ANALYSIS OF A LNG PLANT SUBJECTED TO SEISMIC LOADING

Abstract eng:
“Special risk” industrial plants can be highly vulnerable when subjected to natural phenomena such as earthquakes, flooding and explosions. Very often in these cases, standards and design practices do not provide proper design guidelines, like the ones used for nuclear power plants. Thus, in the case of earthquakes, due to the lack of uniform hazard versus uniform risk design levels, most of the European guidelines are based on importance factor applied to design peak ground accelerations very different from each other. The purpose of INDUSE-2-SAFETY European project is the seismic safety assessment of “special risk” petrochemical plants through a fragility analysis of main components like tanks, piping systems with bolted flange joints and support structures. Two different sub-plants were selected as possible Case Studies: one of them consists in a regasification LNG plant with a 50000 m3 ethylene tank. Moreover, a piping system supported by steel and/or concrete structures, connects the tank to the process area and several substructures are placed along the pipelines racks. In this paper, we will discuss the FE-based modelling aspects including plasticity of piping components and the results of a seismic performance assessment carried out on the LNG plant described above. In particular, in order to discover leakage events on pipelines elbows and bolted flange joints, a 3D numerical model was developed using the Ansys software and several dynamic analyses were performed by means of natural seismic records. In this respect, to define a proper leakage model in terms of resistance and stiffness, for piping systems involved in the simulations, experimental tests on real scale specimens were carried out at the UNITN structural laboratory. Nonlinear FE models were built both for bolted flange joints and pipelines elbows. Our results indicate that bolted flange joints do not experience leakage at realistic values of PGA. Conversely, elbow elements experience possible loss of containment for a certain level of the seismic action intensity. Additionally, with the aim of estimating the probability of leakage due to seismic events during the reference life of the LNG plant, we first built fragility curves by the means of a Cloud Analysis. Then, operating with the PBEE approach, we used the site-specific seismic hazard curve to calculate the overall probability.

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