Owners and operators of high-value assets need to understand the cost implications of ignoring the effects of corrosion that poses a threat to all infrastructure through the degradation of structures such as buildings, roads, bridges, pipelines and towers. The economic impact of corrosion represents an annual cost of many billions of dollars to the economy.
Some of the advantages of planning for corrosion control and mitigation at the design phase include extending the life of an asset – thus making it more profitable – and reducing maintenance time and costs thereby increasing an asset’s utilisation.
According to Craig Ross, Director of Napier Sandblasting (NSB) in New Zealand, some construction contractors sought to save money on infrastructure projects by using substandard coatings with the result that some buildings, towers and bridges are already showing signs of fatigue and distress. “While the majority of the cowboy coatings applicators that applied poor coating systems have gone, many of their structures already require remediation,” he said. “Luckily changes in regulations and better enforcement of standards means that new designs should have a much longer operational life.”
Justin Rigby, coatings consultant at Remedy Asset Protection, added that steel structures within industrial facilities are usually located in ‘aggressive’ environments. “Domestic steel buildings do not face the same stresses as offshore or maritime structures,” he said. “Owners of offshore platforms or dock cranes exposed to the marine environment cannot afford for corrosion to degrade their assets.”
“Coastal and maritime areas are harsh and corrosive environments for all structures, but more so for steel ones,” Ross added.
Rigby stated the best way to protect an asset from corrosion is to select a corrosion resistant metal or to apply a protective coating as a barrier to separate the structural steel from the corrosive parts of the environment, such as moisture, oxygen and pollutants.
Ross added that even relatively non-reactive stainless steel requires protection in certain situations. “NSB does a lot of work in the hide tanning industry and other really severe environments, generally where acid attack or abrasion is an issue,” he said.
Cathodic protection is one technology that can be used to impress a current into a structure to alter the surface reactive characteristics of a metal to minimise corrosion.
According to Rigby, it is important that a protective coating project is carefully planned. Protective coatings projects are usually unsuccessful for relatively simple reasons. Planners often do not fully comprehend the technical complexity of many coatings projects, especially if the coating is to be applied to an existing steel structure; even more so if the site is in a remote location. As a consequence, they fail to invest the time and resources to manage it effectively which results in substantial cost implications when things go wrong.
Protective coatings are not just paint. Coatings are engineered products that undergo rigorous testing and refinement to provide specific properties that will protect a structure from its service environment. “The most important considerations are the operating environment and choice of the appropriate coating,” said Rigby. “A simplistic analogy would be that a structure is plastic coated.”
There is a wide selection of coating 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 a ‘one size fits all’ approach made by some manufacturers.
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 of the coating.
It is important to be flexible and adaptable when developing protective coating projects. While identifying areas of risk at the start of a project is an extra expense, it will help ensure a project’s success. Managed well, a protective coatings project can provide owners with great outcomes.
The Australasian Corrosion Association (ACA) works with companies like Remedy and NSB, along with academia, to research all aspects of corrosion in order to provide an extensive knowledge base that supports best practice in corrosion management, thereby ensuring all impacts of corrosion are responsibly managed, the environment is protected, public safety enhanced and economies improved.
“The quality of the finished project is dependent on how skilfully and effectively a coating is applied,” Rigby said. The technicians chosen to apply a coating must have the appropriate skills. Obvious selection criteria are experience with the protective material and the equipment used to apply it to a structure. A less obvious criterion, especially for any sort of tower structure, is abseiling skills; technicians might have to be in a harness and suspended in mid-air which requires a particular mix of physical and psychological attributes.
There are many standards relating to the application of protective surface coatings but sometimes compromises may need to be made. When planning protective coatings it is important to take account of factors such as the geography, access to the structure and climate, all of which impact the cost of the project.
According to Rigby, there are a range of quality tests available that comply with Australian and international standards, many of which are covered in the ACA’s NACE Inspector courses. A good coating specification will reference AS/NZ 2312 as a minimum and categorise the service environment according to its corrosivity and then nominate a coating system based on the desired design life of the coating.
One vital aspect of coatings projects is to have certification that the job complies with all the appropriate legislation, regulations and standards. There are two ways to achieve this; to pay for third party inspection and engage a contracting firm that has a PCCP accreditation. This ensures they have staff with the necessary skills and accredited processes, providing peace of mind to customers that quality is ‘built in’ throughout project planning and execution.
The cost to coat a structure with an appropriate and effective protective material varies depending on whether it is applied in a workshop or on-site and averages between $80 and $300 per square metre. “This is a relatively minor cost, compared to the cost of not coating the steel,” said Ross. “However, cost is very much relative to what the required durability expectation is, the level of aesthetics required and how harsh the environment is.”
If a structure to be protected is in a remote location, it will be necessary to select the most cost effective means of transporting materials and personnel to the site. Additionally, remote sites may be exposed to climatic extremes which impact on applying a coating. For example, monsoonal rains in tropical regions would make it difficult to spray a coating on to any type of structure.
The health and safety analysis of a project must look at how to effectively protect a structure and address any environmental considerations. It must also consider how to properly apply the coating to minimise its effects on the surrounding areas as well as protect the technician who might be working in a harness tethered metres above the ground.