ISO 6996:2024

International
Standard
ISO 6996
First edition
Bunkering — Meter verification using
2024-03
master Coriolis mass flow meter
Soutage — Vérification des compteurs au moyen d’un compteur
massique étalon à effet Coriolis
Reference number
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ii
Contents  Page
Foreword .iv
Introduction .v
1  Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  Safety, health and environment during meter verification . 3
5  Metrological requirements for master meter . 4
5.1 General .4
5.2 Master meter requirements . .4
5.3 Maintenance of master meter status .5
6  Meter verification process . . 5
6.1 General .5
6.2 Requirements .5
6.3 Meter verification setup .5
6.4 Procedures .8
6.4.1 Pre-test meeting .8
6.4.2 Steps and actions .8
6.5 Documentation .9
Annex A (informative)  Safety, health and environment . 10
Annex B (informative)  Uncertainty budget for meter verification .13
Annex C (normative)  Critical performance parameter checklist for meter under test . 14
Annex D (normative)  Meter verification report .15
Bibliography . 17

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 28, Petroleum and related products, fuels
and lubricants from natural or synthetic sources, Subcommittee SC 2, Measurement of petroleum and related
products.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
The objective of this document is to set qualifying requirements for the master Corolis mass flow meter in
the bunkering context as well as to establish meter verification requirements and a verification procedure
for using the master meter. The meter verification is performed to:
a) verify the mass flow meter (MFM) that is used for custody transfer;
b) track the meter stability of the duty meter used in the MFM system at regular intervals during its
commercial service.
Regular meter verification provides another option to MFM users other than regular re-calibration. It is
more efficient, less costly and less time-consuming to monitor the measurement performance of the MFM
over time in compliance with the metrological requirements for custody transfer.
This document is intended to complement the meter verification requirements in ISO 22192 and ISO 6963.
In this document, the following verbal forms are used:
— “shall” indicates a requirement;
— “should” indicates a recommendation;
— “may” indicates a permission;
— “can” indicates a possibility or a capability.

v
International Standard ISO 6996:2024(en)
Bunkering — Meter verification using master Coriolis mass
flow meter
1  Scope
This document specifies the criteria and metrological requirements to qualify a master meter and
subsequently maintain its qualification. It establishes requirements and procedures for meter verification,
using a master mass flow meter to verify the accuracy and functionality of a duty meter installed on a
bunker tanker or at a terminal.
2  Normative references
There are no normative references in this document.
3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
accuracy
closeness of agreement between a measured quantity value and a true quantity value of a measurand
[SOURCE: ISO/IEC Guide 99:2007, 2.13, modified — Notes 1, 2 and 3 to entry deleted.]
3.2
error
E
measured quantity value minus a reference quantity value
[SOURCE: ISO/IEC Guide 99:2007, 2.16, modified — Notes 1 and 2 to entry deleted.]
3.3
error percentage
E %
error (3.2) divided by the same reference quantity value
3.4
master meter
Coriolis mass flow meter which is qualified to verify the meter under test (3.9)
3.5
maximum mass flow rate
Q
max
maximum flow rate to which the meter under test (3.9) and the master meter (3.4) have been qualified to
operate in compliance with the required accuracy

3.6
measurement uncertainty
non-negative parameter characterizing the dispersion of the quantity values being attributed to a
measurand, based on the information used
[SOURCE: ISO/IEC Guide 99:2007, 2.26, modified — Notes to entry deleted.]
3.7
meter factor
totalized mass quantity from the master meter divided by totalized mass quantity from the meter under test
3.8
meter stability
property of a measuring instrument whereby its metrological properties remain constant over time
Note 1 to entry: Stability may be quantified in several ways:
— in terms of a time duration over which a metrological property changes by a stated amount;
— in terms of the change of a property over a stated time.
[SOURCE: ISO 22192:2021, 3.32]
3.9
meter under test
MUT
Coriolis mass flow meter or any mass flow meter approved for custody transfer that is undergoing meter
verification (3.11)
3.10
meter verification report
report generated after the completion of the meter verification (3.11) containing the results and relevant
critical data pertaining to meter verification
3.11
meter verification
verification of the accuracy (3.1) of a meter under test (3.9) from the start of the first run to the end of the
final run
3.12
meter verification process
requirements and procedures for verifying the accuracy of the meter under test (3.9) by the master meter (3.4)
3.13
minimum mass flow rate
Q
min
minimum flow rate to which the meter under test (3.9) and the master meter (3.4) have been qualified to
operate in compliance with the required accuracy (3.1)
3.14
nominal K factor
NKF
coefficient entered in the accessory equipment by the verification officer (3.23), which relates a frequency
(mass) input from the Coriolis transmitter to a mass flow rate
Note 1 to entry: The nominal K factor is expressed in pulses per unit quantity (mass).
3.15
repeatability
proximity of a match among a series of results obtained with the same method on identical test material,
under the same conditions (same operator, same apparatus, same laboratory and short intervals of time)
[SOURCE: ISO 22192:2021, 3.39]

3.16
run
activity during which a quantity of flow is measured and assessed during meter verification (3.11)
3.17
run density
average density recorded during a run (3.16)
3.18
run pressure
average pressure recorded during a run (3.16)
3.19
run temperature
average temperature recorded during a run (3.16)
3.20
test service provider
company that is competent in all provisions of this document and qualified as a third party (3.21) to carry
out the meter verification process (3.12) for custody transfer purposes
3.21
third-party
person or organization that is unrelated to the manufacturer or supplier of the object of conformity or their
customers
3.22
verification flow rate
flow rate during meter verification (3.11) that is between the minimum mass flow rate (Q ) (3.13) and the
min
maximum mass flow rate  (Q ) (3.5) of the meter under test (3.9) and the master meter’s Q and Q
max min max
calibrated on oil
Note 1 to entry: The verification flow rate is determined from the data on historical operational flow rates of a bunker
tanker/terminal in consultation with a test service provider (3.20) during a pre-test meeting.
Note 2 to entry: Historical operational flow rates data show the data on flow rate typically used during bunkering.
This data lies between
...