In-Service Tank Inspection and API 653: What Asset Owners Need to Know
PetroBot Technologies ·
API 653 governs the inspection, repair and reconstruction of atmospheric storage tanks. Its internal inspection requirements have historically meant draining, cleaning and degassing a tank before anyone can assess the floor — weeks of lost service and significant cost. Robotic in-service inspection changes the economics of that decision.
What API 653 requires from internal inspection
API 653 requires periodic internal inspection primarily to assess the condition of the tank bottom, which cannot be evaluated from outside. The interval is set from the measured or assumed corrosion rate of the floor plates, capped by the standard. When floor condition data is missing or outdated, owners are forced into conservative assumptions and earlier shutdowns.
The quality of the next interval calculation therefore depends directly on the quality of floor thickness data. More measurement points, taken more recently, produce a defensible basis for risk-based inspection planning.
Where robotic in-service inspection fits
In-service robotic crawlers enter the tank through existing openings and survey the floor while the tank remains in operation — no draining, cleaning or degassing. The robot performs ultrasonic thickness (UT) measurements and visual inspection on the bottom plates, mapping wall loss while the product stays in the tank.
That data serves two purposes. It gives the inspection engineer a current picture of floor condition to support interval decisions and repair planning, and it lets owners rank which tanks in a farm actually need to come out of service first, rather than scheduling shutdowns by calendar alone.
- UT thickness mapping of bottom plates while the tank stays in service
- Visual records of coating condition, pitting and weld areas
- No confined-space entry, scaffolding or human exposure to product vapours
- Inspection data delivered in a format the certifying inspector can use
Safety and certification considerations
Tanks holding hydrocarbons are explosive atmospheres, so equipment that enters an in-service tank must be certified for the zone. PetroBot's ITIS Rover carries ATEX certification for explosive atmospheres, and inspections are planned through a technical suitability review covering product type, temperature, access openings and floor layout before mobilisation.
In-service robotic inspection does not replace the role of the authorised inspector or the standard itself — it supplies the data that makes their decisions better-informed and their intervals defensible.