💧 Kinematic Viscosity

Petrochemistry PN-EN ISO 3104

Overview

STATUS (as of 30.10.2026). PN-EN ISO 3104:2024-01 — Polish and English versions, implements EN ISO 3104:2023 and ISO 3104:2023 [IDT]; the Polish version was published on 20.05.2025. It replaced PN-EN ISO 3104:2021-03 (Polish and English versions, implementing ISO 3104:2020), which the PKN catalogue marks as withdrawn and replaced. ISO 3104:2023 is the fourth edition of the standard, published on 7.11.2023; on 29.09.2026 ISO decided to revise it — the current edition applies until a new one is published.

SCOPE (clause 1). The standard gives procedure A with manual glass viscometers and procedure B with capillary viscometers in an automated assembly — for determining the kinematic viscosity ν of transparent and opaque liquid petroleum products, fatty acid methyl esters (FAME), paraffinic diesel, HVO, GTL and diesel blends with up to 50 % FAME. Range: from 0.2 mm²/s to 300 000 mm²/s at temperatures from −20 °C to +150 °C. The dynamic viscosity η is calculated by multiplying the kinematic viscosity by the density of the liquid. The result depends on the behaviour of the sample: the method is intended for Newtonian liquids, and when the viscosity varies with the rate of shear, viscometers with different capillary diameters can give different results; the standard nevertheless includes the procedure and precision data for residual fuel oils, which under some conditions behave in a non-Newtonian way. The corresponding American standard ASTM D445 (5.1) notes that the correct operation of equipment in which petroleum products are used as lubricants depends on the appropriate viscosity, and that the viscosity of fuels is important for estimating their storage, handling and operating conditions.

EDITION (foreword). The fourth edition replaced ISO 3104:2020. Changes: manual procedure A has been designated as the referee method in case of dispute, the requirements for digital contact thermometers (Table 1) and the permissible drift of such a thermometer (7.3) have been updated, instructions for quality control referring to ISO 4259-4 have been added, the list of thermometers (Table B.2) has been updated and the calculation in Annex D has been corrected.

APPARATUS (clause 6). Viscometer calibrated in accordance with ISO 3105, with a calibration certificate from a laboratory meeting ISO/IEC 17025; when the acceleration of gravity in the testing laboratory differs by more than 0.1 % from that in the calibration laboratory, the constant is corrected: C₂ = (g₂/g₁) · C. The viscometer is suspended vertically within 1° (0.3° for types whose upper meniscus is offset from the lower one). Bath with a transparent liquid: no part of the sample may be less than 20 mm below the surface or less than 20 mm above the bottom; between 15 °C and 100 °C the temperature may not deviate from the set value by more than ±0.02 °C (largest difference in the bath 0.04 °C), outside this range — by more than ±0.05 °C. From 0 °C to 100 °C the temperature is measured with a calibrated liquid-in-glass thermometer with a CMC of ±0.04 °C after correction or with a digital contact thermometer (resolution at least 0.01 °C, maximum permissible error 0.02 °C, drift below 0.02 °C per year); outside this range — with a liquid-in-glass thermometer with a CMC of ±0.1 °C. Timing device: discrimination of 0.1 s or better, uncertainty of ±0.07 % of the reading over intervals of 200 s and 1 000 s. Automated apparatus is accepted if it matches the accuracy and precision of the manual apparatus; flow times shorter than 200 s are acceptable in it provided that the kinetic energy correction is calculated and does not exceed 3 % of the measured viscosity.

REAGENTS AND VERIFICATION (clauses 5 and 7). Strongly oxidizing or alkaline cleaning solution — alkaline solutions with a pH above 10 are not recommended because they change the viscometer constant, and after their use the calibration has to be verified. The sample solvent must be completely miscible with the sample (asphaltenic material may require a prewash with an aromatic solvent, for example toluene); the drying solvent must be volatile at the working temperature — when cleaning in a bath above 50 °C, acetone is not suitable. The viscometer calibration is verified with a certified viscosity reference standard (CRM) produced in accordance with ISO 17034 and traceable to the viscosity of water of 1.0034 mm²/s at 20 °C (ISO/TR 3666), by procedure A or B, with the acceptable tolerance band from Annex D. Viscometers used for silicone fluids, fluorocarbons and other liquids that are difficult to remove are not used for other samples.

