LACI_ing_03_CHAPTER Industrial Conservation and Reliability_v160411

Enrique Dounce Villanueva.

CHAPTER 3 INDUSTRIAL CONSERVATION AND RELIABILITY

CHAPTER 3 INDUSTRIAL CONSERVATION AND RELIABILLITY. 42

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CHAPTER 3

INDUSTRIAL CONSERVATION AND RELIABILLITY

Its development started about 1958.

CHAPTER’S OBJECTIVES

At the end of this chapter, the reader will:

Understand the concept of industry and its mission in the human context

Demonstrate the importance of industrial products to sustain Earth’s habitat

Will explain what is Availability in industry

Interpret the meaning of industrial Effectiveness

Understand the concept of “product’s useful life time” (PULT).

Distinguish between the meanings of Reliability and Dependability.

Explain what are the Systems in Series, Parallel and Series-parallel.

Describe RCM’S general evolution in industry.

Identify the 6 “Failure Patterns” existing in a system.

Interpret the meaning of “Continuous Improvement”.

Illustrate what the 4 “Conservation Strategies” consist of.

Make generalizations about RCMII development.


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Contents

3.1 INTRODUCTION ......................................................................................................................... 44

3.1.1 Industry and its mission. ........................................................................................................ 44

3.1.2 Industry and its product. ....................................................................................................... 44

3.1.3 The product and its market. ................................................................................................... 46

3.2 INDUSTRIAL AVAILABILITY ....................................................................................................... 46

3.2.1 Industrial Maintainability ............................................................................................................ 47

3.2.3 Industrial Reliability. .................................................................................................................. 48

3.2.3 Industrial Logistics. ................................................................................................................... 49

3.3 INDUSTRIAL EFFECTIVENESS. ................................................................................................ 49

3.3.1 The integration of an industrial company. ................................................................................. 50

3.3.2 Product useful life time (PULT). ............................................................................................... 52

3.4 INDUSTRIAL RELIABILITY. ........................................................................................................ 57

3.4.1 Dependability for a system in series Dss .................................................................................. 59

3.4.2 Reliability for a system in parallel Rsp....................................................................................... 60

3.4.3 Dependability of a system in series-parallel Dssp. .................................................................... 60

3.4.4 Summary................................................................................................................................... 64

3.4.5 Service is first. ........................................................................................................................... 64

3.4.6 Maintenance for a vital service. ................................................................................................. 65

3.5 CONSERVATION CENTERED IN RCMII. ................................................................................... 66

3.5.1 Failure patterns ......................................................................................................................... 69

3.5.2 The industrial “Maintenance” Manual. ....................................................................................... 72

3.5.3 Continuous improvement team. ................................................................................................ 72

3.5.4 Product’s conservation status. .................................................................................................. 74

3.5.5 Conservation General Strategies. ............................................................................................. 75

3.5.5.1 Preservation General Strategies ............................................................................................ 75

3.5.5.2 Maintenance General Strategies ............................................................................................ 76

3.6 RCMII IN CONSERVATION. ........................................................................................................ 78


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3.1 INTRODUCTION

Current knowledge about maintenance, even though important, will be tremendously enhanced when

we become conscious at World level that we are mistaken calling Industrial Maintenance what truly is

Industrial Conservation. At present, this change is a real Challenge that demands scientifically

prepared minds in this subject. We only need to study and work to reach our highest possible

summit. In the way, with our own efforts, we will find the knowledge we need to improve, at World

level, not only the different existing industries, but also our habitat. This book will help you to find the

path to change and to know, in depth, about industrial conservation and its importance for industry all

over the world.

Let us remember that in subtopic 2.4 we defined Industrial Conservation as “human action in a

system, that through the application of scientific and technical knowledge, contributes to the optimum

use of existing resources in a human habitat thus favoring man’s and his ecosystem integral

development. Industrial conservation’s study is divided in two large branches, one is Preservation

which refers to the material part of the system and Maintenance which is related to the service

provided by the matter.”

The material we have seen so far has provided the required foundations for readers and scholar to

understand Maintenance as a branch of Industrial Conservation. The following chapters of this book

are structured with this focus on mind.

3.1.1 Industry and its mission.

By definition, industry is the group of operations and processes that have the objective of

transforming raw material into manufactured products that, when operating, will form a

system or human satisfactor.

The establishment of industry was initiated by men to obtain food and clothes to be able to

survive. However, industry has grown exponentially to such a degree that it destroys human

habitat at the same rate and velocity. Thus, it is vital to humanity to pay special attention to

industry’s development

3.1.2 Industry and its product.

Let us analyze the concept of product under the following Premises:

A product is any item capable of providing a human satisfactor.

A satisfactor is a complete system which when functioning, provides a service.

A satisfactor is comprised of matter, intelligently interlinked in such a way, that when

it is functioning it provides a service with a predetermined quality

A functioning product becomes a system providing satisfaction to its user (figure 3.1)

The satisfactors reason for being is the quality of the service they provide to their

final consumer.


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Industrial effectiveness is found in the equilibrium between the quality of the matter

integrating a product and the quality of the service it provides during its useful life

time.

Figure 3.1 Example of different products working as systems

Therefore, the tasks we must perform for the care of both are of two types: matter must be

cleaned, protected, not over charge it; in other words, it must be Preserved to obtain a good

output and durability in good condition during its useful life time (PULT). In regard to the

service this matter provides, we must make sure to Maintain it within the expected quality

parameters, and if for some reason it is not achieved, we will need to strengthen or change

the arrangement of the matter that comprises the product. We should emphasize that we are

referring to the products manufactured by our company and not to the machines that produce

them.

If a satisfactor has been appropriately designed, all its components fulfill a function and thus,

are all necessary. Then, as long as the needs that created them do not change, the

conservation tasks will be focused on guaranteeing the appropriate operation of said

satisfactor, preserving its matter and maintaining the quality of its service. It provides and the

user expects, all of which should happen during all of the product useful life time (PULT).

Idle ProductFunctioning System = Satisfactor

Working product Service obtained

hot

Battery Battery

Idle ProductFunctioning System = Satisfactor

Working product Service obtained

Cold

20°C 0°CProducto ocioso

Sistema funcionando = Satisfactor

Producto trabajando Servicio obtenido

Unclean H2O Unclean H2O Distilled H2O

Product in operation = System = Satisfactor


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3.1.3 The product and its market.

The product must be designed to function as a satisfactor within the market to which it is

directed. This is the reason why any company, before designing its product, must define the

market it wants to target since there is an indeterminate number of markets. This variability

stems from the fact that markets are comprised by people.

Let us remember that every person is different due to his/her individual characteristics (age,

socioeconomic, intellectual, cultural, temperamental levels, etc.). That is, we are continually

undergoing transformation throughout our lives. Despite these differences, human beings

share a common denominator: our gregarious nature which propels us to seek approval from

others regarding our thoughts and actions. We all have physical and psychic needs to be

satisfied in order to survive in this world. So, ever since we are born we search for the things

that satisfy our needs or whishes. We are pleased when our search ends with a satisfactor

that provides the quality that we want and can afford to pay. This, in fact, is precisely what

causes the establishment of markets that conform to the different human expectations,

which, in turn, define the quality, cost, and type of products or services that are required . It

has also generated the rapid growth of high “Availability” industries

3.2 INDUSTRIAL AVAILABILITY

Industrial Availability can be defined as the ability of an industry to keep performing a specific function

within predetermined quantity, quality, cost, and time parameters.

