ISO 18335:2024

Overview

ISO 18335:2024 is an international standard that specifies a precise procedure for determining the kinematic viscosity of petroleum and related products. This method focuses on calculating kinematic viscosity from the measured dynamic viscosity and density using a constant pressure viscometer. It applies to middle distillate fuels, fatty acid methyl ester (FAME) fuels and their blends, lubricating oils including base and formulated oils, and synthetic oils.

The standard covers a broad viscosity range, from 0.5 mm²/s to 2000 mm²/s, with specified precision at different temperatures (40 °C and 100 °C). It primarily applies to Newtonian fluids, where shear stress and shear rate are proportional, providing reliable viscosity data critical for quality control and product specification in fuel and lubricant industries.

Key Topics

• Dynamic Viscosity Measurement: Utilizes a constant pressure viscometer based on the Hagen-Poiseuille principle, measuring the flow time of a liquid sample through a capillary at controlled temperature and pressure.
• Density Determination: An oscillating U-tube densitometer measures the fluid’s density simultaneously, ensuring high accuracy in subsequent calculations.
• Kinematic Viscosity Calculation: Derived by dividing dynamic viscosity by density, calculated automatically by the instrument to ensure efficiency and repeatability.
• Applicability: Suitable for middle distillate fuels, FAME fuels up to 60% blends, lubricating oils, and synthetic products with viscosity ranges typical to industrial and laboratory settings.
• Precision and Repeatability: The standard includes detailed precision data based on international interlaboratory studies ensuring reliability of results.
• Sample Preparation and Handling: Guidelines ensure proper homogenization and temperature control of samples, crucial for achieving accurate viscosity readings.
• Equipment Calibration and Verification: Mandates periodic validation of viscometer and densitometer calibration through certified reference materials to maintain measurement integrity.

Applications

ISO 18335:2024 is essential for laboratories and industries involved in the production, quality control, and certification of petroleum-based fuels and lubricants. Its practical applications include:

• Fuel Quality Assessment: Ensuring kinematic viscosity meets specifications for middle distillate fuels, including diesel and heating oils, which directly impact engine performance and emissions.
• Renewable Fuels Evaluation: Supports testing of biodiesel blends (FAME), helping monitor viscosity changes impacting fuel handling and combustion characteristics.
• Lubricant Formulation and Testing: Used for base oils and formulated lubricants to verify flow behavior, influencing lubrication effectiveness and machinery reliability.
• Product Development and Research: Assists in R&D to optimize fuel and lubricant formulations by providing consistent viscosity data under controlled conditions.
• Regulatory Compliance: Aids adherence to national and international regulations by providing standardized viscosity measurements, facilitating trade and technical acceptance.

Related Standards

• ISO 3170 - Petroleum liquids - Manual sampling: Defines procedures for representative manual sampling which is critical for obtaining accurate test samples used in viscosity measurement.
• ISO 3171 - Petroleum liquids - Automatic pipeline sampling: Describes automatic sampling methods complementary to ISO 18335 for consistent sample collection.
• ISO 4259-1 - Petroleum products - Determination and application of precision data in relation to methods of test: Provides statistical methods referenced for precision assessment in viscosity measurements.
• Other viscosity-related standards in petroleum testing, offering alternative or supplemental measurement techniques for dynamic and kinematic viscosity under different conditions.

By following ISO 18335:2024, laboratories can achieve standardized, accurate, and reproducible viscosity measurements, vital for product quality and performance in the petroleum and lubricant sectors, while supporting compatibility with international trade and regulatory requirements.