基于多故障冲击模型和故障树的PFDavg计算方法研究*

为提高安全仪表功能（SIF）要求时危险失效平均概率（PFDavg）计算结果的精确度，提出1种能准确计算SIF在多重共因失效影响下的PFDavg的数学模型。建立包含多重共因失效的系统失效故障树，然后利用多故障冲击模型区分普通失效率和多重共因失效率，根据瞬时不可用率的定义和故障树的逻辑关系计算出SIF的瞬时不可用率；基于PFDavg的定义，计算出SIF的PFDavg，以某化工企业SIF为例进行验证。结果表明:方法有效考虑了多重共因失效对SIF的影响，通过模型计算出SIF的PFDavg大于基于马尔可夫（Markov）方法的软件计算结果，但二者处于相同的数量级。模型在评估SIF的PFDavg时比传统方法偏保守，能提高安全仪表功能的安全性。

Research on calculation method of PFDavg based on multiple error shock model and fault tree

In order to improve the accuracy of the calculation results of average probability of dangerous failures on demand (PFDavg) in the safety instrument function (SIF),a mathematical model for accurately calculating the PFDavg of SIF under the influence of multiple common cause failures was proposed.A fault tree of system failure containing multiple common cause failures was established.Then,the multiple error shock model (MESH) was used to distinguish the common failure rates from multiple common cause failure rates,and the instantaneous unavailability of SIF was calculated according to the definition of instantaneous unavailability and the logical relationship of fault tree.According to the definition of PFDavg,the PFDavg of SIF was calculated and validated by taking the SIF of a chemical enterprise as an example.The results showed that the method effectively considered the influence of multiple common cause failures on SIF,and the PFDavg of SIF calculated by the model was greater than that calculated by the software based on Markov method,but they were in the same order of magnitude.The model was more conservative than the traditional method in evaluating the PFDavg of SIF,which can improve the safety of SIF.The failure probability of component caused by each fault impact should be further studied precisely.