Long-term protective coating success

Corrosion poses a threat to all infrastructure through the degradation of structures – such as buildings, roads, bridges, pipelines and towers – and the economic impact of corrosion represents an annual cost of billions of dollars to the economy.

It is important that owners and operators of high-value assets understand the cost implications of ignoring the effects of corrosion. There are many advantages of planning for corrosion control and mitigation. Two of the main ones are: that the life of an asset is extended, thus making it more profitable; and maintenance time and costs are reduced thus increasing the asset’s utilisation.

According to Justin Rigby *, coatings consultant at Remedy Asset Protection, there are two main ways to protect an asset from corrosion. One is to alter the physical properties of a metal by using a technology such as cathodic protection to impress a current into a structure to minimise corrosion. The other is to physically isolate a structure from the environment by applying a protective coating.

It is important that a protective coating project is carefully planned. One thing to avoid is underestimating the technical complexity of a project, especially if the coating is to be applied to an existing structure; even more so if the site is in a remote location.

“A protective coating is not just paint. It is an engineered product that undergoes rigorous product development to provide specific properties that will protect a structure from its service environment,” said Rigby. “The most important considerations are assessment of the service environment and selection of the required coatings.”

There is a wide selection of coatings products available to the market so it is essential that the appropriate coatings system is chosen. There is no single product that meets every coating situation as the desired attributes may be mutually exclusive; so during the planning of a project, a compromise may need to be made, but is important to not be fooled by the claims made by manufacturers.

According to Rigby, a good specification will reference AS/ NZ 2312 and categorise the service environment according to its corrosivity and then nominate a coating system based on the desired design life of the coating. He recommends seeking advice from a competent colleague or external consultant when building a specification and selecting the most appropriate coating system. The major coatings manufactures, such as Akzo Nobel, Altex, Dulux, Jotun, PPG, and Valspar, are also good sources for reputable advice.

Traditionally, coatings protect a structure by being a physical barrier to the environment. Modern technology has developed active pigments which are being incorporated into primers to provide additional protection. Active anticorrosive pigments are added to primers which can give further protection for areas with coating damage in addition to their barrier effect. These pigments prevent corrosion of a metal substrate by building up permanently passive conditions at the metal surface and/or by a build-up of solid compounds which fill the damaged area to the coating.