EPRI TR-108935

Infrared Thermography Anomalies Manual TR-108935

Final Report, August 1997

Prepared by EPRI Monitoring & Diagnostic Center #3 Industrial Highway Eddystone, PA 19022 Authors S. Braden B. Hammaker B. Woyshner Effective December 6, 2006, this report has been made publicly available in accordance withSection 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. ExportAdministration Regulations. As a result of this publication, this report is subject to only copyrightprotection and does not require any license agreement from EPRI. This notice supersedes theexport control restrictions and any proprietary licensed material notices embedded in thedocument prior to publication.

Prepared for Electric Power Research Institute 3412 Hillview Avenue Palo Alto, California 94304 EPRI Project Manager R. Pflasterer Generation

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THIS REPORT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM: (A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS REPORT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS REPORT IS SUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR (B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THIS REPORT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS REPORT. ORGANIZATION(S) THAT PREPARED THIS REPORT EPRI Monitoring & Diagnostic Center

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REPORT SUMMARY

Infrared thermography (IRT) is non-intrusive diagnostic technique that can play an important role in predictive maintenance programs. This manual shows how IRT can be applied in the field to detect anomalies in a wide-range of power plant systems. This activity is part of EPRI’s Plant Maintenance Optimization development efforts under Target 43, Turbine, Generator and BOP O&M Cost Reduction (1997), and Target 54, Plant Maintenance Optimization (1998), which are intended to help utilities reduce the cost of production by developing and demonstrating cost-effective maintenance methods. Background Most of the equipment found in a typical electric generating station exhibits some type of abnormal thermal pattern prior to failure. IRT is a non-invasive diagnostic technique that can detect abnormal thermal patterns by making simultaneous temperature measurements of multiple points on the surface of a piece of equipment. These data are displayed as pictures, commonly referred to as thermograms, that can be analyzed in real-time or stored electronically and analyzed later. Information from thermograms can be used by electric utilities to plan maintenance and avoid catastrophic equipment failures and unscheduled downtime. Objective To provide a guide to the use of comparative infrared thermography to monitor the condition of power plant equipment. Approach The 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 of power plant equipment. Results After a brief introduction to the technical background IRT, the manual describes how infrared thermography can be used to detect thermal anomalies in power plant equipment. The thermal anomalies illustrated in this document include station electrical applications, rotating equipment applications, transmission and distribution applications, and performance applications. Some of the cases are analyzed quantitatively, while others are analyzed qualitatively. Most of the cases feature a iii

thermal image that is accompanied by a corresponding visual image. An arrow superimposed on the visual image allows the reader to match locations on the visual image with the corresponding locations on the thermal image. The information contained in this document was acquired while using IRT to identify potential problems in the field. In each case feedback was received from maintenance personnel 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 of preventive maintenance. All detected anomalies should also be reinspected with IRT after repairs are completed to verify that the problem has been corrected. EPRI Perspective EPRI’s Monitoring & Diagnostic Center was established to demonstrate the value of diagnostic monitoring and the importance of networking diagnostics to plant maintenance, controls, and operations. The Center’s primary objectives are to validate, improve, integrate, and network diagnostic technologies, to develop program guidelines, and to transfer the technologies to the utility industry. TR-108935 Interest Categories Fossil steam plant performance optimization Fossil steam plant O&M cost reduction State-of-the-art power plants Key Words Infrared thermography Non-destructive evaluation Predictive maintenance

