Implementing 2oo2 from 1oo2 Voting Without Degrading SIL Rating

Abstract This paper presents a modification to the LNG Tank Level High-High (HH) voting logic at PT. Donggi Senoro LNG to enhance reliability while ensuring safety compliance based on Safety Integrity Level (SIL) calculations. The goal is to mitigate spurious trips from false sensor readings and improve Safety Instrumented System (SIS) integrity. The modification shifts from a 1oo2 to a 2oo2 voting system, providing a more reliable safety interlock. The new voting logic is designed based on SIL calculations to enhance reliability and safety compliance. It begins with failure rate analysis of sensors, logic solvers, and final elements, followed by PFDavg computation to evaluate system performance. Hardware Fault Tolerance (HFT) assessment ensures redundancy configurations like 1oo2 or 2oo2 meet SIL standards. The calculated PFDavg is then validated against IEC 61508/61511 criteria. Additionally, Partial Valve Stroke Testing (PVST) improves actuator reliability, optimizes test intervals, and lowers PFDavg, ensuring a robust and fault-tolerant LNG tank safety system. SIL PFDavg analysis confirms that adopting a 2oo2 voting system with a 6-month Partial Stroke Test (PST) and a 3-year Full Stroke Test (FST) lowers the Probability of Failure on Demand (PFD) compared to the 1oo2 configuration with a 1-year FST. PVST recalculations further reduced PFD from 0.00886 to 0.00833, enhancing reliability. Consequently, no false trips have occurred due to sensor faults linked to power supply issues. SIL verification ensures compliance with IEC 61508/61511, affirming safety standards and operational integrity. Additionally, PVST implementation improves system availability by enabling early fault detection without major process disruptions. The transition from 1oo2 to 2oo2 logic at PT. Donggi Senoro LNG (DSLNG) has yielded notable gains in efficiency and reliability while maintaining SIL certification. This optimized voting strategy sets a new industry benchmark for LNG process safety, reinforcing long-term resilience and sustainability. Implementing 2oo2 voting logic for LNG tank level monitoring enhances reliability by eliminating false HH trips and preventing unnecessary shutdowns, addressing 1oo2 limitations while ensuring safety compliance. Integrating Partial Stroke Testing (PST) and Full Stroke Testing (FST) optimizes PFD reduction, reinforces SIL compliance, and strengthens fault tolerance. This advancement equips engineers with a data-driven approach to boosting system reliability, operational efficiency, and proactive fault detection while minimizing disruptions.