ISO 19970:2017

Overview

ISO 19970:2017 provides minimum requirements for metering and energy accounting of boil-off gas (BOG) used as fuel on LNG carriers during cargo transfer operations. The standard defines how to measure BOG flow, calculate calorific value, and verify the performance and calibration of the BOG measurement system so that the energy consumed on board can be reliably included in custody transfer and energy-balance calculations. It applies primarily during cargo transfer operations and, with modification, to BOG consumption at sea. Safety requirements are not covered.

Key topics and technical requirements

• Scope and definitions: Clear definitions for BOG, custody transfer, CTMS (custody transfer measurement system) and related terms used for LNG cargo operations.
• Design requirements: Flowmeters must be gas-tight, chemically compatible with BOG and suitable for installation in gas-dangerous zones; electrical components must meet area classification and safety standards.
• Meter selection and installation: Any flowmeter type may be used provided it meets the performance and installation constraints; meters are typically installed downstream of the low-duty gas compressor and gas heater.
• Resolution and accuracy: Indicating device (totalizer) resolution shall be better than or equal to 1 m or 1 kg. Maximum permissible error (MPE) at factory calibration: ±2% of reading across the operating range. Indicating device MPE: ±1% of the upper range limit. Thermometer and pressure gauge accuracy requirements are also specified (thermometers ≤ ±0.5 °C; pressure gauges ≤ ±1%).
• Calibration & verification: Flowmeters must be calibrated by the manufacturer against national-traceable standards before delivery; expanded uncertainty (k=2) of calibration shall not exceed 0.6%. Indicating devices require post-installation calibration and periodic verification with documented records. Reference-standard uncertainty for indicating-device verification shall be one-third of the MPE or 0.3%, whichever is greater.
• Metering & energy calculation: Procedures for measuring BOG quantity and calculating heating (calorific) value to determine the energy transferred during cargo operations.

Applications and users

ISO 19970:2017 is intended for professionals and organizations involved in LNG cargo handling and measurement:

• Shipowners and operators of LNG carriers
• LNG terminal operators and custody transfer teams
• Flowmeter and instrumentation manufacturers and calibration laboratories
• Classification societies, surveyors and regulators managing LNG custody transfer and reporting
• Naval architects and shipyards designing BOG fuel systems and CTMS integration

Practical uses include accurate fuel accounting during loading/discharge, compliance with commercial custody transfer procedures, energy balance reporting and supporting low-emission operations when BOG is used as fuel.

Related standards

Standards and documents referenced or relevant to ISO 19970:2017 include:

• ISO 10976 (terms related to refrigerated hydrocarbons)
• ISO 18132-1 (CTMS concepts)
• OIML R 140 (meter performance references)

Keywords: ISO 19970:2017, boil-off gas (BOG), LNG carriers, metering, flowmeter calibration, custody transfer, calorific value, CTMS, BOG measurement.