Abstract: In order to study the features of the temperature and the thermal stress distribution in water wall tubes under different conditions, the 3D FEM model of a water wall tube of a 1 000-MW ultra-supercritical pressure boiler is built and the computation is taken in the scenarios of the normal heat transfer and the deteriorated heat transfer. The computation results show that the temperature and the thermal stress are strongly affected by the fire-side heat flux and the tube internal heat transfer coefficient, and there is a linear relationship between the temperature and the thermal stress before the water wall tube yields. In the normal heat transfer scenario, the temperature and the thermal stress in fins are bigger than that in the fire-side apex, while in the deteriorated heat transfer scenario, the temperature and the thermal stress in the fire-side apex grow greatly, and they are much bigger than that in fins. The alternating stress caused by the repeated heat transfer crisis will make transversal cracks in the tube.

Key words: ultra-supercritical pressure boiler, water wall tube, temperature distribution, transversal crack, thermal stress, heat transfer crisis, finite element method (FEM)