Corrosion of water and wastewater infrastructure, and in some cases the subsequent leakage, costs the industry in excess of $1 billion each year. The main assets that are affected by corrosion are the pipelines, storage tanks and treatment plants.
As much of this infrastructure is ageing, it is starting to require refurbishment or replacement. One method of refurbishment of water industry assets is to carry out surface repairs and then apply protective coatings.
When refurbishing or repairing any pipes, channels or tanks that carry potable water, special coatings are required as it is essential that no chemicals leach into the drinking water. For pipelines, different coatings can be applied to the inside and outside of the pipes, especially if the pipes are buried in ground.
For concrete storage reservoirs, water authorities are lining the insides to stop corrosion and prevent leaks. The structure of the polymer used for wastewater and sewerage treatment infrastructure, such as clarifier tanks and sewage channels, has to be resistant to abrasion and chemical attack. A major consideration in applying any surface treatment to a structure is the requirement to minimise downtime.
Rhino Linings’ ‘high build coatings’ are 1000 microns thick as opposed to paints and epoxies, which might only be several hundred microns. High build polymer coatings are also flexible that allows them to stretch and shrink as substrates expand and contract due to temperature and ground fluctuations.
All coatings developed by Rhino Linings are tested for compliance with AS4020 at the Australian Water Quality Centre in Adelaide.
The Rhino Linings Polyurethane and Pure Polyurea coatings have a patented mix ratio that has been determined over many years. The company’s coatings contain no solvents or VOCs (volatile organic compounds) and its procedures contain and manage overspray.
A recent major project by a Rhino Linings Applicator was for the Hospital Hill Reservoir in Murwillumbah, NSW. The applicator won the tender to repair the inside and outside of the 80 metre diameter, above ground steel potable water storage tank. The tank sits on a concrete ring beam with the floor of the tank a series of concrete segments. The repair was required due to the expansion joints in the floor failing and the tank starting to leak. The joints were resealed and then a Rhino Pure Polyurea coating applied over all floor joints, over the ring beam and a further 500 mm up the side of the tank.
To prevent water or material getting between the coating and substrate, terminating grooves are cut in the floor concrete and the edge of the coating is bevelled by special termination tape which has a wire in it which cuts the polymer at an angle as the tape is removed.
In repairing the NSW water storage reservoir, the surface was given a Class 2 ½ blast profile as specified by the relevant Australian Standard. For steel surfaces, a Rhino primer is applied to further improve adhesion, which is then coated. For concrete, the profile used is usually between 3 and 5 according the standard profiles established by the International Concrete Repair Institute. After profiling, a Rhino primer is again applied and then the polymer coating is sprayed on.
Accessibility to a project site is an important planning issue. In the case of the NSW storage tank it was not too difficult. However, when working on structures—such as mine sites and oil rigs—in remote locations, the logistics require careful management. All equipment and materials need to be available and shipped together. Rhino Linings Australasia assists its dealers in developing best method procedures and practices for chemicals and machinery to be driven to site or transported by rail, road or sea to the nearest location.
Rhino Linings Australasia (RLA), part of the American-based corporation Rhino Linings, is the only manufacturer of spray-applied coatings in Australia.