Development of Two-Variable Fragility Functions for Piping Systems in Industrial Plants

Abstract

Regarding that refineries are essential facilities in oil and gas industries, evaluation of their equipment’s vulnerability, including piping systems, tanks and … subjected to natural hazards is of great importance. This issue is more crucial in Iran as a highly seismic country. In this research a case study has been carried out with the aim of seismic evaluation of a part of piping system of Isomax unit of Tehran oil refinery. For this purpose, first all required information and drawing maps have been gathered to identify the materials’ characteristics, geometry, and applied loadings. Then, the considered piping system has been modeled in ABAQUS finite element software, subjected to gravity, internal pressure and 3-component earthquake acceleration records of 157 earthquakes, by time history analyses (THA). In the third stage, by using the maximum von Mises stress in the piping system for all 157 cases of THA, the single-variable fragility curves, once by using PGA, and once more using PGV as the IM, have been developed. Finally, the two-variable fragility function (fragility surface) has been developed for the piping system. Results show that the two-variable fragility functions are much more reliable than single-variable ones. Results also show that the two knees in the piping system are the more vulnerable parts.

Keywords

• fragility curve
• two-variable fragility function
• fragility surface
• time history analyses
• isomax unit of tehran refinery