Equipment reliability - Reliability assessment methods

This International Standard describes early reliability assessment methods for items based on field data and test data for components and modules. It is applicable to mission, safety and business critical, high integrity and complex items. It contains information on why early reliability estimates are required and how and where the assessment would be used.

Zuverlässigkeit von Geräten - Verfahren zur Zuverlässigkeitsbewertung

Fiabilité de l'équipement - Méthodes d'évaluation de la fiabilité

Cette Norme Internationale décrit des méthodes d'évaluation initiale de la fiabilité d'entités, basées sur des données d'exploitation et d'essai des composants et des modules. Elle est applicable aux entités dont la mission est vitale pour la sécurité et le fonctionnement, et aux entités électroniques complexes et à intégration élevée. Elle contient des informations explicitant pourquoi des estimations initiales de fiabilité sont requises et indique pourquoi et quand les résultats de l'évaluation sont susceptibles d'être utilisés.

Zanesljivost opreme - Metode ocenjevanja zanesljivosti (IEC 62308:2006)

General Information

Status
Published
Publication Date
14-Dec-2006
Technical Committee
Drafting Committee
Parallel Committee
Current Stage
6060 - Document made available
Due Date
15-Dec-2006
Completion Date
15-Dec-2006

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Zanesljivost opreme - Metode ocenjevanja zanesljivosti (IEC 62308:2006)Zuverlässigkeit von Geräten - Verfahren zur ZuverlässigkeitsbewertungFiabilité de l'équipement - Méthodes d'évaluation de la fiabilitéEquipment reliability - Reliability assessment methods21.020Characteristics and design of machines, apparatus, equipment03.120.01Kakovost na splošnoQuality in generalICS:Ta slovenski standard je istoveten z:EN 62308:2006SIST EN 62308:2007en01-februar-2007SIST EN 62308:2007SLOVENSKI

STANDARD
SIST EN 62308:2007
EUROPEAN STANDARD EN 62308 NORME EUROPÉENNE
EUROPÄISCHE NORM December 2006

CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2006 CENELEC -

All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 62308:2006 E
ICS 03.120.01; 03.120.99
English version
Equipment reliability -
Reliability assessment methods (IEC 62308:2006)
Fiabilité de l'équipement -
Méthodes d'évaluation de la fiabilité (CEI 62308:2006)
Zuverlässigkeit von Geräten -
Verfahren zur Zuverlässigkeitsbewertung (IEC 62308:2006)

This European Standard was approved by CENELEC on 2006-11-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

SIST EN 62308:2007
EN 62308:2006
- 2 -

Foreword The text of document 56/1110/FDIS, future edition 1 of IEC 62308, prepared by IEC TC 56, Dependability, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 62308 on 2006-11-01. The following dates were fixed: – latest date by which the EN has to be implemented

at national level by publication of an identical
national standard or by endorsement
(dop)
2007-08-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)

2009-11-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 62308:2006 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following note has to be added for the standard indicated: IEC 61751 NOTE

Harmonized as EN 61751:1998 (not modified). __________
SIST EN 62308:2007
- 3 - EN 62308:2006 Annex ZA
(normative)

Normative references to international publications with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

NOTE

When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.

Publication Year Title EN/HD Year
IEC 60050-191 1990 International Electrotechnical Vocabulary (IEV)
Chapter 191: Dependability and quality of service - -
IEC 60300-1 -1) Dependability management
Part 1: Dependability management systems EN 60300-1 20032)
IEC 60300-3-1 2003 Dependability management

Part 3-1: Application guide - Analysis techniques for dependability - Guide on methodology EN 60300-3-1 2004

IEC 60300-3-2 -1) Dependability management

Part 3-2: Application guide - Collection of dependability data from the field EN 60300-3-2 20052)

IEC 60300-3-3 -1) Dependability management
Part 3-3: Application guide - Life cycle costingEN 60300-3-3 20042)
IEC 60300-3-4 1996 Dependability management

