Reliability and Maintenance

24
Reliability and Maintenance (MANE 4015 ) Instructor: Dr. Sayyed Ali Hosseini Winter 2015 Lecture #1

description

Introduction to reliability

Transcript of Reliability and Maintenance

Page 1: Reliability and Maintenance

Reliability and Maintenance

(MANE 4015 )

Instructor: Dr. Sayyed Ali Hosseini

Winter 2015

Lecture #1

Page 2: Reliability and Maintenance

What is Reliability?

2MANE4015 Reliability and Maintenance Lecture #1

The RELIABILITY of an item/system is the probability that the

item/system performs a specified function under specified

operational and environmental conditions at and throughout a

specified time.

Reliability is the capability to operate as intended, whenever

used, for as long as needed.

Reliability is performance over time, probability that

something will work when you want it to.

Page 3: Reliability and Maintenance

3MANE4015 Reliability and Maintenance Lecture #1

Reliability

• Is a time dependent concept

• Can only be determined after an elapsed time

• But can be predicted at any time.

Reliability Characteristics

Administrator
Highlight
Reability decreases over time
Administrator
Highlight
reability can only be measured after it is used. even after a failure of just one part, it is not impossible to say that a second part will failure in the same time.
Page 4: Reliability and Maintenance

Reliability Measures

4MANE4015 Reliability and Maintenance Lecture #1

• Availability

• Mean Time to Failure (MTTF) or Mean Time Between Failures (MTBF)

• Mean Time to Repair (MTTR)

What is failure?

Failure is the termination of the ability of an item to perform its

required function.

What is Maintainability?

The ability of an item, under stated conditions of use, to be retained

in, or restored to, a state in which it can perform its required

function(s), when maintenance is performed under stated conditions

and using prescribed procedures and resources. The time takes to

repair or maintain an item is expressed as Mean Time To Repair

(MTTR).

Administrator
Highlight
It is the time that the machine can be used but is not because it is being repair. Higher availability means a higher reliability.
Administrator
Highlight
Necessary time to fix a machine.
Page 5: Reliability and Maintenance

Availability

5MANE4015 Reliability and Maintenance Lecture #1

The AVAILABILITY is the probability that a system is available for

use at a given time. In the other word, it is the probability that

the system is operational at any random time (�) . The

availability is a function of reliability and maintainability.

Availability

• Is used for repairable systems

When equipment is in a failed state it is no longer available for

work, and its reliability decreases. As the length of time in a

failed state (downtime ) increases, the maintainability of the

equipment decreases.

Administrator
Highlight
can not be used, for example, to lights, because once is broken, you replace it.
Page 6: Reliability and Maintenance

6MANE4015 Reliability and Maintenance Lecture #1

Mean Time To Failure (MTTF) or Mean Time Between Failures

(MTBF) is the average expected time to failure (or between

failures)

Remarks

• MTBF provides a reliability figure of merit for expected failure free operation

• MTBF provides the basis for estimating the number of failures in a given period

of time

• Even though an item may be discarded after failure and its mean life

characterized by MTTF, it may be meaningful to characterize the system

reliability in terms of MTBF if the system is restored after item failure.

MTTF or MTBF

Administrator
Highlight
if the MTBF is low, the reliability is also low
Page 7: Reliability and Maintenance

7MANE4015 Reliability and Maintenance Lecture #1

Mean Time To Repair(MTTR) is the average expected time to

repair a damaged item after failure.

MTTR

Page 8: Reliability and Maintenance

Maintenance

8MANE4015 Reliability and Maintenance Lecture #1

Maintenance is a combination of all necessary actions for

retaining an item, or restoring it, to a serviceable condition.

• It may include servicing, repair, modification, overhaul, inspection and

condition verification.

• It increases the availability of a system.

• It keeps system’s equipment in working order.

Administrator
Highlight
Page 9: Reliability and Maintenance

Some Important Questions

9MANE4015 Reliability and Maintenance Lecture #1

Why do we need maintenance?

What are the costs of doing maintenance?

What are the costs of not doing maintenance?

What are the benefits of maintenance?

How can maintenance increase profitability of company?

Page 10: Reliability and Maintenance

Purpose of Maintenance

10MANE4015 Reliability and Maintenance Lecture #1

• Attempt to maximize performance of production equipment efficiently and

regularly

• Prevent breakdown or failures

• Minimize production loss from failures

• Increase reliability of the operating systems

Page 11: Reliability and Maintenance

Principle Objectives in Maintenance

11MANE4015 Reliability and Maintenance Lecture #1

• To achieve product quality and customer satisfaction through adjusted andserviced equipment

• Maximize useful life of equipment

• Keep equipment safe and prevent safety hazards

• Minimize frequency and severity of interruptions

• Maximize production capacity – through high utilization of facility

Page 12: Reliability and Maintenance

Problems in Maintenance

12MANE4015 Reliability and Maintenance Lecture #1

• Lack of management attention to maintenance

• Little participation by accounting in analyzing and reporting costs

• Difficulties in applying quantitative analysis

• Difficulties in obtaining time and cost estimates for maintenance works

• Difficulties in measuring performance

Why these problems exist?

