CH-2,3&4 Maintenance (1).pptx

Chapter 2: Fundamental Theories of Damages
Chapter 3: Typical Damages of Machine Parts
Chapter 4: Determination of the State of Damage
Maintenance and Installation
of Machinery (MEng - 5231)

Chapter 2: Fundamental Theories of
Damages

 Machines fail for a variety of reasons. Likewise, not all failures are
the same.
 The term "machinery failure" or "malfunction" usually implies that
the machine has stopped functioning the way in which it was
intended or designed. This is referred to as “loss of usefulness” of
the machine or component.
 This loss of usefulness (called failure modes) is broken down into
three main categories:
- Obsolescence,
- Surface degradation and
- Accidents.
Of these three, surface degradation of machine parts results in the
machine’s loss of usefulness in the vast majority of cases. Surface
degradation is comprised mainly of corrosion and mechanical wear.

• Corrosion of machine parts is quite common,
especially for those with water-contamination
issues.
• Water not only rusts iron surfaces, but it can also
increase the oil’s oxidation rate, leading to an
acidic environment within the component.
• Acids can also be formed as byproducts of
reactions between certain additives in the oil and
water. Product contamination through seals can
create caustic environments and corrosive wear as
well.

• Mechanical wear occurs when machine surfaces mechanically
wearing against each other. Abrasive wear is a method in which
particle contamination causes the majority of the wear.

Identifying Root Causes of Machinery Damage with
Condition Monitoring
Generally, eight mechanisms lead to component failures in industrial
machinery.
Those are: 1. Abrasion, 2. Corrosion, 3. Fatigue, 4. Boundary
lubrication, 5. Deposition, 6. Erosion, 7. Cavitations and 8. Electrical
discharge.
These mechanisms are driven by various forces, reactive agents, the
environment, temperature and time as well.

Failure Mechanisms
Four wear mechanisms are commonly associated with the majority
of root causes that lead to component failures of industrial machinery:
abrasion, corrosion, fatigue and boundary lubrication. The latter is
related to adhesion and other sliding wear modes.
Abrasion Wear:- Abrasive wear is usually a result of three-body
cutting wear caused by dust contamination of the lubricating oil
compartment. Dust, which is much harder than steel, gets trapped at a
nip point between two moving surfaces.
Abrasion involves localized friction, which produces high-frequency
stress waves that propagate short distances through metals.

• Abrasive wear particles look like the cuttings often
found on the shop floor under a lathe. Sometimes
these particles are described as ribbons. Wear
particle analysis (WPA),

Corrosion Wear
• Corrosion is a chemical reaction that is accelerated by temperature.
The Arrhenius rate rule suggests that chemical reaction rates double
with each increase in temperature of 10 degrees c. Corrosion of metal
surfaces tends to be somewhat self-limiting because metal oxide
forms on surfaces to a finite depth. Oxide layers are very soft and
rub away easily. Rubbing exposes underlying metal and permits
deeper penetration of oxidation in the presence of oxidizing corrosive
media. Corrosive wear is typically caused by moisture or another
corrosive liquid/gas.

Fatigue wear
• Fatigue wear is a consequence of subsurface cracking,
which is caused by cumulative rolling contact loading of
rollers, races and pitch lines of gear teeth.
• Fatigue is a work-hardening process during which
dislocations migrate along slip planes through a metallic
crystalline morphology. Eventually, the metallic
hardening progresses to subsurface cracks accompanied
by acoustic emissions like miniature earthquakes.

Boundary Lubrication (Adhesion)
• Boundary lubrication is a lubrication regime/system in which
loads are transferred by metal-to-metal contact. For most machine
designs, this is abnormal because preferred lubrication methods
provide a lubricant film between load-bearing surfaces.
• Inadequate lubrication results in boundary lubrication due to one
of four reasons:
- no lubricant,
- low viscosity,
- excessive loading or
- slow speed (or a combination of these).

• In addition to the four principal mechanisms
mentioned previously, four other mechanisms contribute
to component failures in industrial machinery. These
four modes are not as pervasive/universal as abrasion,
corrosion, fatigue and boundary wear, yet in particular
applications,
• material deposition,
• surface erosion,
• cavitation and
• electrical discharge can be critically important.

