Table Of ContentRELIABILITY, MAINTAINABILITY AND RISK
Also by the same author
Reliability Engineering, Pitman, 1972
Maintainability Engineering, Pitman, 1973 (with A. H. Babb)
Statistics Workshop, Technis, 1974, 1991
Achieving Quality Software, Chapman & Hall, 1995
Quality Procedures for Hardware and Software, Elsevier, 1990 (with J. S. Edge)
Functional Safety: A Straightforward Guide to IEC 61508, 2nd Edition, Butterworth-Heinemann,
2004, ISBN 0 7506 6269 7 (with K. G. L. Simpson)
The Private Pilot’s Little Book of Helicopter Safety, Technis, 2010, ISBN 9780951656297
Reliability, Maintainability
and Risk
Practical methods for engineers
Eighth Edition
Dr David J Smith
BSc, PhD, CEng, FIET, FCQI, HonFSaRS MIGEM
AMSTERDAM • BOSTON • HEIDELBERG • LONDON
NEW YORK • OXFORD • PARIS • SAN DIEGO
SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO
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Eighth edition 2011
First published by Macmillan Education Ltd 1981
Second edition 1985
Third edition 1988
Fourth edition published by Butterworth-Heinemann Ltd 1993
Reprinted 1994, 1996
Fifth edition 1997
Reprinted with revisions 1999
Sixth edition 2001
Reprinted 2002, 2003 (twice)
Seventh edition 2005
Reprinted 2007
Copyright © 1993, 1997, 2001, 2005, David J. Smith. Published by Elsevier Ltd.
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11 12 13 14 15 10 9 8 7 6 5 4 3 2 1
Contents
Preface .............................................................................................................xix
Acknowledgements .............................................................................................xxi
PART 1 Understanding Reliability Parameters and Costs ...................................1
Chapter 1: The History of Reliability and Safety Technology .....................................3
1.1 Failure Data ...........................................................................................................3
1.2 Hazardous Failures ................................................................................................5
1.3 Reliability and Risk Prediction ..............................................................................5
1.4 Achieving Reliability and Safety-Integrity ............................................................8
1.5 The RAMS Cycle ..................................................................................................9
1.6 Contractual and Legal Pressures ..........................................................................11
Chapter 2: Understanding Terms and Jargon .........................................................13
2.1 Defining Failure and Failure Modes ....................................................................13
2.2 Failure Rate and Mean Time Between Failures ...................................................15
2.2.1 The Observed Failure Rate ...............................................................................15
2.2.2 The Observed Mean Time Between Failures ...................................................16
2.2.3 The Observed Mean Time to Fail .....................................................................16
2.2.4 Mean Life .........................................................................................................17
2.3 Interrelationships of Terms ..................................................................................17
2.3.1 Reliabilty and Failure Rate ...............................................................................17
2.3.2 Reliabilty and Failure Rate as an Approximation ............................................19
2.3.3 Reliabilty and MTBF .......................................................................................20
2.4 The Bathtub Distribution .....................................................................................20
2.5 Down Time and Repair Time ...............................................................................21
2.6 Availability, Unavailability and Probability of Failure on Demand ....................25
2.7 Hazard and Risk-Related Terms ..........................................................................26
2.8 Choosing the Appropriate Parameter ...................................................................26
Chapter 3: A Cost-Effective Approach to Quality, Reliability and Safety ..................29
3.1 Reliability and Optimum Cost .............................................................................29
3.2 Costs and Safety ..................................................................................................33
3.2.1 The Need for Optimization ..............................................................................33
3.2.2 Costs and Savings Involved with Safety Engineering ......................................33
3.3 The Cost of Quality .............................................................................................34
v
PART 2 Interpreting Failure Rates....................................................................39
Chapter 4: Realistic Failure Rates and Prediction Confidence ..................................41
4.1 Data Accuracy .....................................................................................................41
4.2 Sources of Data ....................................................................................................43
4.2.1 Electronic Failure Rates ...................................................................................44
4.2.2 Other General Data Collections .......................................................................46
4.2.3 Some Older Sources .........................................................................................48
4.3 Data Ranges .........................................................................................................48
4.3.1 Using the Ranges .............................................................................................50
4.4 Confidence Limits of Prediction ..........................................................................52
4.5 Manufacturers’ Data ............................................................................................54
4.6 Overall Conclusions .............................................................................................55
Chapter 5: Interpreting Data and Demonstrating Reliability ...................................57
5.1 The Four Cases ....................................................................................................57
5.2 Inference and Confidence Levels .........................................................................57
5.3 The Chi-Square Test ............................................................................................59
5.4 Understanding the Method in More Detail ..........................................................62
5.5 Double-Sided Confidence Limits ........................................................................63
5.6 Reliability Demonstration ....................................................................................63
5.7 Sequential Testing ................................................................................................68
5.8 Setting Up Demonstration Tests ..........................................................................69
Exercises .....................................................................................................................70
Chapter 6: Variable Failure Rates and Probability Plotting .....................................71
6.1 The Weibull Distribution .....................................................................................71
