Thermography measurement is an essential part in the predictive maintenance system of underground district heating networks. The results of the measurement are processed so that possible locations of damage are clearly discovered from the thermogram. A special image processing method is developed for analyzing the infrared measurements. The images are processed to produce ground temperature distribution curves. The measurements are carried out in different parts of the network every year and the results are compared to those of previous measurements. The measurement system consists of a mobile computer and an infrared thermal scanner to store the data and thermography measurements. The image processing system consists of an office computer and video systems for the analysis of the measurements. The analyzing system can be used for comparing the thermograms from previous measurements and for producing scaled temperature distribution curves of the measurements. The measurement also produces a large amount of other data and comments which are not included in the thermography measurement. The database system is intended for managing the data and for making it possible to use the image processing system as a part in the predictive maintenance system. The maintenance database contains a large amount of data needed for planning the measurements, inspections and renovations. The database is also used for storing the information of the past measurements and analyses. It also makes it possible to manage the large number of tapes and pictures which are produced by the analysis system. The measurement data is stored as an archive in the memory of the computer.

Maintenance methodologies are in developmental stages throughout the world as global competitiveness drives all industries to improve operational efficiencies. Rapid progress in technical advancements has added an additional strain on maintenance organizations to progressively change. Accompanying needs for advanced training and documentation is the demand for utilization of various analytical instruments and quantitative methods. Infrared thermography is one of the primary elements of engineered approaches to maintenance. Current maintenance methodologies can be divided into six categories; Routine ('Breakdown'), Preventive, Predictive, Proactive, Reliability-Based, and Total Productive (TPM) maintenance. Each of these methodologies have distinctive approaches to achieving improved operational efficiencies. Popular though is that infrared thermography is a Predictive maintenance tool. While this is true, it is also true that it can be effectively integrated into each of the maintenance methodologies for achieving desired results. The six maintenance strategies will be defined. Infrared applications integrated into each will be composed in tabular form.

In the Nuclear Power Generation Industry, Emergency Diesel Generators are a critical component in ensuring the ability to safely operate the plant. Relegated to a standby role, this equipment must be immediately available to provide power to important plant equipment needed to safely shutdown the reactor, in the event of a loss of normal off-site sources of power. Consequently, maintenance, operation, and surveillance of these generators is performed under close scrutiny, and any deviations from established parameters can potentially lead to the mandatory shutdown of the reactor, and subsequent loss of power generation revenue. At Peach Bottom Atomic Power Station, Thermographic Inspection has become an integral part of the operation of the Diesel Generators. Generators are operated according to the required surveillance tests, and a Thermographic Inspection is made at least twice a year. Some of the applications include checking for exhaust leaks, generator end bearing and cylinder exhaust temperatures, observing the effects of thermal mixing between crosstied cooling systems, and other mechanical and electrical troubleshooting.

An investigation is made using non-contact thermal infrared measurements to detect and measure wall thinning. Several NDE techniques are presently being used to detect and measure wall thinning. These techniques generally consist of radiography, eddy current, ultrasonic thickness measurements and visual examination. The most commonly used method for the detection of wall thinning, such as that caused by erosion/corrosion, is by ultrasonics thickness measurements. Taking ultrasonic thickness measurements can become very time consuming. In addition the examination must be performed from a suitable surface free from weld spatter, roughness, scale and/or other conditions that may interfere with free movement of the search unit or impair the transmission of ultrasound. Non-contact thermography, on the other hand, is much faster than ultrasonics and requires very little surface preparation. This paper will focus on the feasibility of using non-contact thermal infrared to detect and measure wall thinning.

This paper provides an introduction to EPRI's Infrared Inspection Technical Evaluation (IRITE) Project currently under development. The paper will describe objectives, planned efforts, status and preliminary results. The IRITE project is a computer based system that is intended to facilitate a rapid and consistent interpretation of typical infrared inspections. The system will prompt the user in the diagnosis via systematic evaluation of available information. Based on the results of laboratory and field testing, the evaluation system will identify the most likely root cause of the problem and provide information that will assist in preparing a cost benefit analysis on the appropriate corrective action. The increased attention on infrared thermography in the nuclear and fossil utilities has created a greater demand for information on the use of this technology. The main goal of the IRITE project is to provide a product that will identify both simple and complex component deficiencies. This information will provide a complete package that can be used by infrared thermographers with all levels of experience.

