Seismic risk assessment of supporting structures and process piping for accident prevention in chemical facilities

The seismic risk assessment of supporting structures and process piping elevated on supporting structures plays an important role in accident prevention inside process plants. Process piping is an essential yet complex network of pipes that is used inside petrochemical facilities for connecting equipment items. Even though the seismic vulnerability of process piping and supporting structures is high, as demonstrated during past accidents, the risk assessment has hitherto relied on generalized and obsolete fragility models, e.g. from HAZUS, without addressing specifically the idiosyncrasies of dynamic coupling, soil effects or source conditions. To this effect, the present study addresses the risk assessment and accident scenarios due to earthquake of a realistic process unit in a refinery. By virtue of a recent update of seismic hazard maps in the region of interest, the seismic performance of the unit should be investigated. The methodology includes five main steps that pertain to structural modelling accounting for soil effects, hazard identification, dynamic analyses and description of seismic demand – intensity relationship, fragility derivation and risk estimation as well as analysis of the accident's consequences using JRC's in house tool, ADAM. Overall, the steel structure was considerably more vulnerable than piping. Also, soil deformability and source conditions caused higher uncertainty and increased the risk. The derived fragility curves and risk estimation are tailored to a process plant that can commonly be found in modern oil refineries, and the proposed analytical framework can be easily implemented in a quantitative risk assessment for the most vulnerable equipment, at least, which is necessary for risk reduction and consequence mitigation inside chemical facilities