The most important attribute for a manufacturing company is its capital assets high Availability, which

means that they must fulfill three characteristics:

1. That they can easily be protected or restored so that they can continue to perform their

required functions (MAINTAINABILITY).

2. That the company, as a moral person, has achieved in its markets, the reputation of being

reliable (RELIABILITY).

3. That its markets be served strategically and logically so that its products be present at the

right place, with the proper quality, quantity, and time (LOGISTICS).

Graphically, we can illustrate Industrial Availability in the following way:


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Figure 3.2 Pillars of Industrial Availability

Let us analyze each part of Industrial Availability.

3.2.1 Industrial Maintainability

Maintainability is defined as the simplicity an item has to be protected or restored in order to

be able to perform its required functions. The above leads us to think that an item has good

maintainability the faster and easier we can successfully perform programmed conservation

or restoration so that it continues its predetermined performance. Maintainability refers to the

industry’s capital assets and it depends on many factors such as the asset’s design and

manufacture, the quality of the materials comprising it, the installing personnel’s ability, the

asset’s level of preservation, maintenance, and operation, the work space provided for its

operation and conservation, its ease of access, the availability of spare parts and appropriate

test equipments, the ease to disassemble, assemble, and change spare parts, environment,

etcetera.

The asset’s design must cover maintainability criteria as follows:

That it consists of very inexpensive and easily interchangeable modules to allow the

“use and discard” concept.

That its parts and modules be standardized to allow minimization and exchange

quickly and easily.

That the tools required to deal with the asset be ordinary, not specialized..

That the connectors joining the different asset’s modules be done in such a way that

they cannot be exchanged by mistake.


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That the asset’s operation and conservation tasks can be performed without

endangering persons or vitally important assets.

That the asset has brackets, handles, supports, and holders that allow the whole or

its parts to be easily moved and to lean them without danger while it is attended.

That the asset has diagnostic indicators or self-diagnosis modules that enable to

rapidly identify a cause for failure.

That the asset has an appropriate system to identify modules and test points, easy to

see and interpret.

There are many other criteria regarding this topic. However, the criteria we have already

covered are enough for us to understand that it is in our hands to significantly improve, with

our will and skill, the efficiency of a company’s resources, by increasing their maintainability.

For example, if our company is going to purchase a new machine, we can help providing our

point of view about the maintainability criteria the machine should fulfill, choose the place

where the machine should be installed, and during its installation, supervise that its

maintainability be safeguarded; also, with the aid of the supplier, we can design the

conservation strategies for the machine, combining the suppliers recommendations with the

advantages and disadvantages of the machine’s installation site.

Moreover, if we see an equipment’s frequent failure, which is caused by the same set of

elements, we can research the feasibility of making a module for such set so that we can

have one or more of these modules available to install at the appropriate time. This way, the

next failure, it would be easier and quicker to change the module, than the tasks that were

previously performed..

3.2.3 Industrial Reliability.

Industrial Reliability is the degree of trust given to an industry by its clients or market.

Ever since the initial idea of creating a Business, it is necessary to consider its reliability. At

present, Business firms, regardless of their type or size, are immersed in an environment of

highly competitive markets. Thus, the behavior of each firm is severely judged.

In the 60’s, Business planning began to be done more carefully, process which was called

“Long term planning”. By the middle of the 70’s, the development of “Strategic planning”

started. All these trends were the result of the need to support businesses reputations. The

above has resulted in modern Management using methods that have been proved successful

for developing “Life Plans” for physical quality persons, as can be confirmed in internet. If we

analyze any type of important company’s “Business plan”, we will find that it includes a

“Vision”, a “Mission”, its “General Objectives”, and many other criteria that are important


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enough to be currently studied by true modern scientists. Among these scientists, we can

mention Stephen R. Covey, “The 7 Habits of Highly Effective People”, Nathaniel Branden,

“How to Improve your Self-Esteem”, Howard Gardner, “The five minds of the future”, Daniel

Goleman, “Emotional Intelligence”, Luis Castañeda “A Life Plan for Young People”, to cite a

few. We consider this topic so important that we will study it in subtopic 7.5.

3.2.3 Industrial Logistics.

Logistics, from industrial conservation perspective, is the administrative labor required to

strategically see to the flow and storage of raw materials, work in process, finished goods,

etcetera, to take them from their point of origin to the appropriate places with the quality,

quantity, and timeliness required by the user. In other words, it is the appropriate

Management of a supply chain.

Industrial logistics originated from American war industry, around the same time that

Productive Maintenance (PM) was developed, during World War II (1939-1945). The

products manufactured by the war industry (arms, ammunitions, explosives, war vehicles,

etc.), as well as their destination, were vital for the war effort, which created a strong

relationship between the military allies and the American industrialists. Due to the experience

and profound knowledge of the military, it was decided to use military logistics to distribute

war products to the places they were needed the most. The industrialists learned and later

adopted this system.

3.3 INDUSTRIAL EFFECTIVENESS.

Industrial Effectiveness is the achievement of the expected effect in terms of quantity, time, place and

form.

An industry so considered is deemed as highly productive. However, to reach this status, it is

necessary that it is continuously reaching its planned objectives, that it obtain results, that it be

efficacious, and at the same time, that it uses its resources appropriately, that it be efficient. Thus, we

have the industrial quality parameters:

.

Industrial Effectiveness = Efficaciousness + Efficiency

Efficacy is the optimum achievement of the time, place, and form objectives.

Efficiency is the optimum use fo resources to achieve the objectives.


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We need to consider that one can be efficient without being efficacious, and that one can also be

efficacious without being efficient. We have witnessed the failure of many industries even though they

had great material and technical resources both in quantity and quality. They did not reach their

objectives because as work tools, they did not consistently obtained the expected results, or

misapplied or misused their resources; in other words, they were inefficacious, or inefficient, or both.

That is, they were not effective.

3.3.1 The integration of an industrial company.

The reason for the existence of an industry is to obtain profits, and its general objective is to

become a sustainable and competitive moral being; in an Effective industry, constantly

growing, in spite of the instability that will appear with time. Let us study figures 2.9 and 2.10,

and use this criteria to build Figure 3.3.

Figure 3.3 Industrial Effectiveness

If we want to create a successful company, we must, from its beginning, plan it so that it is

effective. to better understand This concept, we can consider a figure comprised of the main

subsystems that are involved in its effectiveness such as the “Efficacious work teams”

subsystem and the “Efficient product” subsystem. (See Figure 3.4).

The subsystems “Efficacious work teams” are comprised by our operators with their

machines purchased from our suppliers, which are, in turn, responsible for the machines’

fulfillment of the warranty they gave us. That warranty is supported by the Product useful life

time pattern (PULT), which we studied and accepted when we purchased the machine.

The subsystem “Efficient products” refers to our products which we have designed and

manufactured with our work teams, and therefore, only our company has the ability to make

the product useful life time pattern (PULT) to be delivered to our clients.