6.2 Using the Weibull Method ...................................................................................73
6.2.1 Curve Fitting to Interpret Failure Data .............................................................73
6.2.2 Manual Plotting ................................................................................................75
6.2.3 Using the COMPARE Computer Tool .............................................................77
6.2.4 Significance of the Result ................................................................................79
6.2.5 Optimum Preventive Replacement ...................................................................81
6.3 More Complex Cases of the Weibull Distribution ...............................................81
6.4 Continuous Processes ..........................................................................................82
Exercises .....................................................................................................................83
PART 3 Predicting Reliability and Risk .............................................................85
Chapter 7: Basic Reliability Prediction Theory .......................................................87
7.1 Why Predict RAMS? ...........................................................................................87
7.2 Probability Theory ...............................................................................................88
7.2.1 The Multiplication Rule ...................................................................................88
7.2.2 The Addition Rule ............................................................................................88
7.2.3 The Binomial Theorem ....................................................................................89
7.2.4 Bayes Theorem.................................................................................................90
7.3 Reliability of Series Systems ...............................................................................91
7.4 Redundancy Rules ...............................................................................................92
7.4.1 General Types of Redundant Configuration .....................................................92
7.4.2 Full Active Redundancy (Without Repair) .......................................................92
7.4.3 Partial Active Redundancy (Without Repair) ...................................................94
7.4.4 Conditional Active Redundancy ......................................................................95
7.4.5 Standby Redundancy ........................................................................................96
7.4.6 Load Sharing ....................................................................................................98
7.5 General Features of Redundancy .........................................................................98
7.5.1 Incremental Improvement ................................................................................98
7.5.2 Further Comparisons of Redundancy .............................................................100
7.5.3 Redundancy and Cost .....................................................................................101
Exercises ...................................................................................................................101
Chapter 8: Methods of Modeling .......................................................................103
8.1 Block Diagrams and Repairable Systems ..........................................................103
8.1.1 Reliability Block Diagrams ............................................................................103
8.1.2 Repairable Systems (Revealed Failures) ........................................................105
8.1.3 Repairable Systems (Unrevealed Failures) ....................................................107
8.1.4 Systems With Cold Standby Units and Repair ...............................................109
8.1.5 Modeling Repairable Systems with Both
Revealed and Unrevealed Failures ...........................................................................110
8.1.6 Conventions for Labeling ‘Dangerous’, ‘Safe’,
Revealed and Unrevealed Failures ...........................................................................110
8.2 Common Cause (Dependent) Failure ................................................................111
8.2.1 What is CCF? .................................................................................................111
8.2.2 Types of CCF Model ......................................................................................112
8.2.3 The BETAPLUS Model .................................................................................114
8.3 Fault Tree Analysis ............................................................................................118
8.3.1 The Fault Tree ................................................................................................118
8.3.2 Calculations ....................................................................................................119
8.3.3 Cutsets ............................................................................................................122
8.3.4 Computer Tools ..............................................................................................122
8.3.5 Allowing for CCF ..........................................................................................124
8.3.6 Fault Tree Analysis in Design ........................................................................126
8.3.7 A Cautionary Note .........................................................................................126
8.4 Event Tree Diagrams .........................................................................................126
8.4.1 Why Use Event Trees? ...................................................................................126
8.4.2 The Event Tree Model ....................................................................................127
8.4.3 Quantification .................................................................................................129
8.4.4 Differences .....................................................................................................130
8.4.5 Feedback Loops .............................................................................................131
Chapter 9: Quantifying the Reliability Models .....................................................133
9.1 The Reliability Prediction Method ....................................................................133
9.2 Allowing for Diagnostic Intervals .....................................................................135
9.2.1 Establishing Diagnostic Coverage .................................................................135
9.2.2 Modeling ........................................................................................................135
9.2.3 Partial Stroke Testing .....................................................................................137
9.2.4 Safe Failure Fraction ......................................................................................137
9.3 FMEA (Failure Mode and Effect Analysis) ......................................................137
9.4 Human Factors ...................................................................................................140
9.4.1 Background ....................................................................................................140
