How Long Do Plastic Bunded Oil Tanks Last?

If you’re going to invest in a new heating oil tank, you’ll naturally want to know how long it will last before you need to replace it. As a rule of thumb, plastic bunded oil tanks can be expected to last on average between ten and fifteen years, but several factors influence how long your tank will last.

Not All Plastics Are Equal

Bunded oil tanks are generally rotationally moulded in one of two plastics: high-density polyethylene (HDPE) or cross-linked polyethylene (XLPE).

HDPE is a robust, UV-resistant plastic, chosen for its resilience and resistance to chemical interactions with heating oil. It is also highly resistant to impact damage and will survive minor impacts without cracking or splitting. Most plastic bunded oil tanks are made from HDPE.

XLPE is a more costly material than HDPE but offers greater resistance to warping, cracking and UV damage. For this reason, it is more popular for use in more extreme environments.

How Environmental Exposure Affects Tank Longevity

While plastic bunded oil tanks are designed to last outdoors, extreme conditions can shorten their lifespan. These include:

New 1000 litre slimline plastic bunded oil tank

New 1000 litre slimline plastic bunded oil tank

Sunlight

The UV radiation in sunlight is a prime cause of plastic degradation, leading to it gradually warping, discolouring and weakening. The plastic will also become more brittle, making it prone to cracking and splitting.

To delay this process, the HDPE and XLPE used to rotationally mould plastic bunded oil tanks contain UV stabilisers. However, prolonged exposure to direct sunlight will accelerate this deterioration.

Temperature

Plastic is put under stress by the extremes of climate temperatures, particularly if it is exposed to them for long periods. As with UV radiation, cold weather can make the plastic brittle, and if this is followed by hot weather that causes expansion, the plastic can crack. 

Water

Plastic oil tanks are themselves highly resistant to water, particularly compared with steel tanks which rust, but long-term exposure to rain can affect the strength and stability of the base that the tank is mounted on if the rain isn’t drained away.

If the base deteriorates, this can place uneven stresses on the tank that, with the added internal pressure from the oil, can warp and crack.

How Proper Installation Prolongs Tank Life

Attention to detail when siting and installing your plastic oil tank can make a significant difference in how long it will last. The following steps will ensure you get the best from your tank.

  • Choose the Right Location

The ideal location for a plastic oil tank is a well-drained site that offers shelter from direct sunlight. The north side of a building will always have more shadow but pay attention to the regulations on siting an oil tank near a building.

  • Make a Good Base

An oil tank should always be installed on a level base, as the slightest tilt or undulation will place unwanted stresses on the tank. Please see our detailed advice on the topic here.

Use materials such as wet-pour concrete or paving slabs on a firm, compacted sub-base, as these are not only non-combustible but are less likely to shift or sink over time.

Finally, ensure that the area around the base is well-drained and free of tree roots. If the area tends to retain moisture, consider installing a small land drain to divert surface water away from the tank.

  • Ventilate the Area

Maintaining a balanced temperature inside the tank requires good airflow around the tank, as this can mitigate the effects of temperature extremes.

Maintenance Tips to Extend the Life of Your Bunded Oil Tank

No oil tank – whether bunded or unbunded, plastic or steel – can be installed and forgotten and be expected to have a long lifespan. Routine checking and maintenance are essential not only to extend the life of your tank but also to protect the environment and prevent the loss of valuable oil.

Regular Inspection

An oil tank should be inspected every three to six months and more frequently if it is exposed to particularly harsh conditions. During an inspection, look for:

  • cracks or warping, as these may indicate that UV exposure or temperature fluctuations are causing the plastic to degrade
  • discolouration and surface changes, which are also signs of UV exposure
  • leaking fuel or patches can be early signs of tank failure that should be attended to immediately.

Keeping Clean

Maintaining a clean oil tank will make it easier to spot the above changes while keeping the area around the tank clean and clear of vegetation and debris will help prevent corrosion of metal fittings and erosion of the foundation. Be particularly strict about preventing plants such as ivy from spreading to the area, as these will quickly erode mortar and brickwork.

Shield the Tank from Sunlight

If the tank cannot be protected against sunlight, consider using a UV-resistant cover as an extra layer of protection.

Maintain Drainage

If you have already taken the precaution of installing a land drain, make sure this works efficiently during and after heavy rainfall. If you have used an open channel drain, clean this out regularly to remove any debris such as dead leaves.

If the drainage problem is relatively minor, excavating a small trench around the tank base and backfilling it with gravel might be sufficient.

When to Consider Replacing Your Tank

Regular inspection will generally reveal when your tank should be replaced, and as plastic bunded oil tanks last ten to fifteen years on average, you may want to inspect it more frequently as it approaches this age. Small cracks, warping and persistent leaks are all signs that you should replace your tank; even though they seem minor, and you may feel tempted to wait a bit longer, replacing the tank before major issues arise will save you the cost of spillage in terms of lost oil, and possibly fines for environmental pollution.