The most dangerous casse is not the steady operating case, but the transient case at the moment that the shell-side fluid is just shut down, but tube side pressure load and thermal load still retain.

• 本题研究的管板的危险工况不是发生在管程载荷、壳程载荷和温度载荷同时作用的正常操作工况下，而是发生在可能出现的壳程压力先停(管程载荷和温度载荷同时作用)的瞬态工况下。