Performing a complete thermographic survey for a utility, process plant, etc. involves looking at hundreds of components. Generally, they are multiple pieces of identical equipment which operate simultaneously, and the redundancy allows for comparative evaluation between these pieces of equipment. When performing this evaluation with thermography, valuable information can be obtained for a predictive maintenance program. Some applications exist where quantitative data is not required to diagnose and recommend appropriate corrective action. In these cases, qualitative techniques may be adequate in providing the needed information. Most applications, however, require assigning values to observed thermal patterns for the purposes of trending, designating severity levels, and assigning priorities. In these cases, comparative thermography can be used to provide the best available data in lieu of ideal thermal measurement capabilities. Changing load considerations, techniques in performing rough emissivity estimates, and the ability to differentiate emissivity differences on energized or rotating equipment give the predictive maintenance engineer the ability to provide useful information under the less—than—ideal circumstances frequently encountered in the field.

The success of a thermographic program hinges on many factors. These include, among others, the selection of appropriate inspection equipment training of personnel having the necessary backgrounds and technical skills; and creating a management plan. Also critical to success is developing the day to day protocol of the program. These guidelines and procedures not only help the thermographers optimize their inspections, they also ensure the fmdings will produce maximum benefits within the organization. This paper discusses a general protocol of operations developed from examples of practicing thermographers. During the early stages of developing a program, there is protocol that creates an organizational climate conducive to utilizing thermography, while also establishing some of the logistics needed to support inspections. The inspections themselves benefit greatly from structure—everything from plotting inspection routes to creating data files. After the inspection further protocol suggests how the fmdings will be analyzed and reported. Other issues, such as safety, education, and designing inspectable equipment, must be addressed on an on-going basis to maintain and refme a program. While no single protocol is right for all situations, the generalizations presented in this paper will serve as a valuable framework for many thermographers, both those who work within organizations as well as those providing consulting services. We have found the end result of a well developed protocol is a more efficient inspection program and a program that produces higher quality and more consistent benefits.

This paper will address actual cash savings due to infrared preventative maintenance in electrical, roofing and steam applications. It will investigate the positive savings when recommendations were implimented and the cost attributed to recommendations ignored.

This paper describes the development of an integrated infrared program within a nuclear operatingcompany (chartered to run 3 large nuclear plants - Hatch, Vogfle, Farley) from the early conceptual stages to the beginnings of a workable end product. We have learned through this process that the program we fashioned can never be finished but must always be evolving with change and the equipment we survey.

The purpose of this paper is to look forward into the future of "Predictive Maintenance" as it applies to infrared thermography. A discussion on what "Predictive Maintenance" really means is necessary to lay the groundwork for the look forward.

Vattenfall (Swedish State Power Board) was the first company to use the thermographic technique for inspection of high tension electrical equipment. The method has mainly been used for inspection of switchgear- and transformer stations. Recently Vattenfall has introduced a high resolution imager mounted in a helicopter for inspection ofjoints in the transmission lines. The inspection programme has started due to some phase dropping caused by increased resistance in the joints. The Rank Taylor Hobson Talytherm 8-1000 camera is mounted in a vibration free rig under the fuselage of the helicopter. The inspector, seated alongside the pilot, controls all the functions of the camera, together with the viewing angle pan and tilt, with the use of a single control panel. Mounted in front of the inspector is a 9" monitor on which the thermal image is displayed. The complete inspection is recorded on a S-VHS video tape for later retrieval together with comments and inspection data such as line identification, tower number, load and weather conditions. A HP-computer with the Talytherm T.E.M.P.S. Imager/Data analysing system is used to determine over-temperature compared with the transmission line. As the reconditioning criteria is based on the joint resistance an FEM computer programme has been developed to calculate the resistance using the temperature pattern on the surface of the joint and the connecting lines. The temperature pattern based on data such as: geometrical data, resistance, load, wind speed and direction can be calculated with the programme. The resistance can then be determined by comparing the results with the measured temperature pattern by the thermal inspection.

