Thermodynamic Safety Audit Checklist (API RP 521 Aligned)

Thermodynamic safety auditing centers on preventing catastrophic failures arising from uncontrolled energy release due to deviations in temperature, pressure, or phase behavior. API RP 521 provides foundational guidance for sizing and selecting pressure-relieving devices, emphasizing the need for accurate thermodynamic characterization of process fluids under upset conditions—including fire exposure, blocked outlets, chemical runaway, and utility failure. The audit checklist operationalizes this guidance by requiring rigorous verification of fluid property inputs (e.g., critical point, heat capacity, vapor pressure, Joule–Thomson coefficient), identification of non-ideal behavior (e.g., retrograde condensation, azeotropy), and validation of EoS selection (e.g., Peng–Robinson, Soave–Redlich–Kwong, or specialized models like CPA for associating fluids) against experimental or high-fidelity simulation data. A core element involves calculating worst-case thermodynamic scenarios—such as adiabatic reaction calorimetry-derived ΔT_ad and ΔP_ad, vapor fraction evolution during emergency depressuring, or choked two-phase flow mass flux—to ensure relief system capacity exceeds credible demand. Furthermore, the checklist mandates documentation traceability: linking EoS parameters, binary interaction coefficients, and thermodynamic assumptions directly to process safety information (PSI) and process hazard analysis (PHA) findings, thereby closing the loop between thermodynamic modeling and mechanical integrity assurance.