The increasingly recognized applicability of infrared thermography has caused developments of remote-sensing diagnoses for various engineering applications. A significant advantage of this technique is that we can diagnose invisible defects nondestructively and safely. For maintaining and managing various structures satisfactorily, it is very important to detect many kinds of invisible defects such as separation, cavity, inclusion and so on. Although the infrared thermography for NDT and E has therefore been examined extensively, few fundamental investigations have addressed the numerical computation to evaluate the detection mechanism and the quantitative limit under various conditions. It is important to discuss them theoretically with the aid of the appropriate numerical computation. In this paper, therefore, we certify them using a series of fundamental numerical computation with the aid of the concerned experimental investigation using the infrared thermography. From the numerical and experimental investigations, the effects of defect's depth and size on the detection are elucidated. In addition to the fact, it is obvious that the applicability of the present NDT and E depends on a heating condition and a relative difference of thermophysical property between the defect and its surrounding.

On the NDT and E for the diagnosis of defects using infrared thermography

Due to its great convenience for inspection of pipelines under special conditions, leakage localization with a single acoustic emission (AE) sensor has attracted increasing attention. However, the reported study achieves a good accuracy of leakage localization only for short source-to-sensor distance. In this work, an improved method for pipeline leakage localization with a single sensor is proposed based on modal acoustic emission and empirical mode decomposition with Hilbert transform (EMD-HT). The pipeline is considered as a cylindrical shell to compute the velocity dispersion curves of different guided wave modes. A criterion to select the specific wave modes for leakage localization is presented with the consideration of frequency matching, dispersive properties, and the modes’ confusing possibilities. Integrating the empirical mode decomposition (EMD) with wavelet transform (WT), the framework of the proposed method is developed. A number of field experiments were performed on a steel pipe with a continuous leakage source. The results show that using the proposed method, a maximum relative leakage localization error of 7.32% for the source-to-sensor distances from 0 to 33 meters (m) can be achieved, which is much improved than those of the reported method. With the capacity of precisely locating the leakage source within the range of 33m for each side of the sensor, the proposed method provides a promising way to make the AE technique more suitable for in-situ inspection of pipelines.

An Improved Method for Pipeline Leakage Localization With a Single Sensor Based on Modal Acoustic Emission and Empirical Mode Decomposition With Hilbert Transform

Water is one of the most precious commodities around the world. However, significant amount of water is lost daily in many countries through broken and leaking pipes. This paper investigates the use of low and high resolution infrared systems to detect water leakage in relatively dry countries. The overall aim is to develop a non-contact and high speed system that could be used to detect leakage in pipes remotely via the effect of the change in humidity on the temperature of the ground due to evaporation. A small scale experimental test rig has been constructed to simulate water leakage in The Great Man-Made River Project in Libya, taking into consideration the dryness level of the desert sand and the scaled dimensions of the system. The results show that the infrared technology is an effective technology in detecting water leakage in pipes. The low resolution system has been found as valuable as the high resolution system in detecting water leakage. The results indicate the possibility of distant remote detection of leakage in water systems using infrared technologies which could be mobilised using drones, helium balloons, aeroplanes or other similar technologies.

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Detection of water leakage in buried pipes using infrared technology; A comparative study of using high and low resolution infrared cameras for evaluating distant remote detection

Metro systems in urban cities demand rapid inspection methods, in order to identify critical structural defects in a timely manner. However, traditional inspection methods are only specific to one kind of structural defect, which reduces the overall efficiency of inspection. This study proposes an integrated solution for rapidly acquiring and identifying two kinds of structural defects (surface defects and cross-sectional deformation) in a metro tunnel, using a cart equipped with non-metric cameras. The integrity and rapidity are considered in formulating a systematic design for the development of the acquisition device. Methodologies based on image processing and photogrammetry are proposed to identify the structural defects of the metro tunnel. A series of on-site tests validate that the proposed method has enough speed and has acceptable accuracy in detecting critical structural defects of metro tunnels. The cost and efficiency analysis shows that the proposed method is competitive, which will greatly improve the efficiency and reduce the costs of the inspection of metro tunnels.

Rapid Acquisition and Identification of Structural Defects of Metro Tunnel.

Continuous monitoring of mechanical parameters determining the state of natural and man-made systems is essential in a wide range of engineering disciplines from mechanical to civil and geotechnical engineering. To be effective, the monitoring response time needs to be commensurate with the characteristic time of variation of the processes being monitored e.g. from seconds as for example in some machinery, to weeks and months for mining excavations and years in the case of structures. The methods of measurement can therefore differ significantly for different applications. In spite of this, the methods of information processing—the computational monitoring—have considerable commonality. This review focuses on the methods of computational monitoring in solid and structural mechanics problems in different engineering applications. The traditional methods of monitoring are reviewed along with the corresponding computational and measurement methods. The basic principles of the computational monitoring in real time are established.

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Computational monitoring in real time: review of methods and applications

It is important to check for leakage points of fluids on a surface to maintain and manage various structures satisfactorily. In particular, it is necessary that the leaking walls of a bank, dam, tunnel, pipeline and so on are diagnosed appropriately using some remote sensing technique and that they should be repaired immediately. Recently, infrared thermography for measuring temperature has become attractive in a wide variety of engineering applications. Infrared thermography in near ambient conditions is introduced to check the leakage point and its applicability is estimated by visualizing the temperature field generated around the point. The generated temperature around the leakage point is not usually consistent with the surrounding temperature. When using infrared thermography, we can detect the leakage point at the location where a marked temperature difference occurs.

Yoshizo Okamoto

Papers

Diagnosis of the leakage point on a structure surface using infrared thermography in near ambient conditions