Home > Rhino Linings coatings help minimise water treatment plant degradation and chemical spills

Rhino Linings coatings help minimise water treatment plant degradation and chemical spills

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article image A waste water treatment plant settlement tank being prepared for protection by a sprayed Pure Polyurea coating

Rhino Linings Australasia has developed protective coatings that are helping waste water treatment plants minimise degradation and chemical spills caused by corrosion.

Billions of dollars have been invested by municipal councils as well as industrial and mining companies throughout Australia and New Zealand in equipment and infrastructure to process waste water and sewage. Corrosion of this infrastructure and the subsequent leakage costs industry in excess of $1B each year. The main assets that are impacted by corrosion in waste water treatment plants (WWTP) are the pipelines, storage tanks, clarifier ponds and sewage channels.

Many of these WWTPs have begun ageing, and are starting to require refurbishment or replacement. One method of refurbishing these assets is to carry out surface repairs and then apply protective coatings. These coatings must be strong, flexible and resistant to chemical attack.

According to Dennis Baker, Special Projects Engineer at the Gold Coast-based Rhino Linings Australasia (RLA), corrosion particularly affects the submerged parts of structures in WWTPs. Special consideration, therefore, has to be given when coating structures in sewage treatment plants.

Baker explains that one of the more corrosive by-products of sewage is hydrogen sulphide gas, which reacts with moisture on surfaces in a waste water plant and bubbles up to form sulphuric acid that corrodes concrete and gradually degrades the structure. In a pipeline, this may ultimately result in the collapse of the pipe wall. The modern requirement for capping storages to control excessive odours additionally increases gas concentrations.

RLA’s spray applied coating, Polyurea is ideally suited for waste water treatment, and is manufactured in Australia in a range of consistent formulations to suit various applications. A relatively modern material that has been developing rapidly during the past 10-15 years, Polyurea and particularly Pure Polyurea came to the forefront in 1980 when the entire outer surface of the Alaskan oil pipeline was coated with the formulation.

Pure Polyureas are formed when a liquid isocyanate is mixed with an amine based resin solution. Isocyanates are reactive because the double covalent bond attaching the carbon atom to nitrogen and oxygen atoms is easily broken to form single bonds in the more stable tetrahedral configuration around the carbon atom.

The Rhino Linings Pure Polyurea comes as a two-part solution mixed under high temperature and pressure (3000 psi at 65°C) in a specially designed spray apparatus. When applied, the excellent chemical cross linking produces a dense but flexible surface with the high density making the coating almost impervious to abrasion, water and chemicals.

Observing that many people didn’t know spray applied Pure Polyureas represented a very good solution for protecting most structures, Baker added that the engineering marketplace needed to be educated about the benefits and cost effectiveness of this versatile and adaptable material.

One company that is aware of the benefits of Polyureas is Queensland-based Satintouch, one of the premiere applicators accredited by Rhino Linings.

The chemicals utilised in the Polyurea and Pure Polyurea coatings mean that most of the work carried out by applicators is defined as an Environmentally Relevant Activity (ERA) under government legislation with the main activities falling under ERA 17, 38 and 57. These regulations require a licence for the abrasive cleaning and spray coating work to be conducted, and also place restrictions on the subsequent cleanup to minimise the impact on the natural environment around the worksite.

Satintouch Managing Director and owner Scott Blair commented that they have great support from Rhino Linings whose technical personnel have extensive knowledge of their products and provide advice on the execution of projects. Blair adds that they also get better results because the product is made fresh in Australia.

Key benefits of Pure Polyurea protective coatings include 'snap cure' properties forming a solid surface in a few seconds, which can be walked on without damage in less than a minute; ability to be sprayed at very high thickness (6000 microns and greater) on a sloping or vertical surface without sagging or running; coated surface easy to maintain, clean and recoat if necessary; high flexibility allowing coated surface to move with the expansion and contraction of the underlying structure caused by temperature changes, unlike epoxies and paints that form a solid rigid shell; and quick application and rapid cure time reducing disruption to the client's operations.

Baker states that Pure Polyureas are not affected by ambient moisture or temperature unlike all other coatings, and the facility can be returned to service in four hours with full cure in 24 hours.

Blair's company, Satintouch was involved with an unusual project at a cyanide production plant in Queensland. The company cleaned the existing tanks and concrete structures to remove the original coatings before priming them and applying the new Pure Polyurea coat. Blair recalled that it was a major challenge to recoat surfaces at an operating cyanide plant as there were very strict health and safety guidelines that had to be complied with, both in terms of the team preparing for the work each day and the actual operation of their equipment.

Most of Satintouch’s work is executed at the client’s facility, with about 40 per cent done in one of their yards in Mt Isa, Dalby or suburban Brisbane. For one such mining project, the larger tanks were cleaned and coated onsite, but transportable structures such as smaller tanks were trucked to one of the company's yards where the blasting systems are housed in buildings designed to limit the spread of the abrasive material and debris.

Satintouch's teams usually consist of three technicians and a supervisor working on-site along with an independent QA/QC inspector who oversees projects and ensures all procedures are followed and documentation prepared according to requirements and specifications. This includes the Rhino Linings procedures as well as the rules and guidelines of the ERA legislation.

The durability of Pure Polyurea and Polyurea as surface protection means that money can be saved because the structure has a longer repair/replace cycle. Baker says Polyurea coatings are also easy to repair with the area around a damaged surface reactivated using special primers and then covered with a new layer of Polyurea.

For projects involving heavy traffic and wear, Satintouch will usually install an indicator layer, which is bright red before the final top coat. Once the red layer starts to show through the main coating, it is clear that the structure or surface will need re-covering soon. Recording these wear rates enables better protection planning.

Rhino Linings coatings are covered by long guarantees, extending to 20- and 25-year warranties for water treatment facilities.

Spray applied Pure Polyurea and Polyurethane from RLA offer superior solutions for liquid containment. All coatings developed by the company for the water industry are continually tested to ensure they comply with the latest standards and have been certified safe for applications such as lining potable water storage tanks, marine aquariums, food freezers and grain silos. RLA coatings are tested for compliance with AS4020 at the Australian Water Quality Centre in Adelaide.

RLA's proprietary formulations, combined with innovative substrate preparations, result in excellent adhesion and a seamless surface over virtually any shaped structure. When applied correctly, the spray applied polymer coatings have attachment loads of at least 6 to 10 mPA (750 to 1250 psi); in most cases, the concrete substrate would give way before the coating peeled off.

In addition to hydrogen sulphide being corrosive to structures and pipes at WWTPs, the flammable, colourless gas also poses a health risk to workers. The typical rotten egg smell can be detected by people at concentrations ranging from 0.0005 to 0.3 parts per million (ppm). However, at higher concentrations, a person can lose their ability to smell the gas and might falsely think that H2S is no longer present, exposing them to high levels, which can seriously impact health. The Australian National Occupational Health and Safety Commission (NOHSC) has classified hydrogen sulphide as a hazardous chemical substance since 1995 and has set limits for anyone working around sewer pipes and treatment plants. The Occupational Exposure Limit (OEL) values for H2S are between 10ppm and 15ppm.

Part of the worldwide Rhino Linings Corporation, Rhino Linings Australasia Pty Ltd (RLA) was formed in 2000. RLA is the only manufacturer of spray applied coatings in Australia. 

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