Investigation of Causes for Development of Surface Concave and Convex Defects of Shaped Tube and Relevant Adjustment Measures

When the round tube as the blank is processed into a shaped one，three different concave and convex surface defects are developed to form the unevenness of the tube，including concave defect，convex defect and concaveconvex defect.Causes for these type of surface defects are investigated.As a result，it is revealed that the major cause for the convex defect is the blank tube’s side length is shorter than that of the correspondent groove，whereas the cause for the concave defect is completely on the contrary to that for the convex one，and that formation of the concave-convex defect is mainly due to various defects like different impresses，groove dislocation，“wry mouth”and“cornering”etc.which occur during the weld pipe manufacturing processes like forming，welding and sizing.According to the above mentioned tube surface unevenness defect types，a number of adjustment measurements are proposed.