Overview
ISO 7507-4:2010 - "Petroleum and liquid petroleum products - Calibration of vertical cylindrical tanks - Part 4: Internal electro‑optical distance‑ranging method" specifies a standardized procedure for calibrating large vertical cylindrical storage tanks (diameter > 5 m) using an internal electro‑optical distance‑ranging (EODR) instrument. The standard covers measurement planning, instrument set‑up inside the tank, selection of target points, measurement procedures, and the compilation of tank capacity tables. It applies to tanks with floating roofs or internal floating blankets and to tanks tilted up to 3% (with tilt correction per ISO 7507‑1).
Key topics and technical requirements
- Scope: Calibration method for vertical cylindrical tanks > 5 m diameter; applicable to floating‑roof/blanket tanks; tilt up to 3% with correction.
- Equipment & performance:
- EODR angular resolution/graduation recommended ≤ 0.2 mgon (≈ 3.142×10^-4 rad).
- Distance measurement graduation/resolution recommended ≤ 1 mm.
- Laser safety conformity to IEC 60825‑1.
- Instrument set‑up:
- Stable mounting near tank centre preferred; tripod legs must be steadied (magnetic bearers or equivalent).
- Two fixed reference target points marked inside the shell about 100 gon apart and near the instrument horizontal plane.
- Target point selection:
- Two sets per course (≈ 1/4 course height above lower seam and 1/4 below upper seam).
- Minimum number of target points increases with tank circumference (e.g., 10 points for circumference ≤ 50 m up to 36 points for circumference > 300 m - see Table 1).
- Targets at least 300 mm from vertical welded seams.
- Measurement checks & tolerances:
- Repeat reference target slope distances; uncorrected drift limit ~2 mm (differences beyond require repeat).
- Angular drift tolerance example: 0.01 gon (≈ 1.571×10^-4 rad).
- Supporting content:
- Annex A: verification procedures for EODR instruments.
- Annex B: calculations to derive internal radii.
- Annex C: calibration uncertainty analysis and examples.
Practical applications & users
- Used to produce tank capacity (volume–height) tables required for:
- Custody transfer and inventory control in petroleum terminals.
- Legal metrology and regulatory compliance.
- Terminal operators, calibration laboratories, metrologists, surveyors, and quality managers responsible for tank measurement programs.
- Particularly suited for large tanks and installations where internal EODR access is feasible and high‑accuracy volume data are required.
Related standards
- ISO 7507‑1:2003 - Strapping method; provides tilt correction procedures referenced by Part 4.
- IEC 60825‑1 - Laser product safety, cited for EODR laser classification and safe operation.
Keywords: ISO 7507-4:2010, EODR, tank calibration, calibration of vertical cylindrical tanks, tank capacity tables, petroleum tank measurement, electro‑optical distance‑ranging.
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