What drives the cost, and why the inspection is rarely the biggest number
This page contains no figures, because the inspection is rarely the largest number on the invoice. Cleaning, waste and lost service usually are. What follows is every driver behind the total, and the six questions that make two bids comparable.
Why a price per tank means very little
Two tanks of the same diameter, on the same site, in the same week, can differ by an order of magnitude in total project cost. The steel is identical; everything around it is not.
The drivers, in rough order of weight
1. Cleaning and waste
How much sludge, of what character, and where it can legally go. On heavy product service this frequently exceeds the entire inspection scope, and it is the item most often carried as an allowance rather than a price.
2. Lost service
A tank out of service is a tank not earning, and on a working terminal that number belongs in the business case even though it never appears on a contractor's invoice.
3. NDT coverage
Floor scanning coverage is the parameter that most often separates two bids. See NDT methods for the three numbers that belong in a written scope.
4. Access
Scaffolding, rope access, lifts, lighting and ventilation inside the tank. Tall tanks, insulated tanks and tanks in congested bunds all cost more to reach than to inspect.
5. Engineering hours
The evaluation, the report and any repair design. A bid with no engineering line is not cheaper, it is a data-collection exercise, and somebody else will have to do the thinking.
6. Repairs found on the way
Unknowable in advance, which is precisely why the mechanism for handling them belongs in the contract before the tank is opened.
7. Mobilization and location
Distance, site induction requirements, security clearance, and whether the provider already has crews in the region during that window.
The six questions that make bids comparable
- What floor scanning coverage is included, and how is the critical zone treated?
- How many shell thickness readings, at what pattern, and are locations marked for repeatability?
- Is cleaning included, at what assumed condition, and who owns the waste?
- Is an engineering evaluation included, or only data collection?
- What is the mechanism and rate for work found during the inspection?
- What exactly is excluded, in one list?
One email, sent to every bidder. The bid that answers all six is usually higher on paper and lower on completion.
Where money is genuinely wasted
- Opening a tank without a repair contractor available, then closing it and reopening it later.
- Buying data collection with no evaluation, and discovering months later that nobody can act on the result.
- Accepting a report with unmarked reading locations, which resets the corrosion-rate clock at the next inspection.
- Cleaning to a lower standard than the scan requires, then paying for a second clean.
- Comparing bids on headline price when one includes cleaning and the other does not.
Frequently asked
Why will nobody give a price over the phone?
Because the two largest variables, how much sludge is in the tank and what repairs will be found, are unknown until the work starts. A firm number offered before either is known is an opening position.
Is it cheaper to inspect several tanks at once?
Usually, because mobilization, site induction and equipment setup are spread. Whether it is operationally possible is a different question, see terminals and fleets.
Can we do the cleaning ourselves?
Some operators do, and it changes the commercial structure rather than removing the cost. It also puts the responsibility for the condition the tank is presented in, and for the waste, squarely on the site.
Last reviewed July 29, 2026.
Get the scope priced, not estimated
Coverage, cleaning assumption, evaluation, and the mechanism for found work. Request an inspection quote and providers can bid against the same document.
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.