Abstract: Mechanical damage occurred to the sealing disc of the power joint of the detector during the intelligent internal inspection of the submarine pipeline. In order to find out the cause of the damage and avoid the recurrence of similar failures, the suspicious element elimination method and trace inspection method were applied for the recovered intelligent internal detector.The relevant components of the submarine pipeline system and the internal detector were analyzed, and the cases of mechanical damage to the sealing disc of the intelligent internal detector were investigated. The results show that the main reasons for the external mechanical damage are the insufficient opening of the ball valve spool and the reduced diameter of the ball valve on the pipeline system, which block, collide and squeeze the sealing disc of the intelligent inner detector power joint.