DEMM Engineering & Manufacturing
Corrosion: focus on environmentally friendly solutions
The economic impact of corrosion represents a cost of billions of dollars to the economy every year. Planning for corrosion control and mitigation helps to minimise the cost implications of ignoring the effects by reducing the maintenance time and increasing an asset’s utilisation.
One way to protect an asset from corrosion is to physically isolate a structure from the environment by applying a surface coating. However, it is not only the outside that needs protection. The walls and floors of hospitals, industrial facilities, commercial offices and other built structures require protection. Additionally, internal services ( pipes, equipment, motors, boilers, etc.) need to be protected.
Protective coatings are not just paints. They are engineered products that undergo rigorous product development and testing to provide specific properties that will protect a structure from its service environment or possess particular characteristics static dissipating, abrasion resistance, thermally insulating etc. that make it a functional coating.
During the past 20 years, Graham Carlisle, Principal Corrosion and Coating Engineer at IAS Group in Western Australia, has worked with many contractors and suppliers on projects working to prevent or remediate corrosion. “When working with existing facilities such as a hotel or hospital, a major constraint is getting access,” he said. “It is very difficult to shut down a busy 24 hour a day public health facility, so we have to carefully plan how and when works are carried out.”
The rapid cure times of modern spray-applied polyurea, methyl methacrylate, epoxy and polyurethane coatings make them ideal for use in facilities that cannot easily be shut down. Minimising disruption to the operation of hospitals, hotels and production plants is a key consideration.
Before a coatings project is underway, there are several aspects that need to be carefully managed. “It is important to understand the competence of the applicator and ensure that the main contractor understands all the steps needed to undertake the coating process, the success requirements and does not accept lower quality materials that do not meet specifications,” said Peter Dove, Principal Materials Consultant at GHD one of the largest consultancy engineering groups in Australia. GHD has a Materials Technology Group involved in solving a range of durability and corrosion issues and projects.
The Australasian Corrosion Association ( ACA) works with companies such as IAS Group and GHD as well as academic institutions to research all aspects of corrosion in order to provide an extensive knowledge base that supports best practice in corrosion management, ensuring the environment is protected, public safety enhanced and economies improved.
In addition to providing a physical barrier, surface coatings can also be used as thermal insulation depending on their composition. Coatings are available that have high titanium dioxide content which reflects heat when used on the external walls of buildings.
One emerging market for coatings technology is in protecting HVAC ductwork inside buildings and commercial facilities. “By using coatings with the appropriate thermal characteristics asset owners can achieve performance gains with less expense,” said Carlisle. “There is no need for old style fibrous lagging that degrades over time, collects dust and has to be replaced periodically and can lead to hidden corrosion issues under the insulation.”
Spray- applied thermally insulating coatings ( TIC) can be used when insulating a building’s ductwork, pipes and machinery often involving complex
geometries around valves and levers. Applying such coatings is much easier and can achieve the same performance results of traditional lagging more quickly and with less labor. TICs directly adhere to the substrate, thus minimising or eliminating the space between the substrate and conventional insulation that can hold moisture. Replacing traditional fibrous insulation with an insulating coating reduces energy usage and protects the system from the problem of corrosion under insulation (CUI). It also has the additional benefit of mould and moisture resistance, which in turn improves overall air quality inside buildings.
TICs can also be used on the roof and walls of a building. When properly installed and maintained, a coating can help an asset owner achieve energy savings as well as extend the service life of a building. The latest coatings can withstand extended exposure to water, humidity, temperature extremes, ultraviolet rays, oxygen, and atmospheric pollutants.
Coatings used in the hospital and hotel sector are mostly epoxy- based systems. “The choice as to what coating is used must be based on an assessment of the environment where it is used and what it will be exposed to,” Dove said.
