Abstract: Briefly summarized in the assay are the achievement as made in relevant circles from research on the three typical defects occurring in the pipe piercing process,i.e.,cavity,lamination and torsional deformation. Furthermore,a discussion is made,focusing on the piercing principles and application scopes of the 2-roll barrel type piercer and the cone type piercer,and accordingly,some proposals are put forward. The analysis result leads to the following conclusion. To produce qualified pierced shell with the 2-roll barrel type piercer and the cone type piercer,and achieve the optimized overall effects of product quality,output and consumption,relevant process operations must be ensured,including putting the plug into the non-oxidized porous area in front of the cavity of the bloom for piercing a shell without any inner fold,and determining proper process parameters and operational tool design to eliminate any defective lamination of the shell and minimize the torsional deformation thereof. And this should be regarded as the substantial difference between the above mentioned 2-roll rotary piercing principle and process and that of any other piercing process.