Is it possible to use EDDY CURRENT TESTING Nondestructive testing method to check Inter-metalic phase of Duplex Steel pipes?
Eddy Current Testing (ECT) is a non-destructive testing technique that uses the principle of electromagnetic induction to detect defects in conductive materials. It's primarily used for detecting surface and subsurface defects such as cracks and corrosion, measuring the thickness of thin sheets, and conducting coatings, among other applications.
However, ECT is typically not used to detect intermetallic phases in duplex stainless steel. These phases, which can degrade the material's mechanical properties and corrosion resistance, are typically identified and quantified through metallographic examination (optical or electron microscopy) and sometimes through X-ray diffraction (XRD).
While eddy current testing is sensitive to changes in a material's electrical conductivity and magnetic permeability, the presence of intermetallic phases might not produce a sufficient change in these properties to be reliably detected, especially considering the presence of two phases (ferrite and austenite) in the duplex stainless steel matrix.
Thus, other techniques, such as microscopy or XRD, are usually more effective for assessing the presence and volume fraction of intermetallic phases. For more definitive information, please consult with material scientists, corrosion experts or NDT professionals, as they would better understand the nuances of such inspections.
Nevertheless, Eddy Current Testing can be used for a quick material separation based on the electrical conductivity and the magnetic permeability of the material. Therefore it should, be possible to detect intermetallic phases e.g. sigma phase in duplex stainless steels. In principle, the material properties change the impedance amplitude or/and the phase angle of the "lift off" effect, resulting in different signals when the eddy current probe is removed from the samples surface.
The quality of this separation task strongly depends on the amount and type of the intermetalic phase and it's effect on the signal of the probe (therefore check several frequencies for the applicability). Additionally, the calibration and the production of the reference samples play a major role in determining the correct amount of the intermetalics.
Please have a look at the following article Article Eddy current techniques for super duplex stainless steel cha...
(sadly I don't have access to that paper, however the abstract and conclusion sound very promising)However, you also need to consider that differences in the chemical composition, the tube geometry (especially its radius and wall thickness) and the ferrite to austenite ratio may lead to problems in comparing the reference sample signals with the signal of your pipe.
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