For the anti-corrosion measure, the nonconductive protection coating is normally deployed over the surface of the conductive structure which is widely utilized in the engineering fields including aerospace, nuclear en...
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For the anti-corrosion measure, the nonconductive protection coating is normally deployed over the surface of the conductive structure which is widely utilized in the engineering fields including aerospace, nuclear energy, etc. Nevertheless, due to hostile and corrosive environments, hidden corrosion buried right beneath the nonconductive coating, namely Corrosion Under Coating (CUC) has been found occurring in the conductor surface, and severely undermines the structural integrity. Therefore, it is imperative to non-invasively interrogate CUC via Non-destructive Evaluation (NDE) techniques without removing the protection coating. pulse-modulation eddy current technique (PMEC) has been identified to be advantageous over pulsed eddycurrent testing (PEC) in higher inspection sensitivity to hidden corrosion and accuracy of corrosion imaging. It could be a promising and preferable NDE technique for evaluation of CUC. In this paper, PMEC for recognition and evaluation of the opening profile of CUC is intensively investigated through simulations and experiments. Based on the Extended Truncated Region Eigenfunction Expansion (ETREE) modelling, closed-form expressions of PMEC responses to CUC are formulated. A series of simulations are conducted to compare the evaluation sensitivity of PMEC to CUC with that of PEC. Following this, experiments for profile recognition and evaluation of CUC via PMEC are conducted. The improved Canny algorithm is proposed to enhance the accuracy in identification and assessment of the CUC profile. The results from simulations and experiments reveal that: (1) PMEC is superior to PEC in terms of evaluation sensitivity to CUC;and (2) in conjunction with the improved Canny algorithm, PMEC is capable of identifying and evaluating the CUC profile without much loss in accuracy.
Metallic structures of non-ferromagnetic materials such as aluminum alloy, titanium alloy, etc., are widely used in the engineering field of aviation. Owing to harsh and hostile environments, subsurface corrosion mani...
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Metallic structures of non-ferromagnetic materials such as aluminum alloy, titanium alloy, etc., are widely used in the engineering field of aviation. Owing to harsh and hostile environments, subsurface corrosion manifests itself in the in-service Metallic Structures of Aviation (MSA), and is usually hidden within the structure body, leaving it barely detected. Such defect has been found to be one of the most critical defects posing a severe threat to structural integrity and safety of MSA. Therefore, it is imperative to conduct imaging and quantitative assessment of the subsurface corrosion with effective Non-destructive Evaluation (NDE) techniques. pulse-modulation eddy current technique (PMEC) has been identified to be superior to other electromagnetic NDE techniques in evaluation of corrosion in conductors. In light of this, in this paper PMEC for imaging and 3D profile reconstruction of subsurface corrosion in MSA is investigated. Novel features extracted from testing signals are proposed in a bid to enhance the sensitivity of the PMEC response. An image processing technique based on the modified Theta Map is proposed and utilized for recognition of corrosion opening profile. An efficient inversion method, which is focused on the corrosion-profile reconstruction right within the corrosion region and based on a sectional scanning strategy, is investigated along with the establishment of the database conceiving PMEC responses to regular-shaped corrosion. It has been found from the experimental results that the proposed inversion scheme is feasible and applicable for 3D profiling of subsurface corrosion in MSA with the averaged evaluation accuracy of 95.4%.
Since the nonmagnetic pipe is normally utilized in corrosive and hostile environment, it is prone to the external corrosion which occurs on the outer surface of the pipe and severely undermines the structural integrit...
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Since the nonmagnetic pipe is normally utilized in corrosive and hostile environment, it is prone to the external corrosion which occurs on the outer surface of the pipe and severely undermines the structural integrity and safety. Although pulsed eddycurrenttechnique (PEC) is currently preferred for detection and evaluation of subsurface defects in tubular conductors, it is subject to technical drawbacks. In light of this, pulse-modulation eddy current technique (PMEC) is intensively investigated in the paper for enhancement of the evaluation sensitivity to external corrosion and accuracy of corrosion imaging. Closed-form expressions of the PMEC response and its sensitivity to external corrosion in tubular conductors are formulated via the Extended Truncated Region Eigenfunction Expansion (ETREE) modeling. Following simulations for analysis and comparison of field signals and evaluation sensitivities of PMEC and PEC, experiments of PMEC for evaluation and imaging of external corrosion are carried out. Through theoretical and experimental investigation, it has been found that regarding the evaluation and imaging of external corrosion in nonmagnetic pipes, the PMECbased probe have higher sensitivity and imaging accuracy than that based on PEC. The superiority of PMEC to PEC in inspection of tubular conductors is further identified.
Interlaminar corrosion (ILC) poses a severe threat to stratified conductors which are broadly employed in engineering fields including aerospace, energy, etc. Therefore, for the pressing concern regarding the safety a...
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Interlaminar corrosion (ILC) poses a severe threat to stratified conductors which are broadly employed in engineering fields including aerospace, energy, etc. Therefore, for the pressing concern regarding the safety and integrity of stratified conductors, it is imperative to non-intrusively and quantitatively interrogate ILC via non-destructive evaluation techniques. In this paper, pulse-modulationeddycurrent (PMEC) for imaging and assessment of ILC is intensively investigated through theoretical simulations and experiments. A semi-analytical model of PMEC evaluation of ILC occurring at the interlayer of two conductor layers is established based on the extended truncated region eigenfunction expansion (ETREE) along with the efficient algorithm for the numerical computation of eigenvalues for reflection coefficients of the stratified conductor under inspection. Based on theoretical investigation, PMEC evaluation of ILC in testing samples are further scrutinized by using the PMEC imaging system built up for the experimental study. The theoretical and experimental results have revealed the feasibility of PMEC for imaging and evaluation of ILC in stratified conductors.
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