Abstract: Addressing the problem that scratch defects as made by metallic operation tool often occur on the outer surface of the shell as rolled with the Φ100 mm 3-roll mandrel mill,the causes are investigated,and then identified.Accordingly,a number of measures are taken,including re-distributing the deformation amounts of the workpiece in both the piercing process and the mandrel mill-rolling process,optimizing the passes of the mandrel mill,determining the rolling speed schedule of each stand of the mandrel mill as per the size variation of the shells,and replacing worn-out wedges beneath the roll-stand and so on.As a result,the occurrence frequency of the above mentioned tube scratch defect is obviously reduced.