The research program on energy-economy buildings and building parts (ETRR) has been launched by the Department of Energy in the Ministry of Trade and Industry of Finland. It is a large nationwide research program, which includes both renovation and new building. The project "Renovation concepts for private houses" is a part of the research area of renovation, in which the aim is to find alternati­ ves for renovation procedures for selected private houses representing various decades. These procedures should lead into decrease of 25 - 75 percent of the present consumption of heating energy. The renovation concepts include both structural renovation procedures and repairs of HVAC-systems. The selected houses in the project were submitted into energy performance monitoring with air tightness measurements and thermal imaging.

This paper deals with a case study of a building envelope retrofit of an insulated sheet steel and corrugated metal clad building. The building in discussion is a satellite testing facility which requires specific clean room conditions with controlled interior temperature (22 degree(s)C +/- 1 degree(s)C) and high relative humidity conditions (45% +/- 3%) to facilitate satellite testing programs. Preliminary mechanical system inspections indicated substantial increase in air intake to make up for air leakage losses. An infrared inspection along with an approximate air leakage test of the building envelope was requested by the client to determine the magnitude of the building envelope problem. This investigation concluded that significant air leakage was present throughout the building envelope and that existing mechanical systems did not have sufficient capacity to pressurize the building and negate wind and stack effect. Exfiltration particularly through openings on the top sections of the building were causing interior moisture to saturate wall insulation and render it ineffective. Concern for rusting of metal components was indicated. The subsequent envelope analysis discovered a number of typical metal building details that led to poor air tightness and wall insulation ineffectiveness. These were correlated to infrared investigation data. The retrofit solutions produced for this building not only apply to this building but to other similar building types. Further investigations indicated that air leakage and mechanical system performance were significant problems with buildings using metal cladding systems comparable to this building. Quality control before, during and after construction was identified as an important function of the architectural commissioning of the retrofit work and infrared investigations were used to verify locations of air leakage and insulation effectiveness.

Field documentation of uncontrolled air movement in a newly constructed commercial building can be difficult to pinpoint. This task becomes more complicated when the building is occupied and the parties involved are seeking undisputable evidence as is the case of the building which is the subject of this paper.

Infrared thermography can be effectively utilized as an inspection technique for air distribution systems. Although systems are designed with increasing efficiency every year, the effectiveness of a system often remains without evaluation. Many times inadequate room temperature regulation is blamed on equipment capabilities when it is actually the installation or poor equipment condition that is at fault.

District heating pipelines are often exposed to very hard conditions in their environment. External and sometimes also internal corrosion may soon damage the steel pipes and the ground water may damage the thermal insulation. The planned period of utilization is about 20 to 30 years, but it may also be considerably longer if the pipelines are well maintained. The goal of this project was to develop a measuring system so that potential leak points could be located as early as possible. A method is developed for analyzing the condition of underground district heating pipelines. The method is based on the infrared measurement of the ground surface temperature. The measurement is made by using a mobile infrared scanner which is fixed to a car. The analysis is carried out by using the mobile equipment and a system for image processing. The system is connected to the preventive maintenance data system and the network maps. The infrared video recording is processed to produce a longitudinal temperature distribution curve of the ground above the district heating culvert. The temperature distribution is compared to the network map in order to distinguish the 'normal' temperature peaks from the exceptional ones. The maintenance data system uses an image data base so that the temperature curves of previous measurements can be used for comparison. The reliability of the measurement system was evaluated by making a series of tests and comparative measurements in a test field in which all the most common types of damage were constructed and run for about two years. The test field was run in controlled conditions in order to find out how soon and how well the different kinds of faults could be detected in ground surface temperature.

Paper surface topology analysis with infrared thermography is described. Heat is applied perpendicular to the target. Temperature distribution of the sheet correlates well with the surface height distribution when the sheet is placed on the isothermic plate. Mathematical tools for data analysis and the mechanisms behind the curl and cockles are briefly discussed. Curl in paper and paperboard is defined as deviation from the flat form.

