ISO 12944-5:2019 Corrosion Protection By Protective Coating Systems

ISO 12944-5:2019 is a standard that describes the types of paint and paint system commonly used for corrosion protection of steel structures. It also gives guidelines for the selection of paint systems available for different environments and surface preparation grades, and the durability grade to be expected. This standard is part of the ISO 12944 series, which covers various aspects of paints and varnishes for corrosion protection of steel structures.

Some examples of paint systems that comply with ISO 12944-5:2019 are:

• Epoxy primer + polyurethane topcoat for medium corrosivity category C2.
• Epoxy primer + epoxy intermediate + acrylic epoxy topcoat for high corrosivity category C3.
• Polysiloxane primer + polysiloxane topcoat for very high corrosivity category C3.

Let's cover the six corrosion categories for atmospheric environments, which are based on the corrosivity of the atmosphere and the expected service life of the protective coating system. The corrosion categories are:

• C1: Very low corrosivity, such as heated buildings with clean atmospheres.
• C2: Low corrosivity, such as rural areas and unheated buildings with low humidity.
• C3: Medium corrosivity, such as urban and industrial areas with moderate sulfur dioxide pollution.
• C4: High corrosivity, such as industrial areas and coastal areas with high humidity and salt spray.
• C5: Very high corrosivity, such as industrial areas with high humidity and aggressive atmospheres.
• CX: Extreme corrosivity, such as offshore structures and other marine environments with very high salinity.

Corrosive category CX was added in 2018 by ISO to address extreme corrosivity environments. It applies to structures that are exposed to extreme industrial areas, offshore areas, and salt spray. The corrosion rate of steel, zinc, copper, and aluminum in this category is very high, and the protective coating systems used for corrosion protection must undergo rigorous coating industry testing.

According to ISO 12944-9, paints that are to be applied in corrosive category CX must undergo a cyclic ageing test, where the test subject is exposed to 25 one-week cycles of common extreme coastal environment conditions. Each cycle consists of 72 hours of UV exposure, 72 hours of salt spray, and 24 hours of freezing. The paint system must meet the minimum requirements for adhesion, blistering, cracking, rusting, and delamination after the test.

In addition, there are four corrosion categories for water and soil environments, based on the type and condition of the water or soil and the presence of cathodic protection. These corrosion categories are:

1. Im1: Fresh water, such as river installations and hydro plants.
2. Im2: Sea or brackish water without cathodic protection, such as immersed structures and pipelines.
3. Im3: Soil, such as buried structures and tanks.
4. Im4: Sea or brackish water with cathodic protection, such as immersed structures and pipelines with cathodic protection.

ISO 12944-5:2019 can be used by specifiers to select the appropriate protective coating system for the corrosion protection of steel structures, based on the environmental conditions, the surface preparation, and the expected durability.

Durability categories are:

• Low (L): Up to 7 years.
• Medium (M): 7-15 years.
• High (High): 15-25 years.
• Very High (VH): Greater than 25 years.

Specifiers can use the tables and figures within the standard to compare the performance and costs of different protective coating systems, and to choose the best option for their project. Specifiers can also refer to the certificates of conformity issued by independent testing laboratories to verify that the protective coating systems comply with the ISO 12944-5:2019 requirements.

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