Research On On-Line Monitoringand Safety Evaluation Method For Uneven Settlement Of Vertical Storage Tanks

Analysis of a large number of storage tank accidents at home and abroad shows that uneven settlement is the main cause of storage tank accidents.Uneven settlement of storage tanks can affect the normal operation of storage tanks.Different degrees of deformation of storage tanks wall are also caused by uneven settlement.These different degrees of deformation will gradually increase with time,causing leakage problems in storage tanks.As a result,the tank cannot complete its intended function normally,that is,storaging.The tank are scrapped;Secondly,large-scale settlement of the foundation may cause tearing of the wall of the fixed roof,which directly leads to the leakage of crude oil,which may cause serious hidden danger to the safety of the storage tank.In this paper,the evaluation of uneven settlement of storage tanks based on reliability is constructed.When evaluating the uneven settlement of storage tanks,the existing reliability function function is based on the central settlement structure load effect S and structural resistance of the tank floor.The establishment of factors that affect the reliability of the structure is not applicable to the uneven settlement of the tank foundation.Based on the storage tank's uneven settlement allowable value S_max specified in the standard SYT 6620,combined with the storage tank's settlement value S₀,a functional function model based on the uneven settlement difference of the adjacent monitoring points of the storage tank is established.The reliability of uneven settlement of storage tanks can be calculated.In the process of applying the functional function to solve the reliability,this paper applies the improved second-order moment method,the first-order second-order moment method of orthogonal transformation,the second-order second-order moment Breitung method and the second-order second-order moment Laplace method.And the results are compared with the Monte Carlo method.The results show that the four squares are suitable for solving the functional function of the uneven settlement of the tank,and the reliability and failure probability of the improved first-order second-order method are calculated.The image trend is the same as the Monte Carlo method of direct-important sampling,and the calculation result is more accurate and reasonable.In this paper,an experimental system for simulating the uneven settlement of storage tanks was built to simulate the uneven settlement of the storage tanks.The uneven settlement form of the bottom of the tank and the detection of uneven settlement by the fiber grating detection were observed.It was also verified whether the settlement value converted by the fiber grating detection strain can reflect the true settlement.The monitoring of the settlement degree of the storage tank under different liquid levels of the fiber grating detector was carried out,and compared with the traditional settlement detection method,the feasibility and accuracy of the fiber grating detector for measuring the weekly settlement of the tank were verified.At the same time,the reliability theory is used to calculate the failure probability of the tank under different settlement degrees.The change trend of the failure probability of the uneven settlement of the storage tank with the increase of the settlement value and the change trend of the failure probability of the storage tank in the actual working condition are analyzed.This paper constructs an exponential curve prediction model that accords with the settlement law of storage tanks.The exponential curve method is used to predict and analyze the uneven settlement at the bottom of the tank,and the settlement of the bottom of the tank is predicted.The predicted value of the settlement is compared with the measured value to verify the feasibility of the exponential curve method for predicting the settlement of the tank bottom.