infrared inspection of boiler tubes

8/2/2019 Infrared Inspection of Boiler Tubes

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8 8 C U M G R T K " G R T K E Q O 8 Y Y Y G R T K E Q O

EPRI NDE Center 1300 WT Harris Blvd., Charlotte, North Carolina 28262 PO Box 217097,

Charlotte, North Carolina 28221 USA 704.547.6100


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This document was prepared by

EPRI NDE Center

1300 WT Harris Blvd.Charlotte, NC 28262

Principal InvestigatorI. Zayicek, P.

This document describes research sponsored by EPRI.

The publication is a corporate document that should be cited in the literature in the followingmanner:

Evaluation of an Advanced Infrared Thermography System for Inspection of Boiler Tubes:

EPRI NDE Center, Charlotte, NC: 2000. {1000614}.


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Infrared Thermography (IR) is widely used by electric utilities as a key component of their

predictive maintenance programs. IR can also be used for materials testing. One application,

described in this report, is an advanced IR technique for inspection of boiler tubes. A thermalinjection technique is used to identify areas of wall loss in the tubes. An evaluation of this

technique, conducted at the EPRI NDE Center, used removed from service boiler tubes and

machined flaw targets to assess the effectiveness of this IR technology. The results of this

activity indicate that this technique is very effective for flaw detection and shows potential as atool for through-wall flaw sizing.


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The EPRI NDE Center participated in a demonstration and evaluation of an advanced infrared

thermography system for the inspection of boiler tubes. The activities took place at the EPRI

Charlotte, NC facilities and were monitored by EPRI staff with support from Tennessee Valley

Authority, Carolina Power & Light and Duke personnel. ThermTech Services, Inc.

demonstrated the equipment. The goal of the activity was to define the detection and sizing

capabilities of ThermTechs PVM-4000 IR inspection system. A series of carbon steel flat platesand boiler tube mockups, with machined targets, were used for the evaluation.

$ C E M I T Q W P F

Infrared thermography (IR) is widely used by electric utilities as a predictive maintenance tool

for assessment of operating electrical and mechanical equipment. Thermal images of theoperating equipment are collected with the IR system and analyzed to determine continuedequipment operability. This type of IR inspection is referred to as apassive mode because the

self-emitted radiant energy from the component being inspected is used for the analysis. IR canalso be used for nondestructive evaluation (IRNDE) of materials. This application may require

an active or thermal injection approach to generate a thermal event in a component. Theresulting thermal pattern can then be analyzed to assess material integrity. The active or thermal

injection approach requires generation of a controlled flow of thermal energy across the materialbeing inspected, an IR device to collect the thermal data, and data analysis software to

manipulate and analyze the collected data. Thermal injection for active IR can typically beaccomplished using hot (or cold) water, hot (or cold) air blowers, high power lamps, or induction

heaters.

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The ThermTech PVM-4000 IR inspection system consists of four major components:

a portable aluminum framed scanner assembly that breaks down to fit through a man-way,

a high power quartz lamp to accomplish thermal injection,

an infrared camera to gather thermal information,

a data acquisition system to process the thermal data and facilitate off-line analysis (figures

1a,b).


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The scanner is assembled once inside the boiler and suspended from above by chain fall or other

convenient device. The camera/lamp fixture rolls on tracks attached to the rigid beam frame andis positioned vertically by a variable speed gearmotor hoist. The speed of the motor and

intensity of the quartz lamp are selected to match the characteristics of the material beinginspected. Data acquisition file sizes are set up to accommodate the length of the area to be

scanned. Data is typically collected in 0.1 increments vertically. For the boiler tubeapplication, the speed of the scanner results in an inspection rate of approximately 4 to 5 squarefeet per minute.

The IR camera, currently used with the system, is a Raytheon Amber Radiance 1 with an indiumantimonide, focal plane array detector, operating in the 3-5 micron spectral band. The camera is

scanned in tandem with the quartz lamp over the inspection area (figure 2). During dataacquisition, the camera gathers data ahead of the quartz lamp (unheated area) and behind the

lamp (heated area) to facilitate an initial data conditioning step of image subtraction. The imagesubtraction algorithm minimizes the effects of surface anomalies during the data analysis processand allows pertinent targets to be more readily identified.

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The ThermTech data acquisition/data analysis system runs software based on algorithms initially

developed by NASA for other material inspection applications. ThermTech is the exclusivelicensed user of the patented technology. The software is designed to provide defect detection,

location and sizing information. For boiler tube inspection, three analysis tools are available fordetection and sizing.


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An Excel spreadsheet format is used to organize and store the collected data. The spreadsheet

provides vertical position of the scanner (typically in 0.1 increments), referenced to a knownbenchmark elevation, along with a corresponding wall thickness reading for each tube in thefield of view (usually 4-6 tubes). Table 1 shows a segment of a typical data set.