Efficacious work team

+Efficient product for its user

Industrial Effectiveness


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The product useful life time (PULT) is the pattern used to measure the product’s efficiency

during its warranty time, which is the next topic we will study in depth.

We can now imagine an industry as a system composed by two or more important

subsystems, immersed in the same symbiotic environment, as shown in figure 3.4. The

inputs are taken from other companies and the satisfactors produced are made available to

other companies that coincide in the same environment.

Figure 3.4 Industry as a System of subsystems

This order of ideas allows us to clearly see the following:

Premises:

The concept of industrial conservation and its taxonomy is clarified since with our

work teams we are producing ecologic Systems (Efficient products) for which

conservation tasks are oriented to preserve matter and maintain quality of the

service it provides (see Figure 2.19).

The operation of the “Subsystem Work Teams” is provided by the “Capital Assets”,

which are the goods and Rights with Money value, which are property of the

company, such as machinery, buildings, equipment, land, etc., and they are used

exclusively in the generation of income or profit.

The operation of the complete “Industrial System” is derived from the benefit from or

sale of satisfactors. The above urges us to accept that the paramount objective of

any industry is that its products be true satisfactors for the markets for which they

have been designed. In summary, the user of our product must be satisfied.

Each industry must deliver to its clients their products useful life time (PULT). This clarifies

the extent of the warranty and the conservation conditions to which the items considered as

work capital will be subjected to. It is the foundation for the advantage of purchasing the

product. Similarly, we must also deliver to our clients the PULT for each of our products,


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which explains our warranty, commitment, and care that must be given to our product for it to

work as a quality system.

The effectiveness of an industry is based on the “efficient products subsystem” and not on

the “work Teams”. We would like to stress that we are talking about the products

manufactured by our company and not to the machines which produce them. This clarifies

the “Industrial Effectiveness Principle” which refers to the “Equilibrium between the quality of

the matter that comprises the product and the quality of the service it provides as a system

during its useful life cycle”.

Figure 3.5 Industrial Effectiveness Principle.

3.3.2 Product useful life time (PULT).

Generally stated, a product’s useful life time is a managerial tool used to measure the

effectiveness of a product when it is functioning as a system.

The capture of clients among competing companies starts with market research to know in

depth the needs to cover in regard to the type and quality the clients expect from a product.,

thus achieving the appropriate design. From it, said satisfactor will include, under certain

conditions stipulated by the manufacturer, a useful life time of “T” number of hours, days,

months, or years operating as an effective system. This way, the buyer will know with

certainty if the item he is buying (capital asset) is the correct item to install in his business.

From this point of view, we can derive the premise that the manufacturer is the only one that

can know the true useful life time for his products since he knows the quality of the matter

and technology applied in it manufacturing.

At present, there is a classification and order for the useful life time of a product, shown in

figure 3.6, which we will analyze next. .

Matter quality Service Quality

Satisfactor

Products functioning = SATISFACTOR


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Figure 3.6 Product’s Useful Life Time Taxonomy

Let us study each of its parts in a logical and sequential way:

PRODUCTS’S USEFUL LIFE TIME

Useful life time. It refers to the time

elapsing from the new product being

satisfactorily installed (commissioning)

in its working place until the end of the

manufacturer’s warranty. During this

time, said product only has two status,

Active or Inactive (Figure 3.7).

Figure 3.7

Active time is the time considered as necessary for

the resource’s functioning in the company (Figure

3.8).

Inactive time. It is the time that for planned reasons, is

used to do conservation work on the resource or for it

to be retired because it is no longer useful to the

company (Figure 3.11).

TIEMPO ACTIVO

PRODUCT USEFUL LIFE TIME

ACTIVE TIME INACTIVE TIME

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OPERATION

TIMEDOWN TIME IDLE TIME STORAGE TIME

PRODUCT’S USEFUL LIFE TIME

ACTIVE TIME INACTIVE TIME


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Active time is the time considered

necessary for the resource to operate

in the company. We divide it in

Operation time, when the item is

functioning well, and Down time, when

the item has reached a failure, (Figure

3.8).

Figure 3.8

Operation time. It refers to the time the resource is

functioning within the service quality specified limits

and it is the reason for the existence for said

resource. (Figure 3.9)

Down time. It is when, due to unplanned causes, the

resource ceases to function within the specified limits,

resulting in losses due to waste, resource’s excessive

wear, and inability to be used. (Figure 3.10).

OPERATION TIME

Operation time. It is when the resource is

working within the stipulated limits of

service quality and is the reason for being

of said resource. It is divided in

preparation, warm up, and operation, as

shown below:

Figure 3.9

Preparation time. It is the time used by the operator

before starting work to obtain all that is necessary and

to verify that the resource can function as a system.

Warm up time. It is the time needed to take the

resource to its normal operation level.

Work time. It is when the resource is functioning as a

system and providing the service within the expected

quality (study Figures 3.9 y 3.12).

DOWN TIME

Down time. It is when, due to unplanned

reasons, the resource ceases to function

within stipulated limits causing losses due

to waste, excessive resource wear,

product reprocess, and inability to use. It

Organization time. It is the time required to notify the

contingency personnel about the resources (human,

physical, and technical) that will be needed, and for

them to arrive to the site to attend to the emergency.

Diagnosis time. It is the time used to verify the

ACTIVE TIME

OPERATION TIME DOWN TIME

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OPERATION

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is divided in organization, diagnosis,

enablement, repair, adjustment,

calibration, verification, recording and

statistics.

Figure 3.10

resource’s malfunctioning, its temperature, vibration,

noise, and oil levels, energy input and output,

indicators readings, etc., until the failure cause is

identified and to determine the necessary corrective

actions.

Enablement time. Is the time used to obtain the

necessary parts or spares (tools, test equipment,

material, etcetera).

Repair time. It is used to replace or repair the worn out

resource parts to attain its functioning within stipulated

service quality limits.

Adjustments and Calibration time. It is the time used to

perform the necessary tests and adjustments to

achieve that the resource within the expected service

quality range.

Verification time. It is used to start the resource’s

operation and decide if it can be put into service again.

Recording and statistics time. It is the time used to

record the type of work done, date, hour, and time

spent, and all the information deemed useful to back

up future analysis and diagnosis.

IDLE TIME

Idle time. It is the time planned for

conservation tasks to be done to the

resource, or for the time to take the

resource out of production because it is

no longer useful to the company. It is

divided in idle time and storage time.

Idle time. The time needed to execute the preventive

conservation recommended by the manufacturer. It is

divided in planning, routines, overhaul, and statistics,

as explained below:

Time for planning. It is the time needed to get

to the resource site, observe and record the

behavior of sensors and gauges, and to do the

planning required (Deming Circle) to determine

the corresponding routines and work orders.

Routines and work orders time. It is the time

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Figure 3.11

needed to execute the work covered by the

corresponding planning. It includes its

preparation and the required tests to verify that

the expected results were achieved.

Overhaul time. It is the time needed to perform

in depth maintenance work, usually covered by

a special work order. It includes the

preparation time and the testing required to

verify the work was performed correctly.