Over the past five years, infrared thermography has proven an effective tool to assist in required inspections on new masonry construction. However, with more thermographers providing this inspection service, establishing a standard for conducting these inspections is imperative. To attempt to standardize these inspections, it is important to understand the nature of the inspection as well as the context in which the inspection is typically conducted. The inspection focuses on evaluating masonry construction for compliance with the design specifications with regard to structural components and thermal performance of the building envelope. The thermal performance of the building includes both the thermal resistance of the material as well as infiltration/exfiltration characteristics. Given that the inspections occur in the 'field' rather than the controlled environment of a laboratory, there are numerous variables to be considered when undertaking this type of inspection. Both weather and site conditions at the time of the inspection can vary greatly. In this paper we will look at the variables encountered during recent inspections. Additionally, the author will present the standard which was employed in collecting this field data. This method is being incorporated into a new standard to be included in the revised version of 'Guidelines for Specifying and Performing Infrared Inspections' developed by the Infraspection Institute.

Certain quality requirements have been set for the waterproofing of bridges. Quality during the construction phase is currently controlled in practice by means of individual adhesive strength tests. Studies performed both in the laboratory and on two test bridges indicate that infrared thermography appears to be applicable for assessing the adhesion of waterproofing sheet membranes on the site of bridge works. The method can be used to localize those areas in which a waterproofing sheet membrane is defectively attached or completely detached from the underlay. The method makes it possible to obtain quickly a mainly general picture of adhesion, so infrared thermography and adhesive strength measurement are methods which complement one another very well. As far as the development of the measuring technique is concerned, the effect of the measuring conditions on the thermographic results should be studied in greater detail and heating methods suitable for field use should be developed.

To visualize the air flow into a room, we used a plastic screen, placed parallel to the air flow from a supply air diffuser placed at floor level. The screen takes the temperature of the air stream and registration of the screen temperature is made with an IR-camera. This gives a picture of the temperature distribution of the air stream. The information can be used to control the technical characteristics of the supply air device and to judge the impact of the air flow on human comfort.

The ROOFER program is being used by the U.S. Army to inspect and evaluate its built-up and single-ply membrane roofs. The results of the inspection effort are used to develop an overall roof condition index. The condition of the roof insulation can greatly alter the final condition index. By using an aerial infrared (IR) roof moisture scan, all the insulated roofs at most Army installations can be effectively surveyed in a very short time. The aerial scans have detected numerous areas of wet roof insulation, which has had a profound impact on the results of the ROOFER program. The scans have also provided management personnel with more accurate analysis as to the actual condition of the installation's insulated roofs.

Infrared thermography was employed to identify changes in plate thickness during the arc welding of steel plates. The step changes in plate thickness were found to uniquely affect the surface temperature distributions of the plates during the welding process. A technique was developed to identify the thermal profile irregularities ahead of the weld that were indicative of changes in plate thickness. The results of this investigation suggest that the calculation of the area under the linescan can be successfully used to identify thickness variations in a plate as it is being welded. The gradient of the area beneath the linescan was further found to be indicative of changes in plate thickness.

This paper describes progress made during the last year in identifying weld perturbations using indirect methods based on an infrared sensor. Using changes in the temperature gradient, it is now possible to identify the geometry of the weld pool and weld penetration changes due to welding current variations or plate thickness changes. The procedures for computing each of the penetration indicators were streamlined to reduce the computation time. Bead width was one of the methods used in an on-line control routine. A software was developed for on-line weld penetration control using the beam width as the error signal and the welding current as the control parameter.

In this paper, the effects of shielding gases on weld penetration were studied using infrared sensors. Argon, helium and mixtures of these gases were used in the experiments. Autogenous bead-on-plate welds were made keeping all welding variables except the shielding gas composition constant. Dynamic changes in the shielding gas composition were then introduced and corresponding changes in the thermal distribution of the molten pool and surrounding region monitored. After the fact metallography was used to determine puddle dimensions. These results were then compared to the infrared surface temperature measurements. Gradients in the molten metal pool were found to dramatically change as the puddle shape changed when a different shielding gas composition was introduced. This behavior was used in implementing dynamic weld penetration control.

