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Currently, gas leakage source detection is conducted by the human senses and experience. The development of a remote gas leakage source detection system is required. In this research, an infrared camera was used to detect gas leakage. The gas can be detected by the absorption of infrared rays by the gas and the infrared rays emitted from the gas itself. A three-dimensional reconstruction of a leaked gas cloud was performed to identify the gas leakage source and the flow direction of the gas. The so-called four-dimensional reconstruction of the leaked gas cloud, i.e., reconstruction of three-dimensional images of a gas cloud varying with time, was successfully performed by applying the ART (Algebraic Reconstruction Techniques) method to the multiple optical paths of infrared measurement.

With the retirement of skilled workers and the aging of gas plant facilities, interest in the development of automated and remote gas detection methods is increasing. Therefore, a gas leak detection method using infrared camera has been proposed. Invisible gas can be detected from infrared absorption of gas and the emitted infrared ray from the gas itself. The piping of a gas plant is very complicated, so it is very useful that the gas leak source can be identified. In this study, the gas leak source identification is performed by the inverse problem analysis using the infrared measurement data. The least residual method is one of the typical inverse problem analysis methods, and it estimates the position of the gas leak source from the sequential infrared images of the gas cloud distribution and flow. It was found from numerical simulation and laboratory experiments that it is possible to estimate the position of the gas leak source even when the leak source is hidden by piping in the infrared image.

The current gas leakage source detection was conducted by the human senses and experience. The development of remote gas leakage source detection system is required. In this research, infrared camera was used to detect gas leakage. The gas can be detected by the absorption of infrared rays by the gas, and the infrared rays are emitted from the gas itself. Three-dimensional reconstruction of leaked gas cloud was performed to identify the gas leakage source. The 3D reconstruction of leaked gas cloud was performed by the multiple optical paths of infrared measurement and inverse tomography analysis. Algebraic reconstruction techniques (ART) method was applied to reconstruction. In the experiments, the gas concentration distribution was simulated by the arrangement of gas cells. It was found that the gas concentration distribution composed by gas cell could be estimated by infrared images obtained with few optical path and ART method.

On the infrared thermography image, a false temperature change caused by the relative displacement between moving object and infrared camera is obtained. This paper shows the motion compensation system with the infrared-optical synchronous measurement. Displacement information of the specimen is calculated from the series of visible light image using the digital image correlation method (DIC). The displacement information on the visible image is reflected to the infrared image by the homography transformation. The random white pattern which can’t be detected by the infrared camera was drawn on the measured surface for DIC process. The developed motion compensation system was applied to the thermoelastic stress analysis and dissipated energy measurement. It was confirmed that a false temperature change and edge effect can be removed by using developed motion compensation system.

This paper presents an inverse analysis method for estimating the temperature and thermal residual stress distributions in the pipe from the temperature history measured on the outer surface. A regularization method was introduced. It is found from numerical simulations that the proposed inverse analysis method with regularization is useful for obtaining a reasonable estimate of the inner surface temperature and thermal stress.

The present authors proposed the electric potential computed tomography (CT) method for identifying defects in electric-conductive bodies from electric potential distributions observed on their surfaces under electric current application. When the piezoelectric material is pasted on a cracked body subjected to mechanical load, the electric potential distribution can be obtained due to the direct piezoelectric effect without applying the electric current. The passive electric potential CT method proposed by the present authors uses this distribution. This paper describes the fundamentals of the passive electric potential CT method, inverse analysis schemes and its applications for identification of a through-thickness crack, a surface crack, plural cracks and delamination in a layered composite material. The usefulness of the method is demonstrated.

An inverse heat conduction analysis method for piping elbow was developed to estimate the temperature and stress distribution on the inner surface by measuring the outer surface temperature. In the paper, the accuracy for the thermal stress calculation using the inverse heat conduction analysis method was confirmed by comparing with the reference results from normal FE heat conduction and thermal stress analyses. In the case of the measured-basis fluid temperature input from a high temperature–pressure test, the inverse analysis method estimated the maximum stress change by 7% conservative comparing with the normal FE analyses.

Thermal fatigue may develop in piping elbow with high temperature stratified flow. To prevent the fatigue damage by stratified flow, it is important to know the distribution of thermal stress and temperature history in a pipe. In this study, heat conduction inverse analysis method for piping elbow was developed to estimate the temperature history and thermal stress distribution on the inner surface from the outer surface temperature history. In the inverse analysis method, the inner surface temperature was estimated by using the transfer function database which interrelates the inner surface temperature with the outer surface temperature. Transfer function database was calculated by FE analysis in advance. For some patterns of the temperature history, inverse analysis simulations were made. It was found that the inner surface temperature history was estimated with high accuracy.Copyright © 2013 by ASME

The present authors proposed the passive electric potential CT method using an electric potential distribution appear- ing due to the direct piezoelectric effect on a piezoelectric film pasted on a structure subjected to mechanical load. By applying an electric pulse on the film for emitting pulse-echo due to the inverse piezoelectric effect, the active pulse-echo method was proposed. In this paper a simultaneous application of the passive and the active methods using the piezoelectric film with multi- electrodes was made for the quantitative identification of through-cracks. The electric potential was measured on the film of a cracked specimen subjected to a varying load. The electric pulse was applied to an electrode on the piezoelectric film and reflection waves were received at several electrodes on the piezoelectric film. Inverse analysis was made to identify the cracks from the observed electric potential distributions and the reflected waves. It was found that the active/passive method was useful for the estimation of the crack depth, for which the passive method was not efficient. The effectiveness of the active/passive method was shown.

A new remote nondestructive inspection technique that is based on thermoelastic temperature measurement by infrared thermography was developed for the evaluation of fatigue cracks propagated from welded joints in steel bridges. Fatigue cracks were detected from localized high thermoelastic temperature changes observed at crack tips induced by stress singularity under variable loading resulting from traffic on the bridge. A self-reference lock-in data processing technique was developed for improving the signal/noise ratio of the thermal images recorded in the crack detection process. In this study, remote and nondestructive detection of fatigue cracks in an actual steel bridge in service was performed by the self-reference lock-in thermography method. The accuracy of this method was improved with a motion compensation technique.

A new remote nondestructive evaluation technique based on thermoelastic temperature measurement by infrared thermography was developed for the evaluation of fatigue cracks propagating from welded joints in steel bridges. Fatigue cracks were detected from localized thermoelastic temperature changes at crack tips due to stress singularities generated by wheel loading from traffic on a bridge. A self-reference lock-in data-processing technique was developed to improve the signal-to-noise ratio of the thermal images obtained in the crack detection process. Thermoelastic stress analyses in the vicinity of crack tips were carried out after the crack detection process by self-reference lock-in thermography. The stress distribution under wheel loading by traffic was measured by infrared thermography. Stress intensity factors were directly evaluated from the measured stress distribution. It was found that these fracture mechanics parameters can be evaluated with reasonable accuracy by the proposed technique, enabl...

A new remote nondestructive evaluation technique, based on thermoelastic temperature measurement by the infrared thermography, was developed for evaluation of fatigue cracks propagated from welded joints in steel bridges. Fatigue cracks were detected from localized thermoelastic temperature change at crack tips due to stress singularity under wheel loading from traffics on the bridge. Self-reference lock-in data processing technique was developed for the improvement of signal-to-noise ratio of the thermal images obtained in the crack detection process. In this paper, experimental results of fatigue crack detection by the self-reference lock-in thermography are reviewed.