Written by Kerryn Caulfield, Executive Director, Composites Australia Inc.
For industrial sites including vehicle refuelling facilities, bulk liquid storage tanks are buried for a reason. Stable ambient underground temperatures are a safer option for flammable and combustible liquids and there is less risk of damage from inclement weather, vehicle strike or vandalism.
Before modern materials, oil was once piped into, and transported in, wooden barrels. These were eventually replaced with steel which according to Dale Timms, General Manager and Director at Envirotank Pty Ltd, was the material of choice until the 90s.
‘When we entered the market in 1990, steel tanks were used exclusively for bulk liquid storage. Despite the demonstrated lifetime cost benefits over steel which tended to corrode, introducing fibreglass reinforced plastic as an alternative material was viewed with uncertainty – as a gamble,’ remembered Dale.
At the time, fibreglass tanks were more expensive than steel and asset owners were concerned with the initial costs. There was little concern and no penalties for environmental damage and in the event of corrosion and ultimately leakage, concern was for the cost of a loss of contents. Tanks were buried and out of sight.
According to Dale, product and material acceptance of fibreglass composite technology took close to 30 years. Having graduated from Monash University majoring in Industrial Chemistry, and almost a decade working on resins early with the industrial agrochemical giant, Monsanto, Dale recognized that chemistry could solve the environmental hazard.
The catalyst for change and materials acceptance was the steady introduction of environmental regulations and Australian and international standards that stipulated that buried tanks must be monitored 24 hours per day. Envirotank also introduced a 30 year warranty against corrosion, in line with its licensor’s warranty in the USA. Its double wall fibreglass tanks offer a full 360-degree secondary containment with a variety of monitoring devices, which can be installed in the interstitial space between the two walls. Due to the unique integral rib design, double wall fibreglass tanks are the strongest, most robust underground tanks available. They are rust-proof, maintenance free and formulated to be compatible with all petroleum alcohols and alcohol-gasoline mixtures.
Another catalyst for change has been the steady changes to fuel types; particularly ethanol-blended and oxygenated fuels, biodiesel fuels and ultra-low sulphur diesel. ‘Newer biofuels and the increased use of chemical additives are creating increasing incidents of aggressive microbiological-induced corrosion including the metal components in fuelling systems. Internal corrosion is now just as important as external corrosion.
One challenge was to try and predict where future fuels may go and what impact that would have on the long-term performance of the tank laminates. Consideration had to be given to the types of glass utilized but more importantly what resin would be compatible with both current fuels and potential future fuels. Future fuels were expected to have chemical oxygenates added to them to make them burn cleaner and these could come in a variety of formulations. There was also a push to introduce renewable additives such as ethanol and methanol as examples (these can be made by using agricultural products as the starting point, fermenting then distilling the alcohols for fuel use).
Oxygenates and alcohols are very aggressive to both steel and fibreglass. In partnership with FGI – now allnex – a terephthalic resin was formulated and underwent long-term testing to assess its suitability. Once it had passed these tests the resin was adopted by Envirotank for all fuel storage tanks.
Equally, these systems were developed to be suitable for Australian soil conditions including acidic sulphate soils which when exposed to air tend to be corrosive. These resin system innovations; as Dale explains were also introduced to the American market and are still in use today.
Now, over 30 years later, a heartening 96 per cent of underground fuel tanks in Australia are made from fibreglass of which 100 per cent are double walled including a structural inner and outer wall. To date, Envirotank has produced over 30,000 compartmented tanks. With up to four compartments separated by bulkheads and containing 4 different products, the use of fibreglass for underground fuel storage is not only an environmental win for the country and its taxpayers, it is also a financial win with lower up-front costs for the fibreglass tank versus the equivalent steel tank.
Envirotank has two plants, one based in Auckland and serving the entire country of New Zealand and another in Melbourne, Australia. Both plants have also supplied underground fuel tanks to the Asia Pacific Rim. For fuel storage, tanks range between 2,000 and 120,000 litres. Non-fuel tanks that don’t require a double wall are built to hold up to 450,000 litres.
The manufacturing facility is fully automated ‘chop and drop’ technology over a rotating mandrel and moving carriage delivering the resin. Internally programmed PLC controls to ensure glass and resin content, which in turn controls costs and delivers consistent products. Every tank is internally tested on site. The University of Queensland is used for tensile, flexural and modulus testing.