Abstract | The assets of a hydrodesulphurisation unit of a crude oil refinery are presented in sufficient detail to create a system-wide model for seismic fragility and risk assessment. The assets include pumps, liquid storage tanks, heat exchangers, equipment-supporting buildings, furnaces, process towers, high-temperature separators, and the piping network. Simplified numerical models were employed for the assets, accounting for salient characteristics, functionality, and interconnectivity thereof. Most importantly, a full 3D model of the piping network is provided, which incorporates a simplified representation of the connected structures to capture the dynamic interaction with the piping, enabling cost-effective assessment; increased flexibility in fittings, i.e., elbows, tees, and nozzles, is also accounted for. The end goal is to address the complexities of a small yet critical part of a modern refinery unit and offer a well-documented basis for conducting seismic damage assessment of a critical energy system, which is presented in the companion paper.