Reliability Analysis Of Large In-service Propane Spherical Tank

The spherical storage tank is a typical high-capacity thin-shell pressure vessel.Compared with other pressure vessels,it has many advantages,such as less land occupation,better ability of enduring force,higher bearing ability,more convenient field in stallion and transportation,lower cost and investment,etc.It has been widely used in many industrial fields such as petrochemical,city gas,textile metallurgy,etc.With the development of spherical tank design towards high parameterization and large-scale,the volume of spherical tank is increasing,and its safety and reliability are becoming more complex.At the same time,propane medium belongs to flammable and explosive substances.Once a safety accident occurs,it will lead to huge economic and property losses.Therefore,it is necessary and extremely important to study and analyze the reliability and safety of in-service spherical tanks.This paper takes a 5000 m~3 in-service propane spherical tank of an energy company in Zhuhai as the research object,according to the structural reliability theory,ANSYS analysis technology and field data collected during the internship,the reliability analysis and risk assessment are carried out.The main conclusions are as follows:(1)Taking a 5000 m~3 in-service propane spherical tank as the research object,the finite element parametric model is established by APDL language.When the working pressure is 1.42MPa,the maximum equivalent stress is 271 MPa,which is less than the yield strength 490 MPa,and the maximum displacement is 6.4 mm.The maximum stress and displacement appear in the joint position between the spherical shell and the pallet.Referring to the relevant standards and regulations,the safety check of each structural part of spherical tank shows that it is in a safe state.(2)The maximum stress node is extracted and the limit state function of the spherical tank is established according to the structural reliability theory.In the ANSYS-PDS module,the Monte Carlo method is used for 10,000 sampling cycles.It is concluded that the reliability of spherical tank is 98.61%with 95%confidence.Sensitivity analysis show that the yield strength and shell thickness have a positive impact on its reliability,and the inner diameter and working pressure have a negative impact on its reliability.(3)The effects of working pressure,shell thickness,pallet thickness,pillar thickness and uneven settlement on stress displacement behavior and reliability of spherical tanks are expored.According to the results,the operating pressure of the safety valve is set to 1.7 MPa,which can give full play to the bearing capacity of the spherical tank.It can also provide reference for the subsequent design of spherical tanks.On the basis of ensuring safety and reliability,the structure of spherical tanks is optimized to reduce the stress level of spherical tanks to achieve the effect of economic saving.(4)Combined with the data collected from the practice site,a comprehensive risk assessment system for spherical tanks is established.The weight of each risk index of spherical tank is determined by the method of Fuzzy Analytic Hierarchy Process.Finally,the risk level of spherical tank is relatively safety level.Corresponding improvement measures are been proposed for risk indicators with high weight values such as corrosion,cracks,uneven settlement of foundation,and safety accessories,Thus the risk level of the spherical tank system can be improved to ensure its operation in a safe and reliable state.