Overview
ISO 7120:1987 specifies a laboratory test method to evaluate the rust-preventing characteristics of petroleum oils and other fluids when water becomes mixed with the product. The procedure is intended for inhibited mineral oils (for example steam turbine oils, circulating oils and hydraulic oils) and for non‑hydrocarbon fluids, including fluids denser than water. The method indicates how effective an oil or fluid is at preventing rust on ferrous parts under water‑contamination conditions.
Key topics and technical requirements
- Test principle: 300 ml of oil (or fluid) is stirred with 30 ml of water at 60 ± 1 °C with a polished cylindrical steel specimen immersed; rusting is observed after a defined exposure period.
- Typical test duration: Customarily 24 hours (shorter or longer periods may be chosen by agreement); observations at 12 hours are often indicative.
- Specimen preparation: Steel test specimen dimensions and surface finish are specified; grinding and final polishing with specific abrasive grades are required to produce a uniformly scratched surface before testing.
- Apparatus and operating conditions:
- Thermostatically controlled oil bath to maintain 60 ± 1 °C.
- Stirring apparatus capable of 1 000 ± 50 r/min for the oil/water mixture (stirrer geometry and placement specified).
- Duplicate tests are required to report pass/fail.
- Reagents and media:
- Distilled water or synthetic sea water (composition and preparation method provided for marine simulation).
- Cleaning solvents (iso‑octane) and glassware cleaning solutions (chromic acid noted with safety cautions).
- Result expression and pass/fail criteria:
- An oil “passes” if both specimens are rust‑free at the end of the test period.
- If both specimens show rust, the oil “fails”.
- If one specimen is rusted, two more specimens are tested; failure of either additional specimen means the oil fails.
- Severity classes (light, moderate, severe) are defined by rust coverage.
Practical applications and users
- Who uses it: Lubricant manufacturers, quality control laboratories, petrochemical test labs, maintenance engineers, and purchasers specifying rust protection for turbines, hydraulic systems, circulating oil systems and marine/denser‑than‑water fluids.
- Why it matters: Provides reproducible, internationally recognized evidence of an oil’s ability to protect ferrous components in the presence of water contamination - a common field failure mode.
- Use cases: Product development, batch release, comparative screening of rust inhibitors, procurement specifications and failure analysis.
Related standards
- ISO 3170 - Petroleum products - Manual sampling
- ISO 3171 - Petroleum products - Automatic pipeline sampling
- ISO 3448 - Industrial liquid lubricants - Viscosity classification
Keywords: ISO 7120, rust-preventing characteristics, petroleum oils, lubricants, corrosion testing, inhibited oils, synthetic sea water, hydraulic oil test.
