ISO 4266-5:2002

Overview - ISO 4266-5:2002 (automatic tank thermometers for marine vessels)

ISO 4266-5:2002 provides guidance for the selection, accuracy, installation, commissioning, calibration and verification of automatic tank thermometers (ATTs) used to measure temperature of petroleum and liquid petroleum products in cargo tanks on board marine vessels. It applies to products with a Reid vapour pressure below 100 kPa and is focused on fiscal / custody transfer applications. The part excludes refrigerated and pressurized cargo tanks.

Key topics and technical requirements

• Scope and definitions - terms such as ATT, RTD (resistance temperature detector), single‑point (spot) and multiple‑point ATTs, and temperature transmitters are defined in line with ISO 1998 terminology.
• Precautions and safety - requirements for hazardous‑area certification, compatibility with inert gas systems (IGS), corrosion resistance, earthing (ship hull), and adherence to IMO/IEC/CENELEC/ISGOTT and national rules.
• Accuracy and uncertainty - ATT intrinsic error must be consistent with automatic level gauging so overall volume measurement uncertainty is not degraded. Calibration reference devices should be traceable to national standards.
• Calibration prior to installation - two options:
  • System calibration: ATT readout should agree with a controlled reference bath/oven within 0.25 °C at a minimum of three test temperatures across the working range.
  • Component calibration: temperature-equivalent resistance of sensing elements should agree within 0.20 °C at each calibration temperature; transmitters are also covered.
• Installation and commissioning - sensor location, mounting (thermowells where required), integration with level gauges, and verification at shipyard or during sea trials.
• On‑board verification and record‑keeping - procedures and frequency of subsequent verifications, and sealing/tamper protection for custody transfer use.
• Equipment types - guidance on RTDs, other temperature elements, single‑point vs. multiple‑point systems and readout averaging for temperature profiles.

Applications - who uses ISO 4266-5

• Ship owners and operators transporting petroleum and liquid products
• Terminal operators and cargo surveyors conducting fiscal/custody transfer
• Manufacturers and suppliers of marine ATTs, transmitters and readouts
• Classification societies, national measurement authorities and calibration laboratories
• Marine electrical and instrumentation engineers responsible for installation, verification and compliance

Related standards

• Other parts of ISO 4266 (Parts 1–4, 6) covering level and temperature measurement in other tank types
• ISO 1998 (petroleum industry terminology)
• Relevant IMO, IEC, CENELEC and ISGOTT guidance for marine electrical safety and hazardous areas

Keywords: ISO 4266-5:2002, automatic tank thermometers, ATT, marine vessels, temperature measurement, custody transfer, calibration, RTD, multiple-point ATT, maritime instrumentation.