A tank is not only inspected on its shell. API 653 defines a precise perimeter, starting from the foundation and reaching as far as the first flange of the nozzles.
- ✓ Title: Tank Inspection, Repair, Alteration, and Reconstruction
- ✓ Steel tanks built to API 650 and API 12C
- ✓ Extended perimeter: foundation, bottom, shell, roof, nozzles
- ✓ Fifth edition, November 2014
An atmospheric storage tank is an apparently simple structure and in reality a composite one: it rests on a foundation, has a bottom in contact with the ground, a shell that thins as it rises, a roof, a supporting structure, appurtenances and nozzles. Each of these elements ages by its own mechanisms, and the document that governs their inspection takes account of this by listing them one by one.
API 653 is titled “Tank Inspection, Repair, Alteration, and Reconstruction”, that is «Tank Inspection, Repair, Alteration, and Reconstruction». The document states that it concerns steel storage tanks “built to API 650 and its predecessor API 12C”: built to API 650 and its predecessor API 12C. It is therefore not a universal code for any container, but a code tied to a clearly identified construction family.
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The physical delimitation is equally explicit. The coverage of the document comprises “the tank foundation, bottom, shell, structure, roof, attached appurtenances, and nozzles to the face of the first flange, first threaded joint, or first welding-end connection”: the tank foundation, the bottom, the shell, the structure, the roof, the attached appurtenances and the nozzles up to the face of the first flange, the first threaded joint or the first welding-end connection. Beyond that point one enters the domain of other references.
The perimeter defined by the document
| Element | What the document states |
|---|---|
| Title | Tank Inspection, Repair, Alteration, and Reconstruction |
| Edition | Fifth edition, November 2014 |
| Tanks concerned | Steel tanks built to API 650 and API 12C |
| Parts included | Foundation, bottom, shell, structure, roof, attached appurtenances |
| Limit on nozzles | Up to the first flange, the first threaded joint or the first welded connection |
Large surfaces, numerous measurements
The practical difference between a tank and a pipeline lies in the scale. A shell is a wide surface, organised in overlapping courses, and the bottom can extend over hundreds of square metres. Anyone surveying the condition of such a structure does not collect a few dozen values but campaigns of numerous measurements, which make sense only if they remain traceable to the exact point at which they were taken.
For this reason, in applications of this kind two features of the instrument count more than any others: the speed with which it produces reliable readings and the ability to store them in a structured way. The CMX series reaches 250 readings per second in scan mode, while export to the management software makes it possible to reconstruct the map of the survey afterwards.
Recommended instruments
| Instrument | Why on storage tanks |
|---|---|
| Dakota CMX3-DL | Corrosion gauge with A-Scan and data logger for extensive campaigns |
| Dakota CMX10-DL | Scan mode at 250 readings per second on wide surfaces |
| Dakota MX1-DL | A-Scan and B-Scan for reading the trend along the path |
| DakMaster | Management of the data downloaded from the instrument and reporting |
Frequently asked questions
No. The document states that it concerns steel storage tanks built to API 650 and its predecessor API 12C. Tanks built to other construction rules do not fall within that perimeter.
Up to the face of the first flange, the first threaded joint or the first welding-end connection. Beyond that point one leaves the perimeter described by the document.
The fifth edition dates from November 2014 and has since been supplemented by addenda. Always check which edition and which addenda apply in your contractual context before proceeding.
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