An oil tank fails quietly. The shell thins from the inside, water collects under the base, a weld weeps into the bund — and none of it announces itself until the level drops or the ground smells. Inspection is the only thing standing between a slow problem and an expensive one, and on a commercial site it is also the record that proves you were looking.
This guide covers what an inspection actually examines, how often it should happen, what the findings mean, and when looking at a tank stops being enough.
How Often Should a Tank Be Inspected?
There is no single interval that suits every installation. Frequency follows risk — age, construction, what is stored, and what is downhill of it.
| Check | Typical interval | Carried out by |
|---|---|---|
| Visual walk-round | Monthly, and after any delivery incident or severe weather | Site staff |
| Formal inspection with written report | Annually | A competent engineer |
| Ultrasonic thickness testing | On older steel tanks, on any tank with suspected corrosion, and before a tank is relied on for another service period | Specialist contractor |
| Post-incident inspection | Immediately after any overfill, impact, fire or suspected leak | A competent engineer |
Insurers and landlords frequently set their own intervals, and those can be shorter. Where a tank sits within 10 metres of a watercourse or 50 metres of a borehole, treat the annual inspection as a minimum rather than a target.
The Inspection Checklist
A proper inspection is not a walk past the tank. It works through the whole installation in a fixed order, so nothing is skipped because it was awkward to reach.
Tank Shell
- Corrosion, pitting, blistering and paint failure, especially along the lowest seams
- Distortion, bulging or sagging — a sign the base is not supporting it
- Weld condition on steel tanks; crazing, splits and UV damage on plastic
- Staining or weeping anywhere on the shell or under it
- Impact damage from vehicles or plant
Base and Supports
- Cracking, settlement or movement in the base slab
- Whether the base still extends beyond the tank on every side
- Standing water or debris trapped under the tank
- Full support across the base rather than bridging across piers
- Vegetation growing against or under the tank
Bund and Containment
- Cracks, joint failure or penetrations through the bund wall or floor
- Rainwater standing in the bund — and how it is being removed
- Whether the bund still holds the required volume after any modification
- On integrally bunded tanks: interstitial space clear, no oil in it
- Bund alarm present and working, where fitted
Pipework and Fittings
- Corrosion and support of above-ground runs; flexible connections in date
- Valve condition and operation, including the isolation valve at the tank
- Filter and water trap condition; evidence of water in the system
- Underground lines: any evidence of settlement, staining or pressure loss
- Fire valve fitted, routed correctly and not painted solid
Fill Point and Gauges
- Fill point secure, labelled, lockable and within the containment
- Contents gauge readable and accurate against a dip
- Overfill prevention or alarm present, audible and tested
- Vent clear and correctly positioned
- Delivery area free of spill staining
Surroundings
- Separation distances still met after any building work nearby
- Drains, gullies and watercourses within reach of a release
- Vehicle protection in place and undamaged
- Access for a tanker, and for inspection and maintenance
- Spill kit present, stocked and in date
Where the site has separation distances or siting questions, see oil tank location and siting rules.
What the Findings Mean
A useful report does not just list observations — it grades them, so the site knows what to do on Monday and what can wait for the budget cycle.
| Grade | What it means | Examples |
|---|---|---|
| Monitor | Note it, photograph it, check again next time | Light surface corrosion, minor paint failure, vegetation encroaching |
| Plan | Needs work, but can be scheduled | Base cracking, bund holding rainwater, gauge inaccurate, flexible connection due |
| Act now | Fix before the next delivery | Failed overfill alarm, fire valve inoperative, bund penetration, isolation valve seized |
| Out of service | Stop using the tank | Active leak, shell perforation, severe distortion, wall thickness below safe limit |
A report you received is a defect you know about. From the moment it lands in your inbox, an unremedied finding is a known risk — which is exactly what an insurer or a regulator will ask about afterwards.
Who Should Carry It Out
For a planned assessment and written findings, see Britteco’s commercial fuel and oil tank inspection service.
A site walk-round can be done by anyone who knows what to look for. A formal inspection cannot. The person doing it should be competent in oil storage installations, familiar with current OFTEC technical standards and the applicable Building Regulations, and independent enough to write down bad news.
What a report should contain
- Date, site, tank identification and capacity
- Construction type, approximate age and containment arrangement
- Findings against each part of the installation, not just the tank
- Photographs of anything noted
- A clear grading, with recommended actions and timescales
- The name and competence of the person who carried it out
A verbal “it looks fine” is not an inspection, and it is worth nothing when you need to prove diligence.
When Looking at It Is Not Enough
A steel tank corrodes from the inside outwards. Water settles at the bottom, sits under the fuel, and eats the floor plate where nobody can see it. By the time corrosion shows on the outside, a great deal of wall thickness has usually gone.
Ultrasonic thickness testing measures what is actually left, without taking the tank out of service. It is the difference between an opinion about a tank and a number. Worth doing when a tank is over ten years old, when there is a history of water in the fuel, before committing to another service period, or before buying a site with an existing installation — see ultrasonic thickness testing.
Where the inside of the tank needs to be assessed directly, that is a cleaning and internal inspection job — see tank cleaning.
Keeping the Records
The inspection is half the value; the file is the other half. Keep reports, photographs, the actions taken against each finding, and the commissioning and waste documentation for any work done. If the site is leased, keep a written note of which party is responsible for the tank.
What that file protects you from — and who carries the legal duty — is covered in oil tank regulations UK.
Domestic Tanks
Home heating oil tanks need the same attention on a smaller scale. For domestic tank inspection and servicing, our sister company LV Fuel Services handles that work directly.
Want It Inspected Properly?
Britteco inspects commercial and industrial fuel and oil tanks across the UK, and issues a written report with photographs, findings and clear timescales — not a verbal all-clear.