An integrating-cavity sensor for temperature measurement of the steel sheet in a continuous annealing furnace is described. The sensor includes a fiber optic cable for transmission of the infrared radiation from the sensor head within the furnace to the double-wavelength detection unit located outside the furnace. The sensor head includes a reflecting conical cavity positioned above the steel sheet in order to increase, and thus stabilize, the effective infrared emissivity of the sheet surface as well as to reduce spurious reflections from other sources within the furnace. The fiber optic cable is both decentered and tilted with respect to the cavity axis in order to minimize straight-reflection losses through the fiber cable gate. Preliminary results after in-furnace installation will be described.

Feedback control of the weld process is a step at improving weld quality while reducing lengthy inspection processes. The key to successful control of the weld process is to choose a parameter (or parameters) that can be monitored and provide the information necessary to correctly adjust the weld input parameters. The sensor used for this study detected penetration by monitoring the infrared radiation on the back side of the girth weld.

The presence of cracks significantly decreases the structural integrity of thin metal sheets used in aerospace applications. Thermographic detection of surface temperature variations due to these cracks is possible after external heating. An approximate line source of heat is used to produce an inplane flow of heat in the sheet. A crack in the sheet perturbs the inplane flow of heat and can be seen in an image of the surface temperature of the sheet. An effective technique for locating these perturbations is presented which reduces the surface temperature image to an image of variations in the inplane heat flow. This technique is shown to greatly increase the detectability of the cracks. This thermographic method has advantages over other techniques in that it is able to remotely inspect a large area in a short period of time. The effectiveness of this technique depends on the shape, position and orientation of the heat source with respect to the cracks as well as the extent to which the crack perturbs the surface heat flow. The relationship between these parameters and the variation in the heat flow is determined both by experimental and computational techniques. Experimental data is presented for through-the-thickness, subsurface and surface EDM notches. Data for through-the-thickness fatigue cracks are also presented.

Techniques for processing IR images of aging aircraft lapjoint data are discussed. Attention is given to a technique for detecting disbonds in aircraft lapjoints which clearly delineates the disbonded region from the bonded regions. The technique is weak on unpainted aircraft skin surfaces, but can be overridden by using a self-adhering contact sheet. Neural network analysis on raw temperature data has been shown to be an effective tool for visualization of images. Numerical simulation results show the above processing technique to be an effective tool in delineating the disbonds.

An outstanding problem of thermal wave imaging has been the blurring of the images caused by lateral diffusion of heat in the sample. In this paper we describe a technique for removing this blurring in images of planar subsurface features such as delaminations. This technique is based on a model which allows us to develop an algorithm which performs a mathematical inversion of the scattering process when it is applied to experimental data. The result is a theoretical and experimental demonstration that the blurring of thermal wave images is not due to any inherent loss of information in the diffusion process, but that it can, in fact, be removed by appropriate processing of the image. The result is a very significant improvement of the resolution of the imaging process.

An original concept for IR thermography nondestructive testing is validated. The principles of image and data processing investigated and developed as well as the utilization of AI should be transposable to other nondestructive techniques such as ultrasounds and X-rays. It is shown that modeling can be used in different ways to play a great part in the detection, the interpretation, and the sizing of the defects. The original concept lies in the comparison of experimental data with theoretical ones in order to identify regions of abnormal behavior related to defects. A Laplace transforms analytical method is successfully implemented in the case of composite materials such as graphite epoxy to identify a set of thermal parameters which contributes to the expertise. This approach is extended to a more complicated composite material such as Kevlar, which presents semitransparent characteristics. This modeling technique, which expresses experimental data in terms of thermal parameters, makes it possible to increase SNR and reduce the number of thermal images to be processed.

The thermal tomography technique in the form of ordinary or cross-sectional timegrams completes the transition from the amplitude to the amplitude-time information criterion in thermal NDT. It improves some features of NDT based on the signal images: more efficient identification of defects, detection and separation of internal layers, and better SNR.

