Corrosion of water and wastewater
infrastructure, and in some cases the subsequent leakage, costs the industry in excess of $1B each year. The main assets that are impacted 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.
Rhino Linings, an American corporation based in San Diego, has been manufacturing a range of spray applied polymer coatings for more than 30 years. In early 2000, a local coatings company was acquired by the American company, to form Rhino Linings Australasia Pty Ltd and establish manufacturing and distribution in Australasia.
Based on the Gold Coast, Rhino Linings Australasia is the only manufacturer of spray applied coatings in Australia. The company sources all its materials from local suppliers except for some very specialised chemicals which are imported from the parent company in America. Being a local manufacturer allows the company to be more responsive to customer requests.
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. Special consideration has to be given when coating structures in sewerage treatment plants. One of the by-products of the sewage is hydrogen sulphide gas, which can form sulphuric acid when mixed with water vapour.
A major consideration in applying any surface treatment to a structure is the requirement to minimise downtime. The beauty of the coatings is that they are rapid setting. They can be sprayed them on and they cure in six seconds for Pure Polyurea and 20 seconds for Polyurethane.
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 which allows them to stretch and shrink as substrates expand and contract due to temperature and ground fluctuations.
All coatings developed by Rhino Linings for the water industry are continually tested to ensure they comply with the latest standards. Rhino Linings coatings 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
It is important to prepare the substrate properly before applying any coating. This is done by ‘profiling’ the surface of the structure to the appropriate standard. Profiling involves blasting sand or similar material at a surface under high pressure to roughen the surface which allows the coating to better ‘key’ to the substrate.
To ensure that the polymer coatings are applied correctly, all projects endeavour to comply with Australian Standard 3894, which requires the completion of such elements as substrate condition, weather condition and time reports. Completion of the reports acts as a reminder to the person applying the polymer that the appropriate conditions existed at the project site for the safe and effective application of a coating.
There are various hold points in any project which allow for checking the preparation, primer and coating application. At any of these, accredited inspectors can certify that the work conforms to the standard. Larger Rhino Linings Applicators either have a NACE or ACA inspector on staff or have a very good relationship with a local inspector.
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 futher 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.