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EPRI Licensed Material

ABSTRACT

Infrared thermography (IRT) is a non-invasive diagnostic technique that utilizes infrared sensors to make simultaneous measurements of multiple points on the surface of a piece of equipment. Most of the equipment found in a typical electric generating station exhibits some type of thermal pattern prior to failure. Infrared thermography programs are implemented in generating stations as part of a comprehensive Predictive Maintenance (PdM) program that involves various types of diagnostic tests. This manual, 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 power plant 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 the importance of networking diagnostics with plant maintenance, controls and operations. The Center's primary objectives are to validate, improve, integrate and network diagnostic technologies, to develop program guidelines and to transfer the technologies to the utility industry. Most of the equipment found in a typical electric generating station exhibits some type of abnormal thermal pattern prior to failure. Infrared Thermography (IRT) Programs are implemented 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 temperature measurements of multiple points on the surface of a piece of equipment (a target). IRT is not an “x-ray” technique and will not make measurements through an object. The measurements of the target surface are taken from a distance. It is not necessary to make physical contact with the target. The data is displayed in the form of a picture. These pictures, commonly referred to as thermograms, can be analyzed in the field (real-time), or stored electronically and analyzed at a later time. The thermograms provide predictive information concerning the operating condition of a piece of equipment. This information is used for operations and maintenance planning. It affords an organization the opportunity to take appropriate action to avoid an incident that would result in catastrophic equipment failure, unscheduled downtime and all of the associated costs. The technical personnel that operate IRT equipment, analyzed the data and manage IRT Programs are known as Thermographers. The knowledge accumulated by EPRI M&DC thermographers, during years of employing this technology in electric power plants, has made the development of this document possible. It illustrates a diverse sample of anomalies that can be detected using IRT in, what has proven to be, a continuously evolving arena for the application of infrared thermography to detect incipient equipment failures. Please direct any questions or inquiries to: Bob Hammaker IRT Program Manager (610) 490-3242

Bob Woyshner PdM Specialist-IRT (610) 490-3238

Steve Braden PdM Specialist-IRT (610) 490-3239

1-1


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 read the image. There are various manufacturers of infrared equipment, and many different types of systems available for use in the field. Each instrument displays its data in slightly different formats, and there is a learning curve necessary to gain familiarity with each one. However, it can be said that there are similarities between all of these infrared instruments and they are all designed to yield the same result, a thermal pattern of a particular target. Therefore, an analysis of the method of one type of camera should be sufficient enough to give the reader a basic understanding of thermal image 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 of a 3-phase circuit at the rear of a 480 Volt motor control center. Focusing on Thermal Image #1, observe the numerical information on the “data line” toward the bottom of the picture just above the color band. The 82.4°F displayed at the left (low end) of the scale is the lowest temperature that can be measured at this particular setting. Any areas 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 2-1

EPRI Licensed Material IRT Technical Background

and red colors represent temperatures ranging linearly from the low end value of the scale (82.4°F), to the high end value of the scale (262°F). 262°F is the highest temperature that can be measured at this particular setting. Any areas of the image that show up in white are off scale on the high end (above 262°F). This setting, which enables measurement of temperatures between 82.4°F and 262°F, is called the temperature span. Most infrared instruments are versatile enough to allow the user to change temperature spans (low end values, high end values, colors scales etc.), depending upon necessity dictated by the temperatures of the targets being observed and/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 the Thermographers at the EPRI Maintenance & Diagnostic Center (EPRI M&DC) is typically referred to as “Comparative Thermography”. To analyze a thermogram using Comparative Thermography, a reference point must be identified. A reference point is a spot on a piece of equipment that should exhibit similar thermal characteristics to a spot on a component being analyzed. Thermal characteristics of the reference point are compared to thermal characteristics of the component being analyzed, and an assessment is made. Depending upon the nature of the component(s) being analyzed, comparative analysis of thermal images can be done quantitatively or qualitatively. To analyze a thermogram quantitatively, the numerical temperature value of the reference point must be compared to the numerical temperature value of the component being analyzed. With this data, a temperature rise is calculated and a severity classification is assigned. A qualitative analysis of a thermal image does not require temperature measurement. The reference point is compared to the component being analyzed by observing the thermal pattern of the image. The following examples should serve to further 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 were moved to either of the other two phases (the reference point) they would indicate a temperature of 85°F. The difference between these two measurements is the temperature rise (248-85= 163°F). There is, most likely, a high resistance connection at the right phase of this circuit that is generating an abnormal amount of heat at the connection. Based on the temperature rise calculated above, a severity classification of this problem would be assigned according to published guidelines. A typical guideline is shown below: 2-2


Temperature Rise

Severity Classification

Action

18°F or less

Minor Problem

Address as part of routine maintenance.

19°F - 63°F

Intermediate Problem

Trend temperature. Repair within one month.

64°F - 135°F

Serious Problem

Trend temperature. Repair within one week.

136°F or greater

Critical Problem

Repair Immediately.

