Eddy Current Testing For Railways
Eddy Current Testing
It is widely known that eddy current measurements can provide useful information on the properties of ferrous materials. Modifications of the micro-structure and of the dislocation distribution caused by heat treatment or work hardening result in variations of the magnetic domain wall motion, which affect the electromagnetic response of the sample.
While the underlying microscopic mechanism relating these quantities is difficult to describe quantitatively, the relation between the electromagnetic response and the micro-structure is a very efficient empirical tool to sort parts, both by comparison with reference batches or by statistical analysis of samples.
Eddy current testing services uses electromagnetic induction to detect flaws in conductive materials. The eddy current test set-up consists of a circular coil placed on a test surface. The alternating current in the coil generates changing magnetic field which interacts with the conductive surface and generates an eddy current.
The flow of eddy current can be disrupted due to changes in resistivity or conductivity, magnetic permeability, any physical discontinuity. The change in eddy current flow and a corresponding change in phase and amplitude is measured against known values.
Eddy current test method can detect very small cracks in or near the surface of the material, the surfaces need minimum preparation. The biggest advantage of the eddy current test method is that it can be employed to determine surface flaws on painted or coated surfaces. Eddy current flaw detection is used aerospace industry, crane industry, concrete industry, pumping industry and other general industries where the protective surface coating cannot be removed.
Some notable applications of Eddy current test are;
1) Conductivity measurement
2) Sorting of Material
3) Assessment of heat treatment conditions
4) Sorting of materials on the basis of hardness and strength
5) Measurement of thin components.
There is a growing interest in the application of this technique to the quality control (QC) of parts with complex geometries and/or manufactured using exotic techniques such as EDM, SLS, or water jet. Moreover, eddy currents can prove an attractive complementary technology for the detection of subsurface porosity.
Eddy Current For Railways
Rail wheels are one of the most important moving parts for locomotives, coaches, wagons and EMUs. These wheels are subject to heavy stresses when in service and are prone to many surfaces as well as internal discontinuities. Therefore the quality of wheels is crucial for the safety and smooth operations of locomotives.
Such quality checks are carried out by analyzing the wheels using non-destructive testing (NDT) equipment that can detect even minute flaws, scanning larger areas rapidly with ease. To accomplish this the analyst should be equipped with flexible & durable probes that can adjust with the shape of wheels easily, allowing them to perform inspections without removing the wheels from the assembly during the testing process.
Common discontinuities which can be detected on railway wheels such as,
1) Manufacturing Discontinuities- Casting imperfections, Improper Heat Treatment, Machining Imperfections.
2) Improper Assembly Practices- Change in dimensional tolerances, Ovality on Journals, Taper Journal, Difference in diameters of wheels and axle.
3) Normal wear & tear during service– Thin flange, deep flange, sharp flange, less radius at root flange, Hollow tyre, Thin tyre, Flat tyre.
One of the most effective NDT methods to inspect rail wheels is Eddy Current Array (ECA), which can detect surface aberrations with accuracy. ECA requires no surface preparation prior to an inspection, no chemicals and no electrical outlets. It is faster, easier and more flexible for inspecting the train wheels.
IXAR has been performing Eddy Current Testing (Eddy Current for Railways) for many years and accomplished the most prominent projects in India. IXAR has started NDT Services for Railways in January 2018 by deploying experts in Eddy Current Testing. Currently, IXAR has 20 RDSO-approved operators with 1 QAP Head and 4 technical executives to handle all operations. Currently, IXAR is conducting ECA for surface defect detection on LHB wheels at Mumbai Division ,Jhansi Division, Jodhpur Division,Bikaner Division and Mancheswar Division.
We are using latest equipment for Eddy Current Array from renowed companies like Olympus and S2G2 Canada.