Damage, its Causes and Consequences
Damage: In the sense of rehabilitation, damage is the condition that is inherent or
to be expected in view of the impermissible impairment/loss of functionality.
Wear:-Depletion/reduction of the wear reserve results from mechanical, physical,
chemical, biological and/or bio-chemical influences.
Wear reserve:- Reserve for the possible fulfillment of its function under defined
conditions, which a unit being reviewed inherently possesses on the basis of
manufacture, or as a result of damage elimination.
Damage can cause due to the following factors
Leakiness
Flow Obstacles
Positional Deviations
Mechanical Wear
Corrosion
Deformation
Cracks, shaft or Pipe Breaks, deform or Collapse

Leakiness:
• Leaks are present when water obviously enters or leaves or
when a test for leaks is not successful.
• Leaks can occur with or without recognizable other
damage in;
 Pipe joints or component or structural joints;
 Pipes or pipe walling or shaft and die/hole;
 Connections to pipes;
 As other damages that leaks have occurred, such as cracks,
fragments, pipe breaks and collapse or can lead to these
consequences sooner or later depending on the extent of the
damage and the further development of the damage.

Flow Obstacles:
• Flow obstacles are objects or materials lying in the
cross section of the shaft/pipe, which project into
it or cross through it in such a manner that the
cross section required for a proper flow of the
sewage is no longer completely available.
• Typical flow obstacles often found in practice are:
 Hardened depositing;
 Incrustation;
 Projection flow obstacles;
 Root growth;

Positional Deviations:
• Positional deviation is understood to be the unplanned
deviation of sewers/drains and structures from a
nominal position determined by planning and/or by the
situation during construction and installation.
• With shaft or sewers, one differentiates the positional
deviation between:
Vertical direction (e.g. displacement);
Horizontal direction
Longitudinal direction
• Positional deviations are permitted only within the
scope of the tolerances set by the contracting party or
the standards, guidelines and working sheets

Mechanical Wear:
• Wear is the continuing loss of material from the surface of a
solid body due to mechanical action, i.e. contact and relative
movement of a solid, fluid or gaseous counter body.
• In general usage, the term "wear" is used for the process of
attrition as also for its consequences. In order to distinguish them,
they can be used for the process the term "wear process" and for the
consequences the terms "wear manifestation" or "wear variable".
• "Wear manifestations" and "wear variables" are "wear
characteristics" which apply for describing the occurrence of the
wear.
• The material removed by the wear process is designated as fines.

Corrosion:
Corrosion is understood as the reaction of a material with its environment,
which causes a measurable change in the material (corrosion manifestation)
and which can lead to the impairment of the function of a component or a
complete system (corrosion damage).
• The extent of the corrosion manifestation depends primarily on:
 The aggressiveness of the corrosion medium; as well as
 The available materials
 Unalloyed or low-alloy metallic materials for sewer systems must usually receive
internal and external corrosion protection specifies corrosion protection in the form of
hot galvanizing and/or a plastomer coating for steel materials.
• As regards the types of corrosion and their manifestation distinguished between:
 Corrosion without mechanical stressing,
 Corrosion with additional mechanical stressing.

Deformation:
"Rigid shafts and pipes are those in which the loading does not produce any
appreciable deformation and therefore has no effect on pressure
distribution."
• "Flexible pipes are those whose deformation considerably influences the
loading and pressure distribution as the soil is part of the bearing system."
• It is to be noted that according to the above definitions, the allocation as
a rigid or a flexible shafts or pipe must always be seen in connection with
the stiffness of the machine parts. Thus this deals with a classification of the
whole system of shafts rigidity and parts stiffness and not with a general
evaluation of the shaft rigidity.

Repair: - Repair is understood to be measures to rectify local damages.
• These repair processes include:
 Restoration;
 Injection processes;
 Sealing processes.
• Repairs from outside are carried out to manhole structures as well as to
the sewer itself. They require, among others the digging of an excavation.
Cleaning:
It is carried out for removing deposits within the scope of regular maintenance, in
order to maintain free flow throughout the whole cross section and to prevent the
appearance of smells and gases caused by fouling processes and the creation of
biogenic sulphuric acid corrosion; for the removal of blockage; and as a preparatory
measure for an inspection of the sewer.

