Research On Pulsed Eddy Current Testing Signal Characteristics Based On The Slope Method

Ferromagnetic equipment with insulations is widely used in petroleum, chemicalindustries. Wall thinning caused by corrosion in the long-term use process not only will causeleakage explosion and safety accidents, but also greatly threaten to production security. As anin-service and cost-effective detect method without removal of the insulation, pulsed eddycurrent (PEC) testing technology is increasingly becoming research hotspot. This dissertationis study on the pulsed eddy current testing signal influence factors of ferromagneticcomponent in engineering application.Firstly, the ferromagnetic material PEC signals are analyzed in time domain, indicatingthat the common features such as peak value, time to peak value, time to zero crossing andpoint of lift-off intersection are not suited. For the semi-logarithmic coordinate system latesignal is tending to straight line and corresponding to material thickness, a test method basedon the new feature of late signal slopes is extracted to analyze the PEC signals.Secondly, the signal characteristics of tubular specimens are studied. Finite elementsimulation and experiment are introduced to analyze the influence on slope feature ofcurvature radius, probe circumferential tilt angle, axial tilt angle and eccentric distance etc.factors. On this basis, a probe posture suppression method with the function of automaticalignment and floating tracking is designed to effectively eliminate tilt effect and improvetesting efficiency.Finally, the rule and mechanism of electromagnetic characteristics of ferromagneticmaterial in high temperature are studied. The influence on slope feature of permeability andconductivity is analyzed by ANSYS simulation. Through high temperature experiment ondifferent material specimens, slope-temperature equation of ferromagnetic material such as12Cr1MoV, Q235B, Q345R and15CrMoR etc. are obtained by cubic spline function fitting,further verifies simulation result. Meanwhile, conclusion is illustrated that monotonicdecrease relationship is exist between wall thickness and temperature. Then, a reliable wallthickness evaluation method based on slope-temperature equation is proposed for testing andanalysis under the environment of high temperature.All the work in this dissertation enriches the content of interpretation and analysis inpulsed eddy current signals, provides important support for the drafting and development ofnational standard GB/T28705-2012《Non-destructive testing—Pulsed eddy current testingmethod》 and industrial standard NB/T47013.13《Nondestructive testing of pressure equipments—Part13: Pulsed eddy current testing》, and can help promoting the engineeringapplication of pulse eddy current testing technique.