ISO 4266-2:2023

Overview

ISO 4266-2:2023 - "Petroleum and liquid petroleum products - Measurement of level and temperature in storage tanks by automatic methods - Part 2: Measurement of level in marine vessels" provides guidance for automatic level gauges (ALGs) used aboard tankers and barges. The standard covers both intrusive and non‑intrusive ALGs for liquids with a Reid vapour pressure below 100 kPa, addressing accuracy, installation, calibration and onboard verification. It also explains conditions for use of marine ALGs in fiscal and custody transfer when buyer and seller agree.

Key topics and requirements

• Scope & applicability
  • Marine ALGs for petroleum and liquid petroleum products (RVP < 100 kPa).
  • Not applicable to refrigerated cargo tanks (see ISO 18132‑1 / ISO 18132‑3).
• Definitions
  • Terms such as ALG, dip (innage), ullage, intrusive and non‑intrusive ALGs, still‑pipe, etc.
• Precautions & safety
  • Manufacturer, classification society and ISGOTT considerations; equipment safety and material compatibility.
• Performance and accuracy
  • Intrinsic error, calibration prior to installation, initial shipyard adjustment, errors from operating conditions and overall accuracy expectations.
  • Annexes describe accuracy limitations for level and volume measurement on marine vessels.
• Installation guidance
  • Recommended ALG locations, manual calibration check points, and special considerations for inerted tanks, trim/list and product temperature.
• Onboard verification & calibration
  • Initial and routine verification methods (innage/ullage gauging and alternate methods), adjustment procedures, verification schedules and record keeping.
• Data communication
  • Use of remote readouts, telemetry and data receiving for monitoring and potential use in custody/fiscal transfers.
• Fiscal/custody transfer
  • Guidance on contractual requirements and constraints when marine ALGs are used for commercial transfers.

Applications and who uses it

ISO 4266-2:2023 is intended for:

• Ship operators, tanker and barge owners
• Cargo surveyors and marine measurement technicians
• Oil traders, buyers and sellers engaged in custody/fiscal transfer agreements
• Instrument manufacturers (marine ALGs, radar/microwave gauges, float/servo systems)
• Classification societies, port authorities and regulatory bodies The standard helps ensure consistent level measurement, reliable calibration practices, safe installation, and defensible verification records for commercial and operational decision‑making.

Related standards

• ISO 18132‑1, ISO 18132‑3 - refrigerated cargo tanks
• ISO 4512 - manual methods for tank level measurement
• ISO 1998 series - petroleum industry terminology

Keywords: ISO 4266-2:2023, automatic level gauge, marine ALGs, level measurement, tankers, barges, custody transfer, installation, calibration, verification.