Overview - ISO 11366:2025 (Turbine lubricating oils, in‑service)
ISO 11366:2025 provides guidance and requirements for in‑service maintenance of mineral oils used as lubricating oils and control fluids for steam, gas and combined‑cycle turbines. It covers oils classified under ISO 6743‑5 and specified in ISO 8068, while excluding certain phosphate ester grades (TSD, TGD, TCD - see ISO 11365) and several other specific grades (TGCE, THA, THCH, THCE, THE). The standard focuses on monitoring practices, recommended tests, sampling, interpretation and corrective actions to maximize oil service life and turbine reliability.
Key technical topics and requirements
- Scope and applicability: Types of turbines (steam, gas, combined cycle), oil classifications and exclusions.
- Factors affecting service life: System design, start‑up conditions, original oil quality, operating temperature, contamination and make‑up rates.
- Deterioration mechanisms: Viscosity change, oxidation, sludge and deposits, water, particulate contamination, antirust properties, foaming and air release, total acid number (TAN), flash point.
- Recommended tests (field and laboratory):
- Appearance, odour and colour
- Total acid number (TAN) and remaining oxidation stability
- Sludge and membrane patch colorimetry (MPC)
- Particle counting and wear metal analysis
- Kinematic viscosity and flash point
- Water content, separability, air release and foaming characteristics
- Sampling and handling: Guidance on sampling points, lines, containers and marking to ensure representative oil samples.
- Testing schedules & frequency: Framework for minimum testing, new oil examination, in‑service monitoring and field screening vs laboratory tests.
- Corrective actions and life extension: Procedures such as bleed & feed, inhibitor or antifoam treatment, rust inhibitor application and clay treatment to prolong oil life.
Practical applications and users
ISO 11366 is intended for organizations involved in turbine lubrication management and reliability:
- Power plant operators and maintenance teams (steam, gas, combined‑cycle)
- Turbine OEMs and service providers
- Lubricant manufacturers and formulators
- Oil analysis laboratories and condition monitoring engineers
- Asset managers and reliability/maintenance engineers
Use cases include establishing oil testing programs, interpreting oil analysis results, defining sampling procedures, implementing corrective measures, and optimizing oil change intervals to reduce downtime and lifecycle cost.
Related standards
- ISO 6743‑5 (lubricant classification)
- ISO 8068 (turbine lubricant specifications)
- ISO 11365 (phosphate ester turbine oils - referenced for excluded grades)
Keywords: ISO 11366, turbine lubricating oils, in‑service monitoring, oil testing, turbine maintenance, steam turbine, gas turbine, combined cycle, lubricant sampling, oil condition monitoring.