Part 3: Application guide - Section 4: Guide to the specification of dependability requirements - -

IEC 60300-3-5 2001 Dependability management

Part 3-5: Application guide - Reliability test conditions and statistical test principles - -

IEC 60300-3-9 -1) Dependability management

Part 3: Application guide - Section 9: Risk analysis of technological systems - -

IEC 60300-3-11 -1) Dependability management
Part 3-11: Application guide - Reliability centred maintenance - -
IEC 60300-3-12 -1) Dependability management
Part 3-12: Application guide - Integrated logistic support EN 60300-3-12 20042)

IEC 60812 -1) Analysis techniques for system reliability - Procedure for failure mode and effects analysis (FMEA) EN 60812 20062)

1) Undated reference. 2) Valid edition at date of issue. SIST EN 62308:2007
EN 62308:2006
- 4 -

Publication Year Title EN/HD Year IEC 61025 -1) Fault tree analysis (FTA) HD 617 S1 19922)

IEC 61078 -1) Analysis techniques for dependability - Reliability block diagram and Boolean methods EN 61078 20062)

IEC 61160 -1) Design review EN 61160 20052)
IEC 61165 -1) Application of Markov techniques EN 61165 20062)
IEC 61508

Series Functional safety of electrical/electronic/programmable electronic safety-related systems EN 61508 Series

IEC 61649 -1) Goodness-of-fit tests, confidence intervals and lower confidence limits for Weibull distributed data - -

IEC 61709 -1) Electronic components - Reliability - Reference conditions for failure rates and stress models for conversion EN 61709 19982)

IEC 61710 -1) Power law model - Goodness-of-fit tests and estimation methods - -

IEC 61713 -1) Software dependability through the software life-cycle processes - Application guide - -

IEC 61882 -1) Hazard and operability studies (HAZOP studies) - Application guide - -

IEC/TR 62380 -1) Reliability data handbook - Universal model for reliability prediction of electronics components, PCBs and equipment - -

SIST EN 62308:2007

NORME INTERNATIONALECEIIEC INTERNATIONAL STANDARD 62308Première éditionFirst edition2006-07 Fiabilité de l’équipement – Méthodes d'évaluation de la fiabilité

Equipment reliability – Reliability assessment methods
Pour prix, voir catalogue en vigueur For price, see current catalogue IEC 2006
Droits de reproduction réservés

Copyright - all rights reserved Aucune partie de cette publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit de l'éditeur. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Electrotechnical Commission,

3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, SwitzerlandTelephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch

Web: www.iec.ch CODE PRIX PRICE CODE XA Commission Electrotechnique InternationaleInternational Electrotechnical CommissionSIST EN 62308:2007

62308  IEC:2006 – 3 – CONTENTS FOREWORD...........................................................................................................................7 INTRODUCTION...................................................................................................................11

1 Scope.............................................................................................................................13 2 Normative references.....................................................................................................13 3 Terms and definitions.....................................................................................................15 4 Abbreviations.................................................................................................................17 5 Symbols.........................................................................................................................17 6 Introduction to reliability assessment..............................................................................19 6.1 Introductory remarks.............................................................................................19 6.2 Description of reliability assessment......................................................................19 7 Management of reliability assessment process...............................................................27 7.1 Purpose of reliability assessment..........................................................................27 7.2 Documentation......................................................................................................39 8 Data needs.....................................................................................................................39 8.1 Input data..............................................................................................................39 8.2 Data sources and types.........................................................................................41 8.3 Data collection, storage, and retrieval...................................................................43 9 Reliability assessment methods......................................................................................43 9.1 Introduction...........................................................................................................43 9.2 Similarity analysis.................................................................................................47 9.3 Durability analysis.................................................................................................51 9.4 Sensitivity testing and analysis..............................................................................53 9.5 Handbook predictions............................................................................................57 9.6 Limitations of reliability assessment results...........................................................61 10 Considerations for selecting reliability assessment methods...........................................61 11 Reliability assessment process improvement..................................................................65 11.1 General.................................................................................................................65 11.2 Validating reliability assessment results................................................................65 11.3 Improving the reliability assessment process.........................................................65

