Through its participation in the development of legal metrology standards, NIST works to consider the interest of all stakeholders to avoid conflicts with related hydrogen standards developed by national and international standards and codes developing organizations. Currently, there are two international legal metrology standards which address commercial hydrogen measurement.
OIML R 81
"Dynamic Measuring Devices and Systems for Cryogenic Liquids" (1998)
Recommendation (R) 81 Status: NIST OWM is the Secretariat for the International Organization of Legal Metrology (OIML) Recommendation 81 and has responsibility for initiating work and ensuring that the standard progresses according to practices established by OIML.
This document corresponds to the legal metrology requirements in NIST Handbook 44 Section 3.34 Cryogenic Liquid-Measuring Devices.
The Secretariat’s response to the international project group’s comments on the first working draft of Part 1 Metrological and technical requirements and Part 2: Metrological controls and performance tests of R 81 was distributed on May 27, 2016. The group’s comments were incorporated, where possible, into a first committee draft (1 CD) also distributed on May 27th for review and input. Input on the 1 CD received September 2016 was incorporated into a second committee draft (2 CD) and distributed in late January 2018 for comment from the international project group and U.S. National Work Group. This draft model regulation includes the metrological and technical requirements and metrological controls and performance tests that apply to measuring devices and systems used for the dynamic measurement of cryogenic liquids in stationary, vehicle mounted, and vehicle refueling applications.
OIML R 139
"Compressed Gaseous Fuel Measuring Systems for Vehicles" (2018)
Recommendation (R) 139 is the OIML model regulation for equipment used to deliver compressed gases (natural gas, hydrogen, biogas, etc.) as fuel into motor and fuel cell vehicles, small boats, and aircraft. This document corresponds to the legal metrology requirements in NIST Handbook 44 Section 3.39 Hydrogen Gas-Measuring Devices – Tentative Code.
During its October 2018 meeting in Hamburg, Germany, the CIML approved a final draft revision of OIML R 139 (last published in 2014) expanding the application of the recommendation to further address hydrogen fueling systems. OIML R 139 (2018) is available on the OIML website at: https://www.oiml.org/en/publications/recommendations.
Major changes for hydrogen fueling systems in the document include:
- two new Accuracy Classes with the following maximum permissible errors (MPEs): for meters: 1.5 percent (2.0 AC) and 2.0 percent (4.0 AC); for complete systems: 2.0 percent and 3.0 percent (2.0 AC) and 4.0 percent and 5.0 percent (4.0 AC) for type evaluation/initial verification and for systems when in service, respectively, with no changes proposed to the MPEs for CNG fueling;
- a minimum measured quantity (MMQ) not to exceed 1 kilogram;
- revisions to durability test procedures to require only meters with moving parts be tested. Sections of the R 139 testing procedures were also modified making them applicable specifically to hydrogen fueling systems; and;
- recognizing the “pre-cooler,” depressurization correction device, and compressors as part of the measuring system, where appropriate, in (OIML) R 139, Part 1: Metrological and technical requirements, Part 2: Metrological controls and performance tests, and Part 3: Report format for type evaluation.