Abstract: Based on the background of the internal inspection project of a 12.75-inch production riser on a South China Sea platform， the standards and specifications for pipeline internal inspection were systematically organized. The inspection objectives， methods， precision， and parameters for evaluating the remaining strength of corrosion were established. Using ultrasonic internal inspection equipment， a comparative analysis was conducted between the conventional in-line inspection method based on water driving and the pulling through method. It was found that the operation time of the pulling through method was only 23% of that of the water driving method. Based on the preliminary assessment of internal cleanliness and corrosion conditions obtained through pipeline CCTV system， the ultrasonic pulling through internal inspection solution was employed to conduct wall thickness testing and corrosion evaluation of the offshore riser， identifying defect information where corrosion depth exceeded 10% of the wall thickness. According to the corrosion evaluation index of ASME 31G， the estimated repair factor of the riser defect location was obtained， and a riser repair plan was formulated， providing a reference for subsequent similar inspections.

Key words: riser, in-line inspection of pipeline, ultrasonic, pipeline anomaly, estimated repair factor （ERF）