Abstract: Described here in the article are the morphological characteristics of the outer surface fold defects of the finished pipes as corresponding to different types of billets that is rolled and deformed by the PQF process. The circular hole damage on the surface of the shell produces straight hairlines along the axis of the steel pipe，and the depth of the straight crack is related to the depth of the circular hole damage on the shell. The longitudinal damage of the shell also produces straight hairlines along the axis of the steel pipe，and as the axial damage deepens，the depth and the length of the cracks increase. The circumferential damage of the shell produces circumferential fins on the finished pipe which are serrated-shaped and thus easily peel off. Owing to studying and analyzing the morphological characteristics of then finished pipes as originated from the shell surface defects，the deformation regularity of the PQF mill is investigated，which furthermore provides a reference basis for formulating inspection and acceptance criteria for the billet and determining the NDT methods for the finished pipe.