Seismic performance assessment of oil & gas piping systems through nonlinear analysis

Piping systems, a vital part of energy industries, e.g. petrochemical, oil & gas and chemical plants, have been found particularly vulnerable under earthquake loading, as reported in recent publications. During past earthquakes, piping systems and their components suffered significant damages causing severe consequences. Thus, seismic assessment/evaluation of these structures has become an imperative for their proper design to safeguard them against seismic events. Nevertheless, there exists an inadequacy of proper seismic analysis and design rules for petrochemical piping systems, and designers have to follow seismic standards conceived for other structures such as buildings and nuclear plants. Moreover, the modern performance-based design approach is still not widely adopted for piping systems, where the allowable design method is the customary practice. Along these lines, this paper presents a performance-based seismic analysis of petrochemical plants through two case studies. Initially, main issues on seismic analysis and design of industrial piping systems and components are addressed followed by a discussion on the selection of proper seismic inputs. The current allowable stress and strain based seismic verification methods are presented afterward. Then, nonlinear finite element analyses of two typical petrochemical piping systems under modern design earthquake levels are presented. Finally, performance of these piping systems is commented by comparing the maximum stress and strain levels - found from the analyses-with the allowable design values that exhibited a favourable behaviour of the analysed systems under earthquake limit state levels.