Development of Permanently Installed Magnetic Eddy Current Sensor for Corrosion Monitoring of Ferromagnetic Pipelines

Permanently installed sensors are a cost-effective solution for corrosion monitoring due to their advantages, such as less human interference and continuous data acquisition. Some of the most widely used permanently installed corrosion sensors are ultrasonic thickness (UT) gauges. However, UT sensors are limited by the need for coupling agents between pipe surfaces and sensors. The magnetic eddy current (MEC) method, on the other hand, does not require couplant and can be used over insulations. With the development of powerful rare earth magnets, MEC sensors with low power consumption are possible, and there is the prospect of using them as permanently installed sensors. A novel wireless magnetic eddy current sensor has been designed and optimized using finite element simulation. Sensitivity studies of the sensors reveal that the excitation frequency is a critical parameter for the detection of corrosion defects. An in-depth explanation of the relationship between the sensitivity of the sensor and the excitation frequency is presented in this paper. The results of an accelerated corrosion test, conducted to simulate the service environment of the sensor, are also discussed. It was observed that the sensor signals are very sensitive to corrosion defects and show no subtle differences due to temperature and humidity changes

New Methods of Rail Axle Inspection and Assessment

Three alternative methods of crack detection and corrosion assessment for railway axle inspection have been proposed in the WOLAXIM (Whole Life Rail Axle Assessment and Improvement) project. One method is for the exposed body of the axles (intended primarily for freight wagon or passenger trailing axles) and can be carried out automatically, as the vehicles pass an inspection station that could be installed in carriage sidings or marshalling yards. A second method is specifically for the hollow axles of high speed trains and aims to improve the speed of the inspection and improve crack detection reliability. This could be deployed while the train is in the depot overnight and without dismantling the wheel set. The third method is to improve the measurement of corrosion and therefore the sentencing of corroded axles. This will be linked to newly developed corrosion fatigue assessment models by reliability methods. This paper describes the main principles of these methods and gives some preliminary results

A feature extraction technique based on principal component analysis for pulsed Eddy current {NDT}

Pulsed Eddy current (PEC) is a new emerging {NDT} technique for sub-surface defect detection. The technique mainly uses the response peak value and arrival to detect and quantify the defects. This could suffer from noise and be not sufficient to extract more information about the defects, e.g. depth information of defects. This paper introduces the application of principal component analysis in extracting information from {PEC} responses. A comparative test carried out shows that the introduced technique has performed better than the conventional technique in the classification of defects

From atmospheric corrosive attack to crack propagation for A1N railway axles steel under fatigue: Damage process and detection

In this paper a detailed investigation about the evolution of the corrosion fatigue process of this material is presented. The corrosion pits appear in the early stage of the corrosion fati- gue life and a preferential site of pit nucleation has been observed at the ferrite–ferrite grain boundary. At the bottom of these primary pits, the formation, due to electrochemical action, of a secondary pit that triggers for the pit-to-crack transition has been observed. The growth of micro-cracks has also been analyzed and it is characterized by the develop- ment of a surface pattern of coalescing cracks. An original optical detection method has been proposed to inspect the exposed surfaces of the corroded railway axles and to detect the in situ crack pattern associated to the cor- rosion–fatigue damage. It is shown that the optical detection method is able to identify the damage observed and it has been successfully applied in field observations