Tuesday, April 2, 2019


An OH1* pump of Superflow make failed frequently. High 1x RPM vibrations were evident in the spectrum revealing unbalance/base looseness issues. The pump was added into the bad-actor list due to the failures.
18mm/s vibration at 1x RPM
Pump details:
Speed: 3546 RPM
Type: *OH1 = Overhung, foot mounted pump as per API 610
Service: Ejector water circulation
Flow: 152 m3/hr
Head: 51 mlc
Seal: Single seal plan 11,62
Impeller type: Closed

Observed damages:
  1. Mechanical seal damaged.
  2. Bearing failure.
  3. Broken shaft.
  4. Worn out impeller nose and casing wear ring.

A detailed inspection revealed cracks on the base frame below the pump led to the high vibrations. Furthermore, pipe strains on the pump induced by improper pipe supporting led to the high vibrations, which in turn led to the cracking of the base frame.
The shaft failed at an area of reduced cross-section. The inspection revealed that the corners were sharp and not rounded leading to a high-stress concentration at that area, eventually leading to failure.
Cracked frame
Cracked frame
Corrective actions:
  • On Pump
    • Seal replacement.
    • Bearing replacement.
    • Trimming of impeller nose.
    • Fabrication of new casing wear ring.
    • Fabrication of new shaft and rounding off (fillet/chamfer can be provided) sharp corners.
  • At site
    • Correcting pipe strain by providing proper pipe supports.
    • Weld repair on the cracked base frame.
    • Alignment.
After correction, vibrations are down to 3.569mm/s at 1x
After correcting, the vibrations came down from 18mm/s to 3.569mm/s at 1x.

How it was solved?
  • Eliminated pipe strain at suction and discharge nozzles by providing proper pipe supporting.
  • Repaired the base frame cracks by welding.
  • Ensured proper coupling alignment.

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