Chapter 3: Typical Damages of
Machine Parts

• Component failure / Failure modes: - Failure causes are defects in
design, process, quality, or part application, which are the underlying cause
of a failure or which initiate a process which leads to failure. Where failure
depends on the user of the product or process, then human error must be
considered.
• A part failure mode is the way in which a component fails "functionally"
on component level. Often a part has only a few failure modes. Thus a relay
may fail to open or close contacts on demand.
• The failure mechanism that caused this can be of many different kinds,
and often multiple factors play a role at the same time. They include
corrosion, welding of contacts due to an abnormal electric current, return
spring fatigue failure, unintended command failure, dust accumulation and
blockage of mechanism, etc.

• Seldom only one cause (hazard) can be identified that
creates system failures. The real root causes can in
theory in most cases be traced back to some kind of
human error, e.g. design failure, operational errors,
management failures, maintenance induced failures,
specification failures, etc.
• This manual describes the various hazards of
mechanical motion and presents some techniques for
protecting workers from these hazards. Generally,
where mechanical hazards occur, the hazards created
by different kinds of motions and the requirements for
effective safeguards.
• Where Mechanical Hazards Occur
Dangerous moving parts in three basic areas require
safeguarding:

• Where Mechanical Hazards Occur at the moving parts
in three basic areas require safeguarding:
The point of operation: that point where work is
performed on the material, such as cutting, shaping,
boring, or forming of stock.
Power transmission apparatus: all components of the
mechanical system which transmit energy to the part of
the machine performing the work. These components
include flywheels, pulleys, belts, connecting rods,
couplings, cams, spindles, chains, cranks, and gears.
Other moving parts: all parts of the machine which
move while the machine is working.
• These can include reciprocating, rotating, and
transverse moving parts, as well as feed mechanisms
and auxiliary parts of the machine.

The basic types of hazardous mechanical motions that causes damages are:
Motions
 Rotating (including in-running nip points)
 Reciprocating
 Transversing
Motions: - Rotating motion can be dangerous; even smooth, slowly rotating shafts
can grip clothing, and through mere skin contact force an arm or hand into a
dangerous position. Injuries due to contact with rotating parts can be severe.
Actions Autonomous
 Cutting
 Punching
 Shearing
 Bending

Types of failure causes
Mechanical failure
• Some types of mechanical failure mechanisms are:
excessive deflection, buckling, ductile fracture,
brittle fracture, impact, creep, relaxation, thermal
shock, wear, corrosion, stress corrosion cracking, and
various types of fatigue
• Over time, as more is understood about a failure, the
failure cause evolves from a description of symptoms
and outcomes (that is, effects) to a systematic and
relatively abstract model of how, when, and why the
failure comes about (that is, causes).

Chapter 4: Determination of the
State of Damage

Failure Scenario or state
• A scenario is the complete identified possible sequence
and combination of events, failures (failure modes),
conditions, system states, leading to an end (failure)
system state. It starts from causes (if known) leading to
one particular end effect (the system failure condition).
• A failure scenario is for a system the same as the failure
mechanism is for a component. Both result in a failure
mode (state) of the system / component.

• Rather than the simple description of symptoms that
many product users or process participants might use, the
term failure scenario / mechanism refers to a rather
complete description, including the
- preconditions under which failure occurs,
- How the thing was being used,
- Proximate and ultimate/final causes (if known),
and
- Any subsidiary or resulting failures that result.

A. More on Hazard Identification Techniques
• One example of a system to proactively identify
hazards is to establish groups to identify safety hazards
by following five simple steps:
•
• Identify potential hazards that could threaten the
safety of your employees, customers, passengers,
company facilities, company assets, customer
property.
• Rank the severity of hazards.
• Identify current control measures.
• Evaluate the effectiveness of each control measure.
• Identify additional control measures.

