ISO 4263-1:2003

Overview

ISO 4263-1:2003 specifies the TOST test (Turbine Oil Stability Test) procedure for mineral oils to determine the ageing behaviour of rust- and oxidation‑inhibited oils and fluids. The standard is aimed at mineral‑based turbine oils, hydraulic oils and circulating oils (categories defined by ISO 6743 series). The method evaluates oxidation stability by ageing a test portion at elevated temperature with oxygen, water and a steel/copper catalyst coil and monitoring the increase in acid number until a defined endpoint (oxidation life) is reached.

Key topics and technical requirements

• Test principle: Age the oil sample at 95 °C in the dark with a controlled oxygen flow, water and a steel/copper catalyst coil; remove aliquots at intervals and measure acid number.
• Oxidation life endpoint: Test continues until acid number reaches 2.0 mg KOH/g; hours elapsed are reported as oxidation life.
• Apparatus & materials: Borosilicate oxidation cell, thermostatically controlled heating bath (95 °C ± 0.2 °C), oxygen supply (≥99.5 %), flowmeter, catalyst coils manufactured from specified steel and copper wire diameters, sampling syringes and dark aliquot vials.
• Catalyst coil preparation & storage: Clean, abrade and wind specified lengths of steel and copper wire into a double spiral; store coils in a dry inert atmosphere per Annex B.
• Analytical methods: Acid number measurement per referenced ISO titration methods; water quality and solvent purity requirements referenced (e.g., ISO 3696 for water).
• Precision & limitations: Precision was established for inhibited turbine oils (oxidation lives 700–3 900 h). Oils with synthetic components can be tested but no precision statement is available yet. The test is valuable for oils prone to water contamination but correlation with field performance varies by application.
• Safety considerations: Use of oxygen, acids and cleaning agents can be hazardous; appropriate safety and disposal procedures are required.

Applications and users

• Quality control laboratories in lubricant manufacturing for batch acceptance and shelf-life comparison.
• Specification writers and procurement teams who need comparative oxidation-stability data for turbine, hydraulic and circulating mineral oils.
• R&D and formulation teams evaluating antioxidant packages and water-sensitive oxidation performance.
• Maintenance and reliability engineers / OEMs using oxidation-life data to inform oil change intervals-while recognizing field correlation depends on service conditions.

Related standards

• ISO 6743‑4, ISO 6743‑5, ISO 6743‑6 (lubricant category definitions)
• ISO 3170 (sampling), ISO 3696 (laboratory water), ISO 6618 / 6619 / 7537 (acid number / neutralization titration methods)

Keywords: ISO 4263-1:2003, TOST test, oxidation stability, inhibited mineral oils, turbine oils, hydraulic oils, acid number, catalyst coil, lubrication testing.