Reliability Engineering

A Life Cycle Approach

Edgar Bradley

• Publisher: CRC Press
• Year: 2016
• eBook ISBN: 9781498765848
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Industrial Design
• Index: Technology & Engineering

Reliability Engineering – A Life Cycle Approach is based on the author's knowledge of systems and their problems from multiple industries, from sophisticated, first class installations to less sophisticated plants often operating under severe budget constraints and yet having to deliver first class availability. Taking a practical approach and drawing from the author's global academic and work experience, the text covers the basics of reliability engineering, from design through to operation and maintenance. Examples and problems are used to embed the theory, and case studies are integrated to convey real engineering experience and to increase the student's analytical skills. Additional subjects such as failure analysis, the management of the reliability function, systems engineering skills, project management requirements and basic financial management requirements are covered. Linear programming and financial analysis are presented in the context of justifying maintenance budgets and retrofits. The book presents a stand-alone picture of the reliability engineer's work over all stages of the system life-cycle, and enables readers to:

• Understand the life-cycle approach to engineering reliability

• 
  
  

• Explore failure analysis techniques and their importance in reliability engineering

• 
  
  

• Learn the skills of linear programming, financial analysis, and budgeting for maintenance

• 
  
  

• Analyze the application of key concepts through realistic Case Studies

• 
  
  

This text will equip engineering students, engineers and technical managers with the knowledge and skills they need, and the numerous examples and case studies include provide insight to their real-world application. An Instructor's Manual and Figure Slides are available for instructors.

1

Reliability Fundamentals I: Component Reliability

I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be.

Lord Kelvin

Introduction

The Importance of Reliability

Reliability is sometimes ill-defined but always important in the minds of professional engineers and laymen alike. No one wants an unreliable product. Over time, products do tend to become more reliable. For example, 21st-century cars are demonstrably more reliable than cars of the 1940s, for example. This is because of the enormous production volume of motor vehicles that has enabled and forced manufacturers to correct defects that the market has highlighted. This is in fact the oldest reliability improvement method: try–fix–try. Other more scientific methods have also been used, but try–fix–try has served the motor industry well. For systems other than motor vehicles, reliability improvement happens more slowly unless special techniques are applied to force reliability improvement. Aircraft, which have much lower production runs than cars, are a case in point. So are chemical plants and other types of manufacturing plant.

History

Reliability engineering is a separate branch of engineering developed in World War II (WWII). In fact, engineering as a discipline has been splitting into ever more specific subdisciplines ever since its emergence as a profession centuries ago. It may be said that reliability engineering split off from aeronautical engineering, itself a subset of mechanical engineering. And it is also true to say that, unfortunately, as with many engineering advances, it was the hothouse atmosphere of war that spurred the development of the reliability engineering profession. A German engineer, Robert Lusser, was involved in the V1 weapon program for the Luftwaffe. (More details of this will be given in Chapter 2.) Several of the early concepts of reliability engineering are attributable to him.

Definitions

Lusser was one of many German engineers and scientists who immigrated to the United States after WWII and became part of the U.S. missile and space programmes. In 1956, at a symposium at the Convair aircraft works in San Diego, he defined reliability in engineering terms for the first time. Engineering reliability, he said, was defined as follows.

Reliability

‘The probability that a system will continue to work, for a stated period of time, given defined operating conditions’. From this definition, we can deduce the following:

• Reliability engineering is involved with statistics, as the term probability implies.
• Engineering reliability is a time function.
• Engineering reliability depends on stated conditions. A piece of equipment designed for use in the Antarctic might not do so well in the Sahara.

The significance of reliability in an engineering sense is that it is an engineering parameter like any other, like efficiency, power or whatever. The difference between reliability engineering parameters and more traditional parameters is that they are often statistical or they are only measurable after quite a long period. The efficiency of an electric motor, for example, can be determined in minutes once the motor is instrumented and then put on load. The reliability of the motor can only be ascertained after a long operating period – perhaps years. Also, the answers we get are statistical and probabilistic, rather than deterministic. The answers should always be given with limits of statistical error attached. Reliability is usually denoted by R(t).

Common measures of reliability are the mean time between failures, or MTBF, the mean time to failure, or MTTF and the maintenance-free operating period, or MFOP. The symbol θ is often used for MTBF.

Other definitions of importance are given below.

Maintainability

‘Maintainability is the probability that a system, having failed, will be restored in a given time, given a certain maintenance environment’.

Thus, we see that maintainability is analogous to reliability. It is a statistical function, it is a function of time and it depends on certain conditions, that is, the maintenance environment. Maintainability is usually denoted by M(t).

A common measure of maintainability is the mean time to repair, or MTTR. The symbol used for MTTR is usually φ. MTTR is further elaborated on below.

Availability

‘Availability is the percentage of time that a system is available for use, whether required for...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Foreword
• Preface
• Introduction
• About the Author
• 1. Reliability Fundamentals I: Component Reliability
• 2. Reliability Fundamentals II: System Reliability
• 3. Maintenance Optimisation
• 4. Condition Monitoring
• 5. Incident Investigation or Root Cause Analysis
• 6. Other Techniques Essential for Modern Reliability Management: I
• 7. Other Techniques Essential for Modern Reliability Management: II
• 8. Reliability Management
• 9. Design Issues in Reliability Engineering and Maintenance
• Bibliography
• Appendix 1: The Standard Normal Distribution
• Appendix 2: Dr E. H. Waloddi Weibull, 1887–1979
• Appendix 3: A Perspective on Robert Lusser
• Index