Discussion of safety relief capacity calculation of gas pressure vessels under fire environment in API 521-2020
To further understand the venting design of pressure vessel,the issue of safety relief capacity calculation of gas pressure vessels under fire environment was aimed.The mass and energy balance equations during pressure vessel venting process were derived.The simplified assumptions for solving the equations were analyzed.The derivation of the calculation formula for safety relief capacity of gas pressure vessels under fire environment in API 521-2020 was clarified.The influence of each simplified assumption on the calculated safety relief capacitys was studied.Results indicate that,the API 521-2020 formula for calculating the safety relief capacity is based on the mass balance and energy balance equations,and is appropriately simplified for engineering purposes.The assumed and simplified conditions include:Constant pressure during the release process,complete thermal transfer from flame to gas,free convection of vertical plat in large space,engineering simplification of real gas h'/(cpM1/2)using air properties at constant pressure and temperature,ideal gas,and a constant maximum wall temperature is recommended without vessel wall broken.It is concluded that all assumptions and simplified conditions make the calculation of safety relief capacity conservative,which tends to be safe in real used conditions.The research provides guidance for performing overpressure venting of pressure vessels under fire environment.
gas pressure vesselfire environmentoverpressuresafety relief capacityAPI 521-2020 standard
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