The corrosion category for a screw fastener determines the conditions in which the fastener should be used to ensure the best possible durability of both the fastener and the screwed joint. By following corrosion category classifications, you help ensure that the screwed joint is installed correctly for the environmental conditions the fastener was designed for.
There are six corrosion categories, defined according to the SFS-EN ISO 12944-2 standard.
Permitted use: dry indoor spaces where humidity does not differ from normal indoor temperature and humidity conditions.
Screw fasteners: bright zinc-plated (ZN).
Permitted use: unheated indoor spaces, dry and clean outdoor air, rural climate.
Screw fasteners: hot-dip galvanized (KS, HDG, ZNK), zinc flake coating (ZNF, Ruspert), nail plates, angle brackets, post bases and beam shoes, roofing screws.
Applications: urban and industrial atmospheres with moderate sulfur dioxide pollution. Coastal areas with low salinity. Indoor and production facilities with high humidity and airborne impurities.
Screw fasteners: stainless steel (A2) or A2 fasteners coated with zinc flake coating (ZNF, Ruspert, or similar).
Applications: outdoor industrial and coastal areas with moderate salinity. Coastal shipyards. Indoor chemical industry facilities, chemical production plants, swimming halls, and swimming pools.
Screw fasteners: acid-resistant steel (A4) and HCR fasteners.
Applications: industrial areas with high humidity and a corrosive atmosphere. Indoor spaces where condensation is almost constant and rainfall levels are high.
The product material is determined by the application and must be specified separately. Examples of materials: Duplex and Duplex-alloyed materials.
Applications: marine atmosphere with high salinity. Indoor spaces and construction areas where condensation is almost constant and rainfall levels are high.
The product material is determined by the application and must be specified separately. Examples of materials: Duplex and Duplex-alloyed materials.
Fresh water, river structures, hydropower plants.
Sea and brackish water. Harbor structures such as fire hatches, gates, lock systems, docks, offshore structures.
Soil, underground tanks, steel piles, steel pipes.
The SFS-EN ISO 12944-5 standard does not take into account special stresses affecting paints used for surface treatment, suitability for contact with food, or specific chemical exposure.
The standard divides the durability of paint systems into three categories:
- Low (L): 2 - 5 years
- Moderate (M): 5–15 years
- High (H): over 15 years
Paint substrate designations
Fe = Iron
Zn = Zinc
Al = Aluminum