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Reliability ofEngineered Systems
By
Dr. Edwin Vijay Kumar
Assistant General Manager (Technical Services)
VIZAG STEEL
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Lecture Outline
Engineer Society Expectations
Why Reliability is important?
How is Reliability affected?
Reliability Degradation Maintenance
Strategies for Reliability
Condition Monitoring Reliability Relation
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Expectations of Society fromEngineering Fraternity
Less struggle more comfort
Health
Clean environment
Secure world
Longer & Happy life
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Business Values
Essentially, there are three kinds ofbusiness values to look for whenconsidering Engineered Systems:
Making Human Life Comfortable
Making more money
Saving money
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Examples:
Making Life Comfortable :
Driver less car
Making More Money:
Mobile Communication systems
Saving Money:Energy efficient Home Appliances
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Backbone for achieving BusinessValues
Technology:
User Friendly
Effectiveness:Doing the right task, completingactivities and achieving goals.
Reliability:
Delivering Intended Functionalitywhen
needed
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Engineering Managers Role
Managing engineering assets to deliver
maximum outputwith effectiveuse of
resources with assured reliability
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Constraints to Engineering Manager
Uncertaintyin assets performance
Shortageof resources
Assets degradation
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Cost of Unreliability
Industry Specific
Product Specific
User Specific
Location Specific
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Degradation Asset/EquipmentPerformance Characteristic
t1 tn
Stressor
tf
1.0
Minimal Repair
UnacceptablePerformance
Degradationpattern
Time (Age/Usage)
Performance
Major Overhaul
ReducedPerformance
0
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Performance Failure Characteristic
Pattern 2
Pattern 3Alert Level
Alarm Level
Time (Age/ Monitoring period)
IndicatorLevel(Normalized)
Operating Level
t11t0
1t1t0
Degradation pattern 1
1.0Reliability
P-F Interval
P-F Interval
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Classical Belief on Equipment Failures
All equipment fail after using forsome time.
Early replacement of componentsprevent failures.
Regular Inspection/Maintenanceactivities help to identify impending
failures.
More maintenance - Less failures.
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Basis for development of RCM
Classification of Component Failures
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Stanley NowlanHoward Heap
By 1985 it was a well established system & applied to nuclear stations.
History of RCM
RCM developed in the airlineindustry during the late 60s
-------MSG-1 applied to BOEING 747
------MSG-2 applied to Lockheed 1011,
Douglas DC 10, Airbus A-300, Concorde.
Nowlan & Heaps 1978 book, Reliabi l i ty-Centered Maintenance, showed that a
strong correlation between age and failure rate did not exist, thus the basic
premise of time-based preventive maintenance was false for the majority of
equipment.In 1978 for aviation industry
1970s
-----RCM--Stanley Nowlan & Howard Heap
[MSG-3 applied to BOEING 757 & 767]
1990s RCM-II --- Applied in more than 1000 industries
in 50 countries
Pioneers
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RCMs foundation lies on
Failure Mode Identification
Failure Mode Progression Monitoring
Root Cause analysis of Failure
Elimination/Mitigation of Failure Mode
Review of Maintenance Strategy
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RCM Definition
RCM is an analytical process used to
determine the maintenance
requirements of plant equipment intheir operating context.
Reliability is the probability that an asset
will perform its intended function for aspecified period of time under specified
operating conditions.
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Location
Temperature
Salinity
Humidity
SpeedAcceleration
Pressure
Depth
Altitude
Operating Context:
Systems operate in environment consisting of
Atmosphere
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Operating Context Influence on Motor Failures
Failure ModeFailure Causes
Motor A ( Indoor) Motor B ( Cellar)
1 Bearing Seizure Lack of LubricantBearing Defect
Lack of Lubricant
Ingress of water
Bearing defect
High humidity
2 Winding burnt Over loadInsulation damage
Under voltage
Fluctuating load
Over load
Insulation damage
Under voltage
Water logging
Damp surroundings
High ambient Temperature
Corrosive vapors
Fluctuating load3 Coupling Failure
(Rubber Bushes)Worn out
Fatigue failureWorn out
Fatigue Failure
Chemical action
Thermal stresses
High humidity
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Some Frequently asked questions
Is there any cost incurred if Run-to-Failuremaintenance ispracticed on a certain equipment?
What is the cost of performing Preventive Maintenanceonan equipment?
What type of condition monitoring technologies are
available? How much do they cost to install and maintain?What is the cost of Predictive Maintenance?
