Frequently asked questions about tank inspection
The questions that come up most often, answered as briefly as they can honestly be answered. Where the answer depends on your product, your jurisdiction or your data, that is said rather than glossed over.
One thing before the questions
Almost every answer below depends on two things: what the tanks hold, and what the last inspection actually recorded. Where an answer looks evasive, it is usually because the honest version needs those two facts.
Frequently asked
How often do tanks have to be inspected internally?
The interval is calculated from measured corrosion rates and remaining thickness, within limits set by the applicable standard, it is not a fixed number. [Interval provisions to be cited from the current edition before publication.] See the framework page.
Who is allowed to perform and certify the inspection?
A certified inspector, named in the report with their certification number, supported by qualified NDT technicians working to written procedures. Ask for both at bid stage.
Can the floor be assessed without emptying the tank?
It can be screened by in-service methods, which help decide which tank to open first. It cannot be assessed to the standard of an internal inspection, see NDT methods.
What does an inspection cost?
No figure appears on this site. On an internal inspection the cleaning, the waste and the lost service usually exceed the inspection itself, the drivers are on the cost page.
Is API 653 a legal requirement?
It is an industry standard. It becomes binding through a regulation, an insurer, a contract or a company standard that adopts it, and which of those applies to you varies by product, size and state. [Applicable instruments to be cited before publication.]
Our records are incomplete. Does that matter?
It matters for the corrosion rate, which needs previous readings at the same locations. Without them, the next inspection becomes a baseline rather than a trend, still valuable, and a reason to fix the reporting format now.
What happens if a tank fails an inspection?
“Fails” is not really the vocabulary: an inspection produces findings and an evaluation, which lead to repair, a change of service, a derate or retirement. Which options exist is an engineering judgement, see integrity assessment.
Can the same company inspect and repair?
It often shortens the outage, and it creates an obvious question about who benefits from a finding. Both arrangements are used; the one you choose should be a decision rather than an accident.
Do we own the inspection data?
Only if the purchase order says so. Ask for raw readings and their locations in an editable format, it costs nothing at bid stage and is nearly impossible to obtain afterwards.
How long does the tank have to be out of service?
Long enough to empty, clean, degas, inspect, evaluate and repair. The inspection is days; the outage is usually weeks, see planning the work.
Who carries out the inspection?
We do. The examination, the thickness readings, the bottom evaluation, the calculations and the report are ours, and the report carries the certification number of the inspector who attended. That number and its expiry are on the about page, and checking it against the public register is worth the two minutes.
Last reviewed July 29, 2026.
Ask about a specific tank
General answers only go so far. Tell us the asset, the product and the last inspection date, and we will answer against your actual fleet.
Steel Tank Inspection carries out API 653 and STI SP001 inspections on welded steel storage tanks: external and internal examinations, ultrasonic thickness readings, bottom evaluation, and the report the standard requires.