9.4.2 Models ............................................................................................................140
9.4.3 HEART (Human Error Assessment and Reduction Technique) ....................141
9.4.4 THERP (Technique for Human Error Rate Prediction) .................................143
9.4.5 TESEO (Empirical Technique to Estimate Operator Errors) .........................143
9.4.6 Other Methods ................................................................................................144
9.4.7 Human Error Rates .........................................................................................144
9.4.8 Trends in Rigor of Assessment ......................................................................146
9.5 Simulation ..........................................................................................................147
9.5.1 The Technique ................................................................................................147
9.5.2 Some Packages ...............................................................................................149
9.6 Comparing Predictions with Targets ..................................................................153
Exercises ...................................................................................................................153
Chapter 10: Risk Assessment (QRA) .................................................................155
10.1 Frequency and Consequence ...........................................................................155
10.2 Perception of Risk, ALARP and Cost per Life Saved .....................................156
10.2.1 Maximum Tolerable Risk (Individual Risk) ...............................................156
10.2.2 Maximum Tolerable Failure Rate ...............................................................157
10.2.3 ALARP and Cost per Life Saved ...............................................................159
10.2.4 Societal Risk ...............................................................................................161
10.2.5 Production/Damage Loss ...........................................................................164
10.3 Hazard Identification .......................................................................................164
10.3.1 HAzOP .......................................................................................................165
10.3.2 HAzID .......................................................................................................169
10.3.3 HAzAN (Consequence Analysis) ..............................................................169
10.4 Factors to Quantify ..........................................................................................169
10.4.1 Reliability ...................................................................................................170
10.4.2 Lightning and Thunderstorms ....................................................................170
10.4.3 Aircraft Impact ...........................................................................................170
10.4.4 Earthquake ..................................................................................................173
10.4.5 Meteorological Factors ...............................................................................174
10.4.6 Other Consequences ...................................................................................174
PART 4 Achieving Reliability and Maintainability ...........................................177
Chapter 11: Design and Assurance Techniques ....................................................179
11.1 Specifying and Allocating the Requirement ....................................................179
11.2 Stress Analysis .................................................................................................181
11.3 Environmental Stress Protection ......................................................................184
11.4 Failure Mechanisms .........................................................................................185
11.4.1 Types of Failure Mechanism ......................................................................185
11.4.2 Failures in Semiconductor Components.....................................................186
11.4.3 Discrete Components .................................................................................187
11.5 Complexity and Parts .......................................................................................187
11.5.1 Reduction of Complexity ...........................................................................187
11.5.2 Part Selection ..............................................................................................188
11.5.3 Redundancy ................................................................................................188
11.6 Burn-In and Screening .....................................................................................189
11.7 Maintenance Strategies ....................................................................................190
Chapter 12: Design Review, Test and Reliability Growth ......................................191
12.1 Review Techniques ..........................................................................................191
12.2 Categories of Testing .......................................................................................192
12.2.1 Environmental Testing ...............................................................................193
12.2.2 Marginal Testing ........................................................................................194
12.2.3 High-Reliability Testing ............................................................................195
12.2.4 Testing for Packaging and Transport ...........................................................195
12.2.5 Multiparameter Testing ..............................................................................196
12.2.6 Step-Stress Testing .....................................................................................197
12.3 Reliability Growth Modeling ...........................................................................198
12.3.1 The CUSUM Technique ............................................................................198
12.3.2 Duane Plots ................................................................................................201
Exercises .................................................................................................................202
Chapter 13: Field Data Collection and Feedback .................................................205
13.1 Reasons for Data Collection ............................................................................205
13.2 Information and Difficulties ............................................................................205
13.3 Times to Failure ...............................................................................................207
13.4 Spreadsheets and Databases ............................................................................208
13.5 Best Practice and Recommendations ...............................................................210
13.6 Analysis and Presentation of Results ...............................................................211
13.7 Manufacturers’ data .........................................................................................212
13.8 Anecdotal Data ................................................................................................213
13.9 Examples of Failure Report Forms ..................................................................213
