The Interaction of Earthquakes with Process Equipment in the Framework of Risk Assessment

Earthquakes can produce structural damages on industrial equipment. Whenever prevention and mitigation systems are ineffective, catastrophic accidental scenarios as fires, explosion and dispersion of toxic substances may occur, thus increasing risks to people, environment and properties either within the plant borders or in the close surroundings of industrial plants. This paper deals with a simplified procedure for seismic risk analysis of typical industrial installations containing atmospheric storage tanks, pressurised horizontal tanks and pumps, based on historical database and literature data on natural-technological (Na-tech) accidents. The methodology can be applied for any industrial equipment and implemented in any existing code or procedure for risk assessment. Results are presented in terms of fragility curves with respect to a single degree of freedom for earthquake characterisation (Peak Ground Acceleration, PGA), which is assumed as relevant earthquake intensity measure. Preliminary numerical validation of the methodology has been also carried out via structural analysis that takes into account a single failure mode (Elephant Foot Buckling) that affects atmospheric storage tank, anchored or unanchored to ground. Starting from fragility data, probit analysis has been performed in order to obtain PGA thresholds values for earthquake-related structural damages and loss of containment. These results are certainly of interest for active and passive mitigation actions development, and for the implementation of Early Warning System, i.e., the set of actions that can be taken from the moment when a seismic event is triggered with a significant reliability to the moment the earthquake strikes in a given location.