化工设备失效概率JC修正模型研究

Chemical Equipment Failure Probability Model Based on JC Method

由数据库统计所得的设备通用失效概率,是在设备各失效模式下的参数变量均达到各自均值时所对应的失效概率。本文针对基于风险的检测技术(RBI)设备修正因子的应用缺陷,结合结构可靠度理论,分析均值一次二阶矩法在实际应用过程中的局限性,建立了基于当量正态化(JC)法的通用失效概率修正模型。实例分析表明,JC法考虑了随机变量的实际分布类型,能较准确地预测设备的失效情况。

The chemical equipment general failure probability based on database statistics is the probability when the parameters of all failure modes take their respective mean.Risk Based Inspection（RBI） technology includes qualitative RBI judgment and quantitative RBI calculation.Through qualitative judgments,the relative level of risks can be obtained.The devices with relatively low risks do not need a quantitative RBI,and further quantitative RBI will be focused on those with relatively high risks.It is found that there are two important aspects in the use of pressure equipments in China,that is,severe defects and over-use,and it is proposed to control the risks.The shortcomings of the current API 581 method regarding to the severe defects and over-use are analyzed in this paper.With the reliability theory,the limitations of the mean first order second moment method are shown in practical applications as well as the shortcomings of RBI.In addition,the general failure probability of equipment based on JC model is calculated.This method can be used for any probability distribution and is not limited to the normal distribution.With the actual distribution of random variables being taken into consideration,this method can be used equally well for logarithm normal distribution,Weibull distribution or extreme value type I distribution.Besides,by means of equivalent normal deviation,the non-normal variable is transformed into a normal variable.The linearization point is not located at the mean value but the failure boundary,and is called the design check point,corresponding to the structural maximal failure probability,which can be used to estimate the failure consequence of equipment accurately.