17.6 Chapter Summary & Review
Summary
Reliability is the probability that a component or system performs its intended function over a specified time and conditions. System reliability depends on configuration: in series, overall reliability decreases as more components are added because any single failure stops the system; in parallel, redundancy enhances reliability because a backup can take over the load. Real systems also exhibit interdependence; failures can cascade, so designers often combine redundancy and recovery mechanisms to mitigate this risk. Reliability is quantified with metrics such as failure rate (λ), mean time to failure (MTTF) for non-repairable items, and mean time between failures (MTBF) for repairable systems, which guide expectations, design choices, and service plans.
Maintenance is the operational counterpart to reliability. A strong maintenance culture, characterized by shared ownership, prompt communication, cross-functional collaboration, and continuous training, enhances capacity utilization, quality, safety, and reputation. Organizations mix strategies by asset criticality: reactive (run-to-failure) for low-risk items; preventive (time/usage-based) for predictable wear; and predictive/condition-based for high-value assets, with advanced frameworks like Reliability-Centred Maintenance (RCM) and Risk-Based Maintenance (RBM) aligning actions to failure modes and consequences. Economically, the goal is to balance prevention and repair costs while accounting for opportunity costs. Using historical breakdown data and a full-cost lens helps select the most cost-effective policy and schedule work that maximizes uptime and performance
OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat
Prompt: Please take the chapter content in this document attached and summarize the key concepts into no more than two paragraphs. Reviewed by authors.
Review Questions
- Define system reliability and explain how it changes in a series versus parallel configuration.
- Discuss the role of redundancy in improving system reliability, providing an example.
- Explain reactive maintenance and its main disadvantages.
- Summarize how preventive maintenance differs from predictive and condition-based maintenance.
- Identify and describe one hidden cost of equipment breakdowns that is not directly monetary.
- Compare and contrast reliability-centred maintenance with risk-based maintenance.
- Why is it important to include opportunity costs in a maintenance cost analysis?
- Outline the steps you would take to use historical breakdown data for estimating future maintenance needs.
- Discuss how maintenance strategies might differ between a manufacturing plant and a service organization.
- In your own words, describe how maintenance activities relate to the overall reliability of an asset.
Calculation Questions
- Calculate the reliability of a system with components in series: R1=0.92, R2=0.85, R3=0.70.
- For a 2-unit parallel system where each unit has a reliability of 0.6, compute the overall system reliability.
- Using the observed breakdown data (0, 1, 2, 3 incidents per month over 24 months), calculate the average number of breakdowns per month.
- If the average repair cost per breakdown is $1,500 and there are 8 expected breakdowns per month, what is the total monthly repair cost?
- Compare the total expected monthly costs between paying for breakdown repairs ($2,000 each, average of 6 per month) and hiring a mechanic for preventive maintenance at a rate of $10,000 per month, assuming preventive maintenance prevents 75% of breakdowns.
OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat
Prompt: Create ten discussion questions based on the attached chapter document that assess the student’s knowledge based on the learning outcomes for the chapter. Reviewed by authors.
