🎓 Lesson 5
D3
FMEA for Mechanical Systems: Pump & Compressor Applications
FMEA is a step-by-step method to find out what might go wrong with a pump or compressor, how badly it could fail, and what you can do to stop it before it causes harm or downtime.
🎯 Learning Objectives
- ✓ Analyze a reciprocating air compressor assembly to identify at least five credible failure modes and assign severity, occurrence, and detection (S/O/D) ratings
- ✓ Calculate Risk Priority Numbers (RPNs) for identified failure modes and rank them to prioritize mitigation actions
- ✓ Explain how FMEA integrates with Layer of Protection Analysis (LOPA) and Process Hazard Analysis (PHA) in mining operations
- ✓ Apply ISO/IEC 60812:2018 guidelines to document and validate an FMEA for a slurry pump system
📖 Why This Matters
In underground mines and open-pit operations, pump and compressor failures cause more than 35% of unplanned production stoppages—and pose serious risks including high-pressure fluid release, fire (from oil-lubricated compressors), or catastrophic flooding (e.g., dewatering pump failure). In 2022, a major Australian iron ore operation lost $4.2M in downtime after a cascading failure in its primary booster compressor train—root-caused to undetected bearing wear missed during routine maintenance. FMEA isn’t just paperwork: it’s your first line of defense in designing reliability *into* equipment—not bolting it on after failure.
📘 Core Principles
FMEA begins by decomposing a system into functional components (e.g., suction valve, crankshaft, cooling jacket) and asking three questions per component: (1) How could it fail? (failure mode), (2) What would happen if it did? (effect), and (3) Why would it happen? (cause). Each failure mode is scored on a 1–10 scale for Severity (S), Occurrence (O), and Detection (D); the product S×O×D yields the Risk Priority Number (RPN). Modern practice emphasizes *actionable* RPN thresholds (e.g., RPN ≥ 125 triggers immediate mitigation) and shifts focus from pure RPN ranking to criticality analysis using Action Priority (AP) tables per AIAG-VDA FMEA Handbook. For mining machinery, environmental stressors—dust ingress, vibration, thermal cycling, and abrasive slurry—must be explicitly modeled as root causes, not just generic ‘wear’.
📐 Risk Priority Number (RPN)
The RPN quantifies relative risk magnitude to guide resource allocation for mitigation. While superseded by Action Priority (AP) in latest standards, RPN remains widely used in mining PHA workflows and regulatory submissions. It is calculated for each failure mode independently.
Risk Priority Number (RPN)
RPN = S × O × DQuantitative metric to rank failure modes by relative risk magnitude for prioritization of corrective actions.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| S | Severity rating | dimensionless (1–10 scale) | Assessment of worst-case effect on safety, environment, or operations |
| O | Occurrence rating | dimensionless (1–10 scale) | Estimate of frequency/probability of failure cause based on data or engineering judgment |
| D | Detection rating | dimensionless (1–10 scale) | Assessment of effectiveness of existing detection methods to identify failure prior to occurrence |
Typical Ranges:
High-consequence mining equipment (e.g., hoist air compressors): 100 – 800
Medium-risk slurry pumps: 40 – 300
💡 Worked Example
Problem: A mine’s diesel-driven centrifugal slurry pump (used for tailings transfer) has a failure mode: 'Impeller erosion due to abrasive solids'. Engineering team assigns: Severity = 8 (loss of containment → environmental release + shutdown), Occurrence = 5 (moderate likelihood; historical data shows impeller replacement every 4,200 operating hours), Detection = 3 (vibration monitoring detects imbalance only after >30% material loss).
1.
Step 1: Confirm all ratings are integers on the 1–10 scale per ISO/IEC 60812 Annex B scoring guidance.
2.
Step 2: Multiply S × O × D = 8 × 5 × 3.
3.
Step 3: Compute result: 120. Compare to site-specific RPN threshold (e.g., 125). Since 120 < 125, this failure does *not* trigger mandatory redesign—but requires enhanced inspection frequency per maintenance plan.
Answer:
The RPN is 120, which falls below the site’s action threshold of 125 but exceeds the monitoring threshold of 80—requiring quarterly ultrasonic thickness testing and inclusion in CMMS alert logic.
🏗️ Real-World Application
At Teck Resources’ Highland Valley Copper Mine (BC, Canada), FMEA was applied to the primary mine dewatering compressor system serving shaft sumps. The analysis identified 'coolant pump seal failure' as a high-criticality mode (S=9: compressor seizure → sump overflow → shaft flooding; O=4: seal life degrades 3× faster in high-humidity, silica-laden air; D=2: no real-time seal leakage monitor). Mitigation included installing a differential pressure sensor across the seal flush system and revising PM intervals from 6 to 3 months—reducing related forced outages by 78% over two years. This case is documented in CCPS’ 2021 ‘Mechanical Integrity Best Practices’ compendium.