异型冗余设备KooN结构通用PFD计算模型

Model for calculating generalizing PFD of non-identical redundant KooN configurations

为准确评估异型冗余设备构成的复杂安全联锁功能回路的需求失效概率(PFD),基于IEC-61508标准和PFD基本原理,根据单个通道的失效概率模型,考虑不同失效率、通道失效顺序及共因失效(CCF)对系统失效概率的影响,建立异型冗余设备Koo N结构PFD计算模型。将该模型应用于某天然气制乙炔装置的安全联锁控制系统。结果表明,异型设备失效率差异性过大时,该模型有助于避免假设所有设备失效率均相同而造成的误差,提高了PFD的计算精度,且结果比用一些现有的PFD计算模型计算得到的结果更准确。

For the sake of assessing complex safety instrumented function（SIF） circuits composed of nonidentical redundant components accurately, a model was built for calculating generalized PFD of the circuits on the basis of the IEC61508 standard, the basic principle of PFD, the failure probability model of single channel, and considering the effects of different failure rates, channel failure sequence and the common cause failure（CCF） on the failure probability of the system circuit. The model was applied to a certain plant for making acetylene from natural gas. The results show that this model is helpful to avoid the the error caused by assuming that all equipment failure rates are the same when the difference between non-identical equipment failure rates is too large, and that the modified formula improves the accuracy of calculation of PFD.