Which corrosion protection method is the right one?

    Depending on the location, the metals are subject to varying degrees of stress - the requirements for an anti-corrosion coating therefore vary. These different influences are defined in the corrosivity categories C1 to CX.
    C1: insignificant load

    • E.g. in heated buildings [offices, schools, hotels, sales rooms, etc.].
    • Possible thickness reduction of unalloyed steel =≤ 1.3 µm.

    C2: low load 

    • E.g. atmosphere with low impurities [land areas] or unheated buildings with condensation [warehouses, sports halls, etc.].
    • Possible thickness reduction of unalloyed steel => 1.3 - 25 µm.

    C3: moderate 

    • E.g. urban and industrial atmosphere with low SO2 load coastal atmosphere with low salt load or production rooms with high humidity [laundries, breweries etc.].
    • Possible thickness reduction of unalloyed steel => 25 - 50 µm.

    C4: heavy load 

    • E.g. industrial atmosphere and coastal atmosphere with moderate salt load, chemical plants, swimming pools, coastal shipyards etc.
    • Possible thickness reduction of unalloyed steel => 50 - 80 µm.

    C5: very heavy load 

    • Industrial areas with high humidity and aggressive atmosphere, coastal atmosphere with high salt load, buildings or area with almost constant condensation and heavy contamination.
    • Possible thickness reduction of unalloyed steel => 80 - 200 µm.

    CX: extreme load 

    • Offshore areas with high salt load, industrial areas with extreme humidity and aggressive atmosphere as well as subtropical and tropical atmosphere.
    • Possible thickness reduction of unalloyed steel => 200 - 700 µm.

    Depending on the corrosivity category - i.e. the location and load of the structure as well as the desired protection duration - different corrosion protection coatings are available. Coating materials, e.g. based on alkyd resin, acrylic resin, epoxy resin or polyurethane, are usually used for this purpose. All corrosion protection systems are preceded by an assessment of the initial condition and suitable preparation of the surface. Existing corrosion, loose old coatings and dirt or other inherent and foreign contaminants must be professionally removed. 
    A primer serves as the basis for the coating system. Depending on the system, this is followed by one or more intermediate coats. Finally, the top coat is applied. 

    Sources: 
    http://hendrik-mueller.com/ 
    https://www.chemie.de/lexikon/Korrosionsschutz.html