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ISO 12944: preservation of steel by organic coatings

ISO 12944 is the industry standard for corrosion protection of steel structures using protective coatings. To meet this standard, a product must pass several laboratory tests. These tests include corrosivity class and durability range.

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What does ISO 12944 entail

Steel structures always face corrosion. They are exposed to a humid climate or are used under water or underground. The ISO 12944 standard provides information on the paint technologies used, criteria for paint selection and requirements for surface preparation. In doing so, this certification ensures maximum corrosion protection.

Standard ISO 12944 addresses the protection of steel structures with organic coatings that cure at room temperature. Coatings – such as powder coatings – that are cured at elevated temperatures are outside the scope. For such coatings, it is better to use the Qualisteelcoat standard, which has very similarities to ISO 12944. For aluminum, Qualicoat is the most suitable standard.

Environmental classification and life expectancy

The environment in which a product is applied affects its service life. In combination with the life expectancy, the environment therefore determines the requirements made of a paint system. The performance tests to be carried out are therefore tailored to this.

Six corrosion classes are defined in ISO 12944-2:

C1Very low corrosivityHeated buildings with a clean atmosphere, such as offices, stores, schools and hotels.
C2Low corrosivityAtmospheres with little pollution: rural environments.Unheated buildings where condensation may occur, such as warehouses and gymnasiums.
C3Average corrosivityUrban and industrial environments with average sulfur dioxide pollution: coastal areas with low salinity.Production areas with high humidity and some air pollution, such as in food production, in laundries and in breweries.
C4High corrosivityIndustrial areas with average salinity levels.Chemical plants, swimming pools and shipyards.
C5Very high corrosivityIndustrial areas with high salt concentration.Buildings with constant condensation and a lot of pollution.
CXExtreme corrosivity*• Offshore areas with high salt concentration; • Industrial areas with extreme humidity and aggressive, subtropical or tropical atmosphere.Industrial environment with extreme humidity and aggressive atmosphere.

For structures used underwater or in soil, ISO 12944 describes four environments in addition to corrosion classes:

CategoryEnvironmentExample of constructions and environments
IM1Fresh waterInstallations in and around rivers, hydropower plants.
IM2Sea or brackish waterSubmerged structures without cathodic protection.
IM3SoilUnderground tanks, steel pipes and pillars.
IM4Sea or brackish waterSubmerged structures with cathodic protection, such as off-shore structures.

Durability range

The first part of the standardization speaks of an durability range. This is meant to be a technical parameter that can help in creating a maintenance plan. In other words, this is not a warranty period. That period is normally shorter than the durability range.

The durability ranges are defined in ISO 12944-1 as follows:

Low (L)To 7 years
Medium (M)7 to 15 years
High (H)15 to 25 years
Very High (VH)More than 25 years

Demonstrate that a paint system meets your ISO 12944 standards

To determine what tests must be done to demonstrate that your product meets the standard, it is first important to determine what the corrosivity class, possibly environment and durability range should be. For example, if it is a very high corrosivity environment (C5) and there is also a high durability range (15 to 25 years), there will be more laboratory tests and a longer test duration than for a corrosivity class C1 and a low durability range.

Laboratory tests for the ISO 12944 standard

Tests as part of approval of paint systems are performed on 150×75 mm panels. The panel thickness depends on the test, but is at least 3 mm thick. Unless otherwise agreed, the surfaces of the panels are treated with blast cleaning to the minimum surface treatment class Sa 2½, as defined in ISO 8501/1.

The surface roughness (profile) corresponds to “medium (G)” as defined in ISO 8503-1. This can be checked using a comparator as defined in ISO 8503-2. The panels will not be curved. In all other respects, the panels will conform to ISO 7384.

Sometimes coated products are also subjected to the salt spray test and condensation test in their entirety, for example. This provides valuable information about weaknesses in a coating system, such as welds, pinholes and sharp edges, but these tests are not strictly within ISO 12944-6.

