What you need to know about ISO Corrosivity Categories

Corrosion testing on HVAC coatings can be conducted according to a number of standards, including ASTM-B117, ISO 9227, ISO 12944-6, and ISO 20340. Of these tests, the one we believe represents actual service environments most closely is ISO 12944-9 (formerly ISO 20340) vs. the more common ASTM B-117.

ISO classifies environments in corrosivity categories of C1 through CX based upon long-term material weight loss and surface degradation testing in different corrosive environments. These categories are updated as needed; the 2018 update to corrosion categories replaces the C5-I and C5-X categories with C5 for harsh onshore environments and CX for offshore environments.

It is important to note; paint systems are typically tested against higher levels of corrosivity because a coating that can protect against the most severe C5 or CX environments is certainly capable of providing protection in a less severe environment.

The corrosivity categories are:

C1 – Very Low

• Example environments include: heated buildings with clean atmospheres such as schools or offices

C2 – Low

• Example exterior environments include: atmospheres with low levels of pollution, mostly rural areas
• Example interior environments include: unheated buildings where condensation may occur such as depots or sports halls

C3 – Medium

• Example exterior environments include: urban and industrial atmospheres, moderate sulfur dioxide pollution, or coastal areas with low salinity
• Example interior environments include: production rooms with high humidity and some air pollution such as food processing plants, laundries, breweries, or dairies

C4 – High

• Example exterior environments include: industrial areas and coastal areas with moderate salinity
• Example interior environments include: chemical plants, swimming pools, coastal ship and boat yards

C5 – Very High

• Example on shore exterior environments include: industrial areas with high humidity and aggressive atmospheres
• Example on shore interior environments include: buildings are areas with almost permanent condensation and with high pollution
• Example offshore exterior environments include: coastal and offshore areas with high salinity
• Example offshore interior environments include: buildings or areas with almost permanent condensation and with high pollution
• In 2018, C5-M and C5-I were combined and are now represented by both the new C5 (harsh on-shore) and CX (offshore) categories

CX – Extreme

• This is a new category, added in 2018 for extreme environments
• Example environments include extreme industrial areas, offshore areas, and salt spray