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Questions and Answers
Which maintenance strategy involves using advanced technology to monitor equipment and predict failures?
What is the objective of maintenance and reliability?
To maintain the capability of the system
What is the main advantage of predictive maintenance over breakdown maintenance?
Detection of impending failures and ability to schedule maintenance
What is reliability?
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Predictive maintenance is cost-effective because it reduces the need for any maintenance labor or parts replacement.
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Mean time between failures (______) is calculated as $\frac{1}{FR(N)}$.
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Preventive maintenance focuses on emergency repairs.
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Match the component with the correct definition:
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What is the average cost of breakdown in the maintenance cost example?
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What is the expected number of breakdowns per month according to the maintenance cost example?
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What is the expected breakdown cost per month with no preventive maintenance in the maintenance cost example?
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What is the cost of preventive maintenance per month in the maintenance cost example?
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Which of the following are problems associated with breakdown maintenance?
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What is the main issue with preventive maintenance?
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Study Notes
Maintenance and Reliability
Importance of Maintenance and Reliability
- Failure has far-reaching effects on a firm's operation, reputation, profitability, and customer satisfaction
- The objective of maintenance and reliability is to maintain the capability of the system
Maintenance Definition
- All activities involved in keeping a system's equipment in working order
- Reliability is the probability that a machine will function properly for a specified time
Strategic Importance of Maintenance and Reliability
- Failure can lead to:
- Idle employees
- Reduced value of investment in plant and equipment
- Dissatisfied customers
- Profit losses
- Maintenance and reliability can:
- Improve quality
- Increase capacity
- Reduce inventory
- Improve equipment availability
Maintenance Management
- Employee involvement is crucial
- Maintenance procedures should include:
- Clean and lubricate
- Monitor and adjust
- Make minor repairs
- Keep computerized records
Reliability
- Improving individual components can increase overall reliability
- Rs = R1 x R2 x R3 x … x Rn (equation for overall system reliability)
- Providing redundancy can increase reliability
- Reliability example: Rs = .90 x .80 x .99 = .713 or 71.3%
Product Failure Rate (FR)
- FR(%) = (Number of failures / Number of units tested) x 100%
- FR(N) = Number of failures / Number of unit-hours of operating time
- MTBF (Mean Time Between Failures) = 1 / FR(N)
Failure Rate Example
- FR(%) = 2 / 20 = 10%
- FR(N) = 2 / (20,000 - 1,200) = .000106 failure/unit hour
- MTBF = 1 / .000106 = 9,434 hours
Providing Redundancy
- Probability of needing second component = 1 - (probability of first component working)
- Redundancy example: Rs = .96 (increased reliability)
Maintenance Types
- Preventive maintenance: routine inspection and servicing to keep facilities in good repair
- Breakdown maintenance: emergency or priority repairs on failed equipment
Implementing Preventive Maintenance
- Need to know when a system requires service or is likely to fail
- High initial failure rates are known as infant mortality
- Once a product settles in, MTBF generally follows a normal distribution
- Good reporting and record keeping can aid the decision on when preventive maintenance should be performed
Maintenance Costs
- The traditional view attempted to balance preventive and breakdown maintenance costs
- Typically, this approach failed to consider the true total cost of breakdowns
- Inventory, employee morale, schedule unreliability, and other costs should be considered
Autonomous Maintenance
- Employees accept responsibility for:
- Observe
- Check
- Adjust
- Clean
- Notify
- Predict failures, prevent breakdowns, and prolong equipment life
Total Productive Maintenance (TPM)
- Designing machines that are reliable, easy to operate, and easy to maintain
- Emphasizing total cost of ownership when purchasing machines, including service and maintenance costs### Total Productive Maintenance (TPM)
- Developing preventive maintenance plans that utilize the best practices of operators, maintenance departments, and depot service
- Training for autonomous maintenance so operators maintain their own machines and partner with maintenance personnel
