📋 Case Study
Chemical Reactor Overpressure Mitigation at Midwest Petrochemical Plant
Uncontrolled reaction runaway leading to overpressure exceeding MAWP; prior relief valve sizing based only on thermal expansion
🏗️ Project Overview
Retrofit of exothermic batch reactor system handling nitration chemistry
🎯 Challenge
Uncontrolled reaction runaway leading to overpressure exceeding MAWP; prior relief valve sizing based only on thermal expansion
🔧 Design Approach
Integrated LOPA to validate IPL hierarchy: DCS high-temp alarm (non-SIS), independent SIS with dual pressure transmitters and solenoid shutdown, mechanical relief valve, and operator response procedure
📐 Design Diagram
AI-generated project design illustration
📐 Key Calculations
Initiating Event Frequency
PHA-derived frequency from HAZOP 'High Temp' deviation
Result: 0.5/yr
Baseline for risk quantification
SIS PFD
IEC 61508 FMEDA + proof test coverage
Result: 0.012
Confirms SIL 2 capability
Operator Response RRF
1 / (β × response time reliability)
Result: 15
Validated via task analysis & simulator testing
📊 Results
Final risk reduced from 0.02/yr → 0.0003/yr (< tolerable 0.001/yr); SIL 2 confirmed for SIS; 100% compliance with OSHA 1910.119 Appendix C💡 Lessons Learned
- •Mechanical IPLs (relief valves) require rigorous maintenance verification to qualify as IPLs
- •Alarm-only layers without automatic action cannot be counted unless rigorously validated for timeliness and reliability
✅ Key Takeaways
- 1Mechanical IPLs (relief valves) require rigorous maintenance verification to qualify as IPLs
- 2Alarm-only layers without automatic action cannot be counted unless rigorously validated for timeliness and reliability
📐 Prerequisites
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➡️ Next Step
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🔗 Engineering Applications
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