An On-Line Fatigue Life Monitoring System for Boiler Drums Based on the Inverse Problem of Heat Conduction Method

Abstract

A method based on solution of the inverse heat conduction problem was presented for online stress monitoring and fatigue life analysis of boiler drums. The mathematical model of the drum temperature distribution is based on the assumptions that the difference of temperature along the longitudinal axis of the boiler drum is negligible with changes only in the radial direction and the circumferential direction, and that the outer surface of drum is thermally insulated. Combining this model with the control-volume method provides temperatures at different points on a cross-section of the drum. With the temperature data, the stresses of the boiler drum are derived according to the FEM and the life expectancy of it is calculated　based on the rain flow method. Applying this method to the cold start-up process of a 300 MW boiler demonstrated the absence of errors caused by the boundary condition assumptions on the inner surface of the drum and an applicable technique for the online stress monitoring and fatigue life analysis of boiler drums.