Pressure vessels are a critical element in the natural gas industry and are considered sensitive equipment because of their hazardous products. Therefore, they must be designed against any low-probability, high consequence event that may occur over the lifetime of the vessel plant, but minimal research on their seismic effects has been conducted. The purpose of this project is to examine the seismic risk analysis of tall and slender vertical pressure vessels and their connected pipe with developed simplified models based on natural frequency changes. This project takes into account many vertical pressure vessel design characteristics, as well as the connected pipe system for the parametric study. The data can be reused to analyze a variety of vertical pressure vessel configurations, and to develop fragility curves for the occurrence of specific limit states and relative consequences to further estimate seismic risk. Going forward, this project serves to provide the earthquake engineering community with a simplified technique for pressure vessel seismic risk analysis.