Standards Certification Education & Training Publishing Conferences & Exhibits Automation Connections ISA EXPO 2006

Standards Certification Education & Training Publishing Conferences & Exhibits Safety System Trends & Industry Update Paul Gruhn, PE, CFSE ICS Triplex

Key Points to Cover What is a Safety Instrumented System Fault tolerance requirements –What level of redundancy is required for different integrity levels Separation of control & safety and new vendor platforms –Who’s doing what, and what are the pros & cons of each technique Partial stroking of valves –What’s the point, and who’s doing it

Safety Instrumented System A system composed of sensors, logic solvers, and final control elements for the purpose of taking the process to a safe state when pre-determined conditions are violated. I / P FT Basic Process Control System (BPCS) InputsOutputs Reactor PT1APT1B Safety Instrumented System (SIS) InputsOutputs

Fault Tolerance Requirements SILMinimum Hardware Fault Tolerance SFF < 60%SFF 60% to 90%SFF > 90% See IEC For PE logic solvers. See ISA 84 Section 11.4

Fault Tolerance Requirements SILMinimum Hardware Fault Tolerance See IEC For field devices and non-PE logic solvers. The numbers may need to be reduced or increased by one under certain circumstances. See ISA 84 Section

Standards have evolved and changed New and different platforms available Control and safety systems do need to share information with each other, but how should this be done? –Interfaced –Integrated –Combined Separation of Control & Safety

Interfaced Vendor A Control Vendor B Safety Vendor B Development Station Vendor A Development Station

Interfaced Vendors: –Essentially all Pros Best in class Minimization of common cause Cons Must learn two systems Highest cost –Hardware & software –Gateways (sometimes) –Training –Spares

Integrated Vendor A Control Vendor A Safety Vendor A Development Station

Integrated Vendors: –Moore Products, Yokogawa, Emerson, MTL Pros Only learn one system –Same software –Hardware not interchangeable Ease of communications Cons Increase in potential common cause Mid level costs –Two sets of spares

Combined Vendor A Control & Safety Vendor A Development Station

Combined Vendors: –ICS Triplex, Siemens, ABB Pros Only learn one system Ease of communications Lowest costs Cons Highest level of potential common cause –Personnel –Hardware MOC issues

Partial Stroking of Valves If you have a SIL 2 requirement, would you rather install: –Two standard valves in series –One valve with partial stroking Partial stroking provides diagnostics (a higher safe failure fraction) Numerous vendor packages: – Drallim – Metso – Tyco – Dynatorque – ICS Triplex – ASCO – Emerson – Netherlocks

Summary Fault tolerance requirements –Higher integrity levels require redundant components Partial stroking of valves –Many different solutions on the market Separation of control & safety and new vendor platforms There are pros & cons of the three different approaches SIL Minimum Hardware Fault Tolerance See IEC 61508

Related Resources from ISA Phone: (919) Address: ISA 84 and 91 standards ISA textbooks on: –Safety Instrumented Systems –SIL Determination –Control System Safety Evaluation & Reliability ISA Safety Division ISA web seminars on SIS (3 part series) Many SIS related papers online

Questions and Discussion