Abstract: Addressing several types of defects with crack characteristics as occurring during the production process of the L80-1 oil casing,the material and manufacturing process of the said casing are described,and the macro and micro morphologies of three defects are analyzed.Furthermore based on the on-the-site statuses of hot-rolling,heat treatment and non-destructive detection operations,the possible reasons for the said defects are deduced,and accordingly corrective measures are taken to get the defect occurrence properly controlled.