Integrity assessment: turning readings into decisions somebody will sign

From measurement to decision

The chain is short and every link is a place where quality shows.

1. Measured thickness at defined locations, with the previous values for the same locations.
2. Corrosion rates derived from the difference over the elapsed time, which requires that the locations really are the same.
3. Remaining thickness compared with a minimum determined for that component and that duty.
4. Remaining life, and from it a next inspection date.
5. A repair list, separating what must be done before return to service from what can wait.

Step two is where thin reports fall apart. Without positional data from the previous inspection, a corrosion rate has to be assumed rather than measured, and an assumed rate produces an assumed interval.

What varies between providers

• Whether an engineer reviews the data, or whether the technician's spreadsheet is the deliverable.
• Whether recommendations are separated from requirements, a distinction that matters enormously six months later in a budget meeting.
• Whether the basis of the next interval is stated and reproducible, or asserted.
• Whether the report is usable by a different provider next time, or is a proprietary format that quietly locks you in.
• Whether findings come with enough detail, location, extent, photographs, for a repair contractor to quote from them without a second visit.

The last point has direct money attached. A findings list that a repair contractor can price without re-entering the tank is worth a great deal more than one that says “floor plate thinning noted”.

Repairs: what the assessment triggers

Typical outcomes range from housekeeping to major work, and they should arrive sorted rather than as a list.

• Patch plates or plate replacement on the floor, including the critical zone near the shell.
• Shell repairs, which carry their own design and welding requirements.
• Coating or lining repair or replacement, often the highest-value preventive action available.
• Cathodic protection installation or repair.
• Appurtenance work: nozzles, manways, vents, stairways and platforms.
• Foundation work, where settlement or chime-area condition demands it.

Whether those repairs happen during the same outage is the largest single cost variable in the whole exercise, and it is decided by planning rather than by engineering, see planning the work.

What to ask for in the deliverable

1. Data in a portable format, a spreadsheet you own, not only a bound report.
2. Location conventions documented well enough for another provider to reuse them.
3. The evaluation basis stated: what minimum was used, what corrosion rate, over what period.
4. Findings with photographs and dimensions, sorted by urgency.
5. An explicit statement of what was not inspected, and why.

Frequently asked