The significance of peat as a local source of energy in district heating and electric power production is increasing in Finland and regular limited aerial supervision of peat stockpiles has been carried out from 1990 onwards. The problems for which thermography and auxiliary methods have been applied are as follows: (1) basic drying distribution of production field, (2) condition of the ditching, (3) volume of peat stockpiles, and (4) supervision of the production area's environment. In 1991 - 1992 we started investigating the possibilities of using thermography, infrared photography, false color video scanning and panchromatic photography in peat production. By increasing the basic drying level of the production field it is possible to accelerate the drying of peat and in that way to increase the seasonal yield considerably. No reliable and viable method is available for a quick analysis of this basic drying level on large areas. Our aim was to find differences in the basic drying level of peat production fields by means of aerial thermography. The tests were carried out in the laboratory, in production fields using field measurements and by airborne infrared scanning combined with simultaneous field measurements. The paper presents preliminary results on the use of thermography in defining the differences in the basic drying level of peat production fields.

Preliminary results on inversion of thermal wave images were presented at Thermosense XIV. A technique was introduced for removing the blurring of thermal wave images of planar subsurface features such as delaminations. At that time the technique was limited to the case of thermally isotropic materials, and also ignored multiple scattering effects. In this paper we extend the inversion technique to take into account both anisotropy and multiple scattering. An application to an anisotropic composite is presented.

Thermal wave imaging (TWI) has typically relied upon HgCdTe optomechanical scanning radiometers in the 8 - 12 micrometers spectral range for image acquisition. However, recent improvements in manufacturing technology, spatial resolution, and device efficiency make PtSi and InSb focal plane array (FPA) cameras an attractive alternative in the 2 - 5 micrometers spectral range. We have compared the performance of off-the-shelf imagers of both scanning HgCdTe, and PtSi and InSb FPA types, in typical TWI applications, such as boxcar image processing of plastics and metals. The relative merits of detecting transient surface temperature variations in the 2 - 5 and 8 - 12 micrometers bands are discussed.

A time-resolved infrared radiometry technique is developed which is applicable to detection of hidden corrosion in airframe structures and which implements an InSb focalplane array. The TRIR method can measure the loss of skin thickness due to corrosion and can also detect second layer corrosion when a sealant material is present at a lap joint. It has also been shown that the presence of corrosion product can be detected on the back surface of an aluminum plate free standing in air. Other experimental studies suggest that the presence of corrosion product, corrosion thinning of the plate and morphology changes at the aluminum-corrosion layer interface all affect the TRIR temperature-time signature. This raises the possibility of separating these contributions experimentally.

The aging of the commercial transport fleet increases the possibility of a reduction or loss of structural integrity through corrosion. Thermal imaging is a nondestructive evaluation (NDE) technique that is non-contacting and can rapidly inspect large areas. In this work, thermal NDE is used for characterization of corrosion in aircraft skin. Thermal images from an infrared camera are low in contrast and raw images give only qualitative results. The technique presented will use the time evolution of the thermal images to produce qualitative and quantitative information of the corrosion sample being imaged. This paper is going to show the results from fabricated material loss samples, electro chemical corroded samples and aircraft panels with corrosion. A quantitative comparison of results for the different samples will be shown.

A new algorithm of dynamic thermal tomography based on the numerical solution of 1D thermal testing problem is discussed. Experimental results are presented for carbon plastic material.

The increasing complexity of aerospace structures necessitates the development of advanced Nondestructive Inspection techniques/methods while current economic pressures require these inspections to be performed at lower costs. To this end, an automated infrared (IR) thermographic inspection system has been developed for the inspection of Superplastically Formed/Diffusion Bonded (SPF/DB) titanium structures. The IR thermographic system has demonstrated high reliability, while reducing inspection costs over conventional ultrasonic and radiographic inspections. A robotic system moves a radiometer through a series of preprogrammed locations where thermograms are collected and stored. The thermograms are then assembled into a continuous image for viewing on a scrolling CRT or output as a continuous plot. Aspects of the IR thermographic system, evaluation results from SPF/DB inspections, and potential applications to other advanced structures will be presented.

