Change tube or bellows connected to the larger pipeline stretching temperature is a protective measure. Due to thermal expansion and contraction when solid, the amount of change in length was not much, but it happens to interfere with body deformation, there is a huge force. For example, the cross-sectional area of 1 cm 2, a length of 1 meter steel bars, when the temperature rises 40 ℃, the elongation is only about 0.0005 meters. If you do not stretch it, it will limit its objects produce 104 Newton force. The larger cross-sectional area, the greater the force. To do this in engineering technology for power generated by the thermal expansion, should consider taking the necessary measures. For example, steel bridges must put an end mounting on the movable carriage, so that the bridge can be freely retractable. Another example is when laying the tracks, are also leaving room for expansion segment.