原油储罐底板腐蚀深度的概率分布

Probability distribution of corrosion depth at the bottom plate of crude oil tank

底板腐蚀是原油储罐失效的主要原因。为准确预测在役储罐底板的极限腐蚀深度和储罐的剩余寿命,基于极值统计理论的三参数极值II型分布和三参数极值III型分布,建立了广义极值分布模型(GEV),应用概率权值法估计GEV模型参数,应用矩估计法估计极值I型分布和两参数极值III型分布的参数。对3组储罐底板腐蚀深度的实测数据进行统计分析,并通过拟合优度检验的K-S检验和作图法,对比不同分布形式对腐蚀深度预测的准确性。结果表明:广义极值分布模型可以很好地描述储罐底板腐蚀深度数据的分布情况,但是具体服从极值II型分布还是三参数极值III型分布,还需要根据每个储罐底板腐蚀深度数据来确定,通过K-S检验法和作图法验证得出GEV模型的拟合程度最好。

Bottom plate corrosion is the main cause for failure of crude oil tanks. To accurately predict the limit corrosion depth of the in-service tank bottom plate and the residual life of the tank, according to Type Ⅱ and Type Ⅲ distribution of extreme value of three parameters based on the extreme statistical theory, this paper provides the generalized extreme value （GEV） distribution model, and uses the probability weighting method to estimate GEV model parameters and the moment estimation method to estimate the parameters for Type Ⅰ extreme value distribution and Type Ⅲ extreme value distribution of two parameters. The measured data of bottom plate corrosion depth for three groups of tanks are statistically analyzed, and through the test of goodness of fit of the K-S detection and mapping method, the accuracy of different distribution patterns on the corrosion depth prediction are compared. Results show that the generalized extreme value distribution model can well describe the distribution of tank bottom corrosion depth data, but whether it is subject to Type Ⅱ extreme value distribution or Type Ⅲ extreme value distribution of three parameters must be determined according to corrosion depth of each tank bottom plate. The GEV model shows the best fitting performance as verified by K-S detection and mapping method.