Understanding Defect Severity

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Portable balancer & Vibration analyzer Balanset-1A

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Vibration sensor

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Optical Sensor (Laser Tachometer)

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Balanset-4

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Magnetic Stand Insize-60-kgf

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Reflective tape

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Dynamic balancer “Balanset-1A” OEM

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Definition: What is Defect Severity?

Defect severity is the classification of detected faults based on their seriousness, progression stage, and urgency for corrective action. Severity assessment combines vibration amplitude, rate of change, fault type, and equipment criticality to categorize defects from incipient (minor, early-stage) to critical (severe, imminent failure) enabling prioritization of maintenance resources and appropriate response timing. Severity ratings transform fault detection findings into actionable maintenance priorities.

Accurate severity assessment is essential for optimizing condition monitoring program effectiveness—it determines how quickly to act, what resources to allocate, and how to balance multiple competing maintenance demands across a facility.

Severity Classification Scales

Five-Level Scale (Common)

Level 1: Incipient

• Description: Very early-stage defect, just detectable
• Amplitude: Slightly above baseline, just entering alert zone
• Timeline: 6-12+ months to failure
• Action: Note in database, continue routine monitoring

Level 2: Minor

• Description: Confirmed early-stage defect
• Amplitude: Alert zone, clear trend developing
• Timeline: 3-6 months to failure
• Action: Increase monitoring frequency, plan maintenance

Level 3: Moderate

• Description: Active progressing defect
• Amplitude: Warning/alarm zone
• Timeline: 1-3 months to failure
• Action: Schedule maintenance within weeks, monitor weekly

Level 4: Serious

• Description: Advanced defect, significant degradation
• Amplitude: Danger zone, rapidly increasing
• Timeline: Weeks to failure
• Action: Urgent maintenance, monitor daily, plan rapid shutdown

Level 5: Critical

• Description: Imminent failure, catastrophic risk
• Amplitude: At or exceeding trip levels
• Timeline: Days or hours to failure
• Action: Immediate shutdown and repair, continuous monitoring if running

Severity Assessment Factors

Vibration Amplitude

• Primary indicator for many fault types
• Higher amplitude generally indicates more advanced defect
• Compare to standards and baseline
• Account for fault type (bearing vs. unbalance)

Rate of Change

• Slow Change: Lower severity (stable condition)
• Accelerating Change: Higher severity (active deterioration)
• Exponential Growth: Critical severity (imminent failure)
• Rate often more important than absolute level

Fault Type

• Bearing Spalls: Progress rapidly once advanced → high severity
• Unbalance: Usually stable → lower severity
• Shaft Cracks: Can fail suddenly → high severity
• Misalignment: Chronic but manageable → moderate severity

Spectral Characteristics

• Number of harmonics (more = worse)
• Sideband complexity (extensive sidebands = advanced)
• Elevated noise floor (widespread damage)
• Multiple fault frequencies (multiple problems)

Equipment Criticality

• Same vibration level more severe on critical equipment
• Adjust severity based on failure consequences
• Critical equipment: treat lower vibration as higher severity

Severity-Based Actions

Incipient/Minor

• Monitoring: Continue routine schedule
• Planning: Note for future outage planning (months ahead)
• Action Timing: Next scheduled maintenance or within 3-6 months

Moderate

• Monitoring: Weekly measurements
• Planning: Schedule dedicated maintenance (1-2 months)
• Procurement: Order spare parts
• Action Timing: 2-8 weeks

Serious

• Monitoring: Daily or continuous
• Planning: Expedite maintenance scheduling (days to 2 weeks)
• Resources: Assign priority resources
• Action Timing: 1-2 weeks maximum

Critical

• Monitoring: Continuous
• Action: Immediate shutdown and repair
• Resources: Emergency response, all necessary resources
• Timing: Immediate to days

Documentation

Severity Assessment Records

• Defect identified and described
• Severity level assigned with justification
• Vibration data supporting assessment
• Recommended actions and timeline
• Approval and review signatures

Severity Tracking

• Track severity over time as fault progresses
• Update severity based on new measurements
• Escalate severity as vibration increases
• Historical record of progression

Defect severity assessment is the bridge between fault detection and maintenance action, providing the classification framework that prioritizes response efforts and allocates resources appropriately. Accurate severity assessment—considering amplitude, progression rate, fault type, and equipment criticality—enables optimized maintenance scheduling that balances equipment utilization, maintenance costs, and failure prevention in effective condition-based maintenance programs.

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