Techniques for Enhancing Maintenance
- Simulation: computer analysis of complex situations, model maintenance programs before they are implemented, and physical models can also be used
- Expert systems: computers help users identify problems and select a course of action
- Automated sensors: warn when production machinery is about to fail or is becoming damaged, with goals to avoid failures and perform preventive maintenance before machines are damaged
Providing Redundancy – An Alternate Formula
- The reliability of one pump = the probability of one pump not failing = 0.8
- If there are two pumps with the same probability of not failing, the probability of failure of both pumps = P(failure) pump #1 x P(failure) pump #2 = 0.2 x 0.2 = 0.04
- The probability of at least one pump working = 1.0 - 0.04 = 0.96
Problems With Breakdown Maintenance
- "Run it till it breaks" might be okay for low-criticality equipment or redundant systems, but could be disastrous for mission-critical plant machinery or equipment
- Not permissible for systems that could imperil life or limb (like aircraft)
Problems With Preventive Maintenance
- "Fix it whether or not it is broken" - scheduled replacement or adjustment of parts/equipment with a well-established service life
- Typical example: plant relamping, but sometimes misapplied, e.g., replacing old but still good bearings, over-tightening electrical lugs in switchgear
Predictive Maintenance
- Using advanced technology to monitor equipment and predict failures
- Techniques: visual inspection, scheduled measurements of vibration, temperature, oil and water quality, and comparisons to a "healthy" baseline
- Equipment that is trending towards failure can be scheduled for repair
Predictive Maintenance Tools
- Vibration analysis
- Infrared Thermography
- Oil and Water Analysis
- Other tools: Ultrasonic testing, Liquid Penetrant Dye testing, Shock Pulse Measurement (SPM)
Predictive Maintenance Vibration Analysis
- Using sensitive transducers and instruments to detect and analyze vibration
- Typically used on expensive, mission-critical equipment - large turbines, motors, engines, or gearboxes
- Sophisticated frequency (FFT) analysis can pinpoint the exact moving part that is worn or defective
Predictive Maintenance Infrared Thermography
- Using IR cameras to look for temperature "hot spots" on equipment
- Typically used to check electrical equipment for wiring problems or poor/loose connections
- Can also be used to look for "cold (wet) spots" when inspecting roofs for leaks
Predictive Maintenance Oil and Water Analysis
- Taking oil samples from large gearboxes, compressors, or turbines for chemical and particle analysis
- Particle size can indicate abnormal wear
- Taking cooling water samples for analysis - can detect excessive rust, acidity, or microbiological fouling
Maintenance Strategy Comparison
- Breakdown maintenance: no prior work required, but disruption of production, injury, or death may occur
- Preventive maintenance: work can be scheduled, but labor costs and replacement of healthy components may occur
- Predictive maintenance: impending failures can be detected, but labor costs and equipment costs may occur
Predictive Maintenance Cost Effectiveness
- In most industries, the average rate of return is 7:1 to 35:1 for each predictive maintenance dollar spent
- Vibration analysis, IR thermography, and oil/water analysis are all economically proven technologies
- The real savings is the avoidance of manufacturing downtime, especially crucial in JIT (Just-In-Time) production
Predictive Maintenance and Effective Reliability
- Effective Reliability (Reff) is an extension of Reliability that includes the probability of failure times the probability of not detecting imminent failure
- Having the ability to detect imminent failures allows us to plan maintenance for the component in failure mode, thus avoiding the cost of an unplanned breakdown
How Predictive Maintenance Improves Effective Reliability
- Example: a large gearbox with a reliability of 0.90 has vibration transducers installed for vibration monitoring, with a probability of early detection of a failure of 0.70, resulting in an effective reliability of 0.97
Effective Reliability Caveats
- Predictive maintenance only increases effective reliability if:
- The method can detect the most likely failure mode
- Monitoring is frequent enough to have a high likelihood of detecting a change in component behavior before failure
- Timely action is taken to fix the issue and forestall the failure
Increasing Repair Capabilities
- Well-trained personnel
- Adequate resources
- Proper application of the three maintenance strategies
- Continual improvement to improve equipment/system reliability
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Description
This quiz assesses your understanding of the importance of maintenance and reliability in a firm's operation. It covers the definition of maintenance and its objectives, as well as the concept of reliability.
