Tank Calibration
Mohammed Tazul Islam, GM (Commercial)
What is Tank Calibration?
Tank calibration is the process of precisely determining the relationship between
the measured volume and the height of liquid within a tank. This creates a
calibration chart (or strapping table) that is essential for accurate inventory
management, custody transfer, and loss control
Why is it Important?
Accurate calibration is crucial for financial transactions and regulatory
compliance, ensuring fairness in trades and preventing discrepancies in stock
accounting.
Types of Tank Calibration Process
• External Calibration
• Internal Calibration
External Calibration
• This method involves taking physical measurements of the tank's exterior
using instruments like a strapping tape and a plumb line. It's often used for
large, accessible tanks and is the most traditional method. It can be timeconsuming and labor-intensive.
Internal Calibration
• This is a more modern approach, using a laser scanner or similar technologies
from inside the tank. It provides highly accurate and detailed 3D models of the
tank's interior, accounting for any irregularities or deformities. This method is
faster and safer for tanks with limited external access.
External Calibration Methods
• Manual Strapping (API 2550 / ISO 7507-1)
•
•
Uses a calibrated steel tape to measure tank circumference and height.
Suitable for vertical cylindrical tanks.
• Optical Reference Line Method (ORLM) – ISO 7507-2
•
Uses theodolites to measure tank dimensions based on optical lines.
• External Electro-Optical Distance Ranging (EODR) – ISO 7507-5
•
Laser-based method to measure external dimensions with high precision.
Internal Calibration Methods
• Internal Electro-Optical Distance Ranging (IEODR) – ISO 7507-4
•
Laser scanning from inside the tank to map geometry.
• Physical Calibration with Water
•
Filling the tank and measuring volume at known heights.
• Datum Plate & Deadwood Measurement
•
Measures internal obstructions and floor shape for accurate volume correction.
Calibration Standards
Standard
Description
API 2550
API 2551
API 2552
ISO 7507 (Parts 1–5)
ISO 12917
Manual strapping for upright cylindrical tanks
Horizontal tanks calibration
Spherical tanks calibration
International standards for vertical tank calibration
Calibration of horizontal cylindrical tanks
Calibration for Different Tank Types
• Fixed Roof Tank Calibration: Typically calibrated using strapping (external
measurement) or optical reference line method. The tank is measured from the
outside to create a strapping table that relates liquid height to volume.
• Floating Roof Tank Calibration: Requires specific attention to the weight
and position of the floating roof. The calibration must account for the roof's
displacement at different levels, which affects the liquid volume. A specialized
calibration chart is required to reflect this variable.
• Spherical and Bullet Tank Calibration: Due to their unique shapes, these
tanks are often calibrated using internal optical methods like laser scanning.
This allows for precise measurement of the complex geometry to create a
highly accurate volume chart.
Calibration Type Selection Criteria
• Tank Type: The geometry of the tank (e.g., fixed roof, floating roof,
spherical) dictates the most suitable method.
• Accuracy Requirements: High-value products or custody transfer points
demand higher accuracy, often requiring automated or internal methods.
• Cost and Time: Manual methods are generally less expensive but more timeconsuming. Automated methods have a higher initial cost but offer long-term
efficiency and accuracy benefits.
• Safety and Accessibility: Hazardous environments or hard-to-reach tanks
often necessitate the use of automated or remote-sensing techniques to ensure
personnel safety.
Factors Affecting Calibration Accuracy
• Temperature: The volume of a liquid, as well as the tank material itself, can
change with temperature. Calibration charts must be corrected for temperature
to maintain accuracy
• Tank Deformation: Tanks can warp or deform over time due to pressure,
temperature changes, or foundation settlement. This can significantly affect
the accuracy of the calibration chart.
• Liquid Density and Specific Gravity: The volume-to-weight relationship is
dependent on these factors, which are critical for mass-based measurements
and are incorporated into the final calibration calculations.
Error in Calibration
• Constant Error: The consistent inaccuracy in data persists the constant error
with the major volume reading. So, you should check it.
• Random Error: If you want to check the unpredictable volume and
inaccuracy, there are basic flow that you need to follow for checking the
random fluctuation.
• Systematic Error: The systematic error works with a flow on the consistent
pattern with specific condition on the part of the ongoing inaccuracy.
• Gross Error: The significant mistakes of the measurement accuracy on flow.
Error in Calibration (contd)
• Constant Error: The instrumental errors work with the faults in measuring
the sensor with the calibration of storage tanks.
• Random Error: If you want to check the unpredictable volume and
inaccuracy, there are basic flow that you need to follow for checking the
random fluctuation.
• Systematic Error: The systematic error works with a flow on the consistent
pattern with specific condition on the part of the ongoing inaccuracy.
• Gross Error: The significant mistakes of the measurement accuracy on flow.
Error in Calibration (contd)
• Instrumental Error: The instrumental errors work with the faults in
measuring the sensor with the calibration of storage tanks.
• Reading Error: Reading errors work with the interpretation. The
misalignment has the standard with the measurement scale.
• Calibration Drift: The calibration drift has the accuracy with the
measurement on the unpredictable storage tank.
• Environmental Error: The environmental factors has the errors with tank
measurement on external vibrations.
HOW DO YOU
ENSURE ACCURACY?
You can deal with the ensuring parts on
the maintenance of accuracy with the
basis of correct changes.
Ensuring Accuracy
• Regular Calibration: Ensure accuracy on conducting the storage tank setup.
• Temperature Monitoring: Manage the temperature variation and changes
with the volume of readings.
• Sensor Maintenance: Maintain the sensor of the measuring tank setup level
with the sensor accuracy management on calibration of volume tanks.
• Environmental Controls: Check the reduction of the external factors on the
protection and storage of environmental controls.
Ensuring Accuracy (Contd.)
• Periodic Inspection: Conduct the periodic inspection with storage tank
components with enhancing accuracy.
• Training and Procedures: Look after the tank measurement with the actual
enhancement on accuracy.
• Quality Control Measures: Manage quality control with the measurement
and contribution.
• Data Validation: The regular data validation with cross-checking has the
accuracy with nconsistency.
CONCLUSION
Manage the deals with the aspects with the transparency and
objectives with the basic change with tank calibration.