Decoupling the Influence of Wall Thinning and Cladding Thickness Variations in Pulsed Eddy Current Using Principal Component Analysis

Faris Nafiah,Owen Rees-Lloyd,Gholamhossein Shirkoohi,Zhanfang Zhao,Mohammad O Tokhi,Fang Duan

doi:10.1109/jsen.2021.3100648

Abstract

Corrosion may develop and grow on steel pipes under layers of insulation and cladding. Inspection of the pipes through these protective layers is of paramount importance. Pulsed eddy current (PEC) is a primary non-destructive testing (NDT) technique candidate for this type of inspection as it requires no contact with the inspection material. To overcome the variability in PEC signals due to variations in the cladding thickness, a large measurement set is analysed in this paper using principal component analysis (PCA). The PCA approach decomposes the signal set into a number of uncorrelated variables that explain the maximum amount of the variance in the data set, in which, in this respect, efficiently separate the influences contributed by the difference in the material properties of cladding and pipe wall. The feasibility of using PCA to quantify simulated steel pipe wall independent of confounding cladding thickness variations is investigated. It is found that, with sufficient amount of data, the approach can effectively separate the influences contributed by the wall thickness variations from the cladding thickness variations.

Highlights

P ULSED eddy current (PEC) is a non-destructive testing (NDT) technique within the electromagnetic sector, and is an extension of the conventional eddy current (EC) testing technique
In a bid to move towards a more automated process of pipe profiling, this paper explores the reliability of using principal component analysis (PCA) method to quantify both cladding and pipe wall thickness on a simulated multi-layered pipe structure
This paper has demonstrated that the variations in pipe and cladding have quantifiable responses on PEC signals

Summary

Introduction

P ULSED eddy current (PEC) is a non-destructive testing (NDT) technique within the electromagnetic sector, and is an extension of the conventional eddy current (EC) testing technique. Instead of applying a single frequency for current excitation like EC, PEC exploits the wide-band frequency characteristic of a rectangular excitation current to allow higher depth of penetration. It is known to offer the advantage of non-contact inspection, for aircraft [1]–[4] and pipeline inspection [5]–[8]. Corrosion under insulation (CUI) is a typical corrosion type that grows underneath layers of nonconductive insulation and steel cladding. The multi-layered structure of a pipe, as visualised, adds to the complexity of inspection. PEC offers the potential to detect such corrosion without disassembling the insulation

Methods

Results

Conclusion