Overview
ISO 9120:1997 specifies the impinger method for determining the air‑release properties of steam‑turbine and related petroleum oils. The test estimates how quickly entrained air separates from lubricating oils under controlled conditions by saturating a sample with air, then monitoring density changes until the dispersed air content falls to 0.2% (V/V). This standard is intended for comparative evaluation of an oil’s de‑aeration ability where sufficient residence time exists.
Key topics and technical requirements
- Test principle: Air is blown into an oil sample at a controlled temperature (25 °C, 50 °C or 75 °C depending on oil viscosity), then the air supply is stopped and the escape of entrained air is followed by density measurements versus time.
- Endpoint: Time (minutes) required for dispersed air to reduce to 0.2% (V/V).
- Typical procedure highlights:
- Warm ~200 ml of sample; pour 180 ml into the test vessel.
- Saturate with compressed, dry, oil‑free air at a gauge pressure of 20 kPa for 420 s.
- Use a density balance (accuracy ~0.5 kg/m3) with a 5–10 ml sinker to follow density changes until the 0.2% V/V criterion is reached.
- Test temperature selection is related to kinematic viscosity at 40 °C (lower viscosity → lower test temperature).
- Apparatus: Borosilicate impinger test vessel with baffle and inlet/outlet, circulating bath (±0.1 °C control), heated air supply, thermometer/temperature sensors, density balance and sinker.
- Reagents & cleaning: Analytical solvents and a strongly oxidizing cleaning solution (note: chromosulfuric acid is hazardous and special disposal and PPE are required).
- Precision & reporting: Precision assessed per ISO 4259; results reported to 0.1 min with test temperature and any deviations (e.g., “modified density” when volatile components are lost).
Applications and users
ISO 9120:1997 is useful for:
- Lubricant manufacturers - product development and quality control of steam turbine oils and similar lubricants.
- Independent test laboratories - standardized air‑release testing for comparative data.
- Power plant and turbine OEMs / maintenance teams - evaluating oils for potential issues with sponginess, air‑related malfunctions or hydraulic performance.
- Hydraulic and rotating equipment designers - informing reservoir sizing and residence time requirements.
Keywords: ISO 9120:1997, air‑release properties, impinger method, steam turbine oils, lubricating oil testing, petroleum products, oil de‑aeration.
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