Overview
Above Ground Storage Tank (AGST) Calibration is a precision process used to determine the exact volume of a storage tank for accurate measurement of stored products. Calibration is performed in accordance with the API Manual of Petroleum Measurement Standards Chapter 2, Section 2D (API MPMS 2.2D), using advanced 3D laser scanning technology.
This method, also known as EODR Calibration (Electro Optical Distance Ranging), operates on the principles of LiDAR (Light Detection and Ranging). The process uses a high-precision total station or 3D laser scanner to collect x, y, z coordinates of the internal tank geometry.
Principle of EODR (3D Laser Calibration)
EODR calibration technology uses a laser source that detects surfaces and objects within a 360-degree field and up to 120 meters in range. The scanner captures millions of data points, generating a 3D model of the tank interior, enabling accurate volume computations. This technique minimizes human error, enhances data reliability, and ensures repeatable measurements.
Pre-Assessment for Tank Calibration
Before initiating the calibration process, a pre-assessment must be conducted by the Calibration Engineer to verify that:
- All major repairs or modifications to the tank structure are completed.
- NDT (Non-Destructive Testing) and Hydrostatic Testing have been performed in accordance with API 650 and API 653 standards.
- The tank interior is clean, dry, and free of scaffolding or obstructions.
Fuel Oil Tank Calibration Procedure
Calibration (or strapping) is the science of determining the true volume of a tank at various fill levels. This data is used to develop a calibration chart or volume table, which is critical for inventory control, custody transfer, and product reconciliation.
Key Terminologies in Tank Calibration
| Term | Definition |
|---|---|
| Datum Plate | The plate located at the base of the tank on the vertical axis beneath the dipping reference point. Used as a measurement origin. |
| Dip Hatch | An opening on the tank roof for sampling, dipping, or ullaging. |
| Dip Pipe | A guide pipe installed from the dip hatch down to the datum plate, essential for floating roof tanks. |
| Shell Plate Thickness | Thickness (in mm) of each tank shell course, measured via Ultrasonic Thickness Measurement (UTM). |
| Tank Height | Vertical distance between the dipping reference point and the datum plate. |
| Dip | The distance from the datum plate to the product surface level inside the tank. |
| Course | A horizontal circumferential ring of steel plates forming the tank shell. |
| Deadwood | Internal components that affect tank volume. Positive deadwood adds to volume; Negative deadwood reduces it. |
EODR Calibration Procedure
Setup – The 3D laser scanner is placed inside the tank.
Scanning – The scanner rotates and collects millions of data points from the internal surface.
Data Processing – Specialized software generates a 3D point cloud and computes the actual geometry of the tank.
Volume Calculation – From this 3D model, a detailed volume table is created, showing precise tank capacities at incremental fill heights.
Storage Tank Calibration Chart Includes:
- Shell plate thickness per course
- Total tank height
- Safe filling height
- Tiltness or out-of-plumb deviation
- Elevation or vertical position of tank
- Dimensions of internal appurtenances (nozzles, manholes, heating coils, etc.)
- Floating roof height and design specifics
- Temperature and density of product (for volume correction factors)
Benefits of EODR Calibration
- Non-intrusive and fast data collection
- High-accuracy measurements
- No need for manual strapping or emptying tank
- Enhanced safety and efficiency
- Conforms with API, ISO, and industry standards
Conclusion
Modern above ground storage tank calibration using LiDAR-based EODR technology provides unmatched accuracy and reliability. By leveraging 3D scanning, facilities can optimize inventory control, ensure compliance with international standards, and reduce operational downtime during measurement.