Annex A (informative) Similarity analysis examples...............................................................69 Annex B (informative) Durability analysis..............................................................................93

Bibliography........................................................................................................................107

Figure 1 – Methods requiring a reliability assessment as input..............................................27 Figure 2 – Stages of product life cycle..................................................................................35 Figure 3 – Reliability assessment and improvement process.................................................45 Figure A.1 – Example similarity analysis flowchart................................................................85

SIST EN 62308:2007

62308  IEC:2006 – 5 – Table 1 – Example of constant rate reliability measures........................................................23 Table 2 – IEC Standards providing guidance on methods.....................................................29 Table A.1 – Example characteristic differences.....................................................................83 Table A.2 – Example high-level similarity analysis spreadsheet............................................87 Table A.3 – Example low-level similarity analysis spreadsheet..............................................89 Table A.4 – Example process difference factor tables...........................................................91 Table B.1 – Values for exponent B for equations (B.7) and (B.8).........................................101 SIST EN 62308:2007

62308  IEC:2006 – 7 – INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
EQUIPMENT RELIABILITY − RELIABILITY ASSESSMENT METHODS

FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 62308 has been prepared by IEC technical committee 56: Dependability. The text of this standard is based on the following documents: FDIS Report on voting 56/1110/FDIS 56/1122/RVD

Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. SIST EN 62308:2007

62308  IEC:2006 – 9 – The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be

• reconfirmed; • withdrawn; • replaced by a revised edition, or • amended.
SIST EN 62308:2007

62308  IEC:2006 – 11 – INTRODUCTION This International Standard describes procedures that are intended for use in assessing the reliability of items based on data from: the market of similar items; and field data and test data from suppliers of components and modules. The results of such assessments are intended for use as inputs to early equipment design decisions such as system architecture selection as well as business decisions such as estimating the cost of warranties or maintenance cost guarantees. Furthermore the results can be used as the initial estimate for input to safety analysis, for example FTA analysis. Modern electronic components and items are so reliable that estimating or verifying their reliability by testing is very difficult, therefore data from the field for previous similar items are often the only way to get an initial estimate of the reliability. Component manufacturers have used this method for years under the name of the “similarity principle”. By emphasising the use of data from previously marketed similar products, and requiring similarity to be documented, the method is a modern alternative to the classical but now obsolete handbook prediction.

Reliability assessment results should be viewed as an early estimate of the probability that the product reliability targets and goals can be satisfied using the chosen architecture, modules, components and maintenance policy. As such, they may be used, for example, to authorize advancement to the next step in product development, or to authorize progress payments, or to proceed with delivery and acceptance of products. Reliability assessment results should never be used to support a claim that the reliability targets, goals, or expectations have been satisfied. The only certain measure of reliability requirement having been met is from service/field performance. This standard describes the uses for reliability assessment results as well as providing a list of IEC standards that require such results as input. The approach to reliability assessment in this International Standard – encourages the equipment manufacturer to consider all relevant information regarding equipment reliability which may include the effects of design and manufacturing processes as well as component selection issues. This is in contrast to more traditional methods that focus on component reliability as the most significant contributor to the equipment reliability; – encourages the equipment manufacturer to define and use the processes that are most effective for the manufacturer’s own equipment; – describes a continuous procedure in which a reliability assessment can be updated as more information becomes available during the life cycle of the equipment. This information may be used to improve both the reliability of the equipment and the effectiveness of the assessment process. This International Standard describes the application of three approaches to reliability assessment, namely: similarity analysis, durability analysis, and handbook predictions. This standard does not, however, provide information on assessing the reliability of software systems but can be used for assessing the reliability of hardware systems containing embedded software.

