Corrosion Classifications - What is ISO 12944 (1)

Your steel plant and structures are only as durable as they are corrosion resistant, but corrosion prevention is no simple task. Corrosion occurs when moisture, oxygen, and ferrous steel combine to cause oxidation – a process accelerated by surface pollutants. This means environmental conditions have an important effect on your plant/steelwork.

The location of steelwork above or below ground, the pH level of the surrounding environment and the presence of microorganisms also affect susceptibility to corrosion.

To cover those variations, the International Organisation for Standardisation (ISO) define standards governing corrosion resistant paint systems.


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:

Corrosion Classifications - What is ISO 12944

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.


Your Coatings Strategy

Every coating requires a strategy that’s informed by everything from your raw material to the thickness of your paint. The first step to greater longevity and corrosion resistance lies in choosing the best elements for your component and the best preparation methods for your steelwork. A durable surface coating is a well-planned one, and if you adopt the best practices set out in the revised ISO 12944: 2018 standards, you will achieve a lasting structure.

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