Failure prevention and degradation modelling of triglyceride-based hydraulic fluids under extreme thermal stress using arrhenius kinetics and total acid number analysis

The broader industrial adoption of triglyceride-based biodegradable hydraulic fluids is constrained by their vulnerability to thermo-oxidative degradation and the absence of reliable early-warning failure indicators under dynamic operational stress. Standard condition monitoring often relies on volumetric flow efficiency or kinematic viscosity; however, these physical parameters can mask critical chemical decomposition. To investigate this degradation mechanism, a continuous 150-hour experimental test was conducted on a hydraulic test bench under a constant pressure of 20 MPa across two consecutive thermal regimes (65 °C for 100 h followed by extreme thermal stress of 80 °C for 50 h). While volumetric flow efficiency remained high (>0.93) and kinematic viscosity increased moderately by 8.9%, the Total Acid Number (TAN) escalated by 416.13% (from 0.31 to 1.60 mg KOH−1), breaching critical operational thresholds. This discrepancy demonstrates a ‘silent failure’ mode where mechanical energy transfer persists despite severe fluid acidification. A segmented regression model revealed a 1.83-fold acceleration of the degradation kinetics in the high-temperature phase. Using a two-point Arrhenius evaluation, an effective activation energy of 40.2 kJ.mol−1 was determined, providing a predictive framework for operational degradation kinetics. These findings prove that failure prevention protocols for bio-lubricants must prioritize TAN monitoring over conventional viscosity checks.