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Overview of

Condition Based Maintenance

Presented By:

Jeff Banks

Research Engineer

The Applied Research Laboratory at

The Pennsylvania State University

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RCM and CBM

• Reliability Centered Maintenance (RCM): A process to determine

the optimum combination of maintenance types for any application

or system.

– One of the maintenance types is CBM.

• Condition Based Maintenance (CBM): A maintenance

methodology that utilizes sensors to assess the health of the

system. The health information drives the maintenance activities.

– In a CBM environment, operating platforms, embedded sensors,

inspections, and other triggering events determine when

restorative maintenance tasks are required based on evidence

of need.

– Predictive Maintenance (PdM) is a term widely used in industry

that is synonymous with CBM.

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Human Health Care

• Medical physicians use non-

intrusive techniques and

technologies to determine the health

of their patients before prescribing

the best course of medical treatment

(human maintenance).

• Conventional Techniques:

– Heart Rate

– Blood Pressure

– Blood Tests

• Advanced Technologies:

– X-ray imaging

– MRI (magnetic resonance imaging)

– EKG or ECG (electrocardiogram)

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Terminology

• Diagnostic Capability: the ability to detect and isolate a failure to a

specific platform component or system.

• Predictive Capability: the ability to detect and isolate a fault to a specific

platform component or system while the system is still functional.

• Prognostic Capability: the ability to detect and isolate a fault to a

specific platform component or system while the system is still functional

and the ability to determine the remaining useful life (RUL) until failure.

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Condition Based

Maintenance1. Condition measurement consists of non-invasive data and

information collection events that define the systems operating condition.

– Measurements may be made continuously on-platform from installed transducers and sensors.

– Or periodically at-platform with portable data acquisition systems with transducers and sensors.

2. Condition monitoring and (health) assessment is the individual and collective comparison of condition measurements, value versus time trends to arrive at an appraisal of current condition, identify and analyze defects (diagnostic), project estimated future condition (predictive) and determine remaining useful life (prognostics).

– Condition assessment is also directed at detecting and identifying degradation mechanisms (root cause of failure).

3. Repair and Maintenance actions based on condition monitoring and health assessment — the objective evidence of need.

Reference: OPERATING EQUIPMENT ASSET MANAGEMENT YOUR 21ST CENTURY COMPETITIVE NECESSITY, By John S. Mitchell

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CBM: Expectations

CBM can provide:• Warn of many mechanical problems in time to minimize:

– unexpected failure

– the risk and consequences of collateral damage

– adverse impact on safety, operations, and the environment

• Increase equipment utilization and life:

– minimize disruption to mission and schedule

• Reduce maintenance costs – both parts and labor:

– reduce requirements for spare parts

• Allow safe elimination of a significant amount of PM:

– predictive maintenance should be less time and labor intensive

CBM can not provide:• Elimination of defects and problems, or stop machines from

deteriorating.

– material wear is an accepted consequence of running equipment

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P-F Interval

“The interval between the occurrence of a potential failure and its decay into a functional failure”

Reliability-centred Maintenace , by John Moubray

Point where

failure starts

to occur

Vibration

Analysis

Detection

Oil

Analysis

DetectionAudible

Noise

Detection

Temperature

Detection

Conditio

n

Time Functional

Failure

If the P-F interval is too short,

PT&I technology may not be effective.

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Criteria for Applying CBM

Preliminary Questions:

1. Does the technology monitor a specific critical failure mode? RCM FMECA

2. Is it probable that this failure mode will occur during the lifetime of the equipment? RCM Criticality

Application Criteria:• Changes in specific equipment parameters

(i.e. operating performance, temperature, vibration) must correlate to corresponding failure mode.

• The parameter must be accurately and consistently measurable.

• There must be enough time between potential and functional failure to allow for corrective action.

• The monitoring interval must be shorter then the P-F interval.

– Multiple monitoring points during the P-F interval increases confidence in the diagnosis.

Applying RCM Principles in the Selection of CBM-Enabling Technologies, L&FP November 2000, Kenneth S. Jacobs

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CBM Capability Metrics

Advanced Diagnostics/Predictive: Estimate

the probabilistic distribution of RUL.

Predictive /Prognostics: Estimate the

expected RUL for an individual asset.

Diagnostics/Health Assessment: Determine

current health of system or subcomponents

through diagnostics.

Condition Monitoring/State Detection:

Compare features against expected values or

operational limits. Anomaly detection.

Reduced-Order or

Estimation Models

Applicability

Signal-Based Anomaly Detection

Data-Driven Models

Incre

asin

g c

om

ple

xity a

nd c

ost

Predictive

Prognostics

1

2

3

4

The required level of capability depends upon the technical

problem, the desired outcome and economics

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Aircraft Inspection

• Nondestructive testing is used extensively during the manufacturing of aircraft.

• NDT is also used to find cracks and corrosion damage during operation of the aircraft.

• A fatigue crack that started at the site of a lightning strike is shown below.

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Most basic and common

inspection method.

Tools include

fiberscopes,

borescopes, magnifying

glasses and mirrors.

Robotic crawlers permit

observation in hazardous or

tight areas, such as air

ducts, reactors, pipelines.

Portable video inspection

unit with zoom allows

inspection of large tanks

and vessels, railroad tank

cars, sewer lines.

Visual Inspection

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• A liquid with high surface wetting characteristics is applied to

the surface of the part and allowed time to seep into surface

defects.

• The excess liquid is removed from the surface of the part.

• A developer (powder) is applied to pull the trapped

penetrant out of the defect and spread it on the surface,

where it can be seen.

• Visual inspection is the final step in the process. The

penetrant used is often loaded with a fluorescent dye

and the inspection is done under UV light to increase

test sensitivity.

Liquid Penetrant Inspection

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Eddy Current Testing

• Eddy current inspection is one of several NDT methods that use the principal of “electromagnetism” as the basis for conducting examinations.

• Eddy currents are created through a process called electromagnetic induction.– When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around

the conductor.

• If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor.

• Eddy currents are induced electrical currents that flow in a circular path.

– They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right.

ConductiveMaterial

Coil'sMagnetic Field

Eddy

Currents

Eddy Current'sMagnetic Field

AC

Source

Volt

Meter

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Eddy Current Testing

• Eddy current testing is particularly well suited for detecting surface cracks but

can also be used to make electrical conductivity and coating thickness

measurements.

• Here, a small surface probe is scanned over the part surface in an attempt to

detect a crack.

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Acoustic Emission (AE)

• The ‘stress’ wave provides diagnostic information about the system being evaluated.

• This NDE technique is used widely for the testing of pressure vessels and load be.

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Application Example: C-130

Hercules Wing Structure

Project’s Goals/Objectives:• The objective of this program is

to develop and assess the effectiveness of advanced non-destructive evaluation techniques that can be used to quickly and reliably detect cracks in the rainbow fittings of C-130 Hercules aircraft.

– The primary focus is to develop a ground based inspection technology that can be used on a scheduled basis to evaluate the integrity of the aircraft rainbow fitting.

– The long term goal is to evaluate the feasibility of conducting real time embedded diagnostics on the aircraft during flight operations.

Upper and Lower

Rainbow Fittings

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AE Testing at Little Rock AFB

- Upper Rainbow Instrumentation

• 4 AE sensors positioned along

rainbow length

• Wing moved to ‘No Load’ position

• Multiple AE events detected during

first ‘No Load’ cycle

• Large crack detected and

accurately located along rainbow

length

• Additional ‘No Load’ cycles yielded

very limited AE events

AE Sensors

Crack

Position

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Thermography

• Thermal NDT methods involve the measurement or mapping of surface temperatures as heat flows to, from and/or through an object.

• The use of thermal imaging systems allow thermal information to be very rapidly collected over a wide area and in a non-contact mode. Thermal imaging systems are instruments that create pictures of heat flow rather than of light. Thermal imaging is a fast, cost effective way to perform detailed thermal analysis.

• Thermal measurement methods have a wide range of uses. They are used by the police and military for night vision, surveillance, and navigation aid; by the firemen and emergency rescue personnel for fire assessment, and for search and rescue; by the medical profession as a diagnostic tool; and by industry for energy audits, preventative maintenance, processes control and nondestructive testing.

• The basic premise of thermographic NDT is that the flow of heat from the surface of a solid is affected by internal flaws such as disbonds, voids or inclusions.

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Active Thermography

• Active thermography is a dynamic measurement method (thermal wave analysis).

• The wave is excited sinusoidally with halogen lamps, laser, or hot-air pistols on the surface of the tested component.

• It propagates wavelike in the testing object and is reflected at boundaries due to sudden changes in temperature conductivity and thermal impedance of the material.

Information provided by http://www.edevis.de/profile/profile_en.php

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Aircraft Fuselage Inspection for

Corrosion

Slide provided by Sandia National Laboratory

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Shearography and Holography

• Shearography and Holography systems image and measure test object surface profile changes down to 1 nanometer by analyzing the difference between two shifted or ‘sheared’ images.

• Subsurface defects cause local changes in the surface profile when the test part is subjected to a change in applied load. Typically these loads are in the form of heat, cold, pressure, vacuum, vibration or electromagnetic energy.

• These changes in surface profile reveal subsurface defects such as: – Disbonds, Unbonds, Delamination

– Core damage, Core splice disbonds, crushed core

– Impact Damage, Heat Damage

– Water Ingress

• Images are in JPEG, TIFF or other formats and are displayed for operator interpretation or evaluated automatically using ADR (Automatic Defect Recognition software). http://www.laserndt.com/about_02.htm

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Shearography Applications

Shearing distance about 1 mm

NASA SWIFT Satellite BAT Mask

Identification of Poorly

Bonded Tiles

White Light Sheared Image

(No Fault Detection)

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• High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws.

• Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features that reflect sound.

f

plate

crack

0 2 4 6 8 10

initial

pulse

crack

echo

back surface

echo

Oscilloscope, or flaw

detector screen

Ultrasonic Inspection

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Benchmark

Data Sets

Feature

Extraction

DATA-DRIVEN APPROACH

Feature Processing/

Modeling

MODEL-DRIVEN APPROACH

User-

Centric

Interface

Data

AcquisitionAutomated

Reasoning

Data

FusionInformation

Tu

rbin

e E

ng

ine

wit

h S

en

so

rs

Sensors include:

rotation speed,

temperature,

pressure, oil quality

vibration, etc.

Turbine Health Monitoring

Proficy SmartSignal

PREDICTIVE ANALYTICS FOR

AFFORDABLE READINESS

Reliability Based MaintenanceNow Realistically Within Reach

Monitoring

Software

5-10 min

Sampling

Monitor Failure Pattern # xx

- If found, follow Work Template # xx

Monitoring

Software

5-10 min

Sampling

Monitoring

Software

5-10 min

Sampling

Monitoring

Software

5-10 min

Sampling

Monitoring

Software

5-10 min

Sampling

Monitoring

Software

5-10 min

Sampling

Is detecting or predicting failure feasible?

Effects Driven

Optimization

xx

xx

Focusing on the right work

sooner and more effectively

Engineered, Templated, Scalable Turbine Functional Model Example

Easy User Interaction with Normalized Data

Deviations from

Healthy Patterns

“Blue is True”Where Your Data Is

“Green is Good”Where Your Data Should Be

Amps

Vibr

Temp

The SmartSignal DifferenceDynamic Multivariate Empirical Analysis in Near-Real Time

Axial position

Gas pressure Δ

Speed

Alarm Hi

Bearing Temp

Alarm

ConditionAxial position

Single-sensor analysis or equation based models using traditional thresholds &

rules

Early stages of

variation

SmartSignal alerts before

traditional techniques

Normal operation

Few false alarms

Current status, localizes

to problem area

Status details: trends,

compliance, remaining life

Easy User Interaction with Normalized Data

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Summary

• Condition Based Maintenance+ (CBM+): A proactive equipment

maintenance capability enabled by using system health indications to

predict functional failure ahead of the event and take appropriate action.

CBM+ consists of three basic elements:

– RCM Methodology. Reliability Centered Maintenance provides a

rigorous methodology for developing equipment maintenance task

requirements.

– CBM tasks. CBM Tasks are derived from the RCM process to monitor

equipment to identify impending failure and required maintenance

actions.

– Infrastructure. Implementing the infrastructure, consisting of

numerous technologies and enablers, required to make use of sensor-

based maintenance information.