Pump Failure Analysis

Bearing Failure Analysis

• Fatigue spalling: Surface flaking on the raceway. Caused by normal wear over time or by excessive loading. If premature, check for misalignment, overloading, or vibration.
• Brinelling: Dents in the raceway at ball spacing. Caused by static overload or impact (dropping the bearing, hammering during installation). Use proper installation tools and procedures.
• Electrical pitting: Small craters on balls and raceways, often in a pattern. Caused by current passing through the bearing (stray current from VFD or motor). Install shaft grounding or insulated bearings.
• Lubrication failure: Discoloured (blue or brown) balls and raceways, indicating overheating. Caused by inadequate lubrication, wrong lubricant, or over-greasing. Check lubrication procedure.
• Contamination: Scratches and abrasive wear patterns. Caused by dirt, water, or debris entering the bearing. Check seals and storage practices.
• Water damage: Rust on bearing surfaces. Caused by water ingress through seals, condensation, or water in the lubricant. Improve sealing and use water-resistant lubricant.

Mechanical Seal Failure Analysis

• Dry running: Seal faces are scored, cracked, or heat-checked (fine cracks). Caused by running the pump without liquid. The seal faces need liquid for cooling and lubrication.
• Cavitation: Pitting on the seal faces, particularly the stationary face. Caused by cavitation vibrations hammering the faces together.
• Chemical attack: Swelling, cracking, or dissolution of elastomers (O-rings). Caused by incompatibility between the seal materials and the pumped fluid. Check material compatibility.
• Erosion: Wear on the seal faces from abrasive particles in the fluid. Use harder face materials (silicon carbide, tungsten carbide) or add filtration.
• Misalignment: Uneven wear pattern on faces. Caused by shaft misalignment, bent shaft, or excessive runout. Check alignment and shaft straightness.
• High temperature: Degraded elastomers, heat-checked faces. Caused by dead-heading, high fluid temperature, or inadequate flush. Verify operating conditions and seal flush arrangement.

Impeller and Casing Analysis

• Cavitation pitting: Rough, pitted surface on the impeller inlet vanes (suction side). Caused by insufficient NPSH. Fix the suction conditions, not just the impeller.
• Recirculation damage: Pitting on the impeller inlet or outlet vanes. Caused by operating at too low flow. Install minimum flow protection.
• Erosion: Smooth wear on the impeller and casing, concentrated at the outer diameter. Caused by abrasive particles or high velocity. Use harder materials or add filtration.
• Corrosion: Generalised surface roughness, pitting, or material loss. Caused by chemical incompatibility. Select impeller and casing materials compatible with the fluid.

Root Cause Analysis Process

1. Collect all failed components. Do not discard anything until analysis is complete.
2. Photograph the components before cleaning or disassembly.
3. Examine each component: bearings, seals, impeller, casing, shaft, coupling.
4. Identify the primary failure mode (the first thing that failed).
5. Ask why it failed. Then ask why again. Continue until you reach the root cause.
6. Implement corrective action to prevent recurrence.
7. Document the findings in the maintenance record. PlantLogica's asset management system stores this for future reference.