ISO 23581:2020

INTERNATIONAL ISO
STANDARD 23581
First edition
2020-07
Petroleum products and related
products — Determination of
kinematic viscosity — Method by
Stabinger type viscometer
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents and materials . 2
6 Apparatus . 3
6.1 General . 3
6.2 Stabinger type viscometer . 3
6.2.1 Viscosity measurement . 3
6.2.2 Density measurement . 3
6.2.3 Temperature control . . 4
6.2.4 Stability . 4
7 Sampling and sample handling . 4
7.1 Sampling . 4
7.2 Sample handling . 4
8 Calibration and verification . 4
8.1 General . 4
8.2 Instrument . 4
9 Apparatus preparation . 5
10 Procedure. 5
10.1 Filling and cleaning . 5
10.2 Manual filling and cleaning using syringes . 5
10.3 Manual filling using sample displacement . 6
10.4 Automatic filling and cleaning by a sample changer . 6
11 Calculation . 7
12 Expression of results . 7
13 Precision . 7
13.1 General . 7
13.2 Repeatability, r . 7
13.3 Reproducibility, R . 8
13.4 Bias . 8
14 Test report . 8
Bibliography . 9
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, in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/TC 19, Gaseous and liquid fuels, lubricants and related
products of petroleum, synthetic and biological origin, in accordance with the Agreement on technical
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iv © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 23581:2020(E)
Petroleum products and related products —
Determination of kinematic viscosity — Method by
Stabinger type viscometer
WARNING — The use of this document can involve hazardous materials, operations and
equipment. This document does not purport to address all of the safety problems associated
with its use. It is the responsibility of users of this document to take appropriate measures to
ensure the safety and health of personnel prior to application of this document and fulfil other
applicable requirements for this purpose.
1 Scope
This document specifies a procedure for the determination of kinematic viscosity (ν) at 40 °C in the
2 2
range from 2 mm /s to 6 mm /s by calculation from dynamic viscosity (η) and density (ρ) of middle
distillate fuels, fatty acid methyl ester fuels (FAME) and mixtures of these using the Stabinger type
viscometer.
The result obtained using the procedure described in this document depends on the rheological
behaviour of the sample. This document is predominantly applicable to liquids whose shear stress and
shear rate are proportional (Newtonian flow behaviour). However, if the viscosity changes significantly
with the shear rate, comparison with other measuring methods is only permissible at similar shear rates.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3104, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity
and calculation of dynamic viscosity
ISO 3170, Petroleum liquids — Manual sampling
ISO 3171, Petroleum liquids — Automatic pipeline sampling
ISO 12185, Crude petroleum and petroleum products — Determination of density — Oscillating U-tube
method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
dynamic viscosity
η
ratio of the applied shear stress to the resulting shear rate of a liquid
3.2
kinematic viscosity
ν
ratio of the dynamic viscosity (3.1) to the density (3.3) of a liquid at the same temperature and pressure
Note 1 to entry: The kinematic viscosity is a measure of a liquid's resistance to flow under gravity.
3.3
density
ρ
mass of a substance divided by its volume at a given temperature
3.4
determinability
d
quantitative measure of the variability associated with the same operator in a given laboratory,
obtaining successive determined values using the same apparatus for a series of operations leading to a
single result, defined as the difference between two such single determined values
4 Principle
A test portion of a sample is introduced into the measuring cells, which are at closely controlled and
known temperature. The measuring cells consist of a pair of rotating concentric cylinders and an
oscillating U-tube. The dynamic viscosity is determined from the equilibrium rotational speed of the
inner cylinder under the influence of the shear stress of the test specimen and an eddy current brake in
conjunction with adjustment data. The density is determined by the oscillation frequency of the U-tube
in conjunction with adjustment data. The kinematic viscosity is calculated by dividing the dynamic
viscosity by the density.
5 Reagents and materials
5.1 Cleaning solvent, able to remove the sample from the measuring cell after the measurement and
be completely miscible with all constituents of the sample.
5.2 Drying solvent, highly volatile and miscible with the cleaning solvent, shall be filtered before use
and of an appropriate purity so that it does not leave any residues in the instrument.
NOTE 1 A separate drying solvent is not needed if the cleaning solvent also meets the requirements of the
drying solvent.
NOTE 2 Commercially available volatile petroleum spirit or cleaner's naphtha of technical grade or better has
proven suitable.
5.3 Compressed air, oil-free and filtered with a dew point considerably lower than the lowest
measuring cell temperature at which the instrument should be dried.
The pressure should be limited to 100 kPa.
Instead of compressed air, it is also possible to use inert gases, for example technical nitrogen. The
requirements given for compressed air are also valid here.
5.4 Certified reference liquids for
...