ISO 6250:1997

Overview

ISO 6250:1997 specifies a standardized laboratory method to assess the water reaction of aviation fuels. The test identifies the presence of water‑miscible compounds, evaluates changes in the aqueous layer volume, the tendency to form emulsions, and the state of the fuel–water interface. The procedure is intended as a practical qualitative check useful in fuel quality control and handling.

The principle: a measured volume of phosphate buffer is mixed with a measured volume of fuel in a clean glass cylinder, vigorously agitated for a defined time, allowed to settle, and then observed for volume changes and interface appearance.

Key Topics

• Sample preparation and sampling: Samples should be taken according to ISO 3170 or ISO 3171. Use a laboratory test portion of at least 100 ml and allow particulates to settle; do not filter samples as this may remove detergents or contaminants the test is designed to detect.
• Reagents and cleaning: Use analytical‑grade reagents. Typical solvents noted are acetone and a cleaning solvent such as heptane. A phosphate buffer pH 7 is specified (prepared from monohydrogen and dihydrogen potassium phosphates as described in the standard). The reference glassware cleaner is sulfo‑chromic mixture, but the standard warns of its serious health and environmental hazards and recommends safer non‑ionic cleaners where appropriate.
• Apparatus: A 100 ml glass graduated cylinder (bored and stoppered) and a timing device capable of 120 s ± 2 s.
• Procedure highlights: Introduce 20 ml buffer and 80 ml fuel into the cylinder, cap and agitate vigorously for 120 s (vertical motion), place on a vibration‑free surface and allow to settle for 5 minutes. Perform observations in diffuse light.
• Evaluation: Record any change in aqueous layer volume (to 0.5 ml) and rate the interface and degree of separation using the qualitative rating scales provided in the standard. Note that results are qualitative; precision for volume change or interface rating is not assigned.
• Safety: Follow the standard's warnings on handling oxidizing cleaners and solvent hazards, and observe laboratory safety and waste disposal rules.

Applications

• Fuel quality control and acceptance testing for aviation kerosines and turbine fuels.
• Detection of water‑miscible contaminants (e.g., alcohols, detergents) that alter fuel behaviour with water.
• Assessment of emulsion formation risk during storage, transport and refuelling operations.
• Troubleshooting fuel handling problems such as interface instability or unexpected phase behaviour.

Related Standards

• ISO 3170:1988 - Manual sampling of liquid petroleum products.
• ISO 3171:1988 - Automatic sampling of liquid petroleum products in pipelines.
• ISO 3696:1987 - Water for analytical laboratory use (quality specification).

Use ISO 6250:1997 as part of a fuel quality management program to provide rapid, reproducible qualitative data on fuel–water interactions and to support decisions on further chemical analysis or handling measures.