Verification of appropriate life parameters in risk and reliability quantifications of process hazards

Abstract Failure frequency estimation is one of the important measures of risk quantification. In traditional reliability assessment, mean time to failure (MTTF) is one of the most common life parameter to field failure data analysis. However, it is critically important to use correct life parameter for accurate reliability estimation. One of the uncertainties in reliability assessment is the inappropriate life parameter and how they could be selected. The scope of this study is to select an appropriate life parameters for hydrogen refueling stations (HRS). Field failure data of HRS is used as a case study to compare failure analysis based on two life parameters i.e. survival time vs. number of fillings at the station. A non-parametric estimator is used to estimate cumulative failure function based on number of fillings. The cumulative hazard using the Nelson-Aalen estimator showed a linear relationship with the number of fillings. A parametric estimator using 2-values (β and η) Weibull distribution function is employed to estimate cumulative probability of failure with the survival time. The present study demonstrates that the failure rate can vary by a small to large margin based on the life parameter and estimator chosen for reliability predictions. This shows the importance and need of verification of life parameter in QRA to reduce uncertainty associated with the risk calculation.

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