Damage to the close fitting bushings in the bottom of the stuffing box or in an api seal gland


DAMAGE TO THE CLOSE FITTING BUSHINGS IN THE BOTTOM OF THE STUFFING BOX OR IN AN API SEAL GLANDĀ ST017

Please refer to DB in the following illustration:

Rubbing marks at the inside diameter of the disaster bushing (DB)

  • Partial rubbing at the inside diameter.
    • The API (American Petroleum Institute) gland has slipped.
    • Improper installation. The bushing was not centered to the shaft.
    • The shaft is bending because the pump is operating off its best efficiency point (BEP).
    • The gland bolt holes are often not concentric with the shaft/ sleeve.
    • Misalignment between the pump and its driver.
    • Excessive pipe strain.
  • Rubbing all around the inside diameter.
    • The shaft is not concentric with the sleeve.
    • The seal is not concentric with the sleeve.
    • Bad bearings.
    • Bent shaft.
    • Unbalanced impeller or rotating assembly
    • Cavitation.
    • Any severe vibration will cause this symptom
    • Thermal expansion of the shaft or sleeve

Please take a look at the close fitting bushing in the bottom of the stuffing box in the next illustration. This bushing is called a restrictive or thermal bushing:

Erosion at the inside diameter of the stuffing box bushing

  • Dirt and solids are present in the discharge or suction recirculating fluid. The fluid accelerates through the close fitting bushing in the end of the stuffing box, increasing the rate of erosion. This can be a big problem if you are using suction re-circulation.

Rubbing on the ends of the restrictive or thermal bushing caused by the bushing rotating in the stuffing box. A snap ring, sleeve, etc did not positively retain the bushing.

  • A differential pressure across the bushing can push the bushing into the rotating portion of a mechanical seal.

  • This is similar to what happens with “back to back” dual seals when the stationary inside face is pushed into the inside rotating face.
  • Please notice that a “snap ring” has been installed inside the stuffing box to hold the stationary face if a pressure differential should occur.

Posted

  • On February 18, 2018