The corrosion of structural steel is an electrochemical process that requires the simultaneous presence of moisture and oxygen. Essentially, the iron in the steel is oxidise
d to produce rust, which occupies approximately six times the volume of the original material.
The rate at which the corrosion process progresses depends on a number of factors, but principally the ‘micro-climate’ immediately surrounding the structure. For example, if salt is present, the corrosion will be more rapid. Exposure to sulfur dioxide and carbon dioxide will also hasten the corrosive process.
The international standard EN ISO 12944-2 on corrosion protection of steel specifies the corrosion categories C1 to C5. The corrosion categories refer to the extent of corrosion on zinc and steel in differing environments.
| C1 - Very low | Heated buildings with clean atmospheres, e.g. offices, shops, schools, hotels. |
| C2 - Low | Unheated buildings where condensation may occur, e.g. depots, sports halls. Atmospheres with low level of pollution. Mostly rural areas. |
| C3 - Middle | Production rooms with high humidity and some air pollution e.g. food-processing plants, laundries, breweries and dairies. Urban and industrial atmospheres, moderate sulfur dioxide pollution. Coastal areas with low salinity. |
| C4 - High | Chemical plants, swimming pools, coastal ship- and boatyards. Industrial areas and coastal areas with moderate salinity. |
| C5 - Very high | Buildings or areas with almost permanent condensation and with high pollution. Coastal and offshore areas with high salinity. |
Typical solutions to prevent corrosion include installation and fixing materials made of galvanised material, stainless steel or powder-coated material. Walraven has developed a special surface protection system; BIS UltraProtect® 1000, which is available across a large range of products for both indoor and outdoor use (C1 – C4 environments). The BIS UltraProtect® 1000 products have been specially developed to withstand a salt spray test (ISO 9227) of at least a 1,000 hours with a maximum of 5% red rust.
The system is better than hot dip galvanizing, providing a far superior level of corrosion resistance. Threaded products are also well protected, and the products feel smooth and are visually appealing. The system can be combined with zinc-plated or hot dip galvanized products. We also offer a 20 year warranty (subject to T&Cs) on retention of structural integrity, and against rusting through, when used in an outdoor C1-C4 environment.
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