01Atmosphere: categories C1–CX
ISO 12944-2 (GOST 34667.2) divides the atmosphere into six categories by the first-year mass and thickness loss of carbon steel. The category is set for each element: inside and outside a building, near the sea and far from it, it can differ.
| Category | Steel loss in year 1 | Exterior | Interior |
|---|---|---|---|
| C1, very low | up to 10 g/m², up to 1.3 µm | — | heated buildings with clean air: offices, shops, schools, hotels |
| C2, low | 10–200 g/m², 1.3–25 µm | low pollution, mostly rural areas | unheated buildings where condensation may occur: depots, sports halls |
| C3, medium | 200–400 g/m², 25–50 µm | urban and industrial atmosphere with moderate SO₂; coastal areas with low salinity | humid production rooms with some pollution: food plants, laundries, breweries, dairies |
| C4, high | 400–650 g/m², 50–80 µm | industrial and coastal areas with moderate salinity | chemical plants, swimming pools, coastal shipyards |
| C5, very high | 650–1500 g/m², 80–200 µm | industrial areas with high humidity and aggressive atmosphere; coastal areas with high salinity | buildings with almost permanent condensation and high pollution |
| CX, extreme | 1500–5500 g/m², 200–700 µm | offshore with high salinity; industrial areas with extreme humidity; tropics and subtropics | industrial areas with extreme humidity and aggressive atmosphere |
02Water and soil: categories Im1–Im4
| Category | Environment | Examples |
|---|---|---|
| Im1 | fresh water | river installations, hydroelectric power plants |
| Im2 | sea or brackish water without cathodic protection | harbour structures: sluice gates, locks, jetties |
| Im3 | soil | buried tanks, steel piles, pipelines |
| Im4 | sea or brackish water with cathodic protection | marine structures with cathodic protection |
Systems for immersion and splash zones are selected separately: the portal has no ready Teping® systems for Im1–Im4, so agree the build-up with our technologist.
03Durability
Durability under ISO 12944-1 is the time to the first major maintenance of the coating. It is a planning figure, not a guarantee period: a warranty is agreed separately in the contract.
| Range | Time to first major maintenance |
|---|---|
| L, low | up to 7 years |
| M, medium | 7–15 years |
| H, high | 15–25 years |
| VH, very high | more than 25 years |
04If the design follows SP 28.13330
Russian designs often give not a category but the degree of aggressiveness of the environment under SP 28.13330.2017. An approximate correspondence that helps when moving to ISO 12944:
| Degree of aggressiveness, SP 28 | Category, ISO 12944-2 |
|---|---|
| non-aggressive | C1 |
| slightly aggressive | C2–C3 |
| moderately aggressive | C4 |
| highly aggressive | C5 |
The correspondence is approximate: SP 28 also takes into account the group of aggressive gases, humidity and the type of structure. If the design states a degree of aggressiveness, send it with the conditions and our technologist will check the category.
05How coats and thickness grow
- The higher the category and the longer the durability, the higher the nominal dry film thickness and the number of coats.
- For C4–C5 and long lives a zinc-rich primer often goes first, for example Teping EP-Coat Primer Zinc: zinc protects steel cathodically even where the coating is damaged.
- An epoxy intermediate coat, for example Teping EP-Coat Mastic, builds barrier thickness in one pass.
- A topcoat, for example Teping PUR-Coat Top or Teping PU-Coat Top, shields the epoxy coats from ultraviolet light, which they do not withstand.
- Replacing one coat with another maker's product changes the system: compatibility and durability have to be confirmed again.
Ready Teping® systems with total thickness and durability by category are collected in the ISO 12944 selector.
Sources. ISO 12944, ISO 8501, ISO 8502, ISO 8503, ISO 19840, GOST 9.402, SP 28.13330 and the technical data sheets of Teping® products on tnpgroup.ru. Check project values against the current TDS.