It is important to note that these “guidelines” pertain to electrical equipment that is considered to be critical for production. They are not to be strictly adhered to for less critical 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 serviced by this motor control center was critical to megawatt production, the temperature rise of 163°F would require that a severity classification of “Critical” be assigned.

Visual Image

#2

Thermal Image #2

2-3


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 a suspicion that a steam line had ruptured beneath the floor. An infrared thermography survey was requested. The survey was performed, and it yielded the result displayed in Thermal Image #2. The red area indicates a hot spot on the surface of the floor probably caused by heat transfer from steam leaking from a damaged header. A comparison of the hot area of the floor to the cooler areas (reference point) provides enough information to assess that a leak exists and to show approximately where it is located. It is not necessary to measure any temperatures to determine that there is a problem. The analysis is done qualitatively. A severity assessment of this problem would not be based upon temperature rise. Drawings would be used to try to identify the line, and the temperatures and pressures of the steam flowing through it. Based upon this information, the predictive maintenance group would determine when the repairs should be completed. The remaining part of this document addresses Field Applications of IRT. Thermal anomalies will be discussed on a case by case basis. Some of the cases are analyzed quantitatively, while others are analyzed qualitatively. Each case is marked with either a QT (indicating that the case was analyzed quantitatively) or a QL (indicating that the case 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 apply various types of non-intrusive diagnostic tools to monitor the condition of plant equipment. An infrared thermography camera is one of these tools. The camera is used to detect thermal anomalies (inconsistencies) with plant equipment. The thermal anomalies 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 this document feature a thermal image that is accompanied by a corresponding visual image. There is an arrow superimposed on the visual image to allow the reader to match locations on the visual image with the corresponding locations on the thermal image. The information contained in this document was acquired while using IRT to identify potential problems in the field. The findings were reported to the appropriate contact(s) so that work orders could be generated. Feedback was received from the maintenance personnel involved with the repair work regarding the “as found” condition of the equipment. It is critical for the PdM Group to receive this feedback regarding the condition of suspected equipment that was observed at the time of physical inspection. This feedback makes possible more expeditious evaluations of similar situations encountered during future inspections, and is needed for documentation of cost benefit analyses that inform management of the financial advantages gained by applying IRT and other Predictive technologies in a plant. All detected anomalies should be reinspected with Infrared Thermography after repairs are completed for verification that the problem was corrected.

Station Electrical Applications When considering non-intrusive diagnostic testing of electrical equipment, infrared thermography is regarded as the most powerful of all of the diagnostic tools currently available. Most times it is not necessary to rely on other diagnostic tests when evaluating electrical equipment with IRT. Thermography can usually act as a “standalone” technique in this capacity. This will not hold true with some of the other cases discussed in other sections of this document.

3-1

EPRI Licensed Material Field Applications of IRT

IRT inspections are made while the equipment is in an energized condition. There is no need to take equipment out of service. The electrical equipment inside a typical electric power generating station, that should be inspected during a periodic IRT survey, is listed below: 480 Volt Motor Control Centers 480 Volt Load Center Feeds 4160 Volt Switchgear Associated Ductwork Isophases Some types of problems (anomalies) found with these electrical components, that can be detected with IRT, are illustrated in this section. They include: High Resistance Connections Stranded Conductors Defective Thermal Overloads Open Conductors Defective Fuses & Fuseclips Defective Current Transformers

High Resistance Connection (QT) The crosshairs on the thermal image on the right mark a high resistance connection at the center phase, line side of a molded case circuit breaker (visual image at left), in a 480 volt motor control center compartment. The high resistance connection is probably due to looseness, corrosion, dirt or adjoining dissimilar metals. This assessment is made based upon the observation of concentrated heat at the connection that dissipates away from the connection. The connection should be inspected, cleaned and properly tightened.

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Stranded Conductor (QT) The red arrows, superimposed on the visual image, and the thermal image, point to a single 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 or improperly terminated, leaving too few wires to carry the current load which causes a situation similar to one that occurs when a conductor is undersized. This conductor should be replaced.