Statistics. It is the time used to record the work

orders and routines, once they have been

finished.

At last, we have storage time:

Storage time. It is the time that the equipment is stored

because the company no longer requires its services.

This time ends with the sale of the resource or the

manufacturer’s warranty.

The study of previous chapters has given us new points of view about biology, ecology,

Systems theory, etc. and we have very infrequently used them to attend to the repair of our

machines. But now we have more logical and scientific concepts, and from this perspective,

we will analyze the “Resource’s Useful Life Time” that we have developed.

Let us imagine a time line depicting the useful life of a product, from its birth to its death

(Figure 3.12). We will use the product “AC Generator” to illustrate this concept. Every day, its

operator puts it to work as a system, for which he prepares it, turns it on until the start up is

done, and puts it to work during the 8 hours of his shift. At the end of his shift, he turns it off,

and the system is interrupted, so that the generator, depending on circumstances, will occupy

a position on the time line at Idle, Down, or Storage. Usually, these events are repeated daily

until the useful life time warranted by the manufacturer is finished.

INACTIVE TIME

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IDLE TIME STORAGE TIME


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Figure 3.12.

Let us now think about an “Ideal manufacturing machine” with a 100% reliability, and thus

utopian; that is, it does not need the works mentioned in the Down, Idle, and Storage times. It

does not even require a preparation or a start up time to begin functioning appropriately; it

only needs to be started and it will provide the expected product throughout its useful life

time. This is a very important concept and as such, it should compel us to take it as our ideal

pattern, so that we can try to achieve 100% reliability for both our manufacturing machines as

well as the products they manufacture. That is, the “work” life time should be much longer

than the other times and the latter should be minimized. Thus, we should keep in mind the

following premises:

Operation time is the reason for being of a product and it exists when the product

becomes a system so ideally we should work to minimize the preparation and warm

up times

The time included in Down, Idle, and Storage are not useful for the product but are

necessary and are always present, so we need to study them to minimize them.

3.4 INDUSTRIAL RELIABILITY.

Reliability is the probability that a component, product, or system, works to perform a specific task, in

given conditions, during a predetermined time. Reliability is defined with a value. Reliability’s ideal

value is 100%, therefore, when we state that an item is 100% reliable, we are saying that there is no

doubt that said item will work without failing during that time.

Thus we have:

Ideal Reliability = 100%

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PRODUCT’S USEFUL LIFE TIME VIRTUAL IMAGE

DOWNIDLE

TIME LINE


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In practical terms, it does not exist since there is always the possibility of random failures to

occur, which we call unreliability and define it as the probability that an item does fail. Within

this order of ideas, we have:

Item’s reliability = Ideal Reliability – Item’s unreliability

If we use “R” for Reliability and “U” for Unreliability, we will have:

Item’s Reliability = R = 100% – U

Therefore, an item’s Reliability will never reach 100%

Since the reliability concept is applicable to each of the parts that comprise a product, for all practical

purposes, when undertaking conservation tasks, we should always consider that our main focus

should be centered on the product that our industry is manufacturing for its quality will enable

us to increase our market share.

When a product is used in combination with others to initiate a joint activity, they become a system

and keep a precise behavior in accordance to their position in reference to the set. There are

three general operating positions in which the parts of a system can be placed: in series, in parallel,

or in series-parallel. Let us see what each of these positions involves

System in series. Items are installed one following the next. In this arrangement, if any of the

equipments ceases to operate, the system is immediately lost and with it, its service.

Figure 3.13 Items connected in series.

System in parallel, Items are installed one next to the other. With this arrangement, the three items

provide the same service so that if any of them ceases to function the service will continue to be

provided without loss of quality until the last item fails in which case the system and the

service will fail.

Figure 3.14 Items connected in parallel.


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System in series-parallel. Its reliability depends on the interrelation of the systems that comprise it,

so it is necessary to first calculate the reliability of the system in parallel and then the reliability

of the system in series. For our purposes, we will use the system in series parallel shown in Figure

3.15 which consists of three items installed in series and one in parallel to support the lowest

reliability item. With this arrangement, all four provide a very high reliability and the service will

continue to be provided without quality loss until the last item fails thus failing the system and

with it, the service.

Figure 3.15 Items connected in series-parallel

Let us analyze it:

We will do the math required to calculate the three systems. For our examples, we will use the

following reliability and unreliability values for the four equipments considered above.

Reliability I = RI = 0.96 Unreliability I 0.04

Reliability II = RII = 0.62 Unreliability II 0.38

Reliability III = RIII =0.97 Unreliability III 0.03

Reliability IV = RIV = 0.98 Unreliability IV 0.02

3.4.1 Dependability for a system in series Dss

The reliability of a system in series, (Figure 13) results from the product of the reliability of its

parts.

According to this statement, we only have to multiply the reliabilities to obtain the following

result.

where:

From which we can infer that the reliability of a system in series is lower than the

lowest reliability of any of its parts.


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3.4.2 Reliability for a system in parallel Rsp

The reliability of a system in parallel is equal to the product of the unreliabilities of its parts

subtracted from ideal reliability. Taking figure 3.14 as an example, we have:

The conclusion we reach is that the Reliability of a system in parallel is higher than the

highest Reliability for any of its parts

3.4.3 Dependability of a system in series-parallel Dssp.

The Reliability for a system in series parallel depends on the interrelation of the

Systems that comprise it, therefore, according to what we have learned from the last two

subsystems, and using the reliability and unreliability data to solve these cases, we only need

to first calculate the reliability of the system in parallel and then the reliability in series

for the set.

In order to make our explanation easier, let us consider equipments II and IV as only one

equipment “A” connected in series with equipments I and III (Figure 16) which reliabilities we

already know so that we only need to calculate equipment A’s reliability, comprised by

equipments II and III in parallel:

Reliability A = ideal reliability – (U II X U IV) = 100% - (0.38 X 0.02) = 1 - 0.008 = 0.992

Figure 3.16.

We have turned this group of two Components in parallel into one which reliability is

0.99%, and which we will call Equipment A, placing it between equipments I and III which

thus results in only one system in series, as shown in figure 3.17


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Figure 3.17 Resulting system in series.

From the above, we now only need to calculate the resulting system in series to find out the

reliability of a system in series parallel. Thus we have:

Reliability for the resulting system in series Rsrs = 0.96 x 0.992 x 0.97 = 0.924

As the equipment operates, the reliability of its parts decreases, which in turn increases the

probability that it fails. The preventive conservation routines are meant to diagnose and

restore the lost reliability. If we analyze a machine’s or equipment’s interior, we will see that is

composed of systems, which are made up of subsystems, the subsystems by modules, the

modules by components, and these by elements. All of them are involved in one way or

another in providing a product: They behave as “links” in regard to providing a product,

sometimes in series, others in parallel, or in occasion, in series-parallel. Our labor will be to

analyze these ”links” in order to find those below the expected reliability, observing the type

and frequency of their failures to place another link in parallel, or strengthening it, or

substituting it for better technology to increase its reliability. This analysis must be done again

for subsystems, and so on. We can better appreciate this topic through the following

anecdote.

