01/10/2025

How can you determine if your tank is experiencing corrosion, and what should you do if you discover it? 

Oil tanks are essential for many heating systems across the UK, but corrosion is one of the most common issues that can shorten their lifespan. Left untreated, corrosion can lead to leaks, heating inefficiency, costly repairs, and even complete tank failure. Homeowners who rely on an oil tank should pay close attention to signs of corrosion, especially with older or metal tanks.

What you’ll learn in this blog:

• The main types of oil tank corrosion and where they occur
• How to spot early visual warning signs of corrosion
• Key indicators of internal corrosion that aren’t always visible
• Effective prevention and protection methods to extend tank life
• Why professional tank inspections matter

Types of oil tank corrosion

Different types of corrosion affect tanks in different ways. Knowing how they develop helps you to spot the risks earlier:

1. General corrosion – gradual surface breakdown across the whole tank
2. Local corrosion – appears in specific areas, often where water collects
3. Pitting corrosion – small but deep pits at the bottom or on flat surfaces. Once pits are more than one-third of the wall thickness, replacement may be needed.
4. Weld metal corrosion, caused by electrolytic reactions between welding material and the tank’s metal, weakens joints. 

Conducting an external inspection yourself

Regular inspections are the first line of defence against oil tank damage. When checking your tank, pay attention to the following:

• Rust and flaking – Light surface wear is expected, but heavy rust, pitting, or flaking metal suggests advanced corrosion that could compromise the tank’s integrity.
• Perforation – Even the smallest pinhole, crack, or split in the wall of the tank is a serious warning sign and requires urgent attention.
• Seams and joints – These are natural weak points where corrosion often starts; check closely for any signs of separation, weakness, or rust build-up.
• Tank base condition – An uneven or unstable base can indicate hidden corrosion underneath or structural instability that puts the entire system at risk.
• Leaks or stains – Oil marks, damp patches, or pooling near the tank may point to active leaks caused by corrosion.
• Pipework and fittings – Inspect fill and vent pipes for signs of wear, blockages, or leaks, as these are common failure points that often accompany tank corrosion.

Signs of Internal Corrosion

Internal corrosion can be just as damaging as visible rust, but it’s often harder to spot. Key warning signs include:

• Water inside the tank – Water naturally sinks to the bottom of an oil tank and accelerates corrosion. Using a water detection paste can help identify its presence before it causes serious damage.
• Sediment build-up – Rust particles and sludge often accumulate at the bottom of the tank. This build-up can clog filters, reduce system efficiency, and signal ongoing internal corrosion.
• Reduced heating performance – If your boiler or heating system is running less efficiently, it may be a sign that your oil tank is leaking, failing, or suffering from hidden corrosion.

How to prevent and protect from oil tank corrosion

Preventing corrosion is far more cost-effective than paying for emergency repairs or a full tank replacement. Regular fuel testing, ideally twice a year, helps detect early signs of contamination and corrosion before they cause significant damage. Upgrading to a bunded (double-skinned) tank adds an extra layer of protection, containing leaks and spillages if corrosion does occur. Installing de-watering outlets is another smart step, as they help identify and remove water that gathers at the bottom of the tank. Most importantly, schedule professional inspections: ultrasonic testing can measure tank wall thickness to provide early warning signs of weakness, while full inspections by certified engineers are especially vital for older steel tanks.

Do you think your oil tank is in trouble? The team at Oil Tank Change is professionally trained to safely remove and dispose of your old oil tank and install a new, upgraded version.