Defective Thermal Overload (QT) The thermal overload (tripping mechanism) at the left phase of this circuit is hotter than those at either of the other two phases. Barring any connection problems, this would indicate the existence of a defect in the overload, or possible phase imbalance. The amps on each phase should be checked. Also, the overload and associated connections should 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 conductor coming off of the bottom of a contactor. This conductor is colder than the center and right phase conductors because of a lack of current flow. This was verified by an amp measurement. Upon further investigation it was discovered that the lead was burned off at the motor conduit box, causing an open line and forcing the motor to operate in a single phase mode. If the problem is not repaired the motor could be destroyed, or fail to 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 of the top fuse in this motor control center compartment. This can be caused by looseness at the fuse clip or fuse cap, or a defective fuse. The fuse should be inspected for defects, and the clip should be tightened or replaced.

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480 Volt Bus Bar and Stab Problem (QT) The rear of this 480 Volt motor control center has a high resistance connection at the right phase bus bar connection to the breaker stab. The connection needs to be inspected, cleaned and tightened.

4160 Volt Breaker Disconnect (QT) The rear of this 4160 Volt circuit breaker has a high resistance connection at the center phase disconnect. The connection needs to be inspected, cleaned and tightened.

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Defective Current Transformer (QT) Current Transformers (CTs) send signals to a control location that provide indication of amperage load on circuits in the field. On this thermal image the crosshairs mark a hot spot on a CT that indicates a defect inside the CT, probably a short. The defective component should be replaced.

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Electrical Bus Duct Problem (QT) The crosshairs on the thermal image (top right) mark a hot spot (117°F) on this 4160 Volt service electrical bus duct above an auxiliary power transformer circuit breaker compartment. An investigation into this situation revealed that there was a high resistance condition on the bus plates inside the duct. This high resistance condition was attributed to pitting and corrosion of the bus plates. The heat that was generated by the high resistance condition inside the duct was intense enough to transfer to the surface of the duct, thereby revealing the problem. The recommendation here is to have the bus plates cleaned and tightened, and possibly re-silverplated if deemed necessary by the maintenance department. The thermal image at the bottom was taken during a re-inspection of the duct after the repairs were completed and the equipment was put back into service. The thermal pattern across the duct is now uniform and the crosshairs measure a temperature of 85°F, a decrease of 32°F from the originally detected anomaly. 3-7


Ground Strap Connection (QT) Loose ground strap connections inside of this electrical bus duct are caused by circulating currents in the electrical ground system. The source of these currents needs to be identified and the ground straps should be reworked or replaced.

3-8


Rotating Equipment Applications Infrared Thermography is a useful tool for detecting problems with rotating equipment. Unlike applications to electrical equipment, when evaluating rotating equipment IRT should be used in conjunction with other diagnostic tests. These tests would include vibration analysis, lubricating oil analysis and motor current testing, among others. In a comprehensive PdM Program at a power station, the major rotating equipment such as motors, pumps and fans are tested with IRT, and the thermal profiles are evaluated to help determine operating conditions. Comparative Thermography is applied, quantitatively, to contrast thermal patterns of a component to itself over time, or to contrast thermal patterns of similar pieces of equipment at the same point in time. If a component is compared to itself over time, it is necessary to take a baseline thermogram of the component. When a thermographer is taking data on a piece of rotating equipment, a motor perhaps, the documentation of ambient temperature and motor amps is essential for making consistent comparisons. Some of the major rotating equipment inside a typical coal-fired electric power generating station, that should be scanned during a periodic IRT survey, is listed below: Draft Fans - Driver & Driven (FD and ID) Primary Air Fans - Driver & Driven Pulverizer Mills - Driver & Driven Feed Pumps - Driver & Driven Condensate (Hotwell) Pumps - Driver & Driven Circulating Water Pump Motors This is an abbreviated list that could be added to, based upon the discretion of plant Operations & 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 Operations and Maintenance (O&M) personnel. Some of the more common types of problems (anomalies) found with rotating equipment, that can be detected with IRT, are illustrated in this section. They include: Motor Filter Problems Motor, Pump and Fan Bearing Problems Mill Gear Problems Motor Winding Problems Motor Overloading Pump Flow Restrictions 3-9


