Modeling simulationand analysis of magnetic flux leakage based non destructive testing

Abstract

Non-Destructive Evaluation (NDE) is the science of inspecting materials for flaws without compromising their usefulness. It will provide information on the material quality but doesn t alter or damage the material under test. NDT is used as an economic tool in predictive maintenance approach of plant operators. The Steam Generator (SG) is at the heart of sodium-cooled fast breeder reactors. In these SGs, secondary sodium flows in the shell side exchanges heat with water in the tube side to produce supersaturated steam. The SG is a critical component owing to the fact that both sodium and steam co-exist and can react violently resulting in a catastrophic failure in the case of direct contact. The SG tubes are the structures which separate the sodium and water and they are exposed to hostile operating conditions such as high temperature and pressure. As a result, uniform corrosion, pitting corrosion, fretting wear etc. may form on both the inner and outer surfaces of the SG tubes. In order to avoid the formation of such harmful defects and to ensure the structural integrity of the SG, preventive maintenance through periodic In-Service Inspection (ISI) of the SG tubes is essential. Non-Destructive Evaluation (NDE) plays a vital role in this context. A variety of electromagnetic NDE techniques is applied for the ISI of small diameter SG tubes.These include Eddy Current (EC), Remote Field Eddy Current (RFEC) and Magnetic Flux Leakage (MFL) techniques. The EC technique which works on the principle of Faraday s law of electromagnetic induction is predominantly applied for conducting non-ferromagnetic tubes such as stainless steel, copper and Inconel due to the limited depth of penetration of the eddy currents and noise due to permeability variations. newline