The performance characteristics are determined by the different chemistry of the various coatings. “The curing temperature of a coating impacts the choice of material,” Dove said. “At anything less than 10 ºC, it is unlikely that epoxies would be used.” Alternative coatings are required for use in situations such as commercial freezers. Slight changes in a coating’s formulation changes its balance of properties and thus the way it performs under different environmental conditions.
If a coating is to be exposed to different chemicals, the material used must be of the appropriate type. Carlisle said that caustic substances require a different material from those used for acids. “In a brewery, the internal coatings of floors and walls are mostly exposed to the caustic wash used to clean the tanks and pipework. In a hospital or research laboratory, there may also be many acidic substances used.”
Similarly, different operating processes require alternative coatings; if there is an extraction flue associated with a process, the internal coating must be able to tolerate both the temperature of the hot gasses passing over it as well as the corrosivity of them. According to Graham Carlisle every increase of 10 ºC may approximately double the corrosivity of a gas or liquid.
According to Dove, there are a range of factors that need to be considered. “While coatings are an effective treatment, sometimes it might be more effective to change the material for example, stainless steel used to make the underlying structure. The risks associated with a surface must also be assessed, especially if liquids are being handled. A tiled surface or plastic membranes may be the most appropriate in certain situations in a hotel or hospital.”
The safest way to ensure a positive coating outcome is to select a coating from a reputable coating manufacturer with proven case histories that can be verified, and engage an applicator trained and endorsed by the manufacturer.
For remediation work, while spray-applying is usually the most effective application method, on inside surfaces, brush, roller or trowel application is often used. To remediate concrete structures, it is important to use a material that tolerates alkali. If there is a high moisture level in the concrete mix, an alternative coating material may be required. A project came to Dove from a casino in the Middle East where the high residual moisture content of the concrete used had caused the floors in some areas of the building to completely delaminate.
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.
Protective coatings projects are usually unsuccessful for relatively few reasons. Planners often do not fully comprehend the complexity of many coatings projects and, as a consequence, fail to invest the time and resources to manage it effectively which results in substantial cost implications when things go wrong. It is important to have the knowledge to ask the appropriate questions and understand what the limits are when faced with the many options available.
The lack of detailed design information for a structure sometimes means that there can be poor selection of structural materials. For example, if dissimilar metals are used, this results in restricting the coating options available a coating for one metal is often inappropriate for another.
The cost of applying a surface coating varies depending on whether it is applied in a workshop or on- site. Applying a coating can vary between $ 80 per square metre in a workshop to $300 per square metre or higher on- site. Carlisle and Dove advocate not scrimping on a coatings specification, or the quality verification, as these could be some of the best dollars spent on a project.
There are also 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 into account a number of factors, including the operating environment, access to the structure and climate all of which impact the cost of the project. A good coatings specification will reference relevant Australian and international standards, such as AS/NZ 2312 and categorise the service environment according to its corrosivity and then nominate an appropriate system based on the desired design life of the coating.
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.
Many old style coatings were effective but not very safe according to today’s understanding of the health effects of ‘protective’ substances such as red lead and asbestos. A recent project of Dove’s involved the restoration of one of the historic buildings used by a major educational institution in Melbourne. “It was a rare situation where we were able to see the works being done from start to finish,” Dove added. “Constructed in the 1870s, there were many layers of different paints and other coatings used over the years.” Special paint strippers were required to remove several different coloured coating layers from the building because analysis indicated some had up to 30 percent lead in them and the underlying render could not be damaged by more aggressive forms of coating removal. Before the application of a breathable mineral silicate coating, the render needed extensive repairs by heritage stone masons to restore the durability of the façade. Another vital aspect of coatings projects is to have certification that the job complies with all the appropriate legislation, regulations standards and project specifications through engaging NACE or ACA qualified coatings inspectors for steel or concrete coating applications.
The Australasian Corrosion Association ( ACA) works with companies such as IAS Group and GHD as well as academic institutions to research all aspects of corrosion in order to provide an extensive knowledge base that supports best practice in corrosion management, ensuring the environment is protected, public safety enhanced and economies improved.