Case Study: Jutland Bridge, M3 - Dekro Paints

Case Study: Jutland Bridge, M3

Structural Steel Maintenance

The protection of iron and steel is a serious problem, and many millions of rands are spent annually to prevent or limit corrosion and on the replacement of corroded metal.
The important factors in the protection of iron and steel by painting are:
The thoroughness of the preparatory work before painting.
The type of primer used.
The thickness of the paint system.

As far as preparatory work is concerned, it has been shown that the effective life of a paint coating of perfectly clean steel, free from rust and scales, maybe up to five times longer than that of the same coating applied to imperfectly cleaned steel. The traditional manual methods of preparing new and old steelwork for painting by chipping, scraping and wire brushing are far from ideal, as they cannot remove lightly adherent scale nor deal effectively with rust on pitted or rough surfaces. Alternative methods such as pickling, grit blasting, flame cleaning and chemical de-rusting are either not practical on erected steel or may be considered too expensive. It should be realised that the higher initial cost would be more than offset by a reduction in maintenance costs by the longer life of the paint coatings.
For general use on iron and steel, primers incorporating rust-inhibitive pigments must be used, for example, zinc phosphate, metallic zinc, etc., in various binders such as the conventional linseed oil, or alkyd resins, or epoxy resins, etc. Too often cheap and inferior primers are used containing less than the minimum quantities of anti-corrosive pigments to be effective. Such paints do more harm than good as they must first be removed before a systematic and effective painting operation can be carried out.
Steelwork must be primed as soon as possible after it has been prepared, whether on-site or at the manufacturer’s works, as even a few hours of exposure in a damp or contaminated atmosphere will nullify the value of thorough preparation.