Corrosion Failure Root Cause Analysis (RCA) Framework – Fishbone + FMEA Integration

The framework begins with constructing a fishbone diagram structured around six primary categories—Materials, Environment, Design, Operation, Maintenance, and Monitoring—each populated with corrosion-specific sub-causes (e.g., chloride concentration, galvanic coupling, weld heat-affected zone sensitization, or inadequate cathodic protection). These causes are then transferred into an FMEA worksheet where each potential failure mode (e.g., pitting in UNS S32750 duplex stainless steel exposed to warm seawater) is assigned Risk Priority Numbers (RPNs) using standardized scoring scales (1–10) for Severity (S), Occurrence (O), and Detection (D). Crucially, the integration enforces traceability: every fishbone branch maps to at least one FMEA row, ensuring no causal pathway remains unassessed quantitatively. The framework further incorporates corrosion-specific inputs—such as electrochemical potential data, alloy corrosion rate predictions (e.g., from ASTM G108 or NORSOK M-506), and environmental speciation models—to calibrate O and D scores. Post-FMEA, action plans are generated not only by RPN ranking but also by ‘criticality clusters’—groups of high-S, high-O causes sharing common mitigation levers (e.g., upgrading material grade *and* implementing real-time pH/Cl⁻ monitoring). This dual-layered approach transforms subjective corrosion narratives into auditable, prioritized, and technically grounded integrity interventions.