Motor Filter Problem (QT) A visual image of an induced draft fan motor is shown at the top left. A baseline thermal image of the same motor is shown at the top right, and the crosshairs measure a temperature of 118°F. The ambient temperature at the time the baseline image was taken was 80°F and the motor current measured was 570 Amps. A subsequent survey of this motor yielded the results shown in the bottom thermogram. The crosshairs cannot measure the temperature (see indication on the data line ‘CRS= OVER) because the white area is off scale on the high end, even though the temperature span is the same as the one used in the baseline image. This is because the temperature at this point is greater that 132°F. A measurement taken at this point in another thermogram, in range, measured over 170°F. Considering that ambient conditions and motor amps were nearly the same as in the baseline image, there must have been some kind of operating condition that was causing this temperature rise of 52°F (170 - 118 = 52°F). Further investigation revealed that the filters in this motor had significant blockage causing restricted air flow for the necessary cooling. The filters were changed and the temperature of the motor decreased to the approximate levels that were observed when the baseline image was taken. 3-10


Visual Image - Motor A

Visual Image - Motor B

Thermal Image - Motor A

Thermal Image - Motor B

Motor Bearing Problem (QT) The four images shown above illustrate two identical boiler feed pump motors (4000 Horsepower, 3600 RPM). The temperature measured on the surface of the outboard bearing on ‘Motor A’ is 140°F (see Thermal Image - Motor A). The temperature measured on 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’ outboard bearing, is 37°F (140°F - 103°F = 37°F). These motors are under similar loads, and ambient conditions are the same. The temperature rise is attributable to a restriction in the cooling system or to an internal operating problem. The temperature should be trended, and results of other diagnostic tests (e.g. lubricating oil analysis and vibration analysis) should be reviewed to try to more accurately identify the problem. When all available data has been evaluated, the bearing should be inspected and repaired as necessary. 3-11


Visual Image - Pump Bearing A

Visual Image - Pump Bearing B

Thermal Image - Pump Bearing A

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 Thermal Image - Pump Bearing A). The temperature measured on the same spot on ‘Pump Bearing B’ is 100°F (see Thermal Image - Pump Bearing B). The temperature rise on ‘Pump Bearing A’, with respect to ‘Pump Bearing B’, is 16°F (116°F - 100°F = 16°F). The obvious differences in the thermal patterns of the two bearings indicate some type of internal bearing problem. A subsequent inspection of ‘Bearing A’ revealed significant damage to the radial thrust plate, and the bearing was repaired. The approach taken to evaluate this thermal anomaly is similar to the one taken in the motor bearing case discussed on the previous page, when it was suggested that other diagnostic methods be used in addition to IRT and that feedback from maintenance personnel should be obtained. 3-12


Motor Stator Winding Short (QT) A hot spot detected on the surface of this vertical motor (above) is an indication of a turn-to-turn electrical short within the stator windings of the motor. The camera is not able to see through the motor casing to the windings. The high temperature detected on the motor casing is caused by heat being transferred from a source in the motor windings 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 an internal gear mesh problem between the horizontal worm gear, and the vertical bull gear 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. Five months after this baseline image was taken, a subsequent inspection revealed the results shown in the bottom image. Hot spots were beginning to develop at areas near the bottom of the pump. Operations reported that they were not receiving the expected performance from this piece of equipment. An investigation into the problem revealed that the pump was becoming clogged with mud and sludge in the cooling water system causing the internal valves to overheat. The system needed to be flushed. After the system was flushed, the hot spots faded and pump performance returned to an acceptable level.

3-14


Motor Current Overloading (QT) This condensate pump motor (above) exhibited increased temperatures (173°F) on the casing when compared to another motor of the same design and function. An investigation into this anomaly revealed that this motor was being overloaded with respect to its designed amp rating. The motor should either be operated within specification, 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 damage sustained by the equipment from being exposed to conditions of excessive heat over extended periods of time.

Vertical Pump Motor Thermal Pattern (QL) This vertical motor illustrates an example of the thermal pattern normally observed on a typical vertical type motor (hotwell pumps, fire pumps, river water pumps etc.). Any deviation from this pattern, or increases in the level of temperature should be trended and investigated to determine the existence of a potential problem.

