The Residual Intensity Analysis Of Floating Roof Oil Tank Containing Corrosion Defects

Oil storage tank is a petroleum production, used to store crude oil, gasoline, kerosene, diesel and other oil products. As our country national economy and petrochemical industry rapid development ,whether it is oil fields, refineries or marketing companies are required many types of oil storage tanks, the needs of storage tanks is increasing, and its anti-corrosion and security have arouse an increasing problem attention.In recent years, as the human demands of energy sources is growing up, much of ports and oil refineries set up a large amount of crude oil storage tanks, reliable operation of these facilities has direct relationship to the efficient production and the environment safety. The length of its life have a direct impact on the economic benefits of the refinery, the general tank design life is 20 years, however, the oil stored in tanks often contains hydrogen, sulfuric acid, organic and inorganic salts, water and other corrosive chemicals, together with the tank wall suffering from environmental factors, the life span of oil tank can be shortened to 5 years. Some serious corrosion will enable the tank corrosion perforation in about a year. If corrosion perforation occurred during non-examination and non-repair period, resulting the loss even greater. If giving metal tanks treatment not timely, it will make tank surface corrosion and pollution of oil, so oil colloid, pH, salinity increase, then making the impact of fuel quality; Moreover, corrosion perforation caused oil leakage, not only producing energy waste, pollution of the environment, but also easily causing fire, explosion, so its fatalness can be imagined.Corrosion fatigue damage caused a direct impact on the intensity of oil tank, and it is the main reason to reduce the life-span of oil tank. Therefore it is necessary to study the corrosion fatigue, to assess of the residual intensity of in-service oil tank, for the future of oil production, and maintenance to provide reliable safety data. In the current, the studies of the intensity of oil tank containing corrosion defects are still relatively lack, and there are no universally applicable methods of evaluation, so in order to produce safely, benefits of the country, the enterprise economic, there is an urgent need for a good evaluation of tank corrosion defects method.In this article, finite element analysis is used to analyze a 12.5×104m3 large floating roof oil tank, and evaluate the residual intensity of the tank. The article is divided into four main parts, which are finite element analysis and stress evaluation of no defects tank; the deformation with a tank of defects and the analysis of a variety of stress (radial stress, hoop stress, axial stress) maximum with the defects'size, location, depth changing; the deformation of storage tanks containing two defects and the analysis of the stress maximum with defects attributes change; the interactions of corrosion pit point on the impact of tank residual intensity. Using finite element analysis software ANSYS, setting up model, impose hydrostatic pressure load ( P =ρgh) and make the structural simulation analysis for storage tank, graphical data summarized and summed up, get the following major conclusions: In the no defects tank, when it is under the force, the maximum circumferential stress can happen in the second ring wall, the maximum axial stress can appear in the first lap to the edge of the inner side; for the storage tank containing defects, with defects at different axial location, deformation change is different with the corrosion area increasing and decreasing, and with the increase of the corrosion area, stress value change trends of the storage tank is almost reducing, but at certain locations appearing special change; the defects arranging annularly interaction of defects increased with defect spacing decreased, interaction of defects arranging in radial direction must have a role on the storage tank and with the corrosion defects spacing increased, which means the thickness of the small defects reduced, the limited highest pressure is reduced.