📋 Case Study

Chemical Plant Reactor Pressure Safety Interlock Retrofit

Electro-mechanical interlocks failed twice in 3 years, risking runaway reaction and BLEVE

🏗️ Project Overview

Exothermic batch reactor handling Class 1 flammable monomers

🎯 Challenge

Electro-mechanical interlocks failed twice in 3 years, risking runaway reaction and BLEVE

🔧 Design Approach

Triple-redundant SIL2-certified safety PLC (Siemens Fail-Safe S7-1500F) with independent pressure transmitters, solenoid valve diagnostics, and automatic proof-test scheduling

📐 Design Diagram

Chemical Plant Reactor Pressure Safety Interlock Retrofit Ch 2 failures in 3 yrs → BLEVE risk Siemens S7-1500F SIL2 • Triple Redundant PT-1 PT-2 PT-3 Independent 4–20 mA Transmitters Solenoid Valve Diagnostics Enabled Proof Test Interval = 6 mo √(2×MTTFdd×DC) PFDavg = 1.2×10−3

AI-generated project design illustration

📐 Key Calculations

PFDavg

λDU × T / 2 + λDD × β
Result: 1.2E−3
Meets SIL2 target (<1E−2)

Proof Test Interval

√(2 × MTTFdd × DC)
Result: 6 months
Ensures diagnostic coverage remains >90%

📊 Results

Zero safety system failures in 36 months; incident reporting reduced 100%; successful third-party TÜV audit completed

💡 Lessons Learned

  • Independent sensor paths are mandatory for SIL2
  • Proof test logs must be digitally signed and archived
  • Valve partial-stroke testing improves confidence without shutdown

Key Takeaways

  • 1Independent sensor paths are mandatory for SIL2
  • 2Proof test logs must be digitally signed and archived
  • 3Valve partial-stroke testing improves confidence without shutdown