External inspection: what can be established without emptying anything

What it covers

• Shell condition and coating, course by course, with ultrasonic thickness readings taken from outside.
• Foundation, ringwall, chime area and drainage, plus settlement measurement where it is scheduled.
• Roof condition from the outside, vents, gauging equipment, nozzles and manways.
• Appurtenances: stairways, platforms, handrails, grounding, insulation condition.
• Containment: bund integrity, drain valves, and whether the secondary containment would actually contain.
• Evidence of leakage, staining, past repairs and anything that changed since the last visit.

That is a substantial list, it needs no outage, and it is where a competent inspector earns their fee by noticing things that have been in plain sight for two years. On shop-built tanks the same list applies, as fuel tank inspection describes.

What it cannot establish

The floor. Its underside in particular, which is where aboveground tanks most often lose metal. No amount of external work resolves that question, and a report that implies otherwise should be read again carefully.

In-service screening methods exist, acoustic techniques and robotic tools that work through the product, and they are genuinely useful. What they buy is a better answer to “does this tank need to be opened next year or in five years”, not a replacement for opening it. See NDT methods.

Getting more out of the cheap inspection

1. Ask for thickness readings at fixed, marked, repeatable locations, the value is in the trend, and the trend needs the same points.
2. Ask for the same photographs each time, from the same positions. Change is what you are buying.
3. Include settlement measurement on a schedule, not only when something looks wrong.
4. Have the report separate conditions from recommendations, so a budget conversation does not turn into an interpretation argument.
5. Keep the previous report in the hands of the inspector doing this one. It is astonishing how often nobody does.

None of this costs more than asking. All of it is what turns a series of one-off visits into a dataset that supports a defensible interval.

No-entry, non-entry, external: the same idea under three names

Buyers search for this in at least four ways, and vendors use the words differently, which makes comparing proposals harder than it should be. A no entry tank inspection, a non-entry tank inspection and an external tank inspection all describe the same commitment: nobody goes inside, so the tank keeps working and no confined space entry is required. What differs between proposals is not the name. It is how much of the tank each one actually reaches.

• External examination. The shell, the roof from outside, the foundation, the appurtenances and the containment, with ultrasonic thickness readings taken from the outside. This is the baseline everyone means.
• External plus bottom screening from outside. Some techniques estimate bottom condition without entry. They narrow the uncertainty; they do not remove it, and a proposal that implies otherwise is overselling.
• Robotic or in-service internal inspection. Equipment enters the tank while it stays in service. Nobody enters, but this is not an external inspection, and it is priced and scoped quite differently.

The question that sorts three proposals using the same words is simple and it is about coverage, not method: what percentage of the floor does this reach, and what remains unknown when you hand me the report. A proposal that answers in a sentence is describing a scope. One that answers with a technique name is describing a sales position.

Frequently asked