The Research To The Security Evaluation Of Tank System At Normal Pressure

Oil tanks are important facilities in oil transport system, in which the medium that are tend to burn or explode, or else, may pollute the environment is installed. With the extension of the employing time and the infection of the circumstance medium, the material of oil tanks are inevitably weathering and eroded. As the result, the tank's security degree drops and the resistibility against outburst load also descends, together with the continuous change of the pressure and the fluid depth, the leakage of the medium is easily brought, then serious economic loss and pollution to the environment and ecology is brought out. Therefore, the research to the method of evaluation to the security of the tank at normal pressure is significant to several facets, such as the tank's safe run in daily works, the enhance of the security degree upon outburst load, and the reduce of the disaster loss.Based on the analysis to the forced status of the oil tank in this paper, the corresponding mechanics model is established, which is calculated with the eight-dot limited element, so the stress value of the identified point on the tank and the integer stress distribution fig are obtained. By use of the fuzzy decision making technique, the fuzzy most stress set and the fuzzy least failure set of the large-sized tank structure is obtained, at the same time, the fuzzy fractural stress intension factor set and fuzzy fractural failure set of the cell that involves cracks is also obtained. Based on the normal failure criterion of reliability design, and considering the two sides of the undetermined factor: randomness and fuzzyness. Combined with fractural mechanics theory, the fuzzy equation under fractural limit state is established, the calculated method of the structural fuzzy fractural reliability is confirmed, simultaneously, a fuzzy weight function algorithm for calculating structural reliability of a tank was presented which is relatively applicable and effective, the wholly expression of the structural fuzzy fractural reliability is also presented.The computer software of the analysis to the safely running reliability of the tank at normal pressure is compiled. Then the fuzzy fractural reliability on several kinds of failure boundary of the liquid ammonia tank in a certain chemical plant that is under the force of liquid medium is calculated with the software.