3-15


Transmission & Distribution Applications Infrared Thermography is used extensively for detecting problems with equipment used to transmit electric power from the source of generation to the point of use. IRT can be used as a stand-alone tool for many of these components. However, there are other types of diagnostics that are used to evaluate the overall health of some T & D components 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 visual inspection. This section illustrates some examples of anomalies detected with IRT during field inspections on various equipment necessary for the transmission of electric power. A sample of T & D equipment that is tested during a typical IRT survey is featured in this section, and is listed as follows: Bushings Disconnect Switches Power Transformers Load Tap Changer (LTC) Compartments Circuit Breakers Conductors Insulators Transformer Cooling Systems Distribution Lines Stranded Cable Transformer Control Cabinets Lightning Arrestors

3-16


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 a connection made of dissimilar metals. The assembly at this connection should be inspected and repaired as necessary, then re-inspected with IRT after repairs are completed.

Switchyard Disconnect Switch (QT) Similar to the example at the top of this page, this disconnect switch and hinge assembly also exhibits a high resistance condition; and, is also most likely due to looseness, dirt, corrosion or a misaligned mechanism. The action taken should be the same as that described above.

3-17


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

Lightning Arrestor & Bushing Anomaly (QT) The porcelain insulators on the bushings and lightning arrestor exhibit several hot spots that could be attributable to tracking of current due to buildup of dirt or cracking of the petticoats. If these components are not inspected for cracks and/or cleaned it could result in catastrophic failure of the component, and a loss of service of the transformer. 3-18


Load Tap Changer Internal Contact Problem (QT) The surface of this transformer’s load tap changer (LTC), pictured at the top left, should be uniform in temperature, and should not be hotter than the transformer itself. The crosshairs on the thermal image at the top right indicate a temperature of 147°F at the top section of the tap changer. The source of the heat is inside the tap changer casing and is probably considerably hotter that the 147°F measured temperature. The transformer was taken out of service and the internal contacts of the tap changer were inspected. The contacts were observed to have sustained significant burning and coking. Catastrophic failure would have occurred if this condition was not detected. The contacts were replaced and the transformer was returned to service. The thermal image 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, indicating that 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 burned completely open. As a result of this open condition in the LTC, excessive current developed in the transformer windings. These excessive currents generated heat inside the transformer that was detected on the transformer surface. The crosshairs measure 423°F. Temperatures this extreme are classified as critical, according to generally accepted severity guidelines, and it was suggested that this piece of equipment be removed from service immediately.

Restricted Transformer Cooling Fins (QL) Transformer cooling fins should be free of restrictions in order to allow proper circulation of oil. The thermal image on the right reveals a set of fins that is colder than the 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 the transformer is entering the cooling fin at the top and flowing down as it cools, and eventually re-enters the transformer through the bottom of the cooling fin. The 3-20


assumption in this case is that there is no flow of oil in the set of fins indicated by the arrow. 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 the tanks on the other two phases. Defective internal contacts are generating enough heat to heat the surface of the left phase tank and the oil contained inside. There is a risk of explosion and resultant injury to personnel in the vicinity. This problem is critical and should be trended regularly to determine if it is getting worse. Repairs should be made 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 transmission lines. It is probably caused by a defective component, looseness, dirt or corrosion buildup. This type of repair would be done as part of regularly scheduled maintenance.

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Performance Applications Infrared Thermography can be applied to a large number of plant components that have an impact on generating station performance (heat rate). In general, the performance components targeted are those that are found in the steam cycle system, the fuel system, and the boiler. The techniques involved with thermal analysis of performance equipment are somewhat unconventional, as compared with the other applications discussed thus far in this document. The interpretive approaches used to analyze these anomalies are almost entirely dictated by the thermographer’s knowledge of plant performance and the related systems. Power plant performance related components, that can be evaluated with IRT, are featured in this section. They include: Valves Steam Traps Internal and External Boiler Process Headers Coal Fuel Lines Coal 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 has two un-insulated outlet headers (see arrows on visual and thermal images). Referencing the color scale at the bottom of the thermal image, the temperatures measured on the left outlet are approximately equal to the ambient temperature (75°F - 100°F). The temperatures measured on the right outlet header are consistently hotter. This is an indication of steam passage through the right side of this valve, probably due to a deteriorated valve seat. The valve 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 on the outlet side (top), is passing steam. That is the case here, where a temperature in excess of 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 overall condition 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 is determined by comparing the temperature of the valve at the shell side (approximately 500°F), to the temperature of the valve outlet (394°F indicated by the crosshairs). The combination of a 106°F temperature differential (500°F - 394°F = 106°F), and an extremely hot outlet temperature (394°F) is an almost certain indication that the valve is passing a considerable amount of steam. In the two bottom pictures, the replacement valve is shown visually and thermally. The temperature contrasts between the replacement valve and the defective valve are dramatic. In the thermal image of the replacement valve, the shell side valve temperature is approximately 450°F. Comparing this with the outlet temperature of 141°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 is over 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 for the PdM Group to use to trend this new valve over time. 3-25