C1 to C5 Atmospheric corrosivity

Two test regimes are distinguished for application in standard atmospheric corrosion. Test regime 2 is only applicable for classes C4H, C5H and C5VH. The choice of regime 1 or 2 is free. Keep in mind that the current standard already indicates that regime 2 will probably become mandatory for these classes in the future.

Test regime 1

Corrosion classDurability rangeISO 6270-1 (water condensation)ISO 9227 (neutral salt spray test)
Test durationTest duration
C2low48 hours
medium48 hours
high120 hours
very high240 hours480 hours
C3low48 hours120 hours
medium120 hours240 hours
high240 hours480 hours
very high480 hours720 hours
C4low120 hours240 hours
medium240 hours480 hours
high480 hours720 hours
very high720 hours1440 hours
C5low240 hours480 hours
medium480 hours720 hours
high720 hours1440 hours

Test regime 2

Corrosion classDurability rangeISO 12944-6 Annex B
(cyclic corrosion test)
Test duration
C4very high1680 hours
C5high1680 hours
very high2688 hours
C classificatie ISO 9223

Want to know which tests apply to your product?

IM1, IM2 and IM3, underwater or in soil

Corrosion classDurability rangeISO 2812-2
(water immersion)
ISO 6270-1
(water condensation)
ISO 9227
(neutral salt spray test)
Test durationTest durationTest duration
IM1high3000 hours1440 hours
very high4000 hours2160 hours
IM2high3000 hours1440 hours
very high4000 hours2160 hours
IM3high3000 uur1440 uur
very high4000 uur 2160 uur

After conducting corrosion tests, the following should be assessed according to ISO 4628:

  • Rust formation
  • Blistering
  • Adhesion
  • Cracks
  • Flaking
  • Corrosion from the scratch

ISO 12944-9 for offshore applications

ISO 12944-9 specifies the minimum requirements for protective coatings on offshore structures and structures or structures related to them (such as structures exposed to sea air or immersed in sea or brackish water). Such structures face extreme corrosivity (CX) and/or environmental class IM4.

ISO 12944-9 specifically distinguishes three corrosion categories, each with its own testing regime.

Corrosion class according to ISO 12944-9Cathodic disbondment ISO 15711Sea water immersion ISO 2812-2Cyclic corrosion test ISO 12944-9 annex B
CX (off shore)  4200
CX + IM 4 (splash zone)420042004200
IM 4 (immersion)42004200 

More information on this can be found in our price list. Download it here.

Cost of laboratory tests

Our laboratory testing prices are based on the testing required for the specific environment and life expectancy of the product. A product with medium corrosivity (C3) requires less and shorter testing than a product with high corrosivity and high durability range.

Lead times of laboratory tests

M2lab maintains the shortest possible turnaround times in laboratory testing for ISO 12944 standardization. To provide as much insight as possible into the status of any various orders, we are currently developing a customer portal that will provide an online overview of pending orders and current results.

Call +31 (0)13 – 463 06 88 for more information on turnaround times for your required laboratory tests.

What we require from you

In order to inspect your paint system, we need coated panels. The number of panels required depends on the desired corrosion class.

ISO 12944-6Required number of panels
Test regime 112 panels 150 x 75 mm (3-5 mm thick)
Test regime 29 panels 150 x 75 mm (3-5 mm thick)
ISO 12944-9Required number of panels
CX (off shore)6 coated panels 150 x 75 mm (3-5 mm thick)
CX + IM4 (spash zones)12 panels 150 x 75 mm (3-5 mm thick)
IM4 (immersion)9 panels 150 x 75 mm (3-5 mm thick)

Preparing panels

The results of the tests are strongly influenced by the quality of the pre-treatment. Therefore, always ensure that this has been done very carefully. ISO 12944 indicates which methods are suitable for this purpose.

Make sure that each panel has your own unique coding and supply a clear overview with all the necessary information of the paint system on it. This contributes to clear and error-free reporting.