Composite materials can show their advantages effectively only when material and structure have no failure. To ensure the quality of products, non-destructive testing (NDT) must be executed. Usually non-contact NDT-methods are preferred, and possible methods are thermography, radiography and holography. The most common contact method is ultrasonic. This paper presents results of detecting sub-surface defects from plastic composites using thermography. We have examined glass-fiber reinforced composites, which have several flaws occurring during manufacture. The results of thermography have been verified by using ultrasound or by cutting the specimen. Experimental results show that flaws can be detected if the wall thickness of the object is small enough and delamination-like failure is bigger than wall thickness.

The aim of this paper is to describe a procedure to evaluate the moisture content in porous medium by a non-destructive test. The method is based on the determination of the target thermal inertia by means of the measure of the energy input and the corresponding temperature increase, both obtained by 2-D optical sensors. Since the thermal inertia is strongly dependent from the water content, it is possible to estimate the spatial distribution of the moisture. This is done by applying a suitable mathematical model of the porous media accounting for the heat transfer in the transient state. In this phase of the research, we are chiefly interested in the analysis of the surface layer of the sample, so a simple thermal model of the dynamic energy balance can be used instead of a very complicated heat and mass transfer model. Tests are carried out on a series of flat homogeneous samples of bricks. The samples are first desiccated and afterwards conditioned to various known levels of moisture content. Then specimens are submitted to the test procedure, the measured thermal inertia is compared with computed values and correlated with the moisture content obtained following the gravimetric standard method. The test procedure consists in supplying a radiant flux in the visible and near-infrared band to the sample surface. Meanwhile, the local radiating field is carefully mapped using two spot radiometers and a calibrated CCD camera, working in this spectral range. The irradiation field is produced by standard lighting equipment and continuously monitored. The target global absorptivity in the 0.3 - 3 micrometers range is detected as well. The temperature variation is measured by an infrared thermal camera operating in the 8 - 14 micrometers band, linked to a proprietary real time grabbing, processing, and storing digital equipment. The most important information is contained in the initial temperature variation trend, therefore a very fast sampling rate is required. A dedicated software was developed producing the average temperature trend and also the local value of the thermal inertia.

This paper aims to illustrate the use of infrared thermography as a nondestructive and noncontact technique: (a) to observe the physical processes of damage and fatigue on metallic specimens subjected to rotating bending loadings; (b) to detect the occurrence of energy dissipation; and (c) to evaluate the limit of endurance of the tested materials.

The thermographic technique used for the nondestructive evaluation of bondline integrity in metal and silicone rubber bonded material is described. An AGEMA model 880 IR thermographic scanner combined with a 20-deg lens was used to detect the IR radiation from the test panel. A video tape recorder was used to record the live temperature distribution at 25 picture frames per second. A personal computer with an AGEMA TIC-8000 digital image processor was used to record and plot the temperature vs time. The technique was found to be capable of detecting subsurface disbonds as small as 0.0625 sq in. in 0.187-in.-thick thermal protection system bonded materials. The thermography technique meets all the requirements of other approved NDT techniques, and it works well with complex structures and is noncontaminating, noncontact, real-time, and portable.

Thermography was used to observe and inspect temperatures experienced in the field by the ground pad surface of elastomer track shoes operating on a U.S. Army M1 battle tank. Observations were made to define the temperatures generated by the track pads under paved road, high speed traveling conditions in order to relate them to durability failure modes, such as abrasion, cutting and chunking, and blowout (catastrophic failure of the pad). Elastomers studied and compared included styrene butadiene rubber, natural rubber, highly saturated nitrile rubbers and cellulose fiber-filled reinforcement rubber. Local surface temperatures were affected by the natural asymmetrical weight distribution of the vehicle, track/ground pad design and failure mode. Detection of failed rubber bushings located within the pad connector pins were also observed.

