According to field investigation buckle falling accident that causes electric submersible pump system upside down three:
1. Electric submersible pump in the startup and normal operation, there is a big down torque. This is because the electric submersible pump and the pipe thread connection place adopts a dextral thread connection (M90 * 1.75), and the direction of rotation is clockwise, the motor output torque to the pump cylinder through the pump shaft of the multistage centrifugal pump and impeller, guide the pump tube along the direction of the trend upside down. Especially in the electric submersible pump is started, the starting torque and there is a big big impact, the impact torque, most likely to buckle down pipe thread connection.
2. The pretightening force of electric submersible pump connection of the pipe thread (or lack of pretension is not enough). The size of pre tightening force is an important factor that affects the reliability of screw connection, and the preload is neither too big nor too small. The electric submersible pump on the pipe thread connection, on the one hand, taking into account the existence of electric submersible pump at work down torque, the pretightening force of the pipe thread connection should be able to ensure the axial load electric submersible pump systems (including electric submersible pump system weight, fluid pressure and preload etc.) together with transverse inverted torque, not place upside down phenomenon, even if the tightening torque is greater than a certain value down torque; on the other hand the pretightening force can not be too big. If the preload is too large, coupled with the electric submersible pump axial load, the yield point is likely to thread the cross section of the axial tensile stress exceeds the material pump barrel, the pump tube threaded plastic deformation took place, resulting in pre stress relaxation. At this point, although the 2 parts of each other have not occurred relative rotation, but the thread connection has been loose. If this time has the role down torque, the torque down all the blocks down from the anti bear; if welding is not strong anti down block or insufficient strength, will cause anti block loose weld or cut, resulting in electric submersible pump upside down fall well. Thus, the preload should have an appropriate value. But the actual production of the domestic use of electric submersible pump in the design, no pretightening force of the pipe thread connection technology for accurate calculation, no more strict control of the pre tightening force, which is an important cause of the thread buckle.
3. Anti fall process is not reliable. ESP exists because of the problem upside down, so connected in the pipe thread set up anti down block. Because the anti reverse block thickness is not big, the weld section size is smaller, the bearing capacity is not strong; in addition, the anti back block and pump head, pump tube are medium carbon steel, welding process is poor, the quality of the weld is difficult to guarantee. So, anti fall block anti fall function is not reliable. Anti block sealing off frequent production, cut or even the phenomenon, which illustrates this point.