B. Root Cause Analysis
• The most basic reason for an undesirable condition or problem
which, if eliminated or corrected, would have prevented it from
existing or occurring.
Root Cause is the fundamental breakdown or failure of a process which,
when resolved, prevents a recurrence of the problem
Root Cause Analysis is a method that is used to address a problem
or non-conformance, in order to get to the “root cause” of the
problem.
• Traditional applications of Root Cause Analysis
–Resolution of customer complaints and returns.
–Disposition of non-conforming material (Scrap and Repair) via
the Material Review process.
–Corrective action plans resulting from internal and customer
audits.

There are many analytical methods and tools
available for determining root causes to unwanted
occurrences and problems.
Useful Tools for Determining Root Cause
The “5 Whys” Model or Brainstorming
Fishbone Diagrams
Failure Modes Effects Analysis (FMEA)
Taproot Analysis
Pareto chart, Scatter diagram, Run chart, Histogram,
Control chart, Flowchart, Tree diagram, Design of
experiments.

33 Page 33
1. “5 Whys” Model or Brainstorming
1. As a group, write down the problem
and describe it completely.
2. Ask why the problem occurs and
write down the answer.
3. If the answer you just provided
doesn't identify the root cause of the
problem that you documented in step
1, ask why again and write that
answer down.
4. Return to step 3 until the team is in
agreement that the problem's root
cause has been identified.
– This process may take fewer or more
than five whys.
The “5 Whys”

“5 Why” Example
Event: You are operating a tug that is towing a Gulfstream IV. Suddenly, the tug becomes
uncontrollable, which causes the tow hitch to break and extensive damage to the aircraft nose
gear results.
1. Why did the aircraft become damaged?
- Because the tow bar hit the aircraft.
2. Why did the tow bar hit the aircraft?
- Because the tow hitch broke.
3. Why did the tow hitch break?
- Because the tug was uncontrollable.
4. Why did the tug become uncontrollable?
- Because the aircraft was being pulled with a tug rated below 10K draw bar pull.
5. Why was a tug with a rating that was below minimum being used?
- Because the tug operator was unaware of the guidance.
6. Why wasn’t the tug operator aware of the guidance?
- Because the tug operator was new and had not been trained on the guidance.
- Because the operator was unaware of the guidance.
7. Why hadn’t the employee been trained?
- Because there are no procedures for processing new employees.

Brainstorming is a process in which a group
quickly generates as many ideas as it can on a
particular problem and/or subject.
• Brainstorming is useful because it can help a
group of people utilize its collective brainpower to
generate many ideas in a short period of time. It
stimulates creativity and promotes involvement and
participation.

2. Fishbone Diagram:- A Useful Tool
• Fishbone diagrams help to identify the “6Ms”
(potential causes) that may have contributed to the
undesirable/unwanted condition or problem.
Man (People)
Machines
Mother Nature (Environment)
Methods
Materials
Measurements

37 Page 37
Root Cause Analysis: Fishbone Diagram
Aircraft is
damaged
1. Draw the diagram with the issue to be studied as the fish “head.”

38 Page 38
Aircraft is
damaged
2. Label each “bone” of the fish.
Man
Machine
Methods
Mother
Nature
Materials Measures

39 Page 39
Aircraft is
Damaged
3. Through brainstorming, identify factors in each category that
could affect the undesirable occurrence.
Man
Machine
Methods
Mother
Nature
Materials Measures
Gauge
Tug
Maintenance
Tools
Rain
Training
Driving
Tow Bar
Behavior
Manuals
Wind
Speed

40 Page 40
4. Upon completion of the fishbone, analyze the
results.
5. Then, list the items that were identified in priority
order.
This brainstorming technique, when properly
applied, can be helpful in determining a root
cause to an undesirable condition or problem.

Fishbone Method is
Great brainstorming/thinking tool
Focuses on the cause, not the symptoms.
Identifies areas that may need further
investigation.
Process can be enhanced/improved by
adding “5 whys.”

Pareto chart, Scatter diagram, Run chart, Histogram, Control chart,
Flowchart, Tree diagram, Design of experiments.

CH-2,3&4 Maintenance (1).pptx

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