Overview
ISO 16675:2025 specifies a standardized accelerated aging test for phosphate ester turbine control fluids used in turbine speed and hydraulic control systems. The method evaluates anti‑aging performance by measuring the increase in acid number after a closed, pressurized aging procedure. It applies to new and in‑service fluids classified as HFDR (ISO 6743‑4) and TSD, TGD, TCD (ISO 6743‑5).
Key topics and technical requirements
- Test principle: A 100 g sample mixed with 1.0 g water and a polished copper catalyst coil is aged in a hermetically sealed stainless‑steel vessel charged with oxygen (0.40 MPa) at 105 °C for 24 h. Anti‑aging performance is reported as the change in acid number (∆A = A2 − A1).
- Acid number determination: Use either ISO 6618 (colour‑indicator titration) or ISO 6619 (potentiometric titration). Results are only comparable when the same titration method is used before and after aging.
- Apparatus and materials: Vessel material (AISI 304 or equivalent), digital pressure gauge (±0.01 MPa), copper wire catalyst (1.63 mm diameter, 99.9 % Cu, 1 650 mm length formed into a coil), analytical balance (±0.1 mg), and thermostatically controlled bath (105 °C ±1 °C).
- Sampling and preparation: Follow ISO 3170 for sampling and ISO 3696 for laboratory water. Glassware cleaning, copper coil polishing, and single‑use coils per test are specified.
- Safety and quality: Oxygen purity ≥99.5 % and warnings about oxygen‑enhanced combustion. Vessel pressure testing and storage recommendations for prepared coils are included.
- Precision: Repeatability and reproducibility statistics are provided (e.g., repeatability r ≈ 0.078–0.137 mg KOH/g and reproducibility R ≈ 0.100–0.188 mg KOH/g, depending on acid number range and titration method).
Applications and users
ISO 16675:2025 is intended for:
- Lubricant and hydraulic fluid manufacturers for product development, quality control, and formulation benchmarking.
- Independent testing laboratories performing standardized anti‑aging evaluations.
- Turbine OEMs and operators validating hydraulic control fluid stability for safe, reliable turbine speed control.
- Maintenance and reliability engineers assessing in‑service fluid condition and scheduling fluid replacement.
- Regulatory and procurement teams requiring traceable performance data for specifications and contracts.
Practical benefits include faster, reproducible assessment of oxidative/hydrolytic aging propensity compared with open‑system tests, enabling more informed fluid selection and maintenance planning.
Related standards
Keywords: ISO 16675:2025, phosphate ester turbine control fluids, anti‑aging test, acid number, accelerated aging, hydraulic fluids, turbine control, ISO 6618, ISO 6619.