ISO 4266-4:2023

Overview

ISO 4266-4:2023 specifies requirements and guidance for the measurement of temperature in atmospheric storage tanks containing petroleum and liquid petroleum products (Reid vapour pressure < 100 kPa) using automatic tank thermometers (ATTs). Focused on fiscal/custody transfer applications, the standard covers selection, accuracy, installation, commissioning, calibration and verification of ATTs. It is not applicable to refrigerated tanks or cavern storage.

Key topics and requirements

• Scope & applicability: Defines when ATTs are acceptable for custody transfer and limits (atmospheric tanks, products with RVP < 100 kPa).
• ATT types and descriptions: Single‑point (spot), multiple‑point, averaging and variable‑length ATTs; common sensing elements such as RTDs and associated transmitters.
• Accuracy and error sources: Guidance on intrinsic ATT error, installation/operating condition errors, overall accuracy, and calibration requirements (including calibration prior to installation).
• Installation & thermowells: Requirements for proper placement of spot, averaging and variable‑length sensors and appropriate use of thermowells for electronic elements.
• Calibration & verification: Procedures for initial factory calibration, initial field verification after installation, and subsequent periodic verification and record keeping-emphasizing system-level verification for custody transfer.
• Safety and equipment precautions: Follow manufacturer guidance, safety regulations for hazardous areas and ensure equipment withstands service conditions.
• Data communication: Requirements and considerations for transmitting and receiving ATT temperature data to readout systems for inventory and custody accounting.

Practical applications

ISO 4266-4 is used to ensure reliable, defensible temperature measurements that affect volume correction and value in custody transfer of petroleum. Typical uses include:

• Terminal and tank farm custody transfer systems
• Refinery storage tank monitoring for inventory reconciliation
• Calibration and verification procedures by metrology labs and service providers
• Procurement and acceptance testing of ATT equipment by operators and integrators

Who should use this standard

• Tank storage operators and terminal managers
• Measurement and metrology engineers
• Instrumentation and control technicians
• Custody transfer auditors and regulators
• ATT and thermowell manufacturers and system integrators

Related standards

• ISO 4266 series (other parts covering level and temperature measurement)
• ISO 1998 (petroleum industry terminology) - normative reference used in ISO 4266-4

Keywords: ISO 4266-4, automatic tank thermometer, ATT, storage tank temperature, RTD, custody transfer, petroleum measurement, tank thermowell, calibration, verification.