Electromagnetic Nondestructive Testing Technique Research Articles

Numerical analysis and experimental research on detection of welding defects in pipelines based on magnetic flux leakage

Regular inspection of long-distance oil and gas pipelines plays an important role in ensuring the safe transportation of oil and gas, and inspection on welding defects is an important part of the inspection process. Magnetic flux leakage (MFL) is an electromagnetic non-destructive testing technique which has been commonly utilized to detect welding defects in pipelines. In the present study, Maxwell electromagnetic simulation software was used to carry out numerical study on the welding defects in pipelines, including incomplete penetration and undercut. The Ф406 pipeline with a wall thickness of 7 mm was selected as the study case to establish the numerical model. Setting the life-off value at 1 mm, the distribution of magnetic leakage field was investigated for pipeline without defect, pipeline with incomplete penetration defect and pipeline with undercut defect respectively, the characteristic values describing the depth and width of defects were found. Furthermore, quantified equations which can be used to describe the defect depth were proposed. Finally, experimental research was carried out to validate the effectiveness of the numerical model, and the experimental results showed good consistence with the numerical calculation results. The research results indicate that, it is technically feasible and reliable to diagnose the incomplete penetration and undercut welding defects in pipelines using MFL.

RCF crack direction assessment in moving ferromagnetic material by DC electromagnetic NDT technique

The rolling contact fatigue (RCF) cracks that initiate from the surface of ferromagnetic materials in aviation bearings and high-speed rails are typically inclined at varying angles, posing a serious threat to safety. Therefore, a rapid and quantitative characterization of inclined cracks is of great importance. This paper investigates the distribution of magnetic fields and motion-induced eddy current (MIEC) in direct current (DC) electromagnetic non-destructive testing (NDT), and proposes an approach for measuring the direction of RCF cracks in moving ferromagnetic materials. The magnetic field and MIEC distributions in the moving ferromagnetic material are initially investigated, followed by a numerical simulation exploring the impact of crack inclination angle and depth on detection signals. The resulting relationship between crack propagation angle, depth, and detection signal is then obtained. Furthermore, a DC electromagnetic NDT platform has been designed and a quantitative detection approach for inclined cracks has been proposed and validated through experiments. Finally, a real scenario detection is carried out. The investigation presented in this paper demonstrates that the DC electromagnetic NDT technique is applicable not only for assessment RCF crack direction in moving ferromagnetic materials, such as rotating aviation bearings, but also for characterizing inclined cracks under conditions of fast relative motion between the probe and the ferromagnetic material (e.g., high-speed rail, pipeline, etc.).

An improved generative adversarial network with modified loss function for crack detection in electromagnetic nondestructive testing

In this paper, an improved generative adversarial network (GAN) is proposed for the crack detection problem in electromagnetic nondestructive testing (NDT). To enhance the contrast ratio of the generated image, two additional regulation terms are introduced in the loss function of the underlying GAN. By applying an appropriate threshold to the segmentation of the generated image, the real crack areas and the fake crack areas (which are affected by the noises) are accurately distinguished. Experiments are carried out to show the superiority of the improved GAN over the original one on crack detection tasks, where a real-world NDT dataset is exploited that consists of magnetic optical images obtained using the electromagnetic NDT technique.

Comparison of electromagnetic inspection methods for creep-degraded high chromium ferritic steels

Nondestructive testing (NDT) techniques are used to evaluate the material degradation of ferromagnetic materials, for example, in sensitive environments, such as thermal power plants, where the materials are subjected to creep damage. There is no consensus on the use of an electromagnetic NDT technique to characterize the evolution of creep damage in high-chromium ferritic steels. In this work, an overview and comparison of three different electromagnetic NDT techniques that were applied to high-chromium steels is provided to understand creep evolution in terms of microstructural changes, such as precipitation, dislocation and grain size. To quantify the empirical measurements, a modelling technique was proposed for each applied method. The model parameters were optimized for each NDT technique and tested material. Depending on the model parameters, the accuracy of the parameter determination depends strongly on the NDT technique, which indicates its correlation with the microstructural information.

The Non Destructive Testing Methods Applied to Detect Cracks in the Hot Section of a Turbojet

All aircraft whatever they are; are regularly audited. These controls are mainly visual and external; other controls such as "major inspection" or "general revisions” are more extensive and require the dismantling of certain parts of the aircraft. Some parts of the aircraft remain inaccessible and are therefore more difficult to inspect (compressor, combustion chamber, and turbine). The means of detection must ensure controls either during initial construction, or at the time of exploitation of all the parts. The Non destructive testing (NDT) gathers the most widespread methods for detecting defects of a part or review the integrity of a structure. The aim of this work is to present the different (NDT) techniques and to explore their limits, taking into account the difficulties presented at the level of the hot part of a turbojet, in order to propose one or more effective means, non subjective and less expensive for the detection and the control of cracks in the hot section of a turbojet. To achieve our goal, we followed the following steps: - Acquire technical, scientific and practical basis of magnetic fields, electrical and electromagnetic, related to industrial applications primarily to electromagnetic NDT techniques. - Apply a scientific approach integrating fundamental knowledge of synthetic and pragmatic manner so as to control the implementation of NDT techniques to establish a synthesis in order to comparing between the use of different methods. - To review recent developments concerning the standard techniques and their foreseeable development: eddy current, ultrasonic guided waves ..., and the possibility of the implication of new techniques.

Electromagnetic characterization of material degradation due to neutron irradiation

Most of the materials used in practice show degradation due to fatigue, i.e. cyclic loading. Very often other degradation mechanisms like corrosion and in the high temperature regime also creep are superimposed. In the primary circuit of nuclear power plants the material is additionally exposed to neutron irradiation. According to the licensing conditions the main focus is on the pressure vessel material. The contribution describes measurement results collected at surveillance programme specimen of different nuclear power plants in different European countries. The set of Charpy specimen was measured in the hot cell of the research reactor in Petten in the Netherlands. Electromagnetic non-destructive testing techniques were applied for characterization.

Modelization of cracks in steel subsea structures-application to the optimization of a new electromagnetic detection method

A novel contactless electromagnetic nondestructive testing technique has been developed for the detection of cracks in offshore steel structures. In order to optimize the detection device, a crack model using existing software based on a finite elements method has been proposed. The electrical activity of the modeled crack, interpreted as a back electromotive force (BEMF) source, is investigated. A two-level approach leading to a simplified modeling makes the investigation of this BEMF possible by reducing the size of the numerical problem. Results lead to the understanding of defect magnetic signal shapes and thus to the design of an optimized detection device. >