Will it really improve the bottom line result of ProactiveMaintenance?
The general questions above dont have simple
answers. Each of these general questions need to be
answered individually with reference to criticality of
the equipment...
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Maxim
OLD
Maintenance is about preservingphysical assets
NEW
Maintenance is about preserving thefunctions the of assets
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Safety and environment are to be given utmostimportance in defining function
Crux of RCM Strategy
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Q.1 What is a Function?
Any physical asset is put into service because it is
intended to do something.
So it follows that when we maintain an equipment, the
state must be preserved to continue its intended
function.
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Q.2 In what ways does it fail to fulfill itsfunctions? (Functional Failure)
Q.2 What is Functional Failure?
Functional failure : A functional
failure is the inability of an itemto fulfill a function to a standard
of performance acceptable to theuser.
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RCM divides functional failures in to two
categories
evident failures
hidden failures
Evident failure: a failure that, by itself, becomes
obvious to the crew or operator while they are
performing their normal duties.
Hidden failure: a failure that is not evident to the
crew or operator while performing normal duties
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Potential Failure
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Q.3 What causes its functional failure?
(Failure Modes )
Q.3 What are Failure Modes?
FAILURE MODES: is a specific physical condition
that causes a functional failure.
Failure modes represent the primary focus of the
RCM analysis.
RCM analysis seeks to identify maintenance tasks
that will prevent the consequences that result when
failure modes are allowed to occur.
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CMMS
Faithful recording of data
Technical manuals
OEM recommendations
Hands - on experience
History data
Documentation MTBF data from OEM.(for new eqpt. )
Sources for identifying Failure Modes:
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RCM FMEA
Failure modes are to be analyzed down to a level where the root cause is found
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Q.4 What happens when each failureoccurs ? (Failure Effects)
Q.4 What are Failure Effects?
Failure effect: is the impact that a functional
failure has on the item under analysis, the
surrounding items, and the functional
capability of the end item.
A failure effect should be described in terms ofphysical damage, including both primary and
secondary damages that may occur.
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Q.5 In what way does each failure matter ?(Failure Consequences)
Q.5 What are Failure Consequences?
Failure consequences stem from functional
failures. They are of f ive categor ies:
Safety
Environmental
Operational
EconomicNo effect
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Q.6 What are Proactive Tasks?
Task selection is the last major step in the
RCM analysis process. It looks at each
output from the task evaluation process
andallows selection of the optionthat best
reduces the probability of failure
consequences to an acceptable level.
Applicability and Effectiveness:
A maintenance task to be selected and must satisfy two criteria:
It must be Technically Feasible and must be Worth Doing
Q.6 What can be done to predict or preventeach failure ? (Proactive Tasks)
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They embrace what is traditionally known asPredictive or Preventive Maintenance
RCM uses the terms
proactive tasks :Tasks undertaken before failureoccurs, in order to prevent the item from getting intoa failed state.
scheduled restoration,scheduled discard and
on-condition maintenanceFailure Finding Tasks
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Q.7 What should be done if a suitable proactive task
cannot be found ? (Default Actions)
Q.7 What are Default Actions?
Default actions:
These deal with the failed state, and
are chosen when it is not possibleto identify an effective proactivetask. Default actions includeredesign and run-to-failure.
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Question: Proactive MaintenanceWill it really improve the bottom line result of Proactive Maintenance?
Is it that a symptom treated over and over again? Thesame equipment keeps breaking down andreplaced/maintained?
How much money it costs (Loss) due to treating justthe symptom - and not the root cause - of theproblem?
These questions on proactive maintenance are toughto answer, so lets just table them (we will get back to
them) and take a look at Predictive Maintenancetechnologies.
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Predictive Maintenance Data
What data needs to be collected on each piece ofequipment? How to collect this data? What kind ofhardware it needs?
More data is better. Do not fall into this trap!
Collecting too much data costs money, obscures theproblem, & is a pain.
What data would provide a quick indication of thecondition of the equipment?
Just as a doctor takes a patients temperature and pulse
to get a quick indication of that patients health, whatwould give a quick indication of the health of anequipment?
The answer to this question depends on the type ofequipment complexity, criticality and operating context
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Some Predictive Maintenance Technologies
Vibration Analysis
Bearing Shock pulse analysis
Laser Alignment & ShaftBalancing
Thermography
Ultrasonic Testing
Motor Current SignatureAnalysis
Oil Analysis
Wear Debris Analysis
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Questions Please
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Thanks
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