A common misconception is that corrosion may not be a problem for interior steelwork which is protected from the elements. If there is frequent condensation on its surface, corrosion of inadequately protected steel will be significant. Under these conditions, hot dip galvanizing may give more than 40 years life. Hot dip galvanizing has also been used extensively to protect interior steelwork in harsh environments such as swimming pools and breweries. Corrosion may also arise on exposed non-galvanized steelwork intended for interior environments if there is a delay in assembly or construction.
C1: Very Low
Because steelwork in a warm, dry interior will not corrode, the structural stability of a building will not be impaired during it's design life (generally taken as over 50 years). In such conditions, no coating is required.
Inside dry, heated buildings with neutral atmospheres: Offices, shops, schools, hotels, residences, airport terminals, hospitals etc.
When steelwork is exposed to moisture, corrosion will occur at a rate that
depends on the severity of the environment.
In low risk environments, systems B2, B3, B4, B9, B10, or B11 are proposed.
Inside buildings where condensation may occur: Exhibition halls, vehicle depots, sports halls etc.
In medium risk environments, higher-grade systems are needed. B5, B6, B7, B12, B13, B14 are proposed. Inside production buildings with high humidity and some pollution:
These guides do not cover high corrosion risk internal environments. Users are advised to seek specialist advice.
Buildings with high humidity and corrosive atmospheres: Chemical processing plant, swimming pools, dye works, paper-manufacturing plants, boat yards over seawater, foundries, smelters etc.
C5: Industrial, Very High
C5M: Marine, Very High
The period of reasonable freedom from severe corrosion of the steelwork that might lead to weakening of the structure. This figure assumes no mechanical damage in service, that no maintenance is carried out and that up to 1mm of steel may be lost from the surface at the corrosion rate for each environment given in ISO 12944. Visible steelwork will normally be accessible for maintenance and if repainting is carried out, the quoted life of the structure will be extended.