A quantitative thermographic NDE technique for the characterization of composite materials is under development along with supporting theoretical analysis. The TRIR technique differs from other pulsed thermography techniques in that the surface temperature of the specimen is monitored as a function of time during the application of a step heating pulse to the sample. Full-field images with temporal resolution faster than video frame rates are acquired with an infrared scanner by disabling the vertical galvanometer in the infrared camera and scanning the heating source across the sample. Alternatively, an InSb focal plane array is used to acquire the time-resolved images. The geometry of the heating source is selected to optimize the acquisition of information about the structure of composite materials. Experimental results in both simple and hybrid composite systems are discussed. The depth and lateral extent of interlaminar separation in composites subjected to impact loading are presented and the use of lateral heat flow techniques to image vertical defect structures is examined.

A full-spectrum (encompassing radiation on both sides of the Wien displacement peak) multiwavelength pyrometer was developed. It measures the surface temperature of arbitrary nongray ceramics by curve fitting a spectrum in this spectral region to a Planck function of temperature T. This function of T is modified by the surface spectral emissivity. The emissivity function was derived experimentally from additional spectra that were obtained by using an auxiliary radiation source and from application of Kirchhoff's law. This emissivity was verified by results that were obtained independently by using electromagnetic and solid-state theories. In the presence of interfering reflected radiation this general pyrometry improves the accuracy of the measured temperature by measuring an additional spectrum that characterizes the interfering radiation source.

An experimental investigation is carried out to study the development of Goertler vortices in hypersonic flow (due to 2D and 3D viscous interactions) and their effects on the wall heat transfer. The presence of vortices is detected through the spanwise periodic variation of sector, the wall heat transfer coefficient measured by means of a computerized infrared (IR) imaging system. Owing to the relatively high spatial frequencies contained in the output thermal images, a proper image restoration is developed. Measured wavelengths are compared with theoretical predictions.

An IR detection technique has been developed to detect and map electric fields near radiation sources or scattering bodies. In this paper, this IR technique is used to determine the most accurate use of standard electric D-dot and magnetic B-dot probes when used to measure EM fields in free-space or inside cavities. The measurement accuracy of these probes is determined as a function of frequency for three different measurement configurations. The effect of mutual coupling between two identical probes in close proximity is also presented as a function of the separation distance between the probes. The far-field voltage response of the probes is determined for an incident plane wave. The effect of placing the probes in a cavity on the measurement accuracy of the probes is determined.

An IR imaging technique for testing phased array radars at the system level in the field has been defined and demonstrated in a laboratory test setup. The technique uses a thin radar absorbing film material which is placed near the antenna structure to create thermal patterns which are viewed by an infrared imaging sensor. The thin film sheet resistance can be controlled to vary the absorption, reflection, and sheet temperature characteristics. The infrared image is calibrated radiometrically to provide measures of the microwave power density. Additionally, the thermal profiles show the effect of phasing differences between adjacent antenna elements. This paper describes the predicted and measured thermal characteristics of the absorbing material for a particular S-band waveguide source. This demonstration has shown the feasibility of using an imaging infrared sensor to provide rapid diagnostic evaluation of a phased array antenna.

Temporal aliasing is a problem common to all video imaging systems. Infrared video systems are particularly susceptible because of the relatively low (30 Hz) RS-170 frame rate. We have developed two systems which compensate for the effects of aliasing, and allow above-frame- rate events to be imaged. An optomechanically based system utilizes an unmodified commercial imager (Inframetrics IR 600) and allows images of repetitive thermal events at frequencies up to 4 kHz to be acquired. It acquires data selectively using a line-by-line scheme which compares the motion of the camera's horizontal scanning mirror to a reference signal correlated to the event of interest. The resulting images have an effective integration time of 125 microseconds. The focal plane array system is based on a 160 X 244 PtSi detector operating at the standard 30 Hz frame rate. Frame integration time is variable to a minimum of 100 microseconds. Data can be acquired synchronously with respect to an external reference signal derived from the target. The systems will be compared, and relative merits of each will be discussed.