“In our experience in phone Communications during the 1960’s, to transmit signals from one

place to another instead of physical lines over poles, we used “Microwave relay Stations”

which were usually located at a mountain, 10 to 20 kilometers from the nearest town, with

very well trained personnel living in these buildings. Even so, we could not guarantee a

continuous service since correcting immediately a failure interrupting the service was, for all

purposes, impossible. So in the stations we considered as high risk, and to insure phone

service to users, we would place redundant machines to increase the reliability of the system.

Later, the supplier provided equipments with the redundancy in duplicated modules. Thus, if

the equipment was damaged, the waiting redundant module automatically replaced the

damaged module and in milliseconds, the system was working appropriately. The technician

just and only had to exchange the damaged module and send it to the manufacturer to be

replaced. At present, this process is continually improving, and it is very common in modern

equipment.”


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From the above we can deduce that to achieve a high reliability in our area of competence,

we need not duplicate complete machines but only that part or parts that have a low

reliability.

This is the true labor of those of us dedicated to conservation, to be constantly analyzing the

defects or failures in our assets and industrial products to determine if there is a decrease

in the systems’, subsystems’, modules’ and elements’ reliability.

From what we have already seen, we can apply our knowledge about reliability in a practical

way by doing the following exercises.

Exercise 1:

Let us consider a Communications net between ends A and B, like the one shown below to calculate:

Undependability for each component (Ua, Ub, Uc, Ud, Ue).

Total dependability for a system in series (Dss).

Figure 3.18 System in series.

The total dependability for this system in series is : Dss = 0.44, please calculate it.

Exercise 2:

This system in parallel with equipments a, b, c, and d lacks dependability (D) or undependability (U)

data, please calculate:


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Figure 3.19 System in parallel

Exercise 3:

Calculate total dependability for this system in series parallel.

Let us try to improve the system in series, so we note that the components that highly decrease the

dependability are the copper cables. Fortunately for us, there are optic fiber cables we can use.

Figure 3.20 System in series parallel

Total dependability for this system in series parallel is Dssp = 0.945.

Now try to calculate it.


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3.4.4 Summary.

Up to this point we have analyzed two of the most important of our assets attributes:

Maintainability and Dependability. If we make a comparison, we will realize that a high quality

item will exhibit these attributes as shown in figure 3.21.

Figure 3.21 Criteria for maintainability and dependability

With this knowledge about dependability and remembering figure 2.11, we can observe that

our products, in the hands of users, become functioning Systems (satisfactors) which leads

us to Conserve the system, Preserve the product, and Maintain the service, and that the

specific case for Dependability is directed to the care of the service provided by our product

3.4.5 Service is first.

When an equipment provides a service classified as vital or important, it should never be

allowed to operate outside of its predetermined parameters for any reason. However, there is

always the possibility that in spite of all our care and effort, there may be a contingency which

may cause a service failure.

To minimize the negative impact of contingencies, we must analyze in depth the equipment

to locate the parts or subparts with low dependability and restore them, or it that is not

possible, to think about a replacement or the installation in parallel of an element, part,

subpart, or complete system.


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When a service is classified as vital we must insure that the system that provides it will have

enough redundancies in parallel to increase dependability and decrease the possibility of a

failure.

It is important to emphasize that from the care required by the matter that comprises the

system and the service it provides, Service is first.

3.4.6 Maintenance for a vital service.

Let us take as an example a factory that has evaluated the importance of its electricity supply

in reference to the negative impact caused by a failure in said supply. Therefore, they

determined that electricity transfer to a specific group of machines and offices should be

considered vital. Thus, they proceeded to prepare a “Contingency Plan” similar to the one we

will see in topic 8.6.

Figure 3.22 shows how, through the use of a system comprised of three subsystems, they

seek at any cost to avoid loosing a service classified as vital. The three subsystems are

working at the same time, but subsystem number 1 was initially providing the service. When

an anomaly occurred, the subsystem sent an “outside of service quality” signal to the

automatic change box, which switched to subsystem 2. It continued providing the service

until it was affected by another anomaly, so subsystem 3 took over in order not to loose the

service. If this latter system suffers another anomaly, the service is interrupted..


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Figure 3.22 System to insure a vital service

The reliability of a system comprised of several subsystems keeps its value even if all the

subsystems, but one fail. When this happens, we must restore the affected system or

systems as soon as possible. The above illustrates that by applying the industrial

conservation theory, we are caring more for the service than for the matter since we are

discarding the latter (malfunctioning subsystem) and using a new subsystem in order to

maintain the service within the specified parameters.

3.5 CONSERVATION CENTERED IN RCMII.

Remembering the 60’s, those of us working in conservation tasks for automatic phone switchboards

received verbal and written instructions from our providers that the installed equipment would provide

the service guaranteed by the manufacturer if we performed the following tasks:

Changing the used parts by new parts with the frequency indicated by the manufacturer.

Changing the broken or worn out parts after a routine check.

Changing the damaged parts as required by corrective maintenance.

Protect the equipment with the appropriate environment in the installation site.

In regard to our experience in the phone industry, we had, among other parts in our central phone

boards, “selectors” composed of a stainless steel sheet measuring 40 X 40 centimeters. There were


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gears, springs, and relievers installed over the selectors, which, operating electromagnetically,

moved an arm to an exact position to enable to connect a couple of wires with another wire. So, and

with a specific quantity of these “selectors” we would build a physical road of conduits from one

telephone to another in any part in the world.

The “maintenance” routine required that we had skilled personnel, adept at cleaning the “selectors”

every six months, using grease removers, special oils, test equipment, and new parts to do

replacements. However, in spite of these thorough repairs, and the high costs incurred, some of

these equipments suffered a greater number of failures than before the cleaning and adjustments

routine. Our clients were constantly upset, and we thought that our personnel were not careful

enough and that the changes of parts should be more frequent; but, despite everything, the failures,

and thus the costs continued increasing.

Later on, we replaced the “maintenance” routines by the use of reliability criteria. The central phone

boards were now comprised of transistors, and advanced technology chips, which thus turned these

parts into high reliability components. This change improved considerably the quality of the service

provided to the user.

Something similar was happening in commercial airlines. Air accident statistics .were high so they

were forced to join their efforts to find solutions to catastrophic events. It was 1950 when the

American civil aviation industry, taking advantage of the use of applied statistics, mainly to the

behavior of airplanes, achieved the first advances in this topic. At this time, Weibull analysis was

having very good results in estimating the probability of a machine failure, both with assumed and

real data.

The above led the airplane manufacturers to assemble a group of experts to study in depth these

events and to seek how to provide an optimum conservation for commercial airplanes. Thus, they

organized work groups comprised of specialists from the airplane manufacturers, from commercial

airlines, and the American Air Force, which constituted the Maintenance Steering Groups (MSG).

Sponsored by the American Air Transport Association, these groups researched catastrophic events

during twenty years, as well as the actions and solutions performed to solve or alleviate the

problems. This research resulted in the MSG – 1 Guide, and the Maintenance Evaluation and

Program Development Manual. These documents were presented in 1968

In 1970, at the request of the American government, a document, “Reliability Centered Maintenance,

written by Stanley Nowlan, and Howard Heap, was released. This document deals with the planning

for maintenance programs for manufacturers and airlines. It is called MSG–2, and has had very good

results to date.

