Standards Certification Education & Training Publishing Conferences & Exhibits Automation Connections ISA EXPO 2006
Control System Safety and Reliability Evaluation William M Goble exida Standards Certification Education & Training Publishing Conferences & Exhibits
Key Points • Safety and Reliability Evaluation is done to show to improve, how to save money. – Eliminate weak links – Identify maintenance priorities • New ISA S 84. 00. 01 -2004 (IEC 61511 Mod. ) requires probabilistic evaluation – Regulatory compliance – Optimal safety system design • Safety and reliability evaluation has become practical – Data sources are available – Tools are available • IEC 61508 Certification provides reliability and safety via design integrity
Why do safety and reliability evaluation? System Reliability? “The 9000 series is the most reliable computer ever made. No 9000 computer has ever made a mistake or distorted information. We are all by any practical definition of the words, foolproof and incapable of error. ”
Key Issues • • • Failure rates - HIGH STRENGTH Failure Modes Diagnostic coverage - online test capability Diagnostic coverage – manual proof tests Common cause strength Software reliability
Activities • Get failure rate and failure mode data • Build a model for alternative designs – Markov model? – Fault Tree? – Reliabiity Block Diagram? • Compare results based on objectives – Life cycle cost? – Minimum capital expense? – Risk reduction?
Reliability/Safety Evaluation Process Component Probabilities of Failure for each Failure Mode Failure Rates for each failure mode l RT TI Repair Times Manual Proof Test Interval Manual Proof Test CPT Effectiveness Other… PFDavg MTTFS PFS System Probabilities of Failure for each Failure Mode PFDavg MTTFS PFS SIL
Benefits of Reliability Analysis • • Higher uptime Lower risks Better product quality Lower life cycle costs Understanding system operation during failure conditions Making the right choices Meeting requirements of ISA 84. 00. 01 -2004
Safety Life Cycle – ISA S 84. 00. 01 -2004 Realization Analysis Conceptual Process Design Identify Potential Risks Consequence Analysis Layer of Protection Analysis Develop Non-SIS Layers Determine SIF Target SIL Document Requirements How much safety do I need? Operation Startup Operation Maintenance Periodic Proof Tests Modifications Decommissioning Select SIS Technology Select SIS Architecture Determine Test Frequency SIS Detailed Design SIS Installation SIS Commissioning SIS Initial Validation How much safety do I have with my design? Yes Modify? No How will I keep it safe? Yes Drawing by Hal Thomas Modify? No
Realization Phase - SIF Design Process Safety Requirements Specification Functional Description of each Safety Instrumented Function, Target SIL, Mitigated Hazards, Process parameters, Logic, Bypass/Maintenance requirements, Response time, etc 7 a. Select Technology 7. SIS Conceptual Design Manufacturer’s Failure Database Manufacturer’s Safety Manual Manufacturer’s Installation Instructions Choose sensor, logic solver and final element technology 7 b. Select Architecture Redundancy: 1 oo 1, 1 oo 2, 2 oo 3, 1 oo 2 D 7 c. Determine Test Philosophy No SIL Achieved? Yes 7 d. Reliability, Safety Evaluation 8. SIS Detailed Design 9. Installation & Commission Planning 10. SIS Installation, Commissioning and Pre-startup Acceptance Test Drawing copyright 2006, exida. com LLC, Safety Lifecycle Poster, used with permission SILs Achieved Detailed Design Documentation Loop Diagrams, Wiring Diagrams, Logic Diagrams, Panel Layout, PLC Programming, Installation Requirements, Commissioning Requirements, etc.
PERD – Site Specific Failure Database AICh. E CCPS – Process Equipment Reliability Database Project • Mission - Operation of an Equipment Reliability Database, Making Available High Quality, Valid, and Useful Data to the HPI and CPI Enabling Analyses to Support Availability, Reliability, and Equipment Design Improvements, Maintenance Strategies, and Life Cycle Cost Determination
Failure Rate Data Harvest - PERD 13
Modeling • Fault Trees • Reliability Block Diagrams • Markov Models • Others
Reliability and Safety Modeling Tools • Casspack, L&M Engineering • Safe. Calc, Honeywell • ex. SILentia, exida. com • SIL Solver, SIS-Tech • Others
What about Systematic Faults / Software Errors ? Real needs Specification of requirements, design, implementation Correct Design Incorrect Design Well Designed System: system is correct The system is not correct Systematic Fault Random failure Function required or execution trajectory hits incorrectness The system has a failure
Systematic Faults Complex Systems Reliability and Safety. REALITY? Copyright 1997, Danjaq LLC and United Artists, from the James Bond movie “Tomorrow Never Dies. ” Carter: Mr. Jones, are we ready to release our new software? Jones: Yes Sir. As requested it is full of bugs which means that people will be forced to upgrade for years. Carter: Outstanding!
Systematic Fault Protection IEC 61508 Full Certification • Many instrumentation products are now IEC 61508 certified. The certification process requires a full assessment of the design and testing procedures used to create the product. • The end result of the certification process is a certificate listing the SIL level for which a product is qualified. Higher SIL levels require more stringent procedures and should provide higher reliability and safety. • Sometimes restrictions are listed in the safety manual and must be followed if safe operation is required.
IEC 61508 Certified Instruments Free list of certified instrumentation on www. exida. com
Reliability and Safety Analysis Many understand that these methods help us to minimize risk, optimize the design and lower cost. Remember, things do fail.
Remember – things do fail! Jack Godell, explaining: “A faulty relay in the generator circuit and …a a stuck valve” Copyright 1979, Columbia Pictures, from the movie “The China Syndrome”
Summary • Safety and Reliability Evaluation is done to show to improve, how to save money. – Eliminate weak links – Identify maintenance priorities – Optimize designs • New ISA S 84. 00. 01 -2004 (IEC 61511 Mod. ) requires probabilistic evaluation – Regulatory compliance – Optimal safety system design • Safety and reliability evaluation has become practical – Data sources are available – Tools are available • IEC 61508 Certification provides reliability and safety via design integrity
Questions and Discussion
More Information on Reliability and Safety For more information: ISA best sellers on automation safety and reliability Phone: (919) 549 -8411 E-mail Address: info@isa. org
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