A New Guide Wave Inspection System Using Three Polarized Transverse Wave EMATs without Any Couplant

A guide wave is provided with the characteristic of long range propagation in the axis direction of a pipe, so it is possible to detect many defects over a large pipe area at once. At present, there is a technique to generate a guide wave using a piezoelectric element (PZT). However, the transverse wave-transducer using PZT needs to require a high viscosity couplant because the transverse wave cannot travel into typical liquid like water or oil. A guide wave inspection system that uses an electromagnetic ultrasonic transducer (EMAT) which does not require any couplant has then been developed to solve this trouble. First, a guide wave into a pipe, L, T and F-mode, can be transmitted and received by a polarized shear horizontal transverse wave propagating to the thickness direction when the vibration direction has been adjusted to the best direction. At next stage, the three EMATs for L, T and F-mode with different polarized vibration directions were piled up to improve the performance at the same position under the permanent magnet to inspect the pipe at the same condition. Next, the system with the EMATs can be confirmed to be able to detect three guide wave modes signal with enough intensity. Finally, the detection performance using the test pipes with any artificial defects has been done by the developed pipe inspection system, and any drilled holes and any notches can be detected. It is indicated that the developed system could be useful in real industrial field.

A New Probability of Detection Model for Updating Crack Distribution of Offshore Structures

There exists model uncertainty of probability of detection for inspecting ship structures with nondestructive inspection techniques. Based on a comparison of several existing probability of detection (POD) models, a new probability of detection model is proposed for the updating of crack size distribution. Furthermore, the theoretical derivation shows that most existing probability of detection models are special cases of the new probability of detection model. The least square method is adopted for determining the values of parameters in the new POD model. This new model is also compared with other existing probability of detection models. The results indicate that the new probability of detection model can fit the inspection data better. This new probability of detection model is then applied to the analysis of the problem of crack size updating for offshore structures. The Bayesian updating method is used to analyze the effect of probability of detection models on the posterior distribution of a crack size. The results show that different probabilities of detection models generate different posterior distributions of a crack size for offshore structures.

Study of an Ultrasonic Probe Installed into a Small Diameter-Pipe Using an Electromagnetic Acoustic Transducer

Metal pipes having an inner diameter of about 25 mm or less are frequently used as heat exchangers for power plants, gas pipes, and water pipes. However, erosion and corrosion due to long-term use may cause serious accidents, such as steam leaks, resulting in economic loss and environmental pollution. Therefore, inspection of the entire length and thickness before shipping or monitoring during operation are important technologies. However, no inspection technology including the inside of the wall thickness has been developed. The purpose was to develop an ultrasonic probe that can inspect the inner and outer surfaces from the inside of the pipe at the same time. The developed ultrasonic probe is based on an electromagnetic ultrasonic transducer (EMAT) that does not require a couplant and is then easy to install in a pipe. The EMAT for the longitudinal and for the transverse vibration mode guided wave are connected in series in order to take into account the variety of defects. First, the EMAT was successfully developed for each mode. That is, it was conducted by using the magnetostrictive effect for the longitudinal mode type and by using the Lorentz force for the transverse mode type, and evaluated to improve the performance. The reflected signal from a notch defect was then evaluated in the state that each EMAT was connected in series using any artificial defects and found to be able to detect any notches with about 10% depth or about 15% circumferential length.

An Introductory Note on Finite Element Problems Based on the Eddy Current Testing Approach

The paper addresses the first eddy current benchmark problem proposed by the World Federation of Nondestructive Evaluation Centers (WFNDEC). The problem simulates the eddy current response to the presence of an axisymmetric circumferential defect in an Inconel-600 tube. All simulations employ the axisymmetric code of the electromagnetic field simulator Finite Element Method Magnetics. For three different frequencies of excitation, it is explained how the displacement of the detecting coil inside the tube leads to a variation in the impedance of the eddy current coil. Variations of the resistive and inductive components of the impedance with distance from the defect region are used to build the impedance trajectory for each frequency of analysis.

Detection of butt weld of laser-MIG hybrid welding of thin-walled profile for high-speed train

Purpose–This study aims to solve the problem of weld quality inspection,for the aluminum alloy profile welding structure of high-speed train body has complex internal shape and thin plate thickness(2–4 mm),the conventional nondestructive testing method of weld quality is difficult to implement.Design/methodology/approach–In order to solve this problem,the ultrasonic creeping wave detection technology was proposed.The impact of the profile structure on the creeping wave detection was studied by designing profile structural test blocks and artificial simulation defect test blocks.The detection technology was used to test the actual welded test blocks,and compared with the results of X-ray test and destructive test(tensile test)to verify the accuracy of the ultrasonic creeping wave test results.Findings–It is indicated that that X-ray has better effect on the inspection of porosities and incomplete penetration defects.However,due to special detection method and protection,the detection speed is slow,which cannot meet the requirements of field inspection of the welding structure of aluminum alloy thin-walled profile for high-speed train body.It can be used as an auxiliary detection method for a small number of sampling inspection.The ultrasonic creeping wave can be used to detect the incomplete penetration welds with the equivalent of 0.25 mm or more,the results of creeping wave detection correspond well with the actual incomplete penetration defects.Originality/value–The results show that creeping wave detection results correspond well with the actual non-penetration defects and can be used for welding quality inspection of aluminum alloy thin-wall profile composite welding joints.It is recommended to use the echo amplitude of the 10 mm 30.2 mm 30.5 mm notch as the criterion for weld qualification.

Advancing knowledge of plasma spraying coatings for Li||Sb-Sn liquid metal batteries by X-ray micro-CT

The performance of Li||Sb-Sn liquid metal batteries(LMBs) is hindered by the corrosion of the Sb-Sn cathode on its current collector. Herein, a uniform, dense, and low-oxidized W coating was prepared by plasma spraying, which can effectively resist the corrosion of the cathode and improve the cycle stability of the Li||Sb-Sn LMBs. For the first time, micro-CT nondestructive inspection is applied in the field of LMBs. The corrosion micromorphology and composition evolution of the SS304 matrix and Sb-Sn cathode with or without the plasma-sprayed W coating is obtained without disassembling the battery, which proves that the W coating can effectively protect the SS304 matrix. Our autonomous new LMB device for nondestructive inspection is universal and can be applied to different LMBs systems for advancing knowledge of corrosion mechanism and protection. This work guarantees the ability to directly visualize the inner critical positions in three dimensions and fills the knowledge gap in the field of LMB detection technology.