The last version of the above mentioned document, MSG-3, was released in 1978, with such great

success that it has only required sporadic revisions, done, the first in 1988, the second in 1993, the

third in 2001, and the fourth in 2004. These revisions are due to all kinds of changes naturally


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occurring in the airplane environment. MSG–3 is still the basis of maintenance planning systems for

different items, such as military weaponry, ships, industries, auto fleets, etc.

In regard to the decrease in catastrophic airplane accidents, we must be grateful for the application of

RCM, worldwide, because otherwise, given the evolution of civil aeronautics, the studies show that

we would have had two catastrophic airplane accidents every 20 to 25 days.

In 1980, John Moubray and Associates, with Stanley Nowlan (co-author of the MSG-2 and MSG-3)

as an advisor, was one of the most advanced companies in the study and application of the RCM.

They succeeded in applying RCM to a large range of industries. The above made possible the

development and usage of RCM-2, which focuses on the reliability and safety of items, and adapts it

to the true needs of the manufacturer or company using it.

Let us consider any airplane as a system composed of Man/Machine; that is, the airplane as a

machine is a handled by a crew and their joint effort provides a satisfactor to their users. On the other

hand, there have been many companies interested in applying this system to other industries. These

companies, among them John Moubray and Associates, confirmed that the RCM did not produce the

same results as in the aeronautical industry. This group, consulting with Stanley Nowlan, worked

initially with RCM in the mining and manufacturing industries in South Africa, and later migrated to the

United Kingdom. From there, they expanded their activities to cover the application of RCM to almost

all fields of organized human endeavors, in over 44 countries. Moubray and Associates use Nowlan’s

work as their basis, while keeping their original focus in equipment reliability and safety, they added

environmental topics to the decision taking process, classified the ways in which the operations of the

equipment should be defined, and developed precise rules to select “maintenance” tasks, as well as

their application frequency. They also incorporated directly quantitative risk criteria to a group of

intervals for failure patterns search tasks.

Their RCM version is known currently as RCM2.

Next figure gives us an overview about man’s tendencies to develop “maintenance” for his habitat

and work tools, from where he has had to evolve towards conservation.


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Figure 3.23 Evolution toward the Industrial Conservation.

3.5.1 Failure patterns

Around 1950, the industry’s economy revolved increasingly around the “Maintenance” cost of

the machines. This led to program maintenance with a certain frequency through the change

or repair of items’ parts, since it was believed that usage was a determinant of their useful

life. So, they started applying to physical assets, the same criteria used in studying the life of

peoples, as can be seen in figure 3.24 which shows the Deivis curve. .

Imagine persons comprising any nation. This

conglomerate is composed by three regions: the first

region is the early life, formed by children; the second, is

the useful life region, composed of young and mature

people; the third is the exhaustion region integrated by the

elderly. If we draw a graphic, with real data, we can

confirm that this is the way the life of the people behaves.

That is, at birth, and for some time afterward, we have a

greater risk of dying; as time goes by, it is more probable

that we experience death through sporadic dying of

people in our age range; but death rate increases with

age. This is a rather close description of the pattern of

failures for a nation. It is represented by the Deivis curve

or bath tub curve.

Figure 3.24 Bath tub curve

The frequent use of the bath tub curve, since approximately 1950 on, created in the industrial

environment the mistaken idea that the time of usage of a physical asset was the only factor

determining its good performance. This led to “over- maintenance”, increasing costs and

decreasing the quality of the product, which was actually opposite to expected results. The

above resulted in the commercial aviation studies, in the United States (from ATA) as already

Early life Useful life Exhaustion

TIME

Failures


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mentioned. Besides the introduction of the MSG-3, other important findings were the

discovery of six failure patterns. (See figure 3.25).

Incr

easi

ng C

ompl

exity

Pattern “A” (Deivis curve)

Let us remember that this curve has

two failure regions, the early life,

and the exhaustion, while its useful

life remains with a constant failure

rate. It has been verified that only 4

% of the items behaves according to

this pattern The failure rate

registered during their useful life is

random

Pattern B

This pattern shows no early life, but

rather starts with useful life with a

constant rate of failures, until it

reaches its exhaustion stage. Only 2

% of the items behaves according to

this pattern. The failure rate through

its useful life has a random nature

Pattern C

This pattern does not have early life

nor exhaustion stages, and all its

useful life, it behaves with a slowly

increasing failure rate leading to

exhaustion. Only 5 % of the items

portrays this pattern of behavior.

The failure rate throughout their

useful life is random.

Pattern D

This pattern shows an inverse early

life and has a constant failure rate

throughout its useful life until its end.

7% of the items exhibit this

behavior. The failure rate during its

useful life is random.

TIEMPO

FALLAS

TIME

FAILURES

TIME

FAILURES

TIME

FAILURES


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Pattern E

This pattern displays no early life or

exhaustion regions, and during its

useful life, its failure rate shows a

slight tendency to increase to

exhaustion. 14 % of the items

exhibit this pattern of behavior. The

failure rate throughout its useful life

is random.

Pattern F

In this pattern we can see that it

does have an early life region and

that its useful life shows a constant

failure rate until its end. 68 % of the

items behave according to this

pattern. The failure rate is random

throughout its useful life

Figure 3.25 MSG-3 Failure Patterns in mechanical and electric Items used in airplanes.

.

Based on these results, it is obvious that in terms of both dependability and cost, our

conservation processes must be integrated considering that the failure rates are due to

random events and not by the aging or time of usage of an item, especially for complex

machines.

To have a clearer idea, let us imagine that we have purchased the latest car model of a well

known manufacturer. We will soon feel secure, trusting, and satisfied with the machine, and

we will note many features while driving it. If we open the hood, we will be very favorably

impressed with the motor. It is formed, as the rest of the vehicle, by thousands of parts, each

in its exact place, and many of them also composed of subparts that aid in its operation.

Each of these myriad items has its own failure pattern. They behave as links of a so called

virtual chain net that have been arranged in series, in parallel, or in series-parallel to achieve

our satisfaction. We obviously need this machine to be serviced by experts in shops with

appropriate diagnostic tools, and following the strict routines established by the manufacturer.

If we can get the above within our location, it will insure that the expectations promised by the

manufacturer will be fulfilled. Undoubtedly, we will also verify that the machine in question

requires an owner, an operator, a shop, and mechanics, all according to its quality.

TIME

FAILURES

TIME

FAILURES


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3.5.2 The industrial “Maintenance” Manual.

For the moment, let us not talk anymore about man made systems (equipment, machines,

etc.) and consider the solar system, which is the habitat of millions of species, including

intelligent life, in order to know how it is protected (See topics 2.2 and 2.3). First, we see that

we are within a cyclic system and that to better understand it, we have developed a

science known as ecology which studies the relationships of live beings among themselves

and with their environment. In sociological terms, ecology studies the relation between

human groups and their environment, both physical and social. Its main objective is the

conservation of human habitat, that is, its preservation and maintenance. Our problem is

that nature has not given us a detailed manual or instructive to do it. So we have to carefully

observe its functioning and on this basis, “edit our own manuals”, and whenever

possible, apply it to man made systems so that we act in harmony with nature. We have

learned most of our activities to protect our habitat in the last 120,000 years taking care of

“things” rather than “ecological systems”. Therefore, we have written for our machines the

instructions or “Maintenance Manuals” that although they help, are not appropriate for

caring for the life system on earth, as we shall see later.