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 image displays a pattern that would indicate air infiltration through the upper left hand side of the manway. The manway cools toward the upper left indicating a draft of air across the cover. If there were no air infiltration, the entire manway cover would be uniform in temperature. Undesired infiltration of air into a boiler will impact the thermal efficiency 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 or deteriorated insulation behind the lagging at the spots where the temperatures are the highest. If insulation problems are suspected on a particular unit, IRT can be used in the manner shown above to inspect entire sections of wall in literally seconds. 3-26


Boiler Tube Restriction (QL) The thermal image shown above was taken from the inside of a monotube boiler during a hydro flush test prior to unit start-up. The picture isolates a section of waterwall. When the boiler is filled with 200°F water during the course of this test, all of the tubes should rise in temperature uniformly from ambient to approximately 200°F. If there is a restriction that prohibits flow in one or more tubes, there will be an effect similar to the one in the thermal image above. The arrows point to a single cold tube that is unable to fill because of a restriction (probably slag from welds made during waterwall repairs). A restricted tube will not receive the cooling it needs from the flow of water through it. If it goes undetected, it will probably rupture at a point in time after the unit is brought on line. This would cause unscheduled downtime and associated 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 flame impingement toward the lower right hand corner wall section. The image was taken with a high temperature infrared lens from an inspection port in the boiler roof, while the 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 temperature lens 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 the section 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 a condensate pump reveals air infiltration. This is indicated on the thermal image (at right) by the blue areas to the left of the arrow. The color scale on this thermal image is designed 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 manifests itself 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 of this same section of floor (Thermal Image A) was taken during an IRT inspection in an attempt to try to determine the approximate location of a steam leak in a header somewhere beneath the floor. It was suspected that the hot spot on Thermal Image A was caused by heat transfer from the steam leak to the surface. An excavation of the floor revealed a ruptured Y-Joint in the pipe (Visual Image B). The header was repaired and the floor was replaced. A re-inspection of the floor, performed after the repairs were made and after the unit was put back into service (Thermal Image B), does not 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 visual image on the left, are carrying pulverized coal for combustion from the mill exhauster to the burners at the boiler. The thermal image on the right indicates that the 3rd fuel line 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 combustion efficiency and will naturally warm the fuel lines. The relatively cool fuel line in this example indicates that there is limited, or completely obstructed, flow in this line. This will prohibit the necessary fuel from reaching the burners. The obstruction could be anywhere in the line, or in a diffuser. The line should be blown clear at the next opportunity.

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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. An emergency shutdown prevented operations from running down the stored fuel in the bunker. The outage resulting from this emergency shutdown was estimated to last three months. The bunker would either have to remain full for this extended period of time, 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 approximately 3 to 4 weeks after the shutdown occurred. Hot areas are beginning to develop on the surface of the coal in the bunker. Approximately 5 or 6 bunkers, out of 16, showed similar thermal patterns at different times throughout the outage. In the bunkers where the hot spots were observed, an increased presence of carbon monoxide was also detected. It was determined that the heat and air mixing with the fuel presented a potential for combustion, and fire. The PdM Group sealed off air entry passages, and injected regulated doses of liquid nitrogen (while keeping the ventilation system on!) into the bunkers throughout the duration of the outage. These techniques were successful in stabilizing the potentially dangerous conditions. The plant was able to complete the outage without incident. Additionally, significant labor and equipment costs were avoided because expensive efforts to manually empty the bunkers were avoided.

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EPRI TR-108935

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