Technical Advice - A Guide to the updated ISO 12944

What is ISO 12944?

That standard, ISO 12944 was introduced in 1998, revised in 2007 and updated for a second time in 2018 with some significant changes and additions. It now has nine parts and covers paint and coatings for steel structures in atmospheric, immersed, and buried environments.

Part 6 of the standard (IS0 12944-6) specifies the laboratory test methods and conditions for the assessment of paint systems for the corrosion protection of carbon steel structures and is the part relevant to Selemix offer when certified the first time or when re-certified.

Industry professionals (such as asset owners, corrosion protection or construction companies) use the detailed, unambiguous and easily understandable standards set down in the second part of ISO 12944 to ensure that the coatings they are specifying and/ or providing will deliver the intended level of corrosion protection in the environment that the product or structure will be subject to.

Therefore, when our customers choose SELEMIX®, for their light industrial coating needs, they will know exactly what they will get.                                                                                                       

Environment Classification & Coating Durability

The standard takes into account two factors when protecting steel from corrosion:

1. Environmental corrosivity;

The standard segments environments into different categories that are then evaluated on their ability to corrode unprotected steel.

In the updated version from 2018 a series of changes have been made to the corrosivity categories C1 to C5 (ranging from very low to very high), while a new category, CX (Extreme), has been included for offshore and industrial environments with high humidity.



2. Coating durability

the standard gives guidance on the expected lifetime of a coating system until its first major maintenance. In 2018 a new durability classification of "more than 25 years" was added aligned with the inclusion of the new immersion category Im4 and which applies for marine environments.




These characteristics are evaluated as defined in ISO 12944-6 by artificial-ageing tests to measure the paint cycles resistance to water or moisture and to salt spray as an indication of wet adhesion and barrier properties. The tests have the aim to ensure with a high probability that a paint system really has the characteristics needed for the durability required in the intended application.

The 2018 update of ISO 12944 introduced changes to these laboratory test methods. For categories C4 very high, C5 high and C5 very high, cyclic testing has been introduced so as be more representative of real-world corrosion conditions.



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) Confirming Corrosion Category (ISO 12944-2)

The atmospheric environment is divided into six atmospheric corrosion categories:

C1: Very low corrosion (Very low)

C2: Low corrosion (Low)

C3: Medium corrosion (Medium)

C4: High corrosion (High)

C5: Very high corrosion (Very High)

CX: Extreme corrosion (Extreme)

Immersed in water or buried in the soil is divided into 4 categories:

Im1: Freshwater

Im2: Seawater or slightly brackish water without cathodic protection

Im3: Soil

Im4: Seawater or slightly brackish water with cathodic protection

 

2）Confirming the durability of protective valve coatings  (ISO 12944-1)

The standard specifies four different durability ranges:

Low (L): Not exceeding 7 years

Medium (M): 7-15 years

High (H): 15-25 years

Very high (VH): >25 years

The durability of protective valve coatings  is not a "guarantee period." The guarantee period is usually shorter than the durability, and there are no rules specifying the relationship between these two times. The "environmental type" and the "durability of the coating system" are the main parameters for selecting a coating system and must be given attention.

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Corrosion Risk From Environmental Exposure

The ISO 12944:2018 (Part 2) standard broadly splits environmental corrosion risk into six categories, based on the time needed for untreated zinc or carbon steel to corrode under various atmospheric conditions:


 

Note: the above is an excellent guide for a majority of paint systems, but does not take into account specific chemical, temperature or mechanical needs.

A separate set of risk categories are given for exposure to water or soil. Very briefly (as most steelwork used by our clients in the power generation sector is on land and above ground), these are: Lm1 (fresh water), Lm2 (brackish or sea water), Lm3 (immersion in soil) and Lm4 (deep sea water).

 
Coating Guidelines

ISO 12944 goes beyond environmental causes, providing guidelines for the design considerations, surface types, and preparation needs for every coating. It also specifies the performance tests and execution methods for each type of coating. If your surfaces are already deteriorating, it informs your spot repair and refurbishment strategies as well. While these are only intended as guidelines, regulators often reference them in their directives, making the recently updated ISO 12944 standards a critical part of your legal requirements.

 
How Long Should Coatings Last?

There's no such thing as permanent corrosion protection, so ISO 12944 includes a broad durability range for each coating:

    Low durability (L): <7 years
    Medium durability (M): 7-15 years
    High durability (H): 15-25 years
    Very high durability (VH): >25 years

The guidelines stipulate that each coating should be tested in laboratory conditions on smooth, galvanised, and rough surfaces to determine durability. Inadequate surface preparation will negatively affect the longevity and durability of a protective coating, increasing the risk of corrosion. For more information, refer to our earlier blog Steel Surface cleanliness by Abrasive Blast Cleaning.