Advantage of non-intrusiveness, capability for field measurement, and increased availability of IR imaging systems have resulted in their wider use for aerodynamic research. However, certain difficulties persist while using currently available systems for such applications. A critical evaluation of the IR imaging systems is presented on the basis of the state-of-the-art of IR imaging technology and experiences in wind tunnel and flight testing at NASA's Langley Research Center. The requirements for using IR thermography as a measurement tool in aerodynamic research are examined in terms of range, sensitivity, and accuracy of temperature measurement, temporal and spatial resolution, and features of target. Deficiencies of present IR imaging systems are identified, and user precautions to avoid such problems by proper selection and operation of these units are suggested. Different aspects of imager performance such as imager optics, video capabilities, and environmental tolerance are discussed. Electronic data recording and image processing hardware and software requirements are evaluated. Slit response tests and spatial resolution are discussed with the objective of obtaining reliable, accurate, and meaningful information from IR thermography measurements for aerodynamic studies.

A simple measurement technique for measuring the variation of directional emittance of surfaces at various temperatures using commercially available radiometric IR imaging systems was developed and tested. This technique provided the integrated value of directional emittance over the spectral bandwidth of the IR imaging system. The directional emittance of flat black lacquer and red stycast, an epoxy resin, measured using this technique were in good agreement with the predictions of the electromagnetic theory. The data were also in good agreement with directional emittance data inferred from directional reflectance measurements made on a spectrophotometer.

Laboratories engaged in the investigation of reactions involving the use of hazardous chemicals have a need to demonstrate the performance and safety of their fume hoods. This was done in the present work by using a tracer gas and a suitably modified infrared camera capable of viewing the movement of a tracer gas against a warm background. To further demonstrate the hood effectiveness, a simultaneous air sample is taken at the breathing zone of a manikin in place of an operator and analyzed for small amounts of the tracer gas.

Thermal diffusivity measurements by using flash technique are widely known. Here we focus the attention onto the description of a new method to measure the wear resistance of cemented carbide cutting tools. Wear process is highly influenced by the temperature of cutting and the good correlation between diffusivity and resistance of tools in a wide range of cutting speed was found. It allows to forecast in a non-destructive way the wear resistance of each cutting insert in seria. Finally the method developed tends to reduce the operational time in mechanical processing.

Since time began, people have been born and people have died. For a variety of reasons grave sites have had to be located and investigated. These reasons have included legal, criminal, religious, construction and even simple curiosity problems. Destructive testing methods such as shovels and backhoes, have traditionally been used to determine grave site locations in fields, under pavements, and behind hidden locations. These existing techniques are slow, inconvenient, dirty, destructive, visually obtrusive, irritating to relatives, explosive to the media and expensive. A new, nondestructive, non-contact technique, infrared thermography has been developed to address these problems. This paper will describe how infrared thermography works and will be illustrated by several case histories.

A method for the measurement of the spectral emissivity and temperature of a surface is presented. The spectrum of the infrared radiation of a heated surface is measured by means of a Fourier transform infrared spectrometer. To obtain emission spectra in units of spectral radiance a special calibration procedure is described which uses three black bodies as reference sources thus eliminating the need to measure the black bodies' surface temperatures. A theoretical emission spectrum of the investigated surface's radiance is fitted to the calibrated measurement resulting in (in the Gaussian sense) optimal values of spectral emissivity and temperature of the surface.

Thermography is a generic term indicating a process that results in a thermal map called a thermogram. Several types of thermography are reviewed including visual thermography, liquid crystal thermography, thermal sensitive coating thermography, thermocouple thermography and infrared thermography. Many infrared thermographic practitioners refer to their field as thermography when, in fact, it should be referred to as infrared thermography.

A formal effort to organize a thermographic certification program has been underway since late 1989. This paper outlines its present status and the hopes for its implementation.

Some of the strengths and weaknesses of the Delta-T system of classifying the severity of heating electrical equipment are discussed. An alternate method for prioritizing potential problems is explained. This system is referenced to nationally-recognized electrical equipment temperature standards which are adjusted to account for ambient temperature and load differences.