipmentAir-Cooled Chiller Coil Protection
- EnvironmentsMining and Mineral Processing Sites
- MarketsCoil Coating for HVAC Projects in North America
- GuidesWhy Do Coil Coatings Fail?
Which is worse for coils, salt or industrial pollution?
Both are serious, and together they are worse than either alone. Salt keeps the surface wet and conductive; acid gases lower the pH of that film.
How do I know if acid gases are present?
Look for nearby refineries, chemical plants, fertiliser plants, smelters or coal-fired plants, and check local air-quality data. Send what you have with the enquiry.
Tell us the equipment, the site and the destination port. We reply within 24 hours.