Time-variant reliability analysis of tank bottom shell considering corrosion

Key words:  corrosion  storage tank  reliability  grey theory  generalized random space

Abstract:

The grasping of accurate knowledge of the health status of storage tanks in service can provide decision support for their maintenances. Various factors impacting the strength failure of the bottom shell were analyzed, and the degradation model of structural resistance of the bottom shell was established. Then, a corrosion rate prediction model based on non-equidistance grey model GM (1,1) was proposed according to the grey theory, and its prediction precision was validated by using the past inspection data. Finally, the distribution types of corrosion depth and liquid load were acquired based on the analysis of the measured data. And a time-variant reliability model for the bottom shell was established according to the structural reliability theory, where the reliability indices were solved via modified first-order second-moment method in generalized random space. The results show that, the corrosion depth of the bottom shell and the height of oil, water in tank fit the normal distribution. Fitting accuracy of the prediction model is high. The failure probability of storage tank is more than 10-3 after serving 22 years, and the appropriate repair and maintenance measures can be taken for the bottom shell.