ISO 23581:2024

Overview

ISO 23581:2024 specifies a laboratory procedure for determining kinematic viscosity (ν) of liquid petroleum products and crude oils using a Stabinger type viscometer. The method calculates kinematic viscosity from measured dynamic viscosity (η) and density (ρ) using a combined concentric-rotor (viscometer) and oscillating U‑tube (densitometer) system. The standard covers both transparent and opaque liquids, and is primarily intended for fluids exhibiting Newtonian flow; for non-Newtonian fluids results depend on shear rate and direct comparison with other methods is limited.

Key topics and requirements

• Scope and applicability: Includes base oils, formulated oils, jet fuels, residual fuel oils and crude oils; precision was established for materials and ranges listed in Clause 13, though the method can be applied more broadly.
• Measurement principle: Dynamic viscosity from rotor speed equilibrium in the concentric-cylinder cell; density from U‑tube oscillation frequency; kinematic viscosity calculated as η/ρ.
• Apparatus: Stabinger type viscometer with integrated density measurement, suitable temperature control, and properly fitted temperature probe.
• Reagents and consumables: Approved cleaning solvents, drying solvents (e.g., n‑heptane recommended), and oil‑free compressed air or inert gas for drying.
• Sampling and sample handling: Procedures reference ISO 3170/3171 for manual and automatic sampling; conditioning for residual fuels is specified.
• Calibration and verification: Use certified reference liquids and a reference thermometer (uncertainty ≤ 0.01 °C) for instrument verification and temperature calibration.
• Procedure variants: Manual filling/cleaning, automatic sample changers, and temperature scanning modes.
• Precision and bias: Repeatability and reproducibility defined in Clause 13; discussion of agreement with ASTM methods (e.g., ASTM D7042 vs ASTM D445) is included.
• Safety and limitations: Users must manage hazards; results depend on rheological behaviour and shear-rate sensitivity.

Applications

• Quality control and production testing in petroleum refineries and lubricant manufacturing.
• Fuel and crude oil characterization for trading, compliance, and custody transfer.
• Laboratory method for R&D, additive formulation, and stability studies.
• Instrument manufacturers and calibration laboratories validating Stabinger viscometers.
• Regulatory and standards bodies comparing methods or establishing specification limits.

Related standards

• ISO 3104 - Kinematic viscosity (general)
• ISO 12185 - Density by oscillating U‑tube
• ISO 3170 / ISO 3171 - Sampling of petroleum liquids
• Relevant ASTM methods referenced for comparison (ASTM D7042, ASTM D445)

Keywords: ISO 23581:2024, Stabinger type viscometer, kinematic viscosity, dynamic viscosity, petroleum products, crude oils, viscosity measurement, density measurement, Newtonian flow.