Overview
ISO 7507-5:2000 specifies an external electro‑optical distance‑ranging (EODR) method for the calibration of non‑insulated vertical cylindrical storage tanks used for petroleum and liquid petroleum products. It covers external measurement procedures for tanks with diameters greater than 5 m (including cone‑up, cone‑down and flat bottoms) and describes how to derive 3‑D coordinates, circumferences at vertical levels and the subsequent tank capacity tables.
Key topics and technical requirements
- Scope and applicability: External EODR calibration for vertical cylindrical tanks > 5 m diameter; produces capacity tables for volumetric measurement and inventory control.
- Measurement principle: Use of external stations to obtain angular and slope‑distance data to tank top, bottom and tangential points; computation of 3‑D coordinates and circumferences to create capacity tables compatible with ISO 7507-1 procedures.
- Number of stations: Determined from tank nominal circumference C by N = C / 8, rounded up to the nearest even number. Minimum 8 stations; typical upper limit 36 (more if tank deformation requires it).
- Targeting and points: Tangent measurements on each course (two per set: near lower seam and near upper seam), plus top/bottom bisects on top and bottom courses. Additional points recommended for deformed shells.
- Equipment: EODR instrument (angular and distance units), single‑corner prisms on holders, tribrachs (min. 5), tripods (min. 5), ranging pole, retro‑reflective tape, paint and plate thickness meters; bottom calibration equipment per ISO 7507‑1 Annex C.
- Calibration controls & verification: Instrument verification per manufacturer and ISO 7507‑4 guidance; ensure measurement uncertainty stays within required limits.
- Precautions and safety: Laser class must conform to IEC 60825‑1 (Class 1 or 2). Electrical equipment must meet area classification (IEC 60079‑10). Tanks must have been filled at least once with equal/greater density liquid; if calibrated with liquid on board, contents must be static and temperature/density/dip recorded. If wall temperature differs by >10 °C between empty and full parts, tank must be entirely full or empty.
Practical applications
- Producing accurate tank calibration and capacity tables for inventory management, accounting and custody transfer.
- Non‑intrusive field calibration where internal access is limited or hazardous.
- Periodic verification of tank geometry after repairs, settlement or deformation.
- Use in terminal operations, refineries, storage depots and metrology services.
Who should use it
- Tank calibration specialists and surveyors
- Measurement and custody transfer engineers
- Oil & gas terminal operators and maintenance teams
- Metrology laboratories and third‑party calibration providers
Related standards
- ISO 7507 series (Parts 1–4, 6) - other tank calibration methods (strapping, optical methods, internal EODR, monitoring)
- ISO 4269‑1, ISO 8311, ISO 9091 (related tank calibration and measurement standards)
- IEC 60825‑1 (laser safety), IEC 60079‑10 (hazardous area classification)
Keywords: tank calibration, EODR, electro‑optical distance‑ranging, vertical cylindrical tanks, capacity tables, petroleum storage tanks, ISO 7507-5.
