An enclosure coating is specified in two lines and judged by eye. The two lines decide whether the steel survives twenty years on a coastal site, and neither of them is the RAL number.
ISO 12944 is the series for corrosion protection of steel structures by protective paint systems. Four of its parts carry the weight in an enclosure specification: Part 1 for durability, Part 2 for the corrosivity of the environment, Part 4 for surface preparation and Part 5 for the paint systems themselves. Part 5 is in its fourth edition, approved on 27 September 2019.
Start with the environment, not the finish
Part 2 classifies atmospheric corrosivity into categories. The category is a property of the site, not a preference.
| Category | Typical exterior environment |
|---|---|
| C1 | Interior only — heated buildings with clean atmospheres |
| C2 | Low pollution, mostly rural |
| C3 | Urban and industrial atmospheres with moderate sulfur dioxide; coastal areas of low salinity |
| C4 | Industrial areas, and coastal areas of moderate salinity |
| C5 | Industrial areas of high humidity and aggressive atmosphere; coastal areas of high salinity |
| CX | Offshore with high salinity; industrial areas of extreme humidity and aggressive atmosphere; subtropical and tropical atmospheres |
Durability is a planning range, not a warranty
Part 1 defines durability ranges: low is under 7 years, medium is 7 to 15, high is 15 to 25, and very high is more than 25. The range is the expected time to first major maintenance, under the stated corrosivity category, for a system applied and maintained as specified. It depends on coating technology, structure design, substrate preparation, application quality and actual exposure.
It is not a guarantee period and no supplier should be asked to warrant it as one. The useful discipline is the opposite: state the durability range you are designing for, and then accept that the specification has to pay for it in surface preparation and film thickness rather than in contract language.
Where enclosure work differs from the standard’s subject
ISO 12944 addresses protective paint systems on steel structures. Switchgear enclosures are generally polyester powder coating over pretreated sheet steel, often galvanized, indoors. The series is routinely quoted on enclosures by analogy, and the analogy is useful but not exact. Being explicit about this in a specification avoids an argument at inspection:
- Name the category and durability from ISO 12944-2 and -1 as the performance target. That part transfers cleanly.
- Specify the pretreatment process rather than leaving it to the coater. Degrease, conversion coating, rinse and dry: this sequence, not the topcoat, is what decides whether the film is still attached in year ten. The overwhelming majority of coating failures on enclosures are adhesion failures originating in pretreatment.
- Specify the surface preparation grade where a liquid system over blasted steel is used, referencing ISO 12944-4 and the cleanliness grade required.
- Specify film thickness and how it is measured — minimum and mean dry film thickness, measured to ISO 2808, with the number of readings per enclosure stated.
- Specify the acceptance tests — adhesion by cross-cut to ISO 2409 or pull-off to ISO 4624, and neutral salt spray to ISO 9227 with the duration stated. A salt-spray duration with no stated acceptance criterion is not a test.
What this looks like as a specification line
| Instead of | Write |
|---|---|
| “Powder coated RAL 7035” | Category, durability range, pretreatment process, minimum and mean DFT, finish and color |
| “To ISO 12944” | The parts relied on, and ISO 12944-9 where the category is CX |
| “Salt spray tested” | Neutral salt spray to ISO 9227, duration in hours, acceptance criterion stated |
| “Good adhesion” | Cross-cut to ISO 2409 at a stated classification, or pull-off to ISO 4624 at a stated value |
| “Galvanized where required” | Where galvanized substrate is used, and the pretreatment appropriate to it |
| Nothing about touch-up | The repair procedure for transport and installation damage, and who performs it |
Where we stand
Fabrication and coating are being brought in-house through 2026, which is the single change that moves most of our cost base and our local content position at once. Welder and coating qualifications are confirmed against the scope of work at enquiry stage rather than assumed, the extension of our ISO 9001, 14001 and 45001 scope to the fabrication and coating line is in progress alongside the line itself, and a Schneider Electric audit qualifying the line for licensed enclosure work is scheduled as it is commissioned. The documentation register states where each of those stands, with dates rather than assurances.