Study On Cathodic Protection Potential Distribution Of Floor Adjacent Crude Oil Storage Tank Floor

Once a leak due to corrosion occurs in the bottom plate of the ground adjacent crude oil storage tanks, it will cause a serious damage to the local environment, and will easily bring about a secondary disaster, which will lead to serious economic losses. Timely and accurately grasping the potential distribution of tank bottom has an important significance to prevent the corrosion of the tank bottom. Unlike a single tank, when the adjacent tanks are protected by cathodic protection, the status changes of one side tank will affect the potential value of adjacent tank bottom. Therefore, to study the potential distribution of adjacent tank bottom for improving potential distribution of adjacent tank bottom and increasing the cathodic protection effect has an extremely important practical significance.Based on the electrostatic theory, a mathematical model for the cathodic protection potential distribution of the adjacent tank bottom is established. According to the actual state of the tank bottom, the polarization curves of metal tank bottom are tested under different conditions. The cathode section of the polarization curve is fitted, which determines the cathode boundary of the potential distribution model. The finite element software COMSOL was used to solve the potential distribution model of tank bottom. The maximum relative error of the model is 5.24%, which is verified by the measured potential of tank bottom, and the validity of the model is determined.The study is about the cathodic protection potential distribution of the adjacent tank bottom under the protection of the four anode forms, including deep-well anodes, horizontal anodes, vertical anodes and flexible anodes. The six factors were considered in the thesis, including adjacent distance of the tank, resistivity of tank bottom medium, tank bottom diameter, surface condition of tank bottom, medium contacting with tank bottom and parameters of anodes. The correlation degree between the factors and the potential value of the tank bottom is calculated by using the grey relation method, it determines the influence of various factors on the potential value of the tank bottom. Based on the obtained law to analyze the potential distribution of the adjacent tank bottom in the N-L station and some targeted improving measures are put forward.Through the study of the above contents, the main conclusions are as follows:(1) With the increase of adjacent distance, the potentials of the bottom protected by deep-well anodes or horizontal anodes moved in the negtive direction. There is a best adjacent distance between the two tanks. The potential of the tank bottom protected by vertical anodes or flexible anodes is less affected by the adjacent distance.(2) In four kind of anode forms, the potential distribution of the adjacent tank bottom protected by the flexible anode is the most uniform, and it's in the range of-0.85V?-0.88V; The potential value of the tank bottom protected by the flexible anode is less affected by the adjacent tank.(3) The sequence of influencing factors for cathodic protection potential distribution in adjacent tank bottom is:medium contacting with tank bottom, surface condition of tank bottom, the resistivity of asphalt sand and the diameter of adjacent side tank. Other factors have little influence on the potential of the tank bottom and their influence degree is nearly the same. Dry asphalt sand and surface coating of tank bottom can improve the uniformity for the potential distribution, and reduce the influence of the potential value affected by the status changes of adjacent side tank.(4) Improving output voltage of the anodes or adding deep-well anodes can make N-L station A, B tank bottom center area meet the requirements of the protection. When the tank bottom is replaced, embedding sacrificial anodes can carry out auxiliary protection for the center position of tank bottom, in order to meet the protection requirements.