A Fatigue Life Analysis For A Drum Based On A Coupling Method Of Direct And Inverse Heat Conduction Problem

A drum is the largest think-walled high-temperature bearing component of the boiler. It endures high thermal stress caused by uneven temperature distribution and mechanical stress due to the internal pressure during the start-up and shut-down processes. Frequent changes in stress will cause the drum’s fatigue life. Therefore, An study for the fatigue life of drums has important meanings for the safe and economic operation of the boiler, Which can control the temperature gradient by the admissible stresses and reduce the fatigue life loss. How to improve the calculation accuracy of the temperature and stress field and guarantee higher efficiency at the same time is the key to fatigue life analysis of boiler drum.Directing against the characteristic of the supercharged boiler drum’s outer surface that it is partly heated, a coupling method of direct and inverse heat conduction problem was presented for solving the transient stress distribution of the drum. For the unheated area, the thermocouples are arranged along the circumferential outer surface of the drum, and then the inverse method is used for the calculation of temperature distribution according to the real-time measured data. For the heated area, the direct method is adopted to solve the temperature distribution. At the junction of the two areas, the temperatures determined by the inverse method are used as the known first boundary condition to calculate the temperature distribution of heated area by the direct method. By this way the coupling method of the direct and inverse heat conduction problem is realized, and the whole temperature distribution of the drum is obtained. Then according to the plane strain, the finite element method is applied for the analysis of the drum’s transient field of stresses based on the transient temperature distribution by using the plane eight-nodded isoparametric element. Finally using the principle of Miner linear cumulative to calculate the drum’s fatigue life by rain-flow method, which can obtain the fatigue life loss of the drum and guide the operation for boiler.