HOW THE TEST PROCEEDS — ACCORDING TO THE 1994 EDITION (ISO 3104:1994 with Corrigendum 1:1997; we do not know the course of procedures A and B in the current edition). The viscometer is chosen so that the flow time is at least 200 s (or longer if ISO 3105 says so): a wide capillary for a very viscous liquid, a narrow one for a mobile liquid. Below the dew point the open ends of the viscometer are fitted with drying tubes. A sample containing solid particles is filtered through a 75 µm filter while charging. The charged viscometer stays in the bath until it reaches the test temperature — the time is established by trial (according to a note of the standard 30 min should be sufficient, except for the highest viscosities). The meniscus is set about 7 mm above the first timing mark and the time it takes to pass to the second mark is measured to within 0.1 s; the measurement is repeated, and when both times agree within the determinability, ν = C · t is calculated from their mean. Opaque liquids are tested in parallel in two viscometers; residual fuel oil and similar waxy products are first heated for 1 h at (60 ± 2) °C, stirred and shaken, and a portion in a flask is kept for 30 min in a boiling water bath — the determination is completed within 1 h of this pretreatment. Dynamic viscosity: η = ν · ρ · 10⁻³ (η in mPa·s, ρ in kg/m³ at the test temperature). The result is reported to four significant figures, together with the test temperature.

WHAT WE DO NOT GIVE HERE. The course of procedures A and B according to the current edition (clauses 11 and 12), the preparation and conditioning of samples (clause 10, Annex C), the quality control requirements (clause 9), the way of determining the tolerance band for agreement with the reference standard (Annex D) or the current precision values — determinability, repeatability and reproducibility (clause 16). We only know the titles of these clauses; we do not carry over the precision values of the 1994 edition, because the standard has been revised twice since then.

Method principle

The time is measured for a fixed volume of liquid to flow under gravity through the capillary of a calibrated glass viscometer under a reproducible driving head and at a known and closely controlled temperature. The kinematic viscosity is the product of the measured flow time and the calibration constant of the viscometer: ν = C · t.

The dynamic viscosity is the product of the kinematic viscosity and the density of the liquid at the test temperature. Procedure A (manual viscometers) is the referee method; procedure B uses glass capillary viscometers in an automated assembly.

Applications

• Transparent and opaque liquid petroleum products (clause 1)
• FAME, paraffinic diesel, HVO, GTL and diesel blends with up to 50 % FAME (clause 1)
• Residual fuel oils — the standard includes the procedure and precision data for their non-Newtonian behaviour (clause 1)
• Diesel fuel — requirement of the Polish regulation on quality requirements for liquid fuels: 2.000–4.500 mm²/s at 40 °C, for diesel with improved low-temperature properties 1.500–4.000 mm²/s (Dz.U. 2024 item 1018, Annex 3 No 17)
• Calculation of dynamic viscosity from kinematic viscosity and density

Key parameters

Standard

Standard number

PN-EN ISO 3104:2024-01

Title (PL)

Przetwory naftowe — Ciecze przezroczyste i nieprzezroczyste — Oznaczanie lepkości kinematycznej i obliczanie lepkości dynamicznej

Title (EN)

Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and calculation of dynamic viscosity

Step-by-step procedure

1. Choosing and verifying the viscometer

   A viscometer whose range covers the expected viscosity; the calibration is verified with a viscosity reference standard by procedure A or B, with the tolerance band from Annex D (clause 7). 1994 edition: flow time of at least 200 s.

2. Preparing the bath

   The bath is brought to the test temperature within the limits of 6.5.3, reading the thermometer with the corrections from the calibration certificate; below the dew point the viscometer is protected with drying tubes.

3. Preparing the sample and charging

   Conditioning, visual inspection and filtering of the sample — clause 10 and Annex C. 1994 edition: the charged viscometer stays in the bath until it reaches the test temperature (the time is established by trial).

4. Measuring the flow time

   The time for the meniscus to pass between the timing marks is measured to within 0.1 s. 1994 edition: two measurements whose agreement is assessed against the determinability; opaque liquids in two viscometers.

5. Calculating the result

   ν = C · t (C in mm²/s², t — mean flow time in s); dynamic viscosity η = ν · ρ · 10⁻³ (mPa·s, ρ in kg/m³). 1994 edition: result to four significant figures with the test temperature.

6. Cleaning the viscometer

   Cleaning — clause 13 of the current edition. 1994 edition: between determinations rinsing with the sample solvent, then with the drying solvent, and drying with filtered dry air for 2 min or until the last trace of solvent is removed.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard does not address all hazards associated with its use — safety measures are established by the user (warning of the standard)
• Strongly oxidizing cleaning solutions are highly corrosive and hazardous in contact with organic materials (1994 edition, warning to 5.1: with chromic acid a full face shield and protective clothing with gloves)
• The bath can operate up to +150 °C (scope of the standard) — risk of burns when removing viscometers

Frequently asked questions