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

Standards Certification Education & Training Publishing Conferences & Exhibits Control System Safety and Reliability Evaluation William M Goble exida

Key Points Safety and Reliability Evaluation is done to show how to improve, how to save money. –Eliminate weak links –Identify maintenance priorities New ISA S (IEC 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 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 Failure Rates for each failure mode Component Probabilities of Failure for each Failure Mode Repair Times Manual Proof Test Interval Manual Proof Test Effectiveness Other… System Probabilities of Failure for each Failure Mode RT TI C PT PFDavg MTTFS PFS 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

Modify? Select SIS Technology Select SIS Architecture Determine Test Frequency SIS Detailed Design SIS Installation SIS Commissioning SIS Initial Validation Conceptual Process Design Identify Potential Risks Consequence Analysis Layer of Protection Analysis Develop Non-SIS Layers Determine SIF Target SIL Document Requirements Yes Startup Operation Maintenance Periodic Proof Tests Modifications Decommissioning No Analysis Realization Operation Safety Life Cycle – ISA S Modify? Yes No How much safety do I need? How much safety do I have with my design? How will I keep it safe? Drawing by Hal Thomas

10. SIS Installation, Commissioning and Pre-startup Acceptance Test Safety Requirements Specification - Functional Description of each Safety Instrumented Function, Target SIL, Mitigated Hazards, Process parameters, Logic, Bypass/Maintenance requirements, Response time, etc 7. SIS Conceptual Design 7a. Select Technology 7b. Select Architecture Redundancy: 1oo1,1oo2, 2oo3, 1oo2D 7c. Determine Test Philosophy 7d. Reliability, Safety Evaluation SILsAchieved SIL Achieved? No Yes 8. SIS Detailed Design Failure Data Database Manufacturer’s Installation Instructions 9. Installation & Commission Planning Manufacturer’s Failure Data Detailed Design Documentation - Loop Diagrams, Wiring Diagrams, Logic Diagrams, Panel Layout, PLC Programming, Installation Requirements, Commissioning Requirements, etc. Manufacturer’s Safety Manual Choose sensor, logic solver and final element technology Drawing copyright 2006, exida.com LLC, Safety Lifecycle Poster, used with permission Realization Phase - SIF Design Process

Failure Rate Data Handbook – available from ISA 1.Industry Databases – NOT Application Specific, NOT Product Specific 2. Manufacturer FMEDA, Field Failure Study – Product Specific, NOT Application Specific Get Data - Failure Data Sources Several others including OREDA, AIChE, IEEE, others

PERD – Site Specific Failure Database AIChE 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

Modeling Fault Trees Reliability Block Diagrams Markov Models Others

Reliability and Safety Modeling Tools Casspack, L&M Engineering SafeCalc, Honeywell exSILentia, exida.com SIL Solver, SIS-Tech Others

What about Systematic Faults / Software Errors ? Specification of requirements, design, implementation Real needs Correct Design Incorrect Design Systematic Fault Well Designed System: system is correct Random failure The system is not correct The system has a failure Function required or execution trajectory hits incorrectness

Systematic Faults Complex Systems Reliability and Safety- REALITY? 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! Copyright 1997, Danjaq LLC and United Artists, from the James Bond movie “Tomorrow Never Dies.”

Systematic Fault Protection IEC Full Certification Many instrumentation products are now IEC 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 Certified Instruments Free list of certified instrumentation on

Reliability and Safety Analysis Many understand that these methods help us to minimize risk, optimize the design and lower cost. 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” Remember – things do fail!

Summary Safety and Reliability Evaluation is done to show how to improve, how to save money. –Eliminate weak links –Identify maintenance priorities –Optimize designs New ISA S (IEC 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 Certification provides reliability and safety via design integrity

Questions and Discussion

For more information: ISA best sellers on automation safety and reliability More Information on Reliability and Safety Phone: (919) Address: