Download - EPRI TR-108935

Infrared Thermography AnomaliesManual TR-108935

Final Report, August 1997

Prepared byEPRI Monitoring & Diagnostic Center#3 Industrial HighwayEddystone, PA 19022

AuthorsS. BradenB. HammakerB. Woyshner

Prepared forElectric Power Research Institute3412 Hillview AvenuePalo Alto, California 94304

EPRI Project ManagerR. PflastererGeneration

Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.

DISCLAIMER OF WARRANTIES AND LIMITATION OFLIABILITIES

THIS REPORT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORKSPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHEREPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTINGON BEHALF OF ANY OF THEM:

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EPRI Monitoring & Diagnostic Center

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Copyright © 1997 Electric Power Research Institute, Inc. All rights reserved.

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REPORT SUMMARY

Infrared thermography (IRT) is non-intrusive diagnostic technique that can play animportant role in predictive maintenance programs. This manual shows how IRT canbe applied in the field to detect anomalies in a wide-range of power plant systems. Thisactivity is part of EPRI’s Plant Maintenance Optimization development efforts underTarget 43, Turbine, Generator and BOP O&M Cost Reduction (1997), and Target 54,Plant Maintenance Optimization (1998), which are intended to help utilities reduce thecost of production by developing and demonstrating cost-effective maintenancemethods.

BackgroundMost of the equipment found in a typical electric generating station exhibits some typeof abnormal thermal pattern prior to failure. IRT is a non-invasive diagnostic techniquethat can detect abnormal thermal patterns by making simultaneous temperaturemeasurements of multiple points on the surface of a piece of equipment. These data aredisplayed as pictures, commonly referred to as thermograms, that can be analyzed inreal-time or stored electronically and analyzed later. Information from thermogramscan be used by electric utilities to plan maintenance and avoid catastrophic equipmentfailures and unscheduled downtime.

ObjectiveTo provide a guide to the use of comparative infrared thermography to monitor thecondition of power plant equipment.

ApproachThe project team drew on the experience of thermographers at EPRI’s Monitoring &Diagnostic Center to produce a manual on the application of IRT to the examination ofpower plant equipment.

ResultsAfter a brief introduction to the technical background IRT, the manual describes howinfrared thermography can be used to detect thermal anomalies in power plantequipment. The thermal anomalies illustrated in this document include stationelectrical applications, rotating equipment applications, transmission and distributionapplications, and performance applications. Some of the cases are analyzedquantitatively, while others are analyzed qualitatively. Most of the cases feature a

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thermal image that is accompanied by a corresponding visual image. An arrowsuperimposed on the visual image allows the reader to match locations on the visualimage with the corresponding locations on the thermal image.

The information contained in this document was acquired while using IRT to identifypotential problems in the field. In each case feedback was received from maintenancepersonnel involved with repair work as to the “as found” condition of the equipment.This feedback helps refine diagnostic technique and should be an integral part ofpreventive maintenance. All detected anomalies should also be reinspected with IRTafter repairs are completed to verify that the problem has been corrected.

EPRI PerspectiveEPRI’s Monitoring & Diagnostic Center was established to demonstrate the value ofdiagnostic monitoring and the importance of networking diagnostics to plantmaintenance, controls, and operations. The Center’s primary objectives are to validate,improve, integrate, and network diagnostic technologies, to develop programguidelines, and to transfer the technologies to the utility industry.

TR-108935

Interest CategoriesFossil steam plant performance optimizationFossil steam plant O&M cost reductionState-of-the-art power plants

Key WordsInfrared thermographyNon-destructive evaluationPredictive maintenance

EPRI Licensed Material

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ABSTRACT

Infrared thermography (IRT) is a non-invasive diagnostic technique that utilizesinfrared sensors to make simultaneous measurements of multiple points on the surfaceof a piece of equipment. Most of the equipment found in a typical electric generatingstation exhibits some type of thermal pattern prior to failure. Infrared thermographyprograms are implemented in generating stations as part of a comprehensive PredictiveMaintenance (PdM) program that involves various types of diagnostic tests. Thismanual, based on experience accumulated at EPRI’s Monitoring & Diagnostic Center,shows how infrared thermography can be applied in the field to a wide range of powerplant applications.


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CONTENTS

1 INTRODUCTION...................................................................................................................... 1-1

2 IRT TECHNICAL BACKGROUND......................................................................................... 2-1

How to Read a Thermal Image................................................................................................ 2-1

Comparative Thermography .................................................................................................... 2-2

A Quantitative Analysis of Thermal Image #1 using Comparative Thermography ............. 2-2

A Qualitative Analysis of Thermal Image #2 using Comparative Thermography ............... 2-4

3 FIELD APPLICATIONS OF IRT.............................................................................................. 3-1

Station Electrical Applications.................................................................................................. 3-1

High Resistance Connection (QT) ...................................................................................... 3-2

Stranded Conductor (QT) .................................................................................................... 3-3

Defective Thermal Overload (QT) ....................................................................................... 3-3

Open Conductor (QT).......................................................................................................... 3-4

Defective Fuse and/or Connection Problem (QT)............................................................... 3-4

480 Volt Bus Bar and Stab Problem (QT) ........................................................................... 3-5

4160 Volt Breaker Disconnect (QT) ................................................................................... 3-5

Defective Current Transformer (QT) ................................................................................... 3-6

Electrical Bus Duct Problem (QT) ....................................................................................... 3-7

Ground Strap Connection (QT) ........................................................................................... 3-8

Rotating Equipment Applications ............................................................................................. 3-9

Motor Filter Problem (QT) .................................................................................................. 3-10

Motor Bearing Problem (QT).............................................................................................. 3-11

Boiler Feed Pump Bearing Problem (QT).......................................................................... 3-12

Motor Stator Winding Short (QT) ....................................................................................... 3-13

Coal Pulverizer Mill Gear Problem (QT)............................................................................ 3-13


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Dry Vacuum Pump Cooling Water Restriction (QT) ......................................................... 3-14

Motor Current Overloading (QT)........................................................................................ 3-15

Vertical Pump Motor Thermal Pattern (QL) ....................................................................... 3-15

Transmission & Distribution Applications .............................................................................. 3-16

High Resistance Connection at Bushing (QT) .................................................................. 3-17

Switchyard Disconnect Switch (QT) ................................................................................. 3-17

Stranded Cable (QT).......................................................................................................... 3-18

Lightning Arrestor & Bushing Anomaly (QT) ..................................................................... 3-18

Load Tap Changer Internal Contact Problem (QT) ........................................................... 3-19

Internal Transformer Problem (QT) ................................................................................... 3-20

Restricted Transformer Cooling Fins (QL) ........................................................................ 3-20

Oil-Filled Circuit Breaker (OCB) Contact Problem (QT) ................................................... 3-21

Transmission Line Fuse Cut-Out (QT).............................................................................. 3-22

Performance Applications ...................................................................................................... 3-23

Main Steam Relief Valve Leak (QL) .................................................................................. 3-24

Defective Steam Trap (QL)................................................................................................ 3-24

Defective Feedwater Heater Relief Valve (QT)................................................................. 3-25

Boiler Air-in-Leakage (QL) ................................................................................................. 3-26

Boiler Insulation Problem (QL)........................................................................................... 3-26

Boiler Tube Restriction (QL) .............................................................................................. 3-27

Boiler Wall Flame Impingement - Top View (QL)............................................................... 3-28

Boiler Wall Flame Impingement - Eye Level View (QL)..................................................... 3-28

Air Infiltration into Vacuum Header (QL)............................................................................ 3-29

Process Header Steam Leak (QL).................................................................................... 3-30

Obstructed Fuel Line (QL) ................................................................................................. 3-31

Coal Bunker Anomaly (QL)................................................................................................ 3-32


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1 INTRODUCTION

EPRI's Monitoring & Diagnostic Center (operated by Maintenance & Diagnostics,Inc.) was established to demonstrate the value of diagnostic monitoring and theimportance of networking diagnostics with plant maintenance, controls andoperations. The Center's primary objectives are to validate, improve, integrate andnetwork diagnostic technologies, to develop program guidelines and to transferthe technologies to the utility industry.

Most of the equipment found in a typical electric generating station exhibits some type ofabnormal thermal pattern prior to failure. Infrared Thermography (IRT) Programs areimplemented in generating stations as part of a comprehensive Predictive Maintenance(PdM) Program that involves various types of diagnostic tests. IRT is a non-intrusive,diagnostic technique that utilizes infrared sensors to make simultaneous temperaturemeasurements of multiple points on the surface of a piece of equipment (a target). IRT isnot an “x-ray” technique and will not make measurements through an object. Themeasurements of the target surface are taken from a distance. It is not necessary to makephysical contact with the target. The data is displayed in the form of a picture. Thesepictures, commonly referred to as thermograms, can be analyzed in the field (real-time),or stored electronically and analyzed at a later time. The thermograms providepredictive information concerning the operating condition of a piece of equipment. Thisinformation is used for operations and maintenance planning. It affords an organizationthe opportunity to take appropriate action to avoid an incident that would result incatastrophic equipment failure, unscheduled downtime and all of the associated costs.

The technical personnel that operate IRT equipment, analyzed the data and manageIRT Programs are known as Thermographers. The knowledge accumulated by EPRIM&DC thermographers, during years of employing this technology in electric powerplants, has made the development of this document possible. It illustrates a diversesample of anomalies that can be detected using IRT in, what has proven to be, acontinuously evolving arena for the application of infrared thermography to detectincipient equipment failures. Please direct any questions or inquiries to:

Bob Hammaker Bob Woyshner Steve BradenIRT Program Manager PdM Specialist-IRT PdM Specialist-IRT(610) 490-3242 (610) 490-3238 (610) 490-3239


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2 IRT TECHNICAL BACKGROUND

How to Read a Thermal Image

In order to analyze a thermal image, it is essential to understand how to properly readthe image. There are various manufacturers of infrared equipment, and many differenttypes of systems available for use in the field. Each instrument displays its data inslightly different formats, and there is a learning curve necessary to gain familiaritywith each one. However, it can be said that there are similarities between all of theseinfrared instruments and they are all designed to yield the same result, a thermalpattern of a particular target. Therefore, an analysis of the method of one type ofcamera should be sufficient enough to give the reader a basic understanding of thermalimage analysis. One such analysis is discussed below.

Visual Image #1 Thermal Image #1

Visual Image #1 and Thermal Image #1, above, depict electrical bus bar connections ofa 3-phase circuit at the rear of a 480 Volt motor control center. Focusing on ThermalImage #1, observe the numerical information on the “data line” toward the bottom ofthe picture just above the color band. The 82.4°F displayed at the left (low end) of thescale is the lowest temperature that can be measured at this particular setting. Anyareas of the image that show up in black are off scale on the low end (below 82.4°F).Moving up the color scale toward the high end value, the magenta, blue, green, yellow


IRT Technical Background

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and red colors represent temperatures ranging linearly from the low end value of thescale (82.4°F), to the high end value of the scale (262°F). 262°F is the highesttemperature that can be measured at this particular setting. Any areas of the image thatshow up in white are off scale on the high end (above 262°F). This setting, whichenables measurement of temperatures between 82.4°F and 262°F, is called thetemperature span. Most infrared instruments are versatile enough to allow the user tochange temperature spans (low end values, high end values, colors scales etc.),depending upon necessity dictated by the temperatures of the targets being observedand/or personal choice. Regardless of the color scales, or any parameters that are set,the methods of interpretation remain as described above.

Comparative Thermography

The method of analyzing thermal images (Thermograms) suggested, and used, by theThermographers at the EPRI Maintenance & Diagnostic Center (EPRI M&DC) istypically referred to as “Comparative Thermography”. To analyze a thermogram usingComparative Thermography, a reference point must be identified. A reference point isa spot on a piece of equipment that should exhibit similar thermal characteristics to aspot on a component being analyzed. Thermal characteristics of the reference point arecompared to thermal characteristics of the component being analyzed, and anassessment is made.

Depending upon the nature of the component(s) being analyzed, comparative analysisof thermal images can be done quantitatively or qualitatively. To analyze athermogram quantitatively, the numerical temperature value of the reference pointmust be compared to the numerical temperature value of the component beinganalyzed. With this data, a temperature rise is calculated and a severity classification isassigned. A qualitative analysis of a thermal image does not require temperaturemeasurement. The reference point is compared to the component being analyzed byobserving the thermal pattern of the image. The following examples should serve tofurther clarify these concepts.

A Quantitative Analysis of Thermal Image #1 using Comparative Thermography

The crosshairs on Thermal Image #1 (previous page) measure a temperature of 248°F(see indication on the data line ‘CRS= +248’) at the right phase. If the crosshairs weremoved to either of the other two phases (the reference point) they would indicate atemperature of 85°F. The difference between these two measurements is thetemperature rise (248-85= 163°F). There is, most likely, a high resistance connection atthe right phase of this circuit that is generating an abnormal amount of heat at theconnection. Based on the temperature rise calculated above, a severity classification ofthis problem would be assigned according to published guidelines. A typicalguideline is shown below:



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Temperature Rise Severity Classification Action

18°F or less Minor Problem Address as part of routinemaintenance.

19°F - 63°F Intermediate Problem Trend temperature. Repairwithin one month.

64°F - 135°F Serious Problem Trend temperature. Repairwithin one week.

136°F or greater Critical Problem Repair Immediately.

It is important to note that these “guidelines” pertain to electrical equipment that isconsidered to be critical for production. They are not to be strictly adhered to for lesscritical electrical equipment, or other types of equipment such as motors, pumps, fans,valves, boilers etc..

In the case of Thermogram #1, if it was determined that the equipment being servicedby this motor control center was critical to megawatt production, the temperature riseof 163°F would require that a severity classification of “Critical” be assigned.

Visual Image #2 Thermal Image #2



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A Qualitative Analysis of Thermal Image #2 using Comparative Thermography

Visual Image #2 shows a section of a cement floor at a generating station. There was asuspicion that a steam line had ruptured beneath the floor. An infrared thermographysurvey was requested. The

survey was performed, and it yielded the result displayed in Thermal Image #2. Thered area indicates a hot spot on the surface of the floor probably caused by heat transferfrom steam leaking from a damaged header. A comparison of the hot area of the floorto the cooler areas (reference point) provides enough information to assess that a leakexists and to show approximately where it is located. It is not necessary to measureany temperatures to determine that there is a problem. The analysis is donequalitatively. A severity assessment of this problem would not be based upontemperature rise. Drawings would be used to try to identify the line, and thetemperatures and pressures of the steam flowing through it. Based upon thisinformation, the predictive maintenance group would determine when the repairsshould be completed.

The remaining part of this document addresses Field Applications of IRT. Thermalanomalies will be discussed on a case by case basis. Some of the cases are analyzedquantitatively, while others are analyzed qualitatively. Each case is marked with eithera QT (indicating that the case was analyzed quantitatively) or a QL (indicating that thecase was analyzed qualitatively), depending upon the method used.


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3 FIELD APPLICATIONS OF IRT

In a comprehensive Predictive Maintenance (PdM) Program, PdM professionals applyvarious types of non-intrusive diagnostic tools to monitor the condition of plantequipment. An infrared thermography camera is one of these tools. The camera isused to detect thermal anomalies (inconsistencies) with plant equipment. The thermalanomalies that are illustrated in this document have been separated into four (4)general categories. These categories are Station Electrical, Rotating Equipment,Transmission and Distribution, and Performance. Most of the cases discussed in thisdocument feature a thermal image that is accompanied by a corresponding visualimage. There is an arrow superimposed on the visual image to allow the reader tomatch locations on the visual image with the corresponding locations on the thermalimage.

The information contained in this document was acquired while using IRT to identifypotential problems in the field. The findings were reported to the appropriatecontact(s) so that work orders could be generated. Feedback was received from themaintenance personnel involved with the repair work regarding the “as found”condition of the equipment. It is critical for the PdM Group to receive this feedbackregarding the condition of suspected equipment that was observed at the time ofphysical inspection. This feedback makes possible more expeditious evaluations ofsimilar situations encountered during future inspections, and is needed fordocumentation of cost benefit analyses that inform management of the financialadvantages gained by applying IRT and other Predictive technologies in a plant.

All detected anomalies should be reinspected with Infrared Thermography after repairsare completed for verification that the problem was corrected.

Station Electrical Applications

When considering non-intrusive diagnostic testing of electrical equipment, infraredthermography is regarded as the most powerful of all of the diagnostic tools currentlyavailable. Most times it is not necessary to rely on other diagnostic tests whenevaluating electrical equipment with IRT. Thermography can usually act as a “stand-alone” technique in this capacity. This will not hold true with some of the other casesdiscussed in other sections of this document.


Field Applications of IRT

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IRT inspections are made while the equipment is in an energized condition. There isno need to take equipment out of service.

The electrical equipment inside a typical electric power generating station, that shouldbe inspected during a periodic IRT survey, is listed below:

480 Volt Motor Control Centers480 Volt Load Center Feeds4160 Volt SwitchgearAssociated DuctworkIsophases

Some types of problems (anomalies) found with these electrical components, that canbe detected with IRT, are illustrated in this section. They include:

High Resistance ConnectionsStranded ConductorsDefective Thermal OverloadsOpen ConductorsDefective Fuses & FuseclipsDefective Current Transformers

High Resistance Connection (QT)

The crosshairs on the thermal image on the right mark a high resistance connection atthe center phase, line side of a molded case circuit breaker (visual image at left), in a480 volt motor control center compartment. The high resistance connection is probablydue to looseness, corrosion, dirt or adjoining dissimilar metals. This assessment ismade based upon the observation of concentrated heat at the connection that dissipatesaway from the connection. The connection should be inspected, cleaned and properlytightened.



3-3

Stranded Conductor (QT)

The red arrows, superimposed on the visual image, and the thermal image, point to asingle conductor that is warmer than the others due to an effect known as stranding.Stranding occurs when some of the wires contained in a conductor are either broken orimproperly terminated, leaving too few wires to carry the current load which causes asituation similar to one that occurs when a conductor is undersized. This conductorshould be replaced.

Defective Thermal Overload (QT)

The thermal overload (tripping mechanism) at the left phase of this circuit is hotter thanthose at either of the other two phases. Barring any connection problems, this wouldindicate the existence of a defect in the overload, or possible phase imbalance. Theamps on each phase should be checked. Also, the overload and associated connectionsshould be inspected and either secured or replaced.



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Open Conductor (QT)

The crosshairs on the gray scale thermal image (at left) mark the left phase conductorcoming off of the bottom of a contactor. This conductor is colder than the center andright phase conductors because of a lack of current flow. This was verified by an ampmeasurement. Upon further investigation it was discovered that the lead was burnedoff at the motor conduit box, causing an open line and forcing the motor to operate in asingle phase mode. If the problem is not repaired the motor could be destroyed, or failto start again once it is shut down.

Defective Fuse and/or Connection Problem (QT)

The crosshairs on the thermal image mark a high resistance connection at the left side ofthe top fuse in this motor control center compartment. This can be caused by loosenessat the fuse clip or fuse cap, or a defective fuse. The fuse should be inspected fordefects, and the clip should be tightened or replaced.



3-5

480 Volt Bus Bar and Stab Problem (QT)

The rear of this 480 Volt motor control center has a high resistance connection at theright phase bus bar connection to the breaker stab. The connection needs to beinspected, cleaned and tightened.

4160 Volt Breaker Disconnect (QT)

The rear of this 4160 Volt circuit breaker has a high resistance connection at the centerphase disconnect. The connection needs to be inspected, cleaned and tightened.



3-6

Defective Current Transformer (QT)

Current Transformers (CTs) send signals to a control location that provide indication ofamperage load on circuits in the field. On this thermal image the crosshairs mark a hotspot on a CT that indicates a defect inside the CT, probably a short. The defectivecomponent should be replaced.



3-7

Electrical Bus Duct Problem (QT)

The crosshairs on the thermal image (top right) mark a hot spot (117°F) on this 4160Volt service electrical bus duct above an auxiliary power transformer circuit breakercompartment. An investigation into this situation revealed that there was a highresistance condition on the bus plates inside the duct. This high resistance conditionwas attributed to pitting and corrosion of the bus plates. The heat that was generatedby the high resistance condition inside the duct was intense enough to transfer to thesurface of the duct, thereby revealing the problem. The recommendation here is tohave the bus plates cleaned and tightened, and possibly re-silverplated if deemednecessary by the maintenance department. The thermal image at the bottom was takenduring a re-inspection of the duct after the repairs were completed and the equipmentwas put back into service. The thermal pattern across the duct is now uniform and thecrosshairs measure a temperature of 85°F, a decrease of 32°F from the originallydetected anomaly.



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Ground Strap Connection (QT)

Loose ground strap connections inside of this electrical bus duct are caused bycirculating currents in the electrical ground system. The source of these currents needsto be identified and the ground straps should be reworked or replaced.



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Rotating Equipment Applications

Infrared Thermography is a useful tool for detecting problems with rotatingequipment. Unlike applications to electrical equipment, when evaluating rotatingequipment IRT should be used in conjunction with other diagnostic tests. These testswould include vibration analysis, lubricating oil analysis and motor current testing,among others. In a comprehensive PdM Program at a power station, the major rotatingequipment such as motors, pumps and fans are tested with IRT, and the thermalprofiles are evaluated to help determine operating conditions.

Comparative Thermography is applied, quantitatively, to contrast thermal patterns of acomponent to itself over time, or to contrast thermal patterns of similar pieces ofequipment at the same point in time. If a component is compared to itself over time, itis necessary to take a baseline thermogram of the component. When a thermographeris taking data on a piece of rotating equipment, a motor perhaps, the documentation ofambient temperature and motor amps is essential for making consistent comparisons.

Some of the major rotating equipment inside a typical coal-fired electric powergenerating station, that should be scanned during a periodic IRT survey, is listedbelow:

Draft Fans - Driver & Driven (FD and ID)Primary Air Fans - Driver & DrivenPulverizer Mills - Driver & DrivenFeed Pumps - Driver & DrivenCondensate (Hotwell) Pumps - Driver & DrivenCirculating Water Pump Motors

This is an abbreviated list that could be added to, based upon the discretion of plantOperations & Maintenance personnel. For example, equipment used for air extraction,ash handling, sootblowing, scrubbing etc. could also be candidates for periodic testing,depending upon the availability of resources and the philosophies of plant Operationsand Maintenance (O&M) personnel.

Some of the more common types of problems (anomalies) found with rotatingequipment, that can be detected with IRT, are illustrated in this section. They include:

Motor Filter ProblemsMotor, Pump and Fan Bearing ProblemsMill Gear ProblemsMotor Winding ProblemsMotor OverloadingPump Flow Restrictions



3-10

Motor Filter Problem (QT)

A visual image of an induced draft fan motor is shown at the top left. A baseline thermalimage of the same motor is shown at the top right, and the crosshairs measure atemperature of 118°F. The ambient temperature at the time the baseline image was takenwas 80°F and the motor current measured was 570 Amps. A subsequent survey of thismotor yielded the results shown in the bottom thermogram. The crosshairs cannotmeasure the temperature (see indication on the data line ‘CRS= OVER) because the whitearea is off scale on the high end, even though the temperature span is the same as the oneused in the baseline image. This is because the temperature at this point is greater that132°F. A measurement taken at this point in another thermogram, in range, measured over170°F. Considering that ambient conditions and motor amps were nearly the same as inthe baseline image, there must have been some kind of operating condition that wascausing this temperature rise of 52°F (170 - 118 = 52°F). Further investigation revealed thatthe filters in this motor had significant blockage causing restricted air flow for thenecessary cooling. The filters were changed and the temperature of the motor decreased tothe approximate levels that were observed when the baseline image was taken.



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Visual Image - Motor A Thermal Image - Motor A

Visual Image - Motor B Thermal Image - Motor B

Motor Bearing Problem (QT)

The four images shown above illustrate two identical boiler feed pump motors (4000Horsepower, 3600 RPM). The temperature measured on the surface of the outboardbearing on ‘Motor A’ is 140°F (see Thermal Image - Motor A). The temperature measuredon the surface of the outboard bearing on ‘Motor B’ is 103°F (see Thermal Image - Motor B).The temperature rise on ‘Motor A’ outboard bearing, with respect to ‘Motor B’ outboardbearing, is 37°F (140°F - 103°F = 37°F). These motors are under similar loads, and ambientconditions are the same. The temperature rise is attributable to a restriction in the coolingsystem or to an internal operating problem. The temperature should be trended, andresults of other diagnostic tests (e.g. lubricating oil analysis and vibration analysis) shouldbe reviewed to try to more accurately identify the problem. When all available data hasbeen evaluated, the bearing should be inspected and repaired as necessary.



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Visual Image - Pump Bearing A Thermal Image - Pump Bearing A

Visual Image - Pump Bearing B Thermal Image - Pump Bearing B

Boiler Feed Pump Bearing Problem (QT)

The four images shown above illustrate two identical boiler feed pump outboard bearings.The temperature measured on the hot spot on ‘Pump Bearing A’ is 116°F (see ThermalImage - Pump Bearing A). The temperature measured on the same spot on ‘Pump BearingB’ is 100°F (see Thermal Image - Pump Bearing B). The temperature rise on ‘Pump BearingA’, with respect to ‘Pump Bearing B’, is 16°F (116°F - 100°F = 16°F). The obviousdifferences in the thermal patterns of the two bearings indicate some type of internalbearing problem. A subsequent inspection of ‘Bearing A’ revealed significant damage tothe radial thrust plate, and the bearing was repaired. The approach taken to evaluate thisthermal anomaly is similar to the one taken in the motor bearing case discussed on theprevious page, when it was suggested that other diagnostic methods be used in additionto IRT and that feedback from maintenance personnel should be obtained.



3-13

Motor Stator Winding Short (QT)

A hot spot detected on the surface of this vertical motor (above) is an indication of aturn-to-turn electrical short within the stator windings of the motor. The camera is notable to see through the motor casing to the windings. The high temperature detectedon the motor casing is caused by heat being transferred from a source in the motorwindings to the motor casing.

Coal Pulverizer Mill Gear Problem (QT)

A hot area at one end of this worm gear casing on a coal pulverizer mill is caused by aninternal gear mesh problem between the horizontal worm gear, and the vertical bullgear within the pulverizer bowl.



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Visual Image Baseline Thermal Image

Thermal Image of Anomaly

Dry Vacuum Pump Cooling Water Restriction (QT)

A baseline thermal image of this Dry Vacuum Pump is shown at the top right. Fivemonths after this baseline image was taken, a subsequent inspection revealed theresults shown in the bottom image. Hot spots were beginning to develop at areas nearthe bottom of the pump. Operations reported that they were not receiving the expectedperformance from this piece of equipment. An investigation into the problem revealedthat the pump was becoming clogged with mud and sludge in the cooling watersystem causing the internal valves to overheat. The system needed to be flushed. Afterthe system was flushed, the hot spots faded and pump performance returned to anacceptable level.



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Motor Current Overloading (QT)

This condensate pump motor (above) exhibited increased temperatures (173°F) on thecasing when compared to another motor of the same design and function. Aninvestigation into this anomaly revealed that this motor was being overloaded withrespect to its designed amp rating. The motor should either be operated withinspecification, or replaced with a larger unit designed to handle higher current loads.An internal inspection of the motor should be done in order to assess possible damagesustained by the equipment from being exposed to conditions of excessive heat overextended periods of time.

Vertical Pump Motor Thermal Pattern (QL)

This vertical motor illustrates an example of the thermal pattern normally observed ona typical vertical type motor (hotwell pumps, fire pumps, river water pumps etc.). Anydeviation from this pattern, or increases in the level of temperature should be trendedand investigated to determine the existence of a potential problem.



3-16

Transmission & Distribution Applications

Infrared Thermography is used extensively for detecting problems with equipmentused to transmit electric power from the source of generation to the point of use. IRTcan be used as a stand-alone tool for many of these components. However, there areother types of diagnostics that are used to evaluate the overall health of some T & Dcomponents such as transformers, load tap changers, oil or gas filled circuit breakers,etc. The diagnostic tests that are applied, in addition to IRT, include vibration analysis,oil analysis, sonic & ultrasonic evaluation, acoustic emissions, sound level and visualinspection. This section illustrates some examples of anomalies detected with IRTduring field inspections on various equipment necessary for the transmission of electricpower.

A sample of T & D equipment that is tested during a typical IRT survey is featured inthis section, and is listed as follows:

BushingsDisconnect SwitchesPower TransformersLoad Tap Changer (LTC) CompartmentsCircuit BreakersConductorsInsulatorsTransformer Cooling SystemsDistribution LinesStranded CableTransformer Control CabinetsLightning Arrestors



3-17

High Resistance Connection at Bushing (QT)

The electrical connection at the top of a bushing on this oil-filled circuit breaker (above)exhibits a high resistance condition probably due to looseness, dirt, corrosion or aconnection made of dissimilar metals. The assembly at this connection should beinspected and repaired as necessary, then re-inspected with IRT after repairs arecompleted.

Switchyard Disconnect Switch (QT)

Similar to the example at the top of this page, this disconnect switch and hingeassembly also exhibits a high resistance condition; and, is also most likely due tolooseness, dirt, corrosion or a misaligned mechanism. The action taken should be thesame as that described above.



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Stranded Cable (QT)

The “barber pole” effect, observed on this cable, is an indication of “stranding” which isa condition where some of the conductor strands are carrying minimal current. As aresult, the remaining strands are carrying most of the current. Those strands that arecarrying the current are heating up due to the fact that they are not capable of handlingthe entire load, and are displaying characteristics that would be evident in the case ofan undersized or overloaded conductor.

Lightning Arrestor & Bushing Anomaly (QT)

The porcelain insulators on the bushings and lightning arrestor exhibit several hotspots that could be attributable to tracking of current due to buildup of dirt or crackingof the petticoats. If these components are not inspected for cracks and/or cleaned itcould result in catastrophic failure of the component, and a loss of service of thetransformer.



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Load Tap Changer Internal Contact Problem (QT)

The surface of this transformer’s load tap changer (LTC), pictured at the top left, shouldbe uniform in temperature, and should not be hotter than the transformer itself. Thecrosshairs on the thermal image at the top right indicate a temperature of 147°F at thetop section of the tap changer. The source of the heat is inside the tap changer casingand is probably considerably hotter that the 147°F measured temperature. Thetransformer was taken out of service and the internal contacts of the tap changer wereinspected. The contacts were observed to have sustained significant burning andcoking. Catastrophic failure would have occurred if this condition was not detected.The contacts were replaced and the transformer was returned to service. The thermalimage at the bottom was taken during a re-inspection after the repairs were completed.The temperature of the hot area decreased 72°F, from 147°F down to 75°F, indicatingthat the problem had been corrected.



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Internal Transformer Problem (QT)

The load tap changer (LTC) on this transformer failed when the LTC contacts burnedcompletely open. As a result of this open condition in the LTC, excessive currentdeveloped in the transformer windings. These excessive currents generated heat insidethe transformer that was detected on the transformer surface. The crosshairs measure423°F. Temperatures this extreme are classified as critical, according to generallyaccepted severity guidelines, and it was suggested that this piece of equipment beremoved from service immediately.

Restricted Transformer Cooling Fins (QL)

Transformer cooling fins should be free of restrictions in order to allow propercirculation of oil. The thermal image on the right reveals a set of fins that is colder thanthe others, and it does not show a cooling effect from the top down toward the bottom.Observation of this cooling effect provides verification that hot oil from inside of thetransformer is entering the cooling fin at the top and flowing down as it cools, andeventually re-enters the transformer through the bottom of the cooling fin. The



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assumption in this case is that there is no flow of oil in the set of fins indicated by thearrow. There is probably an internal restriction, a closed valve or a broken valve stem.

Oil-Filled Circuit Breaker (OCB) Contact Problem (QT)

The left phase tank of this circuit breaker has a temperature rise with respect to thetanks on the other two phases. Defective internal contacts are generating enough heatto heat the surface of the left phase tank and the oil contained inside. There is a risk ofexplosion and resultant injury to personnel in the vicinity. This problem is critical andshould be trended regularly to determine if it is getting worse. Repairs should bemade as soon as possible.



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Transmission Line Fuse Cut-Out (QT)

A high resistance connection at a fuse cut-out was observed on residential transmissionlines. It is probably caused by a defective component, looseness, dirt or corrosionbuildup. This type of repair would be done as part of regularly scheduledmaintenance.



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Performance Applications

Infrared Thermography can be applied to a large number of plant components thathave an impact on generating station performance (heat rate). In general, theperformance components targeted are those that are found in the steam cycle system,the fuel system, and the boiler. The techniques involved with thermal analysis ofperformance equipment are somewhat unconventional, as compared with the otherapplications discussed thus far in this document. The interpretive approaches used toanalyze these anomalies are almost entirely dictated by the thermographer’sknowledge of plant performance and the related systems.

Power plant performance related components, that can be evaluated with IRT, arefeatured in this section. They include:

ValvesSteam TrapsInternal and External BoilerProcess HeadersCoal Fuel LinesCoal Fuel Bunkers



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Main Steam Relief Valve Leak (QL)

The main steam relief valve shown above is normally closed during plant operation. It hastwo un-insulated outlet headers (see arrows on visual and thermal images). Referencing thecolor scale at the bottom of the thermal image, the temperatures measured on the left outletare approximately equal to the ambient temperature (75°F - 100°F). The temperaturesmeasured on the right outlet header are consistently hotter. This is an indication of steampassage through the right side of this valve, probably due to a deteriorated valve seat. Thevalve should be inspected at the next opportunity and repaired as necessary.

Defective Steam Trap (QL)

A steam trap that exhibits a similar temperature on the heat exchanger side (bottom), and onthe outlet side (top), is passing steam. That is the case here, where a temperature in excessof 600°F is measured at both points. Thermography alone can identify this type of problem.However, in many cases, other diagnostic tests can be used in order to evaluate the overallcondition of a steam trap to verify that condensate and air are being vented properly.



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Defective Feedwater Heater Relief Valve (QT)

The thermal image at the top shows a defective feedwater heater relief valve. This isdetermined by comparing the temperature of the valve at the shell side (approximately500°F), to the temperature of the valve outlet (394°F indicated by the crosshairs). Thecombination of a 106°F temperature differential (500°F - 394°F = 106°F), and an extremelyhot outlet temperature (394°F) is an almost certain indication that the valve is passing aconsiderable amount of steam. In the two bottom pictures, the replacement valve is shownvisually and thermally. The temperature contrasts between the replacement valve and thedefective valve are dramatic. In the thermal image of the replacement valve, the shell sidevalve temperature is approximately 450°F. Comparing this with the outlet temperature of141°F (see crosshairs), the temperature differential is now in excess of 300°F (450°F - 141°F =309°F). The temperature differential between the old valve and the replacement valve isover 200°F (309°F - 106°F = 203°F). This assures that the problem has been corrected.Additionally, the thermal image of the replacement valve provides baseline information forthe PdM Group to use to trend this new valve over time.



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Boiler Air-in-Leakage (QL)

IRT can detect air-in-leakage through voids into a balanced draft (negative pressure)boiler. The visual image above shows a boiler manway cover. The thermal imagedisplays a pattern that would indicate air infiltration through the upper left hand sideof the manway. The manway cools toward the upper left indicating a draft of air acrossthe cover. If there were no air infiltration, the entire manway cover would be uniformin temperature. Undesired infiltration of air into a boiler will impact the thermalefficiency of the unit, and impact its ability to maintain vacuum.

Boiler Insulation Problem (QL)

The thermal profile of this section of boiler lagging indicates that there is missing ordeteriorated insulation behind the lagging at the spots where the temperatures are thehighest. If insulation problems are suspected on a particular unit, IRT can be used inthe manner shown above to inspect entire sections of wall in literally seconds.



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Boiler Tube Restriction (QL)

The thermal image shown above was taken from the inside of a monotube boilerduring a hydro flush test prior to unit start-up. The picture isolates a section ofwaterwall. When the boiler is filled with 200°F water during the course of this test, allof the tubes should rise in temperature uniformly from ambient to approximately200°F. If there is a restriction that prohibits flow in one or more tubes, there will be aneffect similar to the one in the thermal image above. The arrows point to a single coldtube that is unable to fill because of a restriction (probably slag from welds madeduring waterwall repairs). A restricted tube will not receive the cooling it needs fromthe flow of water through it. If it goes undetected, it will probably rupture at a point intime after the unit is brought on line. This would cause unscheduled downtime andassociated costs. The tube needs to be cleared and re-inspected prior to unit start-up.



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Boiler Wall Flame Impingement - Top View (QL)

A thermal profile of the inside of a boiler, looking down from above, identifies flameimpingement toward the lower right hand corner wall section. The image was takenwith a high temperature infrared lens from an inspection port in the boiler roof, whilethe unit was on line at full load.

Boiler Wall Flame Impingement - Eye Level View (QL)

Another example of boiler wall flame impingement is shown above. The high temperaturelens looks through an observation port in a side wall across the boiler to the opposite wall.The gray scale thermal image on the left serves as a good visual representation of thesection of waterwall, while the color image highlights the affected area.



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Air Infiltration into Vacuum Header (QL)

An IRT inspection of an expansion joint on a large header at the suction side of acondensate pump reveals air infiltration. This is indicated on the thermal image (atright) by the blue areas to the left of the arrow. The color scale on this thermal image isdesigned to show blue to indicate temperatures that are below the low end scale value(+32.9°C). As mentioned in the example of the boiler, air-in-leakage normally manifestsitself as a relatively cool area with respect to the surrounding temperatures.



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Visual Image A Thermal Image A

Visual Image B Thermal Image B

Process Header Steam Leak (QL)

Visual Image A shows a section of cement floor in a power station. A thermal image ofthis same section of floor (Thermal Image A) was taken during an IRT inspection in anattempt to try to determine the approximate location of a steam leak in a headersomewhere beneath the floor. It was suspected that the hot spot on Thermal Image Awas caused by heat transfer from the steam leak to the surface. An excavation of thefloor revealed a ruptured Y-Joint in the pipe (Visual Image B). The header wasrepaired and the floor was replaced. A re-inspection of the floor, performed after therepairs were made and after the unit was put back into service (Thermal Image B), doesnot show a hot spot and indicates that the problem has been corrected.



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Obstructed Fuel Line (QL)

These four coal fuel lines (coming off of the same pulverizer mill), shown in the visualimage on the left, are carrying pulverized coal for combustion from the mill exhausterto the burners at the boiler. The thermal image on the right indicates that the 3rd fuelline from the left is cooler than the other three lines by approximately 20-30 Degrees F.Warm primary air is circulated through the fuel system to increase combustionefficiency and will naturally warm the fuel lines. The relatively cool fuel line in thisexample indicates that there is limited, or completely obstructed, flow in this line. Thiswill prohibit the necessary fuel from reaching the burners. The obstruction could beanywhere in the line, or in a diffuser. The line should be blown clear at the nextopportunity.



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Coal Bunker Anomaly (QL)

A coal bunker (at left) at this particular plant is filled, and the unit is off line. Anemergency shutdown prevented operations from running down the stored fuel in thebunker. The outage resulting from this emergency shutdown was estimated to lastthree months. The bunker would either have to remain full for this extended period oftime, or be manually emptied in an extremely costly, and time consuming, process.This would present a risk of spontaneous combustion under certain circumstances.The thermal image at the right exhibits a profile of the coal in the bunker approximately3 to 4 weeks after the shutdown occurred. Hot areas are beginning to develop on thesurface of the coal in the bunker. Approximately 5 or 6 bunkers, out of 16, showedsimilar thermal patterns at different times throughout the outage. In the bunkers wherethe hot spots were observed, an increased presence of carbon monoxide was alsodetected. It was determined that the heat and air mixing with the fuel presented apotential for combustion, and fire. The PdM Group sealed off air entry passages, andinjected regulated doses of liquid nitrogen (while keeping the ventilation system on!)into the bunkers throughout the duration of the outage. These techniques weresuccessful in stabilizing the potentially dangerous conditions. The plant was able tocomplete the outage without incident. Additionally, significant labor and equipmentcosts were avoided because expensive efforts to manually empty the bunkers wereavoided.

Download - EPRI TR-108935

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