Vulnerability Theory For Process Equipment Exposed To Fire And Pre-control Of Domino Effects

Pre-control of domino effects in chemical plants and clusters is a focus issue for both industry and academy,and the primary measures are quantitative risk assessment of domino effect(DMQRA)and measures based on DMQRA.There are four basic elements,i.e.probability of domino scenario occurring,damage probabilities of equipment exposed to fire thermal radiation,blast wave overpressure and blast fragments.They are addressed to constitute and achieve DMQRA.Furthermore,the first one is some kind of combinatorial operation of the last three.Thus the method to determine the damage probabilities and their results are very important which will impact the availability of DMQRA and the decision-making of pre-control measures.Currently,due to lack of fundamental equipment vulnerability data,empirical statistic method based on Probit function is chosen as a compromise to reduce complexity and computation load when applying DMQRA.Therefore,it is essential and urgent to propose some innovative,more reliable and accurate methods to determine the damage probabilities so as to make DMQRA more available and find some other alternative pre-control measures.This dissertation focuses upon the damage probability of equipment exposed to fire thermal radiation,and defines it as the Vulnerability of Equipment Exposed to Fire.Accordingly,the general theory for Equipment Vulnerability and pre-control strategy of domino effects are built up.The specifics include:(i)Apply statistical analysis to experimental research on process equipment exposed to fire and summarize the thermal response and damage principles.It shows that:(a)the time to failure of accidents is longer than that of experiments;(b)the function of safety valve is to decrease tank pressure as well as liquid temperature and it is non-significant to dry wall temperature;and(c)the importance order of controllable variables to failure is wall thickness > time to failure/fire duration > tank volume > initial filling > initial temperature > setting of safety valve.(ii)Considering relief process of full open spring-loaded safety valve and assuming the wetted wall,liquid and vapor share the same temperature,a two-dimensional lumped temperature model is established to address the thermal response and damage of process equipment exposed to fire.The program is validated by BRL experiment and the result is relatively conservative from the safety perspective.Also the result shows that it should be the liquid thermal-expansion triggered the initial opening of safety valve,not the tank pressure exceeded the setting pressure.The oil tank simulations show that the liquid thermalexpansion can be ignored since very great heat is needed to raise an obvious oil temperature.The sphere LPG tank case shows that a good design of safety valve can keep the tank safe and make the discharge lost smallest before emergency agent arrives.(iii)Propose the stability principle to make structural reliability method applicable to dynamic systems,i.e.the lumped temperature models.The limit state equations for stability and static reliability analysis of vertical plate and horizontal LPG tank exposed to fire are derived from the lumped temperature model.However,if the safety valve is not well designed,the stable state will not appear.The case study corresponding to BRL experiment shows that the tank geometry impacts the static damage probability in an order of magnitude less than 10-4,but the safety valve and flame temperature can make the damage probability sensitive in the order of magnitude of 100.(iv)Stochastic diffusion process and first passage failure theories are employed to research the dynamic damage probability.Respectively,two Kolmogorov backward equations,which one is for the vertical plate and the other for the horizontal LPG tank,are derived from the lumped temperature model,and their numerical difference schemes are developed.The BRL case study shows that the influence of the flame temperature deviation on dynamic damage probability is non-significant,and the order of magnitude is at 10-5 level.When the initial temperature changes from 0 ? to 35 ?,the mean first passage time or mean lifetime of the tank will not exceed 450 s.The dynamic reliability method can describe the duration of damage,and be a complementary method to the static one.(v)Set up the general theory for Equipment Vulnerability according to the research on Vulnerability of Equipment Exposed to Fire,which mainly consists of basic vulnerability concepts,typical vulnerability methods,coupling of multiple damage vectors,and the system of equipment vulnerability assessment.Then propose a five-level hierarchical framework for pre-control of domino effects integrating other process safety techniques.The five levels are: Level 1 – Prevention of loss of containment;Level 2 – Safety distance,safety inventory and layout optimization;Level 3 – Equipment vulnerability assessment and safety design;Level 4 – Reengineering of layer-of-protection analysis;and Level 5 – DMQRA.