On this page you will find a number of questions. When you have read a chapter of the book, you may use these questions to control that you remember the main topics of the chapter.

Chapter 1 - Introduction

1. What is the main difference between the two concepts "reliability" and "quality"?
2. What is the main difference between the concepts "safety" and "security"? - Give some examples that illustrate the difference.
3. What is the main difference between a "primary failure" and "secondary failure"?
4. What is an "evident failure"? - and what is a "hidden failure"?
5. What is the main difference between the concepts "failure mode" and "failure mechanism"?

Chapter 2 - Failure Models

1. List some possible time concepts that may be used to measure the time to failure of a unit - give examples
2. Explain verbally what we mean by the concept "failure rate function"
3. What is the main difference between the two concepts "failure rate function" and "probability density function"?
4. Why is the failure rate function sometimes called the "force of mortality" (FOM)?
5. How can the failure rate function, z(t), be expressed as a function of the survivor function, R(t)?
6. Mention some practical implications of assuming an exponential time to failure distribution.
7. What do we mean when we say that a component with a constant failure rate function is "as good as new" as long as it is functioning?
8. Mention some items that might realistically be modeled by an exponentially distributed time to failure.
9. Describe verbally what we mean by the concept "mean residual life" (MRL)
10. What is the relation between the MRL and the MTTF of the exponential distribution? Give a brief explanation.
11. What assumptions do we have to make to use a homogeneous Poisson process (HPP)?
12. Describe verbally the meaning of the intensity of a homogeneous Poisson process (HPP)
13. What is the distribution of the times between events in a homogeneous Poisson process (HPP)?
14. Describe verbally the main difference between the two concepts "failure rate in an exponential life distribution" and "intensity of a homogeneous Poisson process".
15. Why is the parameter "lambda" in the Weibull distribution called a scale parameter?
16. Why is the parameter "alpha" in the Weibull distribution called a shape parameter?
17. What is the characteristic lifetime in a Weibull distribution?
18. What do we mean when we say that the Weibull distribution is discontinuous as a function of the shape parameter "alpha" for "alpha"=1? Why is this important?
19. Describe the relation between the normal and the lognormal distribution.
20. Why is the median less than the mean of the lognormal distribution?
21. In what type of applications do we assume the lognormal distribution to be realistic?
22. What do we mean by the concept "error factor" when using the lognormal distribution?

Chapter 3 - Qualitative System Analysis

1. What is the main difference between FMEA and FMECA?
2. An FMECA can be carried out as a bottom-up analysis and as a top-down analysis. Describe the main difference between these two approaches.
3. Mention some drawbacks (problems/limitations) related to FMECA.
4. Which questions should be answered in the description of the TOP event of a fault tree?
5. What is the main difference between a "basic event" and an "undeveloped event" in a fault tree?
6. Is fault tree analysis a suitable technique for analysing a dynamic system? (if not, why?)
7. What do we mean when we say that fault tree analysis is a deductive technique?
8. What do we mean when we say that a valve is "fail safe"?
9. What do we mean by saying that a component is "irrelevant"?
10. What is MOCUS?
11. What is a "minimal path series structure"?
12. How can we qualitatively evaluate a fault tree?
13. What is 2-out-of-4 system?
14. What is a "coherent" structure?
15. Draw a reliability block diagram illustrating a non-coherent structure.
16. What is a "critical path set for component no. i"?
17. What is the difference between a "cut set" and a "minimal cut set"?
18. What do we mean by the "order" of a minimal cut set?
19. Mention at least three different approaches to establish the structure function of a system.
20. What is "pivotal decomposition"?

Chapter 4 - Systems of Independent Components

1. What do we mean when we say that two components are "independent"?
2. Explain why the "reliability" of a component can be written as the mean value of its "state variable".
3. In what cases can we use the binomial distribution to determine the reliability of a k-out-of-n structure?
4. What do we mean by a "non-repairable" system?
5. Will all systems of independent components with constant failure rates have a constant failure rate?
6. Give a physical explanation of the form of the failure rate function in Figure 4.3.
7. Can you give a physical explanation of why a 2-out-of-3 system of identical and independent components with constant failure rate will have a shorter MTTF than a single component?
8. What do we mean by the "upper bound approximation" formula?
9. Describe and explain the various elements of the "upper bound approximation" formula.
10. What do we mean when we say that the "upper bound approximation" formula gives a conservative estimate?
11. In what cases will the "upper bound approximation" be a good approximation?
12. What is CARA?
13. What do we mean by "cold standby"?
14. What do we mean by "warm standby"?

Chapter 5 - Component Importance

1. Explain briefly why Birnbaum's measure of component importance can be considered as a "sensitivity".
2. What do we mean by saying that a component is critical for the system?
3. Compare and explain the difference between the two definitions of Birnbaum's measure
4. How can we use formula (5.5) to calculate Birnbaum's measure of component i?
5. How can we use Birnbaum's measure to find the measure Criticality importance?
6. What is the main difference between the measure Criticality importance and Fussell-Vesely's measure?
7. Can you suggest an alternative to the measure Improvement potential?
8. List some possible applications of the verious measures of component importance.

