ISO 12944 "Paints and Varnishes – Corrosion Protection of Steel Structures by Protective Paint Systems" is a comprehensive standard for corrosion protection of steel coatings under specific environmental conditions. It is also a current design guide for protective paint systems for steel structures. Below, we share the "4S" method for selecting a coating system.

ISO 12944 Coating System Selection "4S Method"

01

S1 Confirm the Type of Environmental Conditions

ISO 12944-2 specifies a clear classification for types of environmental conditions.

Atmospheric Corrosion Classification:

C1 Very Low: Dry and clean indoor locations, such as offices, shopping centers, schools, and hotels.

C2 Low: Areas with low atmospheric pollution, mainly rural regions.

C3 Medium: Urban or industrial environments with moderate sulfur dioxide pollution; coastal areas with low salinity.

C4 High: Industrial areas or coastal areas with medium salinity.

C5 Very High: Industrial areas with high humidity and corrosive atmospheres, and coastal areas with high salinity.

CX Extreme: Offshore areas with high salinity or industrial environments in tropical or subtropical atmospheres with extreme humidity.

S2 Confirm the Durability of Protective Coating

The durability of the coating system refers to ISO 12944-1:

Short (Low): 7 years

Medium: 7–15 years

Long (High): 15–25 years

Very Long (Very High): > 25 years

Note: The durability of protective coatings is not a "warranty period" but a technical/planning parameter to help users establish maintenance plans.

S3 Select the Required Coating System

ISO 12944-5 describes common types of coatings used for corrosion protection of steel structures and provides guidance on how to choose a coating system for different corrosion environments, surface preparation levels, and durability requirements.

S4 Conduct Laboratory Verification of the Coating System

When choosing a coating system based on the standard, if the owner requests laboratory testing, it should be performed according to ISO 12944-6 or ISO 12944-9.

Case Study

02

Client: A well-known foreign electrical company

Object: Outdoor electrical control cabinet (made of carbon steel)

Environment: Coastal industrial zone (within 200 meters)

Planned Service Life: 20 years

S1 Identify Corrosion Category ISO 12944-2

This case is located in a coastal industrial zone, which often involves energy, oil, or chemical enterprises. The environment is characterized by high humidity, high salinity, and severe corrosion. Therefore, the environmental category chosen in Step 1 is C5.

S2 Confirm Protective Coating Durability ISO 12944-1

The designed service life is 20 years. According to Step 2, the selected durability is "High" (construction cycles, usually 2 years, are also often considered).

S3 Select the Coating System Required for the Project ISO 12944-5

The sample's base material is carbon steel, the environment is C5, and the required durability is "High." Based on ISO 12944-5 and its appendices, the chosen coating systems are ISO 12944-5/C5.03 or ISO 12944-5/C5.07.

S4 Laboratory Verification/Pre-Certification of the Coating System

Testing is conducted according to ISO 12944-6 or ISO 12944-9 standards.

Main Referenced Standards in ISO 12944