Selecting Protective Coating Systems
ISO 12944 - the universally accepted standard for corrosion protection
Steel should be protected not only from the service environment but also for the proposed lifetime of a structure.
The standard is designed as a guideline in choosing the correct systems to meet the demands of both environment and service life.
Protecting steel structures from corrosion is one of Mengneng’s core expertise and strengths. We protect a wide spectrum of assets from the harshest conditions imagined all year-round for almost any surfaces. With vast experience and expertise globally, Mengneng has coating systems to meet the exact anticorrosive requirements for every situation.
1、Select Environment
Consult the table below to select the most appropriate classification for your project.
| Corrosivity Categories | Exterior | Interior | |
|---|---|---|---|
| C1 | very low | – | Heated buildings in rural areas such as offices, hotels, public buildings |
| C2 | low | Rural areas with low level of pollution. | Unheated buildings where condensation may occur such as warehouses. |
| C3 | medium | Urban and industrial areas with moderate sulphur dioxide pollution. Coastal areas with low salinity. | Industrial facilities with high humidity such as food processing industries, breweries. |
| C4 | high | Industrial and/or coastal areas with moderate salinity. | Chemical plants, swimming pools, boat yards, ship interiors. |
| C5 | very high | Industrial areas prone to high humidity and chemical attack. Coastal areas with high salinity. | Facilities exposed to permanent condensation and chemicals. |
| CX | extreme | Offshore areas with high salinity. Industrial areas exposed to extreme humidity, aggressive atmosphere and tropical areas. | Facilities exposed to extreme humidity and aggressive atmosphere. |
| Note: In previous versions of ISO 12944, the C5 category was split in Marine (C5M) and Industrial (C5I), part 6 requiring additional tests for the industrial (chemical) exposure. Therefore, in older documents C5 M may not refer to C5 medium durability and C5I should not be misread as C5 low durability (C5 L, using the capital letter L instead of lower-case l). | |||
| Category Environment | Examples of environments and structures | |
| Im1 | Fresh water | River installations, hydro-electrical power plants |
| Im2 | Sea or brackish water | Immersed structures without cathodic protection (e.g. harbour areas with structures like sluice gates, locks or jetties) |
| Im3 | Soil | Buried tanks, steel piles, steel pipes |
| Im4 | Sea or brackish water | Immersed structures with cathodic protection (e.g. offshore structures) |
| Note: for corrosivity category Im1 and Im3, cathodic protection can be used with a paint system that has been tested accordingly | ||
|---|---|---|
2、Select Durability
In short, the ISO 12944 standard proposes coating systems for carbon steel and galvanized steel depending on exposure conditions. It also includes a list of laboratory tests to confirm suitability of coating systems, more on the that further down on this page.
