Assessment of Delamination Under Insulation Using Ridge Waveguide

Abstract

Insulation has been widely used to protect metal substrates in various industries such as turbine blades and oil and gas pipelines. Due to aging and cyclic processes, delamination between the metal component and insulation could grow. Such defects represent a critical problem that may result in catastrophic failure of the asset. Therefore, detecting and evaluating delaminated areas is mandatory for providing urgent maintenance solutions before the failure occurrence. In this paper, microwave nondestructive technique (NDT) is proposed for delamination detection and thickness estimation under dielectric insulation. In microwave NDT, the electromagnetic waves are induced into the dielectric material's surface using a ridge waveguide. The complex reflection coefficients are acquired using a vector network analyzer for further analysis in the time domain. Next, a time-domain reflectometry (TDR) technique-based inverse discrete Fourier transform is used to evaluate the complex reflection coefficients in terms of delamination's size and thickness estimation. The delamination evaluation is performed by measuring the maximum peak's time-step variations instead of the magnitude reduction in conventional TDR techniques in terms of the defect and defect-free reflections. Next, a comparison is made between implementing the proposed technique using a ridge waveguide and a regular rectangular waveguide. The results prove the superiority of using the ridge waveguide for delamination evaluation in terms of sizing and thickness with a minimum error rate of 5% and 7.87%, respectively. These novel results of ridge waveguide due to its small aperture and relatively wide bandwidth. The microwave NDT technique reported here could provide a predictive maintenance tool for many industries to minimize the maintenance effort and cost.

Assessment of Defects under Insulation Using K-Medoids Clustering Algorithm-Based Microwave Nondestructive Testing

“…After that, the complex time-domain data is also converted to the magnitude with the 'abs' function in Matlab (R2021a). This is because, in some cases of the time domain, the centroids' borders defined by the magnitude of the centroids in defect-free areas are greater than in the defect areas [15,18]. Therefore, it is easier to observe the defect and non-defect centroids.…”

“…However, there is still some delamination adjacent to the sloping edges that cannot yet be discovered in the sample examined using this technique. The accuracy of delamination detection is enhanced by the work in [18]. A ridge waveguide is employed to enhance delamination detection in ceramic-coated metal samples.…”

Prospect of Using Machine Learning-Based Microwave Nondestructive Testing Technique for Corrosion Under Insulation: A Review

“…Corrosion Under Insulation (CUI) is a severe defect in various critical applications, especially in nuclear, marine, aerospace, power generation, and oil and gas industries [1][2][3][4][5][6]. In these industries, the corrosion is grown invisibly in the metal substrate under insulation due to the intrinsic coating imperfections, humidity, and water invasion that makes structural thinning [7][8][9].…”