Seamless steel pipe inner and outer surfaces is a conventional helical cracking or reticular and bottom ends of the cracks, which are sharp-shaped. Reason: 1, steel adverse subcutaneous pores and skin inclusions. 2, the tube is heated properly. 3, the deformation pressure is too great. 

Hairline a steel pipe characterized in that the outer surface of a continuous or discontinuous fine lines more hairy helical spiral direction opposite to the rotational direction of the piercing mill and some larger pitch approximately rectilinear. Causes: 1, steel adverse subcutaneous pores and skin inclusions. 2, the tube surface is not completely clear. 

Characteristics of the inner flap on the inner surface of the pipe was a straight zigzag defects or generally helical surface in order to improve the quality of seamless steel pipe, it is recommended to use two adjustable rack at least during the production process, one for the pre-finishing, another plane for finishing, pre-finishing for the transition, so that the tube can be a good transition between the non-adjustable rack. Especially when the adjustment amount is large, the middle rack of the pre-finishing effect is more obvious, if the lack of the middle frame, the surface of the roller tube joints prone to blue line. If greater amount and the reduced diameter tube is preferably roundness, it is necessary to add an adjustable rack, its purpose is to adjust the finishing pass to reach a certain diameter correction amount, to compensate for the wall thickness and temperature, slight wear steel grade changes and the impact of the roll. In the mill re-tune the process, usually brings a slight oval and a certain degree of roundness and rolling them into a linear relationship between the amount of reduction. Since the roundness can be corrected in general, a slight ovality and this can be generally ignored in the actual production.