Thermal Degradation Risk Assessment Worksheet (Excel)

Thermal degradation occurs when lubricants undergo irreversible chemical changes—primarily oxidation, nitration, and cracking—due to sustained exposure to elevated temperatures, often accelerated by catalytic metal surfaces and dissolved oxygen. In multi-function gearboxes—where a single lubricant must satisfy gear, bearing, clutch, and hydraulic system requirements—the thermal load profile is highly dynamic, making traditional fixed-interval oil changes insufficient. The worksheet applies a semi-quantitative risk matrix that weights temperature exposure (via Arrhenius-based acceleration factors), cumulative thermal dose (temperature × time), and lubricant inherent stability to compute a composite Thermal Degradation Risk Index (TDRI). This index is mapped to predefined risk tiers (Low/Medium/High/Critical), each linked to actionable recommendations: e.g., High risk triggers real-time oil analysis (FTIR, acid number) and evaluation of heat rejection capacity; Critical risk mandates immediate intervention, such as retrofitting coolers or switching to synthetic PAO or ester-based fluids. The tool also incorporates gearbox-specific variables—including sump volume, flow rate, duty cycle profiles, and metallurgical composition—to contextualize degradation kinetics beyond generic OEM temperature limits.