• Failure to develop written objectives and policy

• Inadequate budgetary control

• Inadequate control procedures for work order, service requests etc.

• Infrequent use of standards

• To control maintenance work

• Absence of cost reports to aid maintenance planning and control system

Page 13: Reliability and Maintenance

Different Types of Maintenance

13MANE4015 Reliability and Maintenance Lecture #1

• Corrective or Breakdown maintenance

• Scheduled maintenance

• Preventive maintenance

• Predictive (Condition-based) maintenance

Page 14: Reliability and Maintenance

Corrective or Breakdown Maintenance

14MANE4015 Reliability and Maintenance Lecture #1

Corrective or Breakdown maintenance implies that repairs are

made after the equipment is failed and can not perform its

normal function anymore

Quite justified in small factories where:

• Down times are non-critical and repair costs are less than other type ofmaintenance

• Financial justification for scheduling are not felt

Page 15: Reliability and Maintenance

Disadvantages of Corrective Maintenance

15MANE4015 Reliability and Maintenance Lecture #1

• Breakdown generally occurs at inappropriate times leading to poor and hurriedmaintenance

• Excessive delay in production & reduces output

• Faster plant deterioration

• Increases chances of accidents and less safety for both workers and machines

• More spoilt materials

• Direct loss of profit

• Can not be employed for equipment regulated by statutory provisions e.g.cranes, lift and hoists etc.

Page 16: Reliability and Maintenance

Schedules Maintenance

16MANE4015 Reliability and Maintenance Lecture #1

Scheduled maintenance is a maintenance procedure that is

repeated on a regular basis. If scheduled maintenance is

neglected, breakdown and failure is likely to occur.

Scheduled Maintenance includes:

• inspection

• lubrication

• repair and overhaul of equipment

Examples:

• overhauling of machines

• changing of heavy equipment oils

• cleaning of water and other tanks etc.

Administrator
Highlight
one example that can be mentioned is the parts of an aeroplane
Page 17: Reliability and Maintenance

Preventive Maintenance

17MANE4015 Reliability and Maintenance Lecture #1

“Prevention is better than Cure”

Preventive Maintenance

• locates weak spots of machinery and equipment

• Provides them periodic/scheduled inspections and minor repairs to reduce thedanger of unanticipated breakdowns

Page 18: Reliability and Maintenance

Advantages of Preventive Maintenance

18MANE4015 Reliability and Maintenance Lecture #1

• Reduces break down and thereby down time

• Less odd-time repair and reduces over time of crews

• Greater safety of workers

• Lower maintenance and repair costs

• Less stand-by equipment and spare parts

• Better product quality and fewer reworks and scraps

• Increases plant life

• Increases chances to get production incentive bonus

Administrator
Sticky Note
When should we use preventive or scheduled maintenance? Generally, preventive maintenance is used in weakness parts of the machine.
Page 19: Reliability and Maintenance

Predictive (Condition-Based) Maintenance

19MANE4015 Reliability and Maintenance Lecture #1

In predictive maintenance, machinery conditions areperiodically monitored and this enables the maintenance crewsto take timely actions, such as machine adjustment, repair oroverhaul. It makes use of human sense and other sensitiveinstruments, such as audio gauge, vibration analyzer, amplitudemeter, pressure, temperature and resistance strain gauges etc.

Examples:

• Unusual sounds coming out of a rotating equipment predicts a trouble.

• An excessively hot electric cable predicts a trouble.

• Simple hand touch can point out many unusual equipment conditions and thuspredicts a trouble.

Page 20: Reliability and Maintenance

Failure Cost VS. Maintenance Commitment

20MANE4015 Reliability and Maintenance Lecture #1

Maintenance Commitment

Co

st

Failure Cost

Administrator
Highlight
Page 21: Reliability and Maintenance

Maintenance Cost VS. Maintenance Commitment

21MANE4015 Reliability and Maintenance Lecture #1

Maintenance Commitment

Co

st

Maintenance Cost

Page 22: Reliability and Maintenance

Total Maintenance Cost

22MANE4015 Reliability and Maintenance Lecture #1

Maintenance Commitment

Co

st

Maintenance Cost

Failure Cost

Total Maintenance CostOptimum

Page 23: Reliability and Maintenance

Emerging Strategies for Maintenance Management

23MANE4015 Reliability and Maintenance Lecture #1

Administrator
Sticky Note
scheduled maintenance
Administrator
Sticky Note
Predective maintenance
Page 24: Reliability and Maintenance

Conclusions

24MANE4015 Reliability and Maintenance Lecture #1

In general, reliability analysis and maintenance procedures are effective tools inthe hands of engineers to:

• Predict the expected life of systems and their major components.

• Predict the availability of systems

• Predict the expected maintenance activities

• Predict the support resources and spare parts required for effective operation

It must be noted that accurate prediction of the above mentioned items can onlybe achieved by careful consideration of reliability and maintainability factors, mosteffectively at the design stage.