Let us return to our topic regarding man made systems:

The normal operation of any system tends to deteriorate its physical state. For the system to

fulfill its expected useful life time, it is necessary to think carefully how it must be protected.

In regard to industry, the life cycle preservation plan for its product (satisfactor) is studied,

written, and delivered by the manufacturer and we know it as the maintenance manual and

it includes the “conservation tactics and strategy” which are a great help for both the

product’s manufacturer and the user. This interaction between the producer and the user

causes a synergy, a continuous improvement process for both firms, when they are involved

in two types of activities which we always need to keep in mind: the “strategic” and the

“tactical”. Let us analyze their meaning and interrelated functioning

.

3.5.3 Continuous improvement team.

The strategic function is developed at any moment in time to achieve future results. The

tactical function is developed to attain immediate results. For a soccer team, let us see the

following matrix as an example:


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CONTINUOUS IMPROVEMENT TEAM

Strategic function Tactical function

The training of the players, the plays previous

analysis on the blackboard, the planning of how,

where, when, and with whom will the team be

playing; that is, all that is focused to future

results but that occupies our present time is a

strategic function.

The activities during the game, like the touch of

the ball between the players, the exchange of

players due to fatigue, or convenience, or any

other reason, the signals given by the team

players among themselves, the assistants, the

trainer; that is, all those activities that as soon as

they are executed, generate a result are

classified as tactical activities.

In a similar way, in a company, the leaders at any level, be they CEO’s, managers,

supervisors, department heads, etc., must accustom themselves to think in terms of these

two approaches to improve the management of the human, physical, and technical resources

they oversee, whether their activities are directed to take a decision, solve a critical situation,

or analyze a possible problem. We always need to keep in mind the strategy and the tactics

of any task. For example, if a part is required urgently, the first step is to obtain the part

(tactical action) as soon as possible, but immediately after, we need to analyze and

implement whatever is necessary to avoid this problem in the future (strategic action). In our

milieu, we generally use only tactical actions which cause problems to become repetitive,

time is wasted, and productivity decreased.

We need to be aware that a good leader plans and acts, in the first place strategically to

analyze and solve any situation he is dealing with, and afterwards, based on his strategic

plan, he programs his tactical activities. We need to emphasize that only in real emergency

situations should one proceed immediately with tactical plans and actions. However, when

the emergency is over, one must think how to avoid this emergency situation from happening

again and plan whatever is necessary to achieve it (strategic action). With any kind of

planning (strategy) or programming (tactics) we should always think of the future, seeking

the largest quantity of information as to how that future will be and how it will intervene in the

actions we want to perform

We should be aware that our thoughts will jump from one level to a different one of the topic

we are analyzing, and we may even talk about other topics looking for practical solutions.

That is the mechanics of human thought, and we must consciously use it during planning or

programming.

It is our belief that a successful company should be designed in such a way that during its

normal operation, it achieves continuous improvement (Kaisen). The above is achieved when

we make sure that our tactical tasks are derived from and give feedback to a strategy.


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We need to always keep in mind that “Every tactic must come from a strategy and every

strategy is improved through the results of a good tactic.”

3.5.4 Product’s conservation status.

From topic 2.4, let us remember from Industrial Conservation and its taxonomy that it is

divided into the branches Preservation (of the matter that comprises the product) and

Maintenance (of the quality of the service provided by the product). It is important that we

note the difference between them since both are applicable to any resource existing in

Nature. Thus, a machine can be subjected to cleaning, oiling, repairs, or painting. All these

tasks can be classified as Preservation tasks if they are done to avoid damage to the

machine. However, they will be described as Maintenance if their objective is that the

machine continues to provide a service with a specified quality. In other words, while

Preservation is focused on the material care of the resource, Maintenance is oriented to

caring for the quality of the service provided by the resource.

The relative situation of a working product (system) regarding its status norm only has two

behavior forms, called status and which are known as:

If the satisfactor is within norm = Preventive status

If the satisfactor is outsider of norm = Corrective status

Preventive status Corrective status

Accumulated dirt that

does not damage

matter.


damages matter.


does not affect service.


affects service (failure)

Figure 3.26 Conservation Status

For each status, there are lists, reports, and plans for conservation tasks that must be

performed during a satisfactor’s complete life cycle. These are called “General Conservation

Strategies” which we will see next.

.


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3.5.5 Conservation General Strategies.

Conservation General Strategies are the tasks included in what we currently know as the

maintenance manual that the manufacturer delivers with its product. This manual explains

the activities required during the useful life time, when the product is at any of its four

conservation status. There are four types of conservation strategies.

Figure 3.27 Conservation General Strategies

3.5.5.1 Preservation General Strategies

All work, done in systems with the objective of caring for the matter that comprise them, is

called Preservation work, and has a corrective and a preventive status, as shown below:

Figure 3.28 Preservation General Strategies

General Conservation

Strategies

a) General Preservation

Strategies

I. Corrective Preservation

Strategies

II. Preventive Preservation

Strategies

b) General Maintenance

Strategies

III. Corrective Maintenance

Strategies

IV. Preventive Maintenance

Strategies

a) Preservation General

Strategies

I. Preventive Preservation

Strategies

II. Corrective Preservation

Strategies


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At present, most companies have system or resources that require many manual

preservation tasks. Although with the development of electronics and computer science,

automation has reached such levels in some organizations that these manual tasks are now

minimal. So, we can say that personnel has evolved form craftsman to technical craftsman,

and now to technician specialized in the Maintainability and Reliability analysis software used

for the systems to be Conserved.

From the above we can conclude that there are two types of Preservation: preventive and

corrective.

Preservation General Strategies.

1.- Preventive Preservation: Deals with protection tasks performed to the matter of a resource

to avoid attacks by harmful agents.

For example, paint a newly installed hopper or a new satisfactor

2.- Corrective Preservation: Refers to the remedial tasks that must be performed to the matter

of a resource when it has degenerated or has been attacked by

harmful agents.

For example, paint a Hopper after it was repaired.

.

Figure 3.29 Preventive and Corrective Preservation

In this subtopic we analyzed only the first conservation branch, that is, the care of the matter

that forms a system. We will now study the second branch which refers to the service that

matter provides.

3.5.5.2 Maintenance General Strategies

Any type of work in systems aimed at continuing to provide or provide again a service with an

expected quality are maintenance tasks; that is, they are focused on attending to the service

and not on the matter that provides the service. The typical maintenance work is the search

and strengthening of the weakest links of a Satisfactor’s service chain.


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Figure 3.30 Maintenance General Strategies

There are only four types of Maintenance, Preventive, Predictive, Corrective, and Detection.

Co

rrec

tive

Mai

nte

nan

ce

stra

teg

ies

3.- Corrective Maintenance.

