The difference between Tank manufacturing materials
Is there a difference between tank manufacturing materials?
Original article is from Bushman Tanks, who are a manufacturer of high quality rainwater tanks and industrial tanks.
Water tanks are available in a range of suitable materials including plastic, galvanised steel, Aquaplate®, Zincalume®, fibreglass, and concrete. All are suitable providing that the materials used are at least of food-grade standard (AS2070). If the water is to be used for human consumption the tank material must comply with the requirements of potable-water standard (AS/NZS4020).
Water tanks – Galvanised Steel
The typical Aussie water tanks that we all remember are the galvanised steel water tanks and until recently was the most common material used in the manufacture of rainwater tanks. Zincalume and Aquaplate® are rust resistant coatings that ensures that Galvanised steel is rust resistan.
The taste of rain water could be affected by a new tank because it can leach excess concentrations of zinc. Galvanised water tanks may need to be flushed out before they are used. The most common material used in the manufacturing of metal rainwater tanks is galvanised steel. Galvanising is the process of applying zinc to steel. These galvanised tanks could be soldered or joined. This join creates what is actually a joint or seam. Solder consists of a combination of lead & tin which is melted with a hot iron and applied to a joint. Galvanised steel is not inherently resistant to corrosion and must have rust-resistant coatings applied. Initial corrosion of galvanised steel normally leads to production of a thin adherent film that coats the surface of the tank and provides protection against further corrosion. Always make sure that this film is not disturbed when cleaning tanks such as these. New steel tanks may leach excess concentrations of zinc, which could affect the taste of stored rainwater, but is not a health risk. Before using these tanks flush them out. Aquaplate® (plastic coated steel) has a food-grade polymer skin bonded to a galvanised steel base. The polymer used in plastic coated steel is not resistant to prolonged exposure to sunlight, so tanks must have a top cover in place at all times. Kerosene or similar chemicals typically used as mosquito larvicides can cause degeneration of the polymer coating and should not be used.
The polymer coating must not be damaged when cleaning or installing the water tank. If the coating is damaged, it should be repaired immediately using an appropriate sealant to prevent corrosion of the metal portions of the tank. A warranty of 20 years is typical for a steel water tank. While the raw material has a 20yr warranty, the manufactured product (the water tank) has a 10yr warranty, on a pro-rata basis. Ensure that you always read the warranty. Most steel tank installations require concrete slab, minimum 100mm thick with steel reinforcing, or else you void the warranty. Water tanks can also be manufactured out of stainless steel. The problems that are typical to galvanised steel tanks (such as rust or corrosion) do not occur in this material. However, the cost is substantially higher than normal plastic coated steel tanks. The stainless steel tanks still require a seam, where the sheets are joined.
Concrete tanks
Concrete water tanks and ferro-cement water tanks are generally strong and long-lasting. They are very heavy, and difficult to handle. 5000G tank would weigh about 8 tonnes. Smaller tanks are available for above ground but most concrete water tanks are installed underground.
New concrete water tanks can often impart tastes and may leach line. This can increase the pH of the water. Accordingly these concrete water tanks will need to be flushed before use. Concrete water tanks can be either delivered complete for small or medium sized tanks, as well as poured on site for medium and large water tanks.
Concrete water tanks delivered on site in a complete form are craned off the truck and onto a prepared sand base. Sometimes these tanks can be in one to three pieces. Concrete sections are sealed primarily with a rubber or synthetic sealing ring or some form of sealant. Sealant is then applied to the inside of the tank at the join to stop the water leaking out. Cracking and leaking is suffered by concrete water tanks and is one of the most common complaints. The cracks can be repaired as long as the tank can be drained. In a few bad cases, a plastic liner is required, which can be very expensive
The standard for concrete tanks allows for a certain amount of leakage, while the standard for plastic tanks does not allow any leakage.
Plastic tanks
The most popular type of water tank in Australia is the plastic or poly water tank, This is typically created with the rotational moulding process. For over 20 years these tanks have been created this way. Plastic tanks and plastic liners must be constructed of materials that are at least of food-grade standard (compliant with AS 2070) and if the water is to be used for human consumption the plastic material must actually comply with the requirements of potable-water standard (AS/NZS4020). The rotational moulding industry is one of the few industries that have a comprehensive standard that covers both the raw materials used, and the manufacturing and workmanship of the completed water tanks. Polyethylene (Poly) is non-corrosive for long life. Polyethylene won’t rust or corrode like metal water tanks do over time, which adds to their services life. Poly tanks are lightweight and easy to handle – no heavy equipment needed.
Poly tanks are usually made in one single piece. They have no joints or seams where part of the tank has been welded together, and no sealants are used to join any parts of the tank together.
Leading manufacturers such as Bushmans Tanks are manufactured from materials that comply with the light transmission standard (AS/NZS4766) that inhibits the growth of algae. Light transmission is a potential problem that fibreglass tanks have a need to manage.
Polyethylene tanks can be recycled at the end of their service life. Only virgin plastics can be used to make water tanks because of potable water regulations. However, there are many other product applications for recycled plastic. The recycled plastic can go on to enjoy another life when new sun and heat protection is added.
Fibreglass
A food grade coating must be on the tanks interior surface when manufactured. The coating is cured before the tanks are put up for sale. The coating is cured before the tanks are offered for sale. One advantage of Fibreglass is that it is very stiff or rigid. This means that tank walls can be relatively thin to manage the water pressure. However the disadvantage of this very rigid material is that it can tend to be brittle in nature, being prone to cracking and leaking. The skills of the individual very much determine the process in this case. The process is dependent on the skill of the individual. Because of the process this means that their can be variations from tank to tank.
Fibreglass water tanks allow more light entry than other types of tanks, which encourages algal growth. To prevent this, tanks should be sealed with a black covering inside or painted on the outside. Some tanks are manufactured with sufficient pigment to stop this problem occuring.