Chapter 6 - Dependent Failures

1. What is a common cause failure?
2. Give an example of positive dependency.
3. Give an example of negative dependency.
4. What are cascading failures? Do know another name of such failures?
5. Describe briefly the common cause failure that happened in Browns Ferry.
6. How can we classify the reasons for common cause failures?
7. Mention some defensive tactics to avoid common cause failures.
8. Describe why diversity can be a means to avoid common cause failures.
9. Describe the main idea behind the square-root method.
10. Describe the main idea behind the beta-factor method.
11. How can we interpret the parameter beta in the beta-factor model?
12. What are the strengths and weaknesses of the beta-factor method?

Chapter 7 - Counting Processes

Nothing yet

Chapter 8 - Markov Processes

1. What is a Markov diagram? Do you know alternative names for the same diagram?
2. What is a state space? Give an example.
3. What is a stochastic process?
4. What do we mean when we say that a stochastic process has the Markov property?
5. What is a Markov process?
6. What are the main assumptions we have to make to use a markov process to model the transitions between the possible states of a system?
7. What do we mean when we say that a Markov process has no memory?
8. What do we mean by the concept transition probability?
9. Describe with words what the Chapman-Kolmogorov equation tells us?
10. What is a transition rate?
11. Why are the transition rates constant (independent of time)?
12. What do we mean by state equations?
13. What is a transition rate matrix?
14. How can we write the state equations on matrix form?
15. What do the diagonal elements of the transition rate matrix tell us?
16. Why does not the transition rate matrix have full rank? What is the practical implication of this with respect to solution of the state equations?
17. What extra information do we need to find a unique solution of the state equations?
18. How can we determine the mean duration of a visit to state j from the transition rate matrix?
19. What do we mean by a departure rate? How can we find the departure rates from state j from the transition rate matrix?
20. What is the formula for the time dependent availability A(t) of a component with constant failure rate and constant repair rate?
21. What do we mean by limiting availability?
22. What do we mean by steady state probabilities?
23. Write the state equations we need to find the steady state probabilities.
24. What do we mean when we say that a Markov process is irreducible?
25. What do we mean by visit frequency?
26. What formula can we use to find the visit frequency to state j?
27. How can we determine the mean time between system failures?
28. How can we find the frequency of system failures?
29. What is an absorbing state?
30. How can we find the survivor function of a repairable system?
31. How can we find the mean time to the firs system failure?

Chapter 9 - Reliability of Maintained Systems

1. What do we mean by the concept "availability"?
2. What is "average availability"?
3. In what cases can we use formula (9.10) to find the "average availability"?

Chapter 10 - Reliability of Safety Systems

1. What do we mean by a "hidden failure"?
2. What is the main difference between the failure modes "fail to function" (FTF) and "false alarm" (FA)?
3. Why do we carry out "periodic testing"?
4. For what type of equipment will it be relevant to carry out periodic testing? (Give some examples)
5. What is PFD?
6. Give at least two interpretations of the concept PFD?
7. In what cases can we use formula (10.3) to calculate the MFDT?
8. Will the approximation formula (10.8) produce a conservative or a non-conservative approximation to PFD?
9. What do we mean by "staggered testing"?
10. What is "staggered testing"? Mention some pros and cons related to "staggered testing".
11. What is the main difference between a "random hardware failure" and a "systematic failure"? Give some examples of failures of each category.
12. Explain the main difference between a "dangerous undetected" (DU) failure and a "dangerous detected" (DD) failure. Give some examples of failures of the two categories.
13. What do we mean by the concept safety instrumented function (SIF)? What is the difference between a SIF and a SIS?
14. What is the meaning of the parameter "beta" in the beta-factor model? Do you consider this mode to be adequate for analyzing common cause failures of an SIS? Mention some pros and cons.
15. What do we mean by "diagnostic testing"? What type of impacts can such testing have on the occurrence of system common cause failures?
16. What is a spurious trip (ST) failure? Give some examples. When designing a safety system, why do we sometimes have a conflict between ST failures and the system availability?
17. What is "imperfect testing"? Give some examples of testing that is not perfect. How will this type of testing affect the PFD formula (10.3)? - Illustrate by drawing a sketch of the unavailability as a function of time.
18. What is (according to IEC 61508) a "safety lifecycle"?
19. What are the main characteristics of the OLF guideline? Do you consider the approach adopted in the OLF guideline to be in accordance with IEC 61508/11?

Chapter 11 - Life Data Analysis

Nothing yet

Chapter 12 - Accelerated Life Testing

Nothing yet

Chapter 13 - Bayesian Reliability Analysis

Nothing yet