(failure repairs)

Inspection, control, and restoration services for an item

working as a system in order to prevent, detect, or

correct failures..

4.- Detection Maintenance.

(search fro hidden flaws)

Inspection, control, preservation, and restoration

services for an item that works as a closed system, with

the purpose of preventing, detecting, or correcting

mistakes or defects that can cause failures

Figure 3.31 The four types of Maintenance strategies

In the preventive maintenance strategies, if a satisfactor or system is operating within the

control limits, it is constantly informing us, through its closed systems (controls for

temperature, pressure, voltage, etc.) about the degree of deviation against the expected

optimum, so that we may start any required actions to correct any abnormality before it

b) General Maintenance

Strategies

IV. Preventive Maintenance

Strategies

Preventive Maintenance

Predictive Maintenance

III.Corrective Maintenance

Strategies

Corrective Maintenance

Detection Maintenance.

Maintenance general strategies

Pre

ven

tive

Mai

nte

nan

ce

stra

teg

ies.

1.- Preventive Maintenance.

(replacement or programmed

repair)

Set of operations and required care restoring or

replacing an item or its components, at programmed

intervals so that a system can continue to work properly

and does not reach failure

2.- Predictive maintenance.

(search for defects and

errors)

Follow up services of the wear of one or more

components of a vital system through symptomatic

analysis, statistical estimates, or through electronic

means with the objective of proceeding on basis of the

condition found.


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reaches a failure level, which would force us to work as established in the preventive

strategies.

Figure 3.26 shows the usual way in which abnormalities occur which lead to preventive or

prediction maintenance.

Status How did we find out about the defect or

error?

Strategy to apply

Preventive

The system showed diverse and sporadic

abnormalities, but did not loose its performance

quality.

Preventive

Maintenance

We used specialized software, prediction

statistics or both which advised us how soon

would the failure occur

Prediction

Maintenance

Figure 3.32 Preventive maintenance strategies.

Corrective maintenance strategies have their own way of expression according to the type of

system, open or closed, to which they are applied. For example, for closed systems, since

they are hermetic and do not inform the system to which they belong what is happening

within them, like temperature, or pressure controls, etc, which have stuck indicators but show

a good reading. For these cases, a thorough investigation or detection is required. (See table

3.27).

Status How did we find out about the failure? Strategy to apply

Corrective

The CA voltmeter showed the delivery tension

outside of tolerance limits.

Corrective Maintenance

It was necessary to detect it through a physical

inspection of the voltmeter.

Detection Maintenance

Figure 3.33. Corrective maintenance strategies.

3.6 RCMII IN CONSERVATION.

John Moubray mentions in his book “Maintenance centered on Reliability”, that in 1950, at world

level, commercial aviation had registered over 60 catastrophic accidents per million flights, and that

66 % of these were caused by equipment failure, in spite of over-maintenance given to the airplanes,

which, sometimes, was also the cause of failures. The seriousness of the problem resulted in highly

trained experts analyzing the causes of these failures. Among these Experts, the Swedish PhD

Walodi Weibull (1877-1979) presented, in 1951, to the American Society of Mechanical Engineers


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(ASME), seven case studies using the “Weibull Distribution”. This technique is used to find the

distribution of failures in a system we want to control.

USA’s Air Transport Association studied this problem during two decades since the loss of human life

in the accidents was very painful and important to the future of aerial navigation at world level.

Therefore, they decided to sponsor groups of specialists which were called Maintenance Steering

Groups (MSG).

Since 1951, Japanese Genichi Taguchi (1924) introduced a methodology to apply statistics to

improve the quality of products since its design, “Robust Design”. This resulted in improvements in

the production process, delivery to clients, and two important aspects of the product, such as its

maintainability and its reliability, characteristics.

In 1961, the Japanese engineer Shigeo Shingo (1909-1990) started developing the Baka-Yoke

Systems, (fool proof), name which was later changed to the present known Poka-Yoke (error proof).

The Poka-Yoke Systems detect events through switches sensitive to light, to pressure, photoelectric,

thermostats, etc. They intervene in a process regulation through an alarm for the operator, or

automatically stopping the process, or both.

We can verify that all these ideas and works that started developing since 1950,have achieved an

increase in human safety in the use of dangerous products (airplanes, transports, tools, ocean

vessels, arms etcetera). They have also aided in clarifying the industrial conservation philosophy.

It is our opinion that the British scientist, John Moubray, with his RCMII

development, has provided revolutionary ideas for applying reliability concepts in the

manufacturing industry. These ideas have served as basis for the advanced thought

we have seen in the last four or five years. We have seen that the most outstanding

strategy, due its versatility and quality assurance for the items where it is applied, is

the Prediction strategy, as we will see next.

The strategy currently called prediction maintenance uses two branches of human knowledge,

Prediction and Condition. Let us analyze each of them.

a) Prediction: It is the action or effect of predicting, with scientific basis, something that will

happen during an item’s operation.

b) Condition: are the events that intervene, positively or negatively, on the prediction about

the operation of an item..

Remember that the search for an equilibrium between Action and ¨Reaction in a system is done

through the application of Prediction Maintenance. This provides the opportunity of performing any

type of Preventive Maintenance, with which we have a closer contact and is based in having

redundant equipment or circuits, appropriate alarm systems, and advanced technology test tools This

is the most reliable of the maintenance strategies.

John Mitchell Moubray

(1949 – 2004)

John Mitchell Moubray

(1949 – 2004)


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To understand the scope of Predictive Maintenance we must keep in mind the following glossary:

GLOSSARY

Conservation. To insure the physical preservation of a system and to maintain the quality of

its product during its useful life cycle.

Defect. Disorder in a system caused by its comprising matter, and influenced by its

environment.

Error. Disorder in a system caused involuntarily by man.

Entropy. Measurement of the disorder in a system.

Status. A system’s relative situation in reference to the quality of the service it is

providing.

Preventive status. When the system is fulfilling its design parameters.

Corrective status. When a system reaches failure.

Failure. The end of the ability of a system to perform a required function, causing

economic losses..

Catastrophic failure. The end of the ability of a system to perform a required function which causes

the loss of human life.

Homeostasis.

Peculiar characteristic of self regulated systems which consists of being able

to keep on a dynamic equilibrium status, within certain limits, changing some

internal structure parameters.

Complaint. Claim against supplier done by users of a system which does not meet

promised quality.

We can historically verify the spectacular increase in the importance of industrial machinery

throughout the years since in 1880, only 10% of production was machine manufactured, and the

remaining 90% was obtained through labor. Currently over 95% of production is done through

machines, which are increasingly more rapid and exact. To attend modern machinery, we are

required to use many diagnosis devices, and analysis techniques for vibrations, temperature,

continuous and alternating current, friction, balancing, etcetera. We need experts in the usage of

diagnosis tools, as well as in the operation and functioning of the machines and systems to be taken

care of. We should always keep in mind that all of this should be based in the employment of the

correct maintenance strategy, which according to what we have analyzed so far, it is predictive

maintenance strategy. This strategy is currently used every day in first level industries with the

application of the criteria used by RCMII (Reliability Centered Maintenance).

LACI_ing_03_CHAPTER Industrial Conservation and Reliability_v160411

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