Corrosion Protection of Steel Columns
While aluminium, stainless steel, composites and concrete have far less problems with deterioration, steel must have protection to avoid loss of section through corrosion, commonly known as rusting.
a) Hot Dip Galvanizing
Now the most frequently used corrosion protection system for steel lighting columns due to its sacrificial properties and its equal protection to the internal and external surfaces of a column. Galvanizing should be carried out to BS EN ISO 1461 and detailed advice can be obtained from the Galvanizers Association at http://www.galvanizing.org.uk/ In the last ten years it is claimed that the life of the galvanized coating has doubled due to the reduction of airborne pollutants and the halving of the rate of loss of thickness.
b) Aluminium Spray
Another sacrificial metallic coating that is also used is aluminium spray which performs better in coastal areas, particularly if the coating has also been treated with a sealer. However, this coating cannot be readily applied to the interior of the column, and alternative corrosion protection systems have to be used, such as wax materials.
There is a very large range of different painting systems that can be applied to bare steel, aluminium sprayed surfaces or galvanised surfaces, however for lighting columns the main problem is protecting the internal surfaces. For this reason columns are usually galvanised first and any required cosmetic painting applied on the visible external surfaces. In coastal areas such painting also protects the galvanising from the continuous sea salt spray. For further information on the safe use of Isocyanates please scroll to the bottom of the page.
d) Root Protection
Generally a different protection system is applied to the root of a column, that part embedded in the ground and for 250mm above ground. This not only has to prevent corrosion, resist mechanical abrasion but also attack from electrolytes in the ground water that can cause the material of the root to be conducted onto surrounding objects by electrolytic action. This is particularly important for aluminium columns.
e) Polymer Coating
High build fusion bonded polymer coatings offer both aesthetic and corrosion protection. This process usually involves heating the column to a temperature of approximately 280 degrees Celsius
(a) Immersing the structure into a bed of fluidised powder granules
(b) Electro statically spraying the column
These granules then melt onto the surface of the structure creating the fusion bonded polymer coating.
This process can also be applied locally to the root section of the column both internally and externally and is an alternative to bitumen or painted root protection systems.
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Isocyanates: These protection systems give rise to known risks during application in confined areas. The BritishCoatings Federation Ltd. give guidance on application in their document 'Safe Use of Isocyanates' and we have received approval to provide the document from this site.
To view the document please click here.
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