Several issues must be resolved before confidence in infrared thermography nondestructive evaluation (NDE) approaches that of more established NDE methodologies. Foremost among these are system sensitivity, repeatability, and interpretation of results. In recent years, synchronous imaging techniques have been demonstrated using a computer to control the thermal excitation, infrared image acquisition, and image processing. Advantages include simplified system setup and operation, repeatable measurements, and signal-to-noise ratio enhancement. In late 1991, LASC began a beta-site evaluation of a prototype Thermal Wave Imaging (TWI) system developed by the Institute for Manufacturing Research at Wayne State Univ. (Detroit, MI). This prototype is the forerunner of a production version currently under development for commercial offering as a fully integrated thermal NDE system. Applications will include quality assurance of manufactured aerospace composite structures and inspection for first and second-layer corrosion in aluminum (aging) aircraft structures. This paper describes the prototype system, and discusses results of specific experiments selected to demonstrate present capabilities of the system.

A thermal technique is presented for imaging subsurface damage and computing the depth of damaged areas for low diffusivity materials. The measurement technique presented uses uniform heating with quartz lamps over a large area. The surface temperature of the sample is collected using a scanning IR radiometer and a real time image processor during the cooling of the sample after heating. Flaw depths are computed by performing a numeric approximation to the surface Laplacian on each temperature image in the time series. The depth of the damage is then calculated from the time required for the amplitude of the surface Laplacian to reach a minimum in the region over the damage. Experimental results from the application of the technique to low diffusivity materials with surface and subsurface defects at various depths are presented showing the technique's ability to give quantitative depth of damage information. Additionally, the effects of variations in defect size on the time for flux minimum, and thus on the calculated depth, is also investigated. Finally, finite element simulations are compared with experimental results.

Every year there is an increase in the number of Glass Reinforced Plastic (GRP) composite vessels the Coast Guard inspects. A fast, nondestructive evaluation (NDE) technique is needed to facilitate these inspections. The technique must be suitable for use in field environments. Through a Small Business Innovation Research (SBIR) contract with the Coast Guard R&D Center, Industrial Quality, Inc. has performed a feasibility study evaluating the use of infrared thermography for such applications. The study demonstrated the ability of infrared thermography to detect hidden flaws through a variety of laminates and sandwich panel core materials. Empirical results matched well with analytical results of the sensitivity of the technique to various sizes of discontinuities at different depths. Following the successful SBIR program results, the Coast Guard R&D Center asked IQI to do a survey of the Steam Yacht Medea. The Medea had been repaired by a unique system of laying foam core and fiberglass over the ship's original steel-clad hull. The hybrid steel/foam core/GRP hull provided an additional structural configuration for the infrared thermography inspection equipment to handle.

Measurement by active thermal testing of effusivity on porous moistened material is analyzed. Moistened bricks show that thermal properties of this porous solid depend on water content. Various solutions of the heat transfer problem are taken into account and approximations introduced to simplify the data reduction are discussed. Error analysis is also considered to justify the adoption of relative technique. Errors analysis speaks strongly in favor of reference method which allows to avoid the measurement of incident energy and optical properties of a specimen. This procedure allows to introduce a rather simple expression to extract moisture values from one-side thermal test. Diffusivity measurement trough flash method is proposed to determine the influence of moisture on the variation of thermal conductivity.

A new thermal radiation technique using an infrared radiometer has been developed to detect flaws of materials, such as inclusion, crack and pinhole. In the present study, several incident radiation energies like sun, lamp and gas, were injected to the test material with an artificial internal flaw. Transient radiation temperature image of the flaw on the CRT represents the existence of the internal flaw with higher radiation temperature than that of the surface without the flaw. The characteristics of various incident energy methods were compared with each other. The detecting limitation of internal flaws is determined by the surface temperature variance of the tested materials. The heat flow around the flaw was numerically analyzed by solving a heat conduction equation to verify the surface temperature behavior above the flaws.

Temperature evolution of the irradiated surface of a layered sample was considered. A function is used to determine the moment and time for reading out the information (temperature) from the irradiated surface, when the time variations of the temperature curve slope are dependent on the thermal properties and thickness of the first layer only, thus enabling determination of the thermal properties of this layer and then the same of the second layer. If the thickness and the thermal properties of the layers are known, it is potentially possible to deduce from the temperature evolution the imperfects in the layers.

