Instantaneous Overpressure Dynamics Analysis And Safety Evaluation For Vertical Fixed-roof Storage Tanks

With the rapid development of the petrochemical industry and the sharp decline in oil and gas reserves,the world built a considerable number of tanks to strengthen the reserves of oil and gas resources,mainly for large-scale tank capacity and storage integration.The storage medium in the tank is easy to burning,explode,vaporize,generate static electricity,thermal expansion,etc..Once the combustible gas burning accidental,the combustion process quickly,the internal pressure increases with the increasing release of chemical energy,the tank will appear instantaneous overpressure phenomenon,resulting in the tank can not be under pressure and damage occurs,causing casualties and property losses.If the explosion caused the surrounding tanks explosion that will lead to more serious consequences,causing heavy losses of lives and property of the State.Therefore,carry on the security research has important significance.Firstly,This paper based on the domestic and foreign research results about the combustible gas burns booster,taking into account the position of the ignition point of the tank and the combustible gas space,establishing the pressure calculation method caused by combustible gas combustion in vertical fixed-roof storage tank and building calculation procedure,a variety of conditions of the typical tanks below 2×104m3 are calculated,getting the curve of combustion pressure changes over time.The smaller the storage tank volume,the position of the ignition source is closer to the center of the combustible gas space,the smaller the combustible gas space,the greater the pressure rise rate.Secondly,establishing 3×103m3 vertical fixed-roof storage tank nonlinear finite element model by use of ANSYS software,loading by the curve of pressure change over time,completing the five kinds of working conditions transient dynamics numerical simulation of the tank under the condition of instantaneous overpressure,getting the over time response curves about the deformation value of the storage tank,the equivalent stress distribution and the maximum equivalent stress values.The results show that the deformation of the tank and the equivalent stress changes in the value the greater the difference within a unit time when the position of the ignition source close to the tank wall moving to the combustible gas space center or combustible gas space is smaller.Finally,starting from the dynamic performance of the material of steel,analyzing the stress-strain characteristics under high strain rate loading,using the relationship between the dynamic yield strength and static yield strength of material obtained yield strength limit under the condition of explosion.According to the numerical simulation results,based on the JB4732 stress intensity evaluation conditions,using maximum equivalent stress of neutral surface reached the material yield strength limit or maximum hoop stress of neutral surface reached the 1.15 times material yield strength limit of the most dangerous area of the tank as a condition of tank damage evaluation.The results show that the ignition sources closer the combustible gas space center or the smaller the gas space,the shorter the time required by the destruction,the greater the damage pressure under the condition of the same damage evaluation.The damage pressure value of maximum equivalent stress of neutral surface reached the material yield strength limit compared to the value of maximum hoop stress of neutral surface reached the 1.15 times material yield strength limit,a difference of less than 8%under the condition of the different damage evaluation.When to do the damage evaluation of the tank,selecting the pressure of maximum stress of neutral surface reached the material yield strength limit as the final failure pressure.