In the process of boiler start-up, continuously rising of temperature puff various components cause thermal expansion, if this kind of thermal expansion was hampered,  the excessive thermal stress in the metal will occur, thus the equipment deforms and even damages. Because the cold water wall tube, header and the drum length is longer and is at higher temperature, the thermal expansion value is bigger. Therefore in the process of boiler start-up,  it is required to special monitor the thermal expansion of water-cooling wall,  steam drum, header, and pipe, and to regularly inspect and record the indicated value on the expansion indicator of these parts. If it is found the thermal expansion has  abnormal situation, the pressure boosting shall be suspended, the reasons shall be found out for handling in time. After the thermal expansion is finished, the pressure boosting can be continued.   （lsh）