What is the Life Expectancy of a Steel Oil Tank?
Most steel oil tanks nowadays are bunded (double-skinned). While these provide greater environmental protection than older, single-skinned tanks (and is the reason why single-skinned tanks are gradually being phased out), bunded tanks also tend to deteriorate more slowly than single-skinned tanks.
The outer skin of steel bunded oil tanks is the first line of defence against harsh environmental conditions that cause corrosion, the main cause of deterioration. While the outer skin may corrode over time, the inner skin remains intact. In our experience, this can make quite a difference. For example, we see that:
– Whereas single skin plastic tanks usually last between 5 to 10 years, their bunded plastic cousins will last 10 to 20 years
– And whilst a single skin steel tank can be relied upon to last 10 to 20 years, a bunded steel tank can usually last 20 to 30 years with proper maintenance. We see even longer lifespans than this for metal bunded oil tanks.
What causes a steel oil tank to deteriorate?
As we have already mentioned, corrosion is the chief reason why a steel oil tank will deteriorate, but there are other factors. Placing a wall, fence or hedging around a tank may do a good job of concealing it but can also encourage moss growth and humidity that will increase corrosion.
Galvanic corrosion happens when the steel of the tank is connected to another metal – for example, copper pipe or fittings – and causes an electrochemical reaction at the point of contact.
Although oil itself has anti-corrosive properties, condensation can accumulate inside the tank. As water is heavier than oil, it sinks to the bottom of the tank and will start to corrode the steel. Microbial growth can develop at the interface between the oil and water layer at the bottom of the tank. Over time, the microbes change the pH (acidity) of the tank contents which can cause corrosion from the inside out on occasion. The same bugs can also contaminate the heating oil
Always ensure your oil tank is positioned on a suitable base which lifts the tank well above the ground and directs rainwater away from the tank. It must also fully support the bottom of the tank and be solid enough to resist ground movement and subsidence; movement and lack of support will put extra strain on the tank welds, causing them to crack.
Damage also shortens a tank’s lifespan. This is obvious in the case of a high-force impact, but even a scratch in the tank’s protective coating, if untreated, will encourage corrosion. Constant vibration is another common, although easily overlooked, physical contributor towards deterioration, as over time it can cause cracks in welds and fittings.
Poor quality and contaminated oil will also cause a tank to deteriorate faster. Don’t be tempted by attractively low prices; always buy from a reputable distributor.
How can I increase the life of my steel oil tank?
Buying a good quality tank and maintaining it regularly will ensure you get the longest use. Painting it regularly, say. every 12 months will also ensure its longevity. Follow the maintenance steps mentioned below (under ‘Maintaining your oil tank’).
Installing it properly
It’s also important to have your oil tank professionally installed. Don’t try to shortcut this stage by installing it yourself or using a cowboy plumber. An OFTEC-approved installer will ensure the oil tank is correctly installed on a suitable base and in a good location. Each of our oil tanks comes with one of these cards which points to clear installation and maintenance instructions for your installer:
Maintaining your oil tank
Regular and thorough maintenance will extend the life of any tank. To maintain the outside of the tank, keep it as clean and dry as possible. Give it a six-monthly wash with mild detergent and a hose-down on a day when it can dry quickly and nip any growth of moss or lichen in the bud.
Once it’s dry, look for any leaks at seams or joints. Check for scratches and remove any flaking paint. If you see exposed bare metal, neutralise any rust and apply a primer, then a topcoat.
Consider buying a Steel Oil Tank Maintenance Pack; ours includes 1 litre of steel tank paint, gloves, small brush, roller and paint tray. It even includes a tank sponge which can absorb up to 0.7 litres of water that may have accumulated at the bottom of your oil storage tank.
If your tank has been fitted with a sacrificial anode, check it is still securely connected to the tank and replace it if required. Signs to look for include flaking or pitting of the anode’s surface, or if it is reduced to half its original size.
Check the base for signs of movement or damage, as a tank on an unstable base will eventually develop cracks around the weld lines and fittings.
If your tank is bunded, regularly check the bund for moisture and debris. Regular draining of any water and sludge from the bottom of the tank will also prevent microbial growth and corrosion.
An internal inspection of the tank should ideally be carried out every five years; the best time for this is when the tank is at its emptiest, just before it is refilled. We recommend using a professional tank cleaning and inspection service for this.