Analysis of the mechanical-thermal coupling fatigue of the primary pump shaft

The paper studies the effect of mechanical stress and thermal stress on the fatigue life of the primary pump shaft. The mechanical stress analysis shows that only mechanical load will not cause fatigue crack of the primary pump under normal conditions. The thermal stress due to particular load-thermal shock in primary shaft service was discussed in detail. The temperature difference between the cold and hot fluids in the mixing area was apparent. The thermal stress of the primary shaft fluctuates rather greatly due to exist of this mixing area. The key parameter in thermal analysis is convective heat transfer coefficient. The variation range and law of this parameter is studied in the paper, with emphasis on several factors affecting the thermal stress Including convective heat transfer coefficient, ambient temperature and thermal shock time. Base on analysis of the temperature field, the distribution of thermal stress is obtained. The fluctuation of thermal stress is the main reason of fatigue crack. Particularly, the degree of convective heat transfer coefficient affecting the thermal stress is discussed. It points out that in some range the reduction of the coefficient can reduce the thermal stress to prolong the fatigue life of the primary shaft. (authors)