chapter 19

Slack, Chambers and Johnston, Operations Management 5th Edition © Nigel Slack, Stuart Chambers, and Robert Johnston 2007

Chapter 19

Failure prevention and recovery

Source: Eurotunnel



Operations strategy

Design Improvement

Planning and control

Operations management


Total quality management

organizes process improvement Failure

prevention and recovery stop

processes becoming worse

Operations process

improvement makes processes

better


Why systems fail

Design failures

Facilities failures

Staff failures

Failures inside the operation

Supply failures Customer

failures


How failure is measured

Time

Fai

lure

rat

e

‘Infant-mortality’ stage

Normal-life stage

Wear-out stage


Bath-tub curves for two parts of an operation

Curve A represents a part with relatively predictable failureCurve B represents a part with a more random failure pattern

Time

Fai

lure

rat

e

‘Infant-mortality’ stage

Normal-life stage

Wear-out stage

Curve B

Curve A

X Y


Time

Fai

lure

rat

e

Service operations, after an early stage of failure detection and improvement, may suffer from steadily rising failure rates

caused by increasing complacency

Early failure detection and improvement Complacency

Chapter 19.


How failure is detected and analyzed

– in-process checks

– accident investigation

– failure mode-and-effect analysis

– fault-tree analysis

Failure detection mechanisms include:

Failure analysis procedures include:

– point-of-departure interview

– machine-diagnostic checks


The three tasks of failure prevention and recovery

Failure detection and analysis

Finding out what is going wrong and why

Improving system reliability

Stopping things going wrong

Recovery

Coping when things do go wrong


Severity of consequence

Effect on customer

Normal operation

Failure

Prevention Mitigation Recovery

Failure management


3.5 inch diskette cannot be inserted unless it is orientated correctly. This is as far as a disk can be inserted upside-down. This feature, along with the fact that the diskette is not square, prohibits incorrect orientation. It is a control method.

Warning lights and chimes alert the driver of potential problems. These devices employ a control method and a warning method.

Poka-yoke (fail-safing)


Filing cabinets can fall over if too many drawers are pulled out. For some filing cabinets, opening one drawer locks all the rest, reducing the chance of the filing cabinet tipping. It is a control method.

The window in the envelope is not only a labour saving device. It prevents the contents of an envelope intended for one person being inserted in an envelope address to another. It is a control method.

Poka-yoke (fail-safing)


Controlled flight into terrain

Flying at wrong altitude p = 0.001

Co-pilot fails to cross-check p = 0.01

Air traffic control fail to notice p = 0.1

Pilots ignore warning alarm p = 0.5

Cumulative probability of occurrence = one in two million

Source: Empics


FailureSeverity of

consequenceEffect on customer

Normal operation

Probability of failure

Degree of severity

Likelihood of detection

Risk priority number

Failure modes effects analysis


Fault-tree analysis for below-temperature foodbeing served to customers

Food served to customer is below

temperature

Key

AND node

OR nodeCold plate

used

Plate taken too early from

warmer

Plate warmer malfunction

Oven malfunction

Timing error by chef

Ingredients not defrosted

Plate is cold

Food is cold


A mixture of maintenance approaches is often used –in a motor car, for example

Use condition-based monitoring

maintenance

Use run-to-breakdown

maintenance

Use preventive maintenance


Failure curve for two machines, A and B

Machine A

Machine B

Pro

babi

lity

of f

ailu

re

Timex y


One model of the costs associated with preventive maintenance shows an optimum level of maintenance effort

Co

sts

Amount of preventive maintenance

Total cost

‘Optimum’ level of preventive maintenance

Cost of providing preventive maintenanceCost of

breakdowns


If routine preventive maintenance tasks are carried out by operators and if the real cost of breakdowns is considered, the ‘optimum’ level

of preventive maintenance shifts towards higher levelsC

ost

s

Amount of preventive maintenance

Total cost

Cost of breakdowns

Cost of providing preventive maintenance


One part in one process can have several different failure modes, each of which requires a different approach

Cutters

Shredding process

Fai

lure

s

Time

Cutter ‘wear out’ failure pattern

Solution

Preventive

maintenance before

end of useful life



Cutters

Shredding process

Fai

lure

s

Time

Cutter ‘damage’ failure pattern

Solution

Preventive damage, fix

stone screen



Cutters

Shredding process

Fai

lure

s

Time

Cutter ‘shake loose’ failure pattern

Solution

Ensure correct fitting

through training


What’s happened

What consequences

Inform

Contain

Follow up

Find root cause

Engineer out

Analyze failure

Plan recovery

The stages in failure planning

Discover Act Learn Plan


Key Terms TestFailure rate (FR)A measure of failure that is defined as the number of failures over a

period of time.

Bath-tub curveA curve describing the failure probability of a product, service or

process that indicates relatively high probabilities of failure at the beginning and end of the life cycle.

ReliabilityWhen applied to operations performance, this term can be used

interchangeably with ‘dependability’. When it refers to a measure of failure, it means the ability of a system, product or service to perform as expected over time, usually expressed as the probability of its performing as expected over time.


Key Terms TestMean time between failures (MTBF) Operating time divided by the number of failures; the

reciprocal of failure rate.

Failure analysisThe use of techniques to uncover the root cause of failures;

techniques may include accident investigation, complaint analysis, etc.

Failure mode and effect analysis (FMEA)A technique used to identify the product, service or process

features that are crucial in determining the effects of failure.


Key Terms Test

RedundancyThe extent to which a process, product or service has

systems or components that are used only when other systems or components fail.

Fail-safeingBuilding-in often simple devices that make it difficult to

make the mistakes that could lead to failure; also known by the Japanese term poka-yoke.

Poka-yokeJapanese term for fail-safeing.


Key Terms Test

MaintenanceThe activity of caring for physical facilities so as to avoid or

minimize the chance of those facilities failing.

Run-to-breakdown maintenanceAn approach to maintenance management that repairs a

machine or facility only when it breaks down.

Preventive maintenanceAn approach to maintenance management that performs

work on machines or facilities at regular intervals in an attempt to prevent them breaking down.


Key Terms Test

Condition-based maintenanceAn approach to maintenance management that monitors the

condition of process equipment and performs work on equipment only when it is required.

Total productive maintenance (TPM)An approach to maintenance management that adopts a similar

holistic approach to total quality management (TQM).

Reliability-centred maintenanceAn approach to maintenance management that uses different

types of maintenance for different parts of a process, depending on their pattern of failure.

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chapter 19