Where coated steel is used, i.e. what corrosive environment it will be exposed to, has a major influence on how long a coating system will last: the durability. In the standard, durability dictates coating type and the minimum film thickness. In ISO 12944, four ranges of durability are used as period to first major maintenance:
| Durability | Years to first major maintenance | |
|---|---|---|
| L | Low | up to 7 years |
| M | Medium | 7 years to 15 years |
| H | High | 15 years to 25 years |
| VH | Very high | more than 25 years |
| Note：the durability range is not a “guarantee time”. | ||
3、Select Coating System
Coating system requirements for C1,C2,C3,C4,C5 in line with ISO 12944-5
| Durability | Low (l) | Medium (m) | High (h) | Very high (vh) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Type of prime r 1 | Zn(R) | Misc | Zn(R) | Misc | Zn(R) | Misc | Zn(R) | Misc | |||||
|
Binder chemistry of primer 1 |
ESI, EP, PUR | EP, PUR, ESI | AK, AY | ESI, EP, PUR | EP, PUR, ESI | AK,AY | ESI, EP, PUR | EP, PUR, ESI | AK,AY | ESI, EP, PUR | EP, PUR, ESI | AK,AY | |
| Binder chemistry of subsequent coats | EP, PUR2, AY | EP, PUR2, AY | AK, AY | EP, PUR2, AY | EP, PUR2, AY | AK, AY | EP, PUR2, AY | EP, PUR2, AY | AK, AY | EP, PUR2, AY | EP, PUR2, AY | AK, AY | |
| C2 | Number of Coats | – | – | – | 1 | 1 | 1 | 1 | 2 | 2 | 2 | ||
| Dry Film Thickness | Note 3 | – | – | 100 | 60 | 120 | 160 | 160 | 180 | 200 | |||
| C3 | Number of Coats | – | – | 1 | 1 | 1 | 1 | 2 | 2 | 2 | 2 | 2 | – |
| Dry Film Thickness | – | – | 100 | 60 | 120 | 160 | 160 | 180 | 200 | 200 | 240 | – | |
| C4 | Number of Coats | 1 | 1 | 1 | 2 | 2 | 2 | 2 | 2 | 2 | 3 | 2 | – |
| Dry Film Thickness | 60 | 120 | 160 | 160 | 180 | 200 | 200 | 240 | 260 | 260 | 300 | – | |
| C5 | Number of Coats | 2 | 2 | – | 2 | 2 | – | 3 | 2 | – | 3 | 3 | – |
| Dry Film Thickness | 160 | 180 | – | 200 | 240 | – | 260 | 300 | – | 320 | 360 | – | |
|
Note 1: Zn(R)= zinc-rich, Misc. = miscellaneous primer, see text, ESI = zinc silicate, EP = epoxy, PUR = polyurethane, AK = alkyd, AY = acrylic (mainly water based) Note 2: in addition to polyurethane technology, other coating technologies may be suitable, e.g. polysiloxane, polyaspartic and fluoropolymer Note 3: if a coating is desired (for C2-low), use a system for higher corrosivity category or durability, e.g. C2-high or C3-medium |
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Coating system requirements for Im1, Im2 and Im3 in line with ISO 12944-5
| Durability | High | Very High | ||||
|---|---|---|---|---|---|---|
| Type of prime r 4 | Zn(R) | Misc. | N/A | Zn(R) | Misc. | N/A |
|
Binder chemistry of primer 4 |
ESI, EP, PUR | EP, PUR | – | ESI, EP, PUR | EP, PUR | – |
| Binder base of subsequent coats | EP, PUR | EP, PUR | EP, PUR | EP, PUR | EP, PUR | EP, PUR |
| Minimum number of coats | 2 | 2 | 1 | 2 | 2 | 1 |
| Dry Film Thickness | 360μm | 380μm | 400μm | 500μm | 540μm | 600μm |
| Note 4: Zn(R)= zinc-rich, Misc. = miscellaneous primer, ESI = zinc silicate, EP = epoxy, PUR = polyurethane | ||||||
Coating system requirements for CX, Splash and Tidal Zones and Im4 in line with ISO 12944-9
| Type of Environment | CX (offshore) | Splash and tidal zones CX (offshore) and Im4 | Im4 | ||||
|---|---|---|---|---|---|---|---|
| Type of primer | Zn(R) | Other primers | Zn(R) 5 | Other primers |
Other primers (single coat) |
||
| Primer Dry Film Thickness | ≥40μm | ≥60μm | ≥40μm | ≥60μm | ≥200μm | – | ≥150μm |
| Minimum number of coats | 3 | 3 | 3 | 3 | 2 | 1 | 2 |
| Dry Film Thickness of full paint system | ≥280μm | ≥350μm | ≥450μm | ≥450μm | ≥600μm | ≥800μm | ≥350μm |
| Note 5: This coating system with an organic Zn(R) primer can also be used for IM4 service if a Zn(R) primer is desired. In this case the thickness of the complete system van be reduced to ≥350μm. | |||||||