📋 Case Study

Offshore LNG Transfer System Fault Tree Analysis and SIS Architecture Optimization

High consequence of LNG spill + ignition in congested maritime corridor; existing SIS used single-channel logic

🏗️ Project Overview

FPSO-based LNG bunkering operation in Singapore Strait

🎯 Challenge

High consequence of LNG spill + ignition in congested maritime corridor; existing SIS used single-channel logic

🔧 Design Approach

Top-down fault tree for 'uncontrolled LNG release' initiating event; redesigned SIS to 2oo3 voting architecture with diverse sensors (radar + Coriolis + ultrasonic), certified per IEC 61511 SIL 3

📐 Design Diagram

_avg = 1.2×10⁻³β = 0.042Diverse Sensors • Redundant Logic • Certified SISSIL VerificationIEC 61508/61511

AI-generated project design illustration

📐 Key Calculations

PFDavg

λDU × TPT / 2 + λDD × β

Result: 1.2×10⁻³

Confirmed SIL 3 capability

Common Cause Failure Beta Factor

β = (PFD_system − PFD_independent) / PFD_system

Result: 0.042

Guided sensor diversity specification

📊 Results

PFDavg improved from 2.8×10⁻² to 1.2×10⁻³; system availability increased from 92% to 99.4%; accepted by DNV GL Class and MPA Singapore

💡 Lessons Learned

•Fault tree depth must extend to maintenance errors and calibration drift
•Sensor diversity requires independent failure modes—not just different technologies
•TPT extension beyond manufacturer recommendation increases spurious trip risk

✅ Key Takeaways

1Fault tree depth must extend to maintenance errors and calibration drift
2Sensor diversity requires independent failure modes—not just different technologies
3TPT extension beyond manufacturer recommendation increases spurious trip risk