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2.12 0.266 0.280 0.302 0.294

2.12 0.262 0.273 0.301 0.290

2.11 0.260 0.272 0.301 0.287

2.11 0.260 0.269 0.299 0.280

2.11 0.259 0.269 0.296 0.274

2.11 0.259 0.269 0.293 0.269

2.10 0.260 0.269 0.290 0.265

2.10 0.259 0.268 0.282 0.262

2.10 0.260 0.268 0.273 0.259

2.09 0.260 0.267 0.267 0.258

2.09 0.261 0.268 0.260 0.257

2.09 0.261 0.269 0.256 0.255

2.09 0.261 0.267 0.253 0.2532.08 0.259 0.268 0.250 0.253

2.08 0.259 0.269 0.249 0.254

2.08 0.259 0.268 0.249 0.256


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The Excel data spreadsheet allows the user to display wall thickness graphically as illustrated in

figure 3. Nodes depicted in the graph correlate with a change in wall thickness, usuallyassociated with general wall wastage or with a localized wall loss condition such as caustic

erosion. Figure 3 is a graph of targets in a carbon steel plate but a similar presentation would begenerated for detected boiler tube targets.

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Series1

Series2

Series3

Series4

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The software can also generate a false color image of the inspection data as shown in figure 4.

This format is useful as a visual aid in screening areas of interest along the tube length. In theimage below, detected targets are presented as bright yellow spots. Each area of interest can alsobe queried to provide location and wall thickness data.

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The analysis software package provides ample information for identification of areas of concern,

a global data storage format to support trending and report generation, and visual aids to supportpresentation of results to those unfamiliar with the technology or with the application.


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The primary goal of the evaluation activities was to determine the detection and sizing

capabilities of ThermTechs PVM-4000 IR inspection system. Several sample plates withmachined targets were fabricated for this exercise. The EPRI NDE Center provided carbon steel

flat plates with thicknesses of 0.312 and 0.375, with a series of flat-bottom and round-bottomholes. Additionally, a section of boiler tubes (0.290-0.312 wall), also containing machined flat-bottom and round-bottom holes, was included in the test.

During the evaluation activities, the ThermTech scanner and support frame was suspended froman overhead crane in the EPRI NDE Center high-bay to simulate positioning inside a boiler (see

figure 1a). Each sample to be inspected was setup in the path of the scanner. Calibration pieceswere attached to the samples prior to scanning to facilitate subsequent detection and sizing

activities.

ThermTech initially collected data on both flat plates and the boiler tube section sample. Themajority of the targets were detected, but no through wall sizing was completed. A recalibration

of the system using thicker calibration pieces was not successful in improving sizingperformance.

ThermTech then collected data on a flat carbon steel plate and a section of boiler tubes with

nominal 0.250 wall thickness. Again, good detection results were obtained on the plate and theboiler tube section. Table 2 lists target sizes and depths in the 0.250 thick carbon steel plate thatwere successfully detected.


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1 .375 flat bottom .188 Y

2 .375 Flat bottom .125 Y

3 .312 Flat bottom .188 Y




7 .375 round bottom .188 Y




11 .250 round bottom .188 N

12 .250 round bottom .125 N











23 1.00 round bottom .188 Y


ThermTech was not able to provide a through-wall depth size for the machined flat-bottom and

round-bottom hole targets. However, it was determined that good through-wall sizing wasachievable on the non-circular boiler tube targets that had their long dimension coincident with

the scanning direction. The sizing results on these types of targets were verified with anultrasonic instrument.


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Successful detection and sizing of the elongated targets in the boiler tube sample indicates that

the system is capable of detecting and sizing areas of general wall wastage and areas withfavorable target shape and orientation. The successful detection of a majority of the targets in

the carbon steel plate indicate that, at a very minimum, the ThermTech equipment is an excellentscreening tool for target identification


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The ThermTech PVM-4000 IR inspection system was also tried on a pipe inspection application.

The pipe is a 12 diameter, 0.375 wall, carbon steel pipe with a 0.250 thick rubber liner. Thepipe is designed to carry a corrosive slurry. The owners of the pipe are looking for a

nondestructive inspection method for early detection of blistering and disbond of the rubberliner. The typical failure scenario of the liner begins with blistering of the liner, probably due to

a combination of inadequate installation techniques and effects of the hot slurry carried in thepipe. The blistered areas eventually tear, exposing the pipe wall to the corrosive effects of the

slurry. Once the liner has been breached, the affected areas are detectable with an IR camera. Itwould be preferable to detect the blistered areas before failure to allow for maintenance planningand mitigation of the situation.

For this application, the intent was to investigate the potential of the inspection technique fordetection of blistering. Note that, the current configuration of the ThermTech system is for

inspection of boiler tubes and therefore is not optimal for pipe inspection. This wasThermTechs first experience with inspection of rubber-lined, carbon steel pipe.

The rubber-lined pipe was stood on end to line up with the scanning direction of the PVM-4000

(figure 5). The system was then calibrated and data was collected on the pipe in an area whereliner blistering was apparent (figure 6).

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Several data sets were collected to optimize the scan speed for detection of blistering. The

resultant reconstructed thermal image showed areas of blistering that correlated withmeasurements taken on the pipe (figure 7).

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Inspection of the rubber-lined pipe indicated that the active thermal injection technique used byThermTech is potentially useful for a variety of material inspection applications. Someadditional development is needed to optimize the scanner hardware and analysis software for thisapplication.


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The EPRI Fossil NDE Center, Target 59, supported the evaluation of the THERMTECH PVM-

4000. For further information on this activity contact Paul Zayicek, (704) 547-6154,[email protected]

For further information on the PVM-4000 system and associated inspection services, contact

Tom Reilly, (973) 661-1748, [email protected], or Ron Jacobstein, (561) 225-2731,[email protected], at ThermTech Services, Inc.


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infrared inspection of boiler tubes

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