1. What are key steps in a failure investigation?
Secure the scene - Document failure location/conditions
Preserve evidence - Protect fracture surfaces from damage
Collect samples - Include adjacent unaffected material
Review records - Operating data, maintenance history
Laboratory analysis - Metallurgical, chemical, mechanical testing
2. How to distinguish failure mechanisms?
| Mechanism | Visual Characteristics | Microscopic Features |
|---|---|---|
| Creep | Bulging, thick oxide | Grain boundary voids |
| Fatigue | Beach marks | Transgranular cracking |
| SCC | Brittle appearance | Branched cracks |
| Erosion | Smooth, directional | No oxide layers |
| Overheating | Thin edges, ductile | Spheroidized carbides |
3. What lab tests determine failure causes?
SEM/EDS: Fractography and elemental analysis
Metallography: Microstructural evaluation
Hardness testing: Material property changes
Chemical analysis: Verify composition
Mechanical tests: Compare to specifications
4. How to present failure analysis findings?
Executive summary: Key conclusions
Background: System description/failure event
Investigation methods: Testing performed
Results: Data and observations
Conclusions: Root cause determination
Recommendations: Corrective actions
5. What are common root cause categories?
Material deficiencies: Wrong alloy, defects
Design issues: Stress concentrations, poor geometry
Operational errors: Improper startup, chemistry control
Maintenance failures: Lack of inspections, overdue repairs
External factors: Contaminants, fuel changes
