Seismic fragility assessment of a pipe rack structure in a petrochemical complex by incremental dynamic analysis

Abstract

A typical petrochemical complex consists of various components of different complexities such as structures of various proportions, critical piping, tanks and massive compressors. The consequences of a seismic event in a process plant is severe compared to conventional civil structures considering that damage to even a single component would result in release of toxic gases and lead to an interruption in the production causing economical losses and threat to society and environment. Pipe rack structures with the supported piping systems represents an important item in petrochemical complexes, refineries and LNG plants as they run in kilometres of length connecting various process units in the complex. The seismic hazard posed by such structures is evident in that they carry piping systems with hazardous fluids and support other critical equipments such as air coolers and exchangers. The paper presents the seismic fragility assessment for a typical steel pipe-rack structure adapted from a petrochemical complex built in a region of moderate seismicity. Pipe rack structure is first verified for its capacity as per the European codes. The Incremental Dynamic Analysis (IDA) is then performed to obtain an insight into the dynamic response of the structural system in both the transverse and longitudinal directions. The fragility curves developed for different performance levels based on the IDA data are used for the seismic assessment.