Safety Assessment of Pressure Vessels in Service for More Than 20 Years

Abstract In recent years, a large number of pressure vessels for the petrochemical plants built in China in the 20th century have been in service for more than 20 years. The Chinese pressure vessel safety specification TSG 21-2016 “Supervision Regulation on Safety Technology for Stationary Pressure Vessel” stipulates that if the pressure vessels without definite design lives have been in service for more than 20 years, they shall be considered to have reached the design service lives. For these pressure vessels, if they are all blindly scrapped, it will cause huge economic losses. However, if they continue to be used blindly, it may bring great safety risks. In this paper, the failure mode, mechanism and damage evolution law are analyzed through a number of failure accident investigations and experimental studies, for typical pressure vessels such as large LPG spherical tanks, pressure swing adsorbers and coke drums. The classification method of pressure vessel for the time-independent and time-dependent failure modes has been proposed. As for the pressure vessels with time-independent failure modes, the principle to determine target life, and the strategy of inspection and maintenance have been proposed. While for the time-dependent failure modes, the safety evaluation and remaining life prediction methods for the pressure vessels with and without defects have been provided. Finally, the advices on amendment to the relevant regulations on pressure vessels have been proposed. The research findings could provide guidance for rationally determining the safety grades and scientifically extending the service lives of pressure vessels.