Case Study: Centrifugal Pump Failure – Root Cause Analysis and Corrective Actions

Background

A chemical processing plant was using a centrifugal pump to transfer water-based process fluid from a storage tank to a production line.

Pump Details

• Pump Type: End Suction Centrifugal Pump

• Capacity: 100 m³/hr

• Head: 40 meters

• Motor: 22 kW

• Operating Hours: 24/7

After 8 months of operation, the pump started showing:

• Reduced flow rate

• Excessive vibration

• Mechanical seal leakage

• Increased power consumption

• Frequent bearing failures

Symptoms Observed

Symptom Observation

Low Flow Flow reduced from 100 m³/hr to 70 m³/hr

High Vibration Vibration exceeded ISO limits

Seal Leakage Continuous leakage from mechanical seal

Bearing Failure Bearings failed every 2 months

Noise Pump produced cavitation-like sound

Investigation

1. Suction Pressure Check

The maintenance team measured the suction pressure and found it was lower than the pump manufacturer's requirement.

Finding:

Available NPSH (NPSHa) was less than Required NPSH (NPSHr).

Root Cause:

Cavitation

When pressure at the impeller eye falls below vapor pressure, vapor bubbles form and collapse violently.

Damage Caused:

• Impeller pitting

• Vibration

• Noise

• Reduced efficiency

• Seal and bearing damage

2. Alignment Check

Laser alignment revealed:

• Motor and pump shafts were misaligned by 0.8 mm.

Root Cause:

Misalignment

Damage Caused:

• Bearing overheating

• Coupling wear

• Mechanical seal failure

• Increased vibration

3. Pipework Inspection

Suction piping had:

• Multiple 90° elbows near pump suction

• Reducer installed incorrectly

Root Cause:

Poor Suction Piping Design

Effects:

• Turbulent flow

• Air pockets

• Cavitation

• Reduced pump efficiency

4. Operating Point Analysis

Pump curve analysis showed the pump was operating far left of BEP (Best Efficiency Point).

Root Cause:

Oversized Pump

Effects:

• Internal recirculation

• Excess vibration

• Increased temperature

• Premature seal failure

5. Bearing Inspection

Failed bearings showed:

• Grease contamination

• Water ingress

Root Cause:

Improper Lubrication Practice

Effects:

• Bearing overheating

• Shaft vibration

• Reduced bearing life

Root Cause Summary

Failure Mode Root Cause

Impeller Damage Cavitation

Seal Leakage Misalignment + Cavitation

Bearing Failure Misalignment + Poor Lubrication

High Power Consumption Operating Away from BEP

Low Flow Cavitation + Worn Impeller

Corrective Actions

1. Eliminate Cavitation

Actions Taken:

✔ Increased suction pipe diameter

✔ Reduced suction line restrictions

✔ Raised liquid level in tank

✔ Installed proper eccentric reducer

Result:

NPSHa > NPSHr

2. Correct Alignment

Actions Taken:

✔ Laser shaft alignment performed

✔ Alignment tolerance maintained within OEM limits

Result:

Vibration reduced by 70%

3. Improve Suction Piping

Actions Taken:

✔ Straight pipe length of 5D before suction

✔ Removed unnecessary elbows

✔ Installed eccentric reducer flat side on top

Result:

Smooth flow into impeller

4. Operate Near BEP

Actions Taken:

✔ Installed VFD

✔ Adjusted pump speed

Result:

Pump operated between 80–110% of BEP

5. Improve Bearing Maintenance

Actions Taken:

✔ Correct grease quantity

✔ Periodic lubrication schedule

✔ Bearing housing seals replaced

Result:

Bearing life increased from 2 months to over 18 months

Results After Rectification

Parameter Before After

Flow Rate 70 m³/hr 100 m³/hr

Vibration 9.2 mm/s 2.3 mm/s

Seal Life 3 Months 24 Months

Bearing Life 2 Months 18+ Months

Power Consumption 24 kW 20 kW

Pump Efficiency 58% 78%

Top 10 Reasons for Centrifugal Pump Failure

1. Cavitation

2. Dry Running

3. Operating Away from BEP

4. Misalignment

5. Pipe Strain

6. Bearing Lubrication Failure

7. Mechanical Seal Failure

8. Air Entrapment

9. Corrosion/Erosion

10. Incorrect Pump Selection

Conclusion

Studies across industries show that more than 60% of centrifugal pump failures are caused by cavitation, misalignment, poor lubrication, and operation away from the Best Efficiency Point (BEP). By ensuring proper pump selection, adequate NPSH, correct alignment, good piping practices, and preventive maintenance, pump reliability can be increased significantly while reducing downtime and maintenance costs.