Abstract: There are great deference between the short cracks' and the long cracks' propagation, the short cracks' propagation are visible as the behavior of cracks in group with the action of stress, there are not only propagation of cracks, but interaction between the neighbor cracks and the combination in neighbor cracks on the basis of propagation, which results in the formation of leading cracks, but the long cracks' propagation performance as the individual behavior of crack. The cracks and defects that are caused during the process of pipe making, transportation and laying are the reason of "Pressure Reversal", and the cracks' propagation and the combination lead to pipe "Pressure Reversal". The "Pressure Reversal" is analyzed with the theory of cracks propagation of fracture mechanics and corresponding protection measures put forward.

Key words: pipe, pressure reversal, short crack, crack propagation, protection measures