SIST EN 62308:2007
62308  IEC:2006 – 13 – EQUIPMENT RELIABILITY − RELIABILITY ASSESSMENT METHODS

1 Scope This International Standard describes early reliability assessment methods for items based on field data and test data for components and modules. It is applicable to mission, safety and business critical, high integrity and complex items. It contains information on why early reliability estimates are required and how and where the assessment would be used. Finally, it details methods for reliability assessment and the data required to support the assessment. To estimate durability (life time or wear-out), the physics-of-failure method is used.

Three types of assessment are discussed in detail: – the similarity approach; – models for durability analysis; – handbook methods. Clause 6 provides an introduction to reliability assessment and Clause 7 the management of the process. Clause 8 describes the data needs, sources and types for assessments and Clause 9 provides details of the assessment methods. Annexes A and B provide additional information to aid understanding of the similarity analysis and durability analysis.

This standard is applicable to making reliability estimates for specifications, design, design modification and support engineering. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-191:1990, International Electrotechnical Vocabulary – Chapter 191: Dependability and quality of service IEC 60300-1, Dependability management – Part 1: Dependability management systems IEC 60300-3-1:2003, Dependability management – Part 3-1: Application guide – Analysis techniques for dependability – Guide on methodology IEC 60300-3-2, Dependability management – Part 3-2: Application guide – Collection of dependability data from the field IEC 60300-3-3, Dependability management – Part 3-3: Application guide – Life cycle costing IEC 60300-3-4:1996, Dependability management – Part 3: Application guide – Section 4: Guide to the specification of dependability requirements SIST EN 62308:2007

62308  IEC:2006 – 15 – IEC 60300-3-5:2001, Dependability management – Part 3-5: Application guide – Reliability test conditions and statistical test principles IEC 60300-3-9, Dependability management – Part 3: Application guide – Section 9: Risk analysis of technological systems IEC 60300-3-11, Dependability management – Part 3-11: Application guide – Reliability centred maintenance IEC 60300-3-12, Dependability management – Part 3-12: Application guide – Integrated logistic support IEC 60812, Analysis techniques for system reliability – Procedure for failure mode and effects analysis (FMEA) IEC 61025, Fault tree analysis (FTA) IEC 61078, Analysis techniques for dependability – Reliability block diagram and boolean methods IEC 61160, Design review IEC 61165, Application of Markov techniques

IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic safety-related systems

IEC 61649, Goodness-of-fit tests, confidence intervals and lower confidence limits for Weibull distributed data IEC 61709, Electronic components – Reliability – Reference conditions for failure rates and stress models for conversion IECI 61710, Power law model – Goodness-of-fit tests and estimation methods IEC 61713, Software dependability through the software life-cycle processes – Application guide

IEC 61882, Hazard and operability studies (HAZOP studies) – Application guide IEC 62380, Reliability data handbook – Universal model for reliability prediction of electronics components, PCBs and equipment 3 Terms and definitions For the purposes of this document, the terms and definitions given in IEC 60050-191, together with the following, apply. 3.1

durability analysis analysis of the equipment’s responses to the stresses imposed by operational use, maintenance, shipping, storage and other activities throughout its specified life-cycle in order to estimate its predicted reliability and expected life 3.2

life-cycle time interval between a product’s conception and its disposal
SIST EN 62308:2007
62308  IEC:2006 – 17 – 3.3

similarity analysis structured comparison of the elements of the equipment being assessed with those of predecessor equipment for which in-service reliability data are available 4 Abbreviations ASIC Application specific integrated circuit BITE Built in test equipment COTS Commercial off the shelf FEA Finite element analysis FFOP Failure free operating period FITS Failure per thousand million hours FMEA Failure mode and effects analysis FMECA Failure mode, effects and criticality analysis FRACAS Failure reporting, analysis and corrective action system FTA Fault tree analysis HALT Highly accelerated life test IC Integrated circuit LCC Life cycle costs LRU Line replaceable unit MCTF Mean cycles to failure MTBF Mean time between failures MTBUR Mean time between unit repair

