Wastewater Treatment Plants (H₂S)
Why H₂S is so hard on copper
Hydrogen sulphide reacts with copper even at low concentrations, forming a black copper sulphide layer that does not protect the metal underneath. Copper tubes thin, return bends and brazed joints leak, and on copper-tube coils the fin collars lose contact.
Where H₂S is oxidised by bacteria on wet surfaces, sulphuric acid forms as well, which attacks aluminium fins and steel casings.
Plant areas are not equal
H₂S is released where sewage is agitated or sludge is stored and treated. Equipment next to inlet works, sludge thickening and dewatering, and odour-control units sees the highest levels. Office and control buildings are exposed through their outdoor-air intakes.
ISO 9223 corrosivity category
Typical category for this environment: C4–C5.
- C1Very low
- C2Low
- C3Medium
- C4High
- C5Very high
- CXExtreme
Recommended protection by plant area
| Condition | ISO 9223 | Recommended system | Note |
|---|---|---|---|
| Inlet works, sludge handling, odour control | C5 | PG-C Air-dry 2K | Highest H₂S levels; review coil material too. |
| Other outdoor units on site | C4 | PG-C Air-dry 2K | H₂S drifts across the site with the wind. |
| Control rooms and offices (filtered air) | C4 | PG-S1 Polysiloxane sol-gel | Outdoor air intakes carry H₂S indoors. |
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
- EnvironmentsIndustrial Atmospheres (SO₂, NOx, Chlorides)
- ComparisonsCoated Cu-Al Coils vs Copper-Fin Coils
- GuidesWhy Do Coil Coatings Fail?
- CoatingsWaterborne Polysiloxane (Sol-Gel) Coil Coating
Also see
Are copper-fin coils better at wastewater plants?
No. Copper-fin coils remove the copper–aluminium couple but put more copper into an atmosphere that attacks copper. Coating is needed either way.
Does ISO 9223 cover H₂S?
Not directly. ISO 9223 is based on sulphur dioxide and chlorides. For electronics, ISA-71.04 classifies gaseous contaminants including H₂S; for coils, treat sites with noticeable H₂S as at least C5.
Tell us the equipment, the site and the destination port. We reply within 24 hours.