The problem with reconstructing the laser beam intensity distribution from temperature distribution over the front surface of the target heated by the beam has been solved analytically. Formulas allow one to retrieve the thermal flux for arbitrary values of thermal and physical parameters. The efficiency of algorithmic implementation is studied in numerical experiments.

Our objective is the development of an infrared system which is able to measure the temperature of a droplet, in order to validate theoretical kinetics models of heating and vaporization. A mathematical model has been derived to compute the performance in terms of sensitivity (signal-noise ratio) of an experimental system that measures the temperature of a methanol droplet using IR thermography. Based on that simulation, an experimental system working in the long wavelength range [8 - 12 micrometers ], has been built and characterized in terms of temperature calibration, and in terms of space and temperature resolutions. Then the system has been used to measure the temperature of a fixed methanol evaporating droplet. Finally, we propose a technique to track a moving droplet injected in a aerothermodynamic facility and simultaneously to measure its temperature and eventually its diameter along the trajectory.

For the past hundred years, government and private industry have produce hazardous waste in ever increasing quantities. These untold millions of tons of environmentally dangerous wastes have been disposed of by undocumented burial, simple carelessness and purposeful abandonment. Society has recently dictated that before new construction may be initiated, these wastes must be found and cleaned up. The first step is to locate these undocumented waste depositories. This paper describes how the non-contact, nondestructive, remote sensing techniques, of Computer Enhanced Infrared Thermography and Ground Penetrating Radar, may be used to detect buried waste sites, buried tanks/pits, and tank/pit leak plumes. This technology may be used from mobile vehicles, helicopters or man-portable system and is able to cover tens of acres per day depending upon the system method used. This proven, but relatively new technology, will be described in theory, by procedure and the use of case studies based upon successful projects during the last ten years.

Quantitative thermographic monitoring techniques are described for high-temperature testing applications. Techniques already used in arc-jet testing are described, along with other techniques used in wind tunnel test facilities which can be applied to solve problems related to quantifying thermographic data from arc-jet testing. These include methods to obtain reliable values for the effective optical properties, the surface emissivity, and the window or media transmittance. In addition, methods are discussed to obtain the required corrections for the spatial resolution, viewing angle, extraneous reflections, etc. and calibrations under conditions close to the test configuration.

Electromagnetic fields can be monitored by infrared thermography, using sensitive paints or coatings deposited on structures or thin films. Enhancement of the method by release of convective losses and conduction effects is demonstrated. This is obtained by modulating the amplitude of the fields and using a lock-in thermographic system. Examples of application are given which concern an interference field and a multimode field inside a wave-guide.

The design, fabrication, and testing of absorbing screens for infrared (IR) detection of magnetic fields at microwave frequencies are described in this paper. The material is developed in the form of thin flexible sheets (for detection screens) and machineable solid compounds (for parameter measurements). Surface currents on radiating structures and scattering objects are measured. The frequency range covered in this paper is 0.2 - 5 GHz.

Thermal imaging is a technique we had known quite a long time before really starting to use it in 1989. Most of the applications have so far been development-related but the process control of production machines is gaining more importance now.

The Nondestructive Testing Handbook series is published by the American Society for Nondestructive Testing (ASNT). The series is the premier U.S. publication in the nondestructive testing field, and it is widely used in other countries, as well. We have recently completed a plan to produce a Volume of the series---plus a Supplement--to support the Thermal/Infrared Method. Through this report, we extend the call for authors to SPIE readers.

The V. C. Summer Nuclear Plant is a 925mw nuclear powered pressurized water reactor located approximately 25 miles northwest of Columbia, South Carolina. The plant went into commercial operation in 1984. Since then, we have been on the Nuclear Regulatory Commissions list of "good" plants for the past two times this list has been released, we have been awarded Category 1 rating by the Institute for Nuclear Power Operations for the years 1987, 1991, and 1992 and we received the Westinghouse "American Beauties" award as one of the top ten most economical Westinghouse designed nuclear plants in the United States.

As this is being written, ASNT is planning to hold the first examinations for Level 3 thermographer in July 1993. This will be an historic event and it marks the culmination of a lot of effort by a lot of people.