Analysis of the causes of the outer surface folding defects in N80-Q oil country tubular goods

The causes to the outer surface folding defects in N80-Q oil country tubular goods (OCTG) were investigated through the observation of the defects’ morphology,microstructure and the analysis of the chemical compositions.It is believed that the defect was resulted from the intrinsic flaws that originally existed on the billet; they were extended and oxidized during the following reheating and rolling processes.With more strict quality control and inspection of the billet,the defect can be prevented effectively from occurring.