MTTF Mean time to failure MTTR Mean time to restoration/recovery/repair MTTSC Mean time to service call MTTSI Mean time to service interruption MTTWC Mean time to warranty claim RBD Reliability block diagram RCM Reliability centred maintenance RET Reliability enhancement test SRU Shop replaceable unit

5 Symbols λ Constant failure rate of the exponential distribution t Time period of interest f(t) Probability density function F(t) Cumulative distribution function R(t) Reliability function T* Accumulated exposure time

SIST EN 62308:2007

62308  IEC:2006 – 19 – 6 Introduction to reliability assessment 6.1 Introductory remarks

The reliability of an item will often have to be assessed for a range of reasons including the following: a) setting targets and specifications; b) comparing options; c) identifying and prioritising problems; d) indicating fitness for purpose; e) optimizing support (e.g. spares); f) to give input to other analysis (e.g. safety analysis); g) to prioritise areas for improvement with the greatest cost-effectiveness improvement potential. This reliability may be quoted in a number of ways, including for example

– accumulated percentage of failures;
– call rate;
– probability of survival; – failure intensity;
– instantaneous failure rate;

– MTTF; – MTBF. The procedure outlined in this standard is aimed at providing reliability analysts, project managers, risk management engineers, designers, safety and reliability engineers, and logistic support engineers with an assessment method for an early estimate of an item’s instantaneous failure rate. The process for estimating life for items with a wear-out failure characteristic is also included. 6.2 Description of reliability assessment 6.2.1 General information Reliability is not an attribute that can be assigned or measured for a single item. It is a stochastic or probabilistic parameter and therefore it cannot be measured exactly and repeatedly. It therefore has to be estimated from information on the amount of usage (e.g. running hours, cycles of operation, etc.) and the number of failures observed. It should be presented in the form of a confidence statement such as "80 % confidence that the true probability of successfully completing the mission lies between X and Y” or “period of time of interest without failure is between 0,963 and 0,995". An explanation of confidence and confidence intervals can be found in IEC 61649. The classical definition of reliability is the probability of providing a specified performance level for a specified duration in a specified environment. Although such a probability is a useful measure for mission-oriented, low-volume products such as spacecraft, it is rarely a suitable measure for most high-volume products for which reliability relates more to product population than the performance of a single system or a mission. Specifying a single characteristic such as mean time to failure (MTTF) is not sufficient for a product that exhibits a time-dependent failure rate (i.e. non-constant failure rate).

SIST EN 62308:2007

62308  IEC:2006 – 21 – 6.2.2 Constant failure rate reliability measures The general expression for reliability, R(t), is given by

()−=∫∞tdtttRλexp)( (1) where ()tλ is the instantaneous failure rate. Another very useful (general) expression is

dttdFdttdRtf)()()(=−= (2) where f(t) is the probability density function of times to failure. In terms of these quantities the instantaneous failure rate is given by

)()()(tRtft=λ (3) Yet another fundamental general expression is that for MTTF. This quantity is given by

∫∞=0)(MTTFdttR (4) Now when )(tλis constant with time, it should simply be written as λ. Under these circumstances, times to failure follow an exponential distribution and the following relationships hold:

)exp()(ttλ−=R (5)
)exp()(ttλλ−=f (6)
λλ=)(t (7)

λ1MTTF= often denoted by the symbol θ (8) This only holds when λ is constant. Another useful but problematic quantity is the total accumulated number of product-hours, sometimes denoted by T*. Under the assumption of constant failure rate there is no difference from a statistical point of view between accumulating 1 000 000 h by one product, or 1 h by 1 000 000 products. In either case a point estimate of the population failure rate if there is one failure would be 10-6 failures per product-hour. The parameter λ being independent of time is referred to as the constant failure rate. A constant failure rate has many useful properties, one of which is that the mean value of the distribution of the product’s time to failure is 1/λ. For non-repaired items (components), this mean value represents the statistically expected average length of time until product failure, commonl

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