In-Service Robotic API 653 Evaluation of Tank Bottom Settlement

September 16, 2022

Square Robot, the world leader in robotic tank inspection, continues advancements in measuring tank bottom settlement. By inspecting the tank bottom while it is under load, in addition to increased data density through robotics, tank owners are able to get a better representation of the tank’s settlement without any concern about the bottom “bouncing back” when it is taken out-of-service for inspection. These advancements allow Square Robot to provide an accurate differential elevation map of the tank in accordance with API 653. 

Traditionally, tank bottom settlement is measured as a part of an API 653 out-of-service inspection, where the inspection team uses laser levels starting at the shell moving across the diameter to the tank center and lasering a point every 10 feet until the center has been reached. This antiquated system poses a number of challenges to tank owners when it comes to reviewing the data. The biggest challenge is the “bounce back” that can occur in tank bottoms, where they revert to their designed shape, after the load from the product is removed. 

Square Robot’s in-service tank inspections are able to provide the most accurate tank bottom settlement reports because the product remains inside the tank. The SR-1 robot naturally contacts the tank bottom via three omnidirectional wheels. While rolling in contact with the bottom, the robot acquires Phased Array Ultrasonic Testing (PAUT) data for bottom thickness examination and simultaneously collects pressure data with its onboard pressure sensor. Pressure measurements are converted to depths based on fluid density and compensated for changes in atmospheric pressure and product height. 

Three depths are computed from each depth measurement using the robot’s position, attitude, and the lever arms between the pressure sensor and each omnidirectional wheel. A fourth virtual depth measurement is created when scanning the critical zone to determine elevations within 1 foot of the shell.  All depth measurements are positioned in a reference frame attached to the tank which allows a 3D point cloud to be created. Subtracting the deepest depth value provides the desired elevation data. The horizontal plane going through the lowest point establishes the datum (zero elevation) for which all differential elevations are reported against. The position and elevation data are then processed to evaluate shell and edge settlement, as well as localized bulges and depressions. 

“We are always looking at ways to provide tank owners with the most accurate reporting on the health of their tank,” said Jerome Vaganay, CTO Square Robot. “By using the sensors on our robot, we can produce an accurate and high density tank bottom differential elevation map.”

As the industry continues to rely more heavily on data, robotics will play an integral part in gathering this data. Square Robot is uniquely positioned through its in-service inspection to provide the most accurate data on the tank settlement and provide tank owners a complete settlement report which is integral to identify any potential issues that may arise.

Please reach out with any questions and to learn more about our robotic inspection services.

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