Detection of outer wall defects on steel pipe using an encircling Rotating electromagnetic Field Eddy Current (RFEC) technique

english

2022

volume 68, issue 1

finite element   influencing factors   non-destructive testing   rotating electromagnetic field

Univerza v Ljubljani, Fakulteta za strojništvo
(Obvezni izvod spletne publikacije)

In recent years, the Rotating electromagnetic Field Eddy Current (RFEC) testing technique has attracted widespread attention due to its various advantages for the inspection of tubular structures. However, most of the related work were focused on the detection of inner wall defects on metal pipes using feed-through probes, which are often not applicable for outer wall defect detection. This work proposed an encircling RFEC technique and demonstrated its feasibility on the detection of outer wall defects. First, the basic principle of the encircling RFEC technique is introduced. Three-dimensional Finite Element (FE) model was built in COMSOL to analyze the distribution of the rotating electromagnetic field and study the interaction between the defects and eddy currents. The axial component of the resultant magnetic field due to defect was selected as a characteristic signal and obtained from the FE models to study the factors, including pipe tilt, defect circumferential location, defect orientation and defect size, that influence the detection performance. An Encircling RFEC system using a probe with six excitation windings and a single bobbin pick-up coil was constructed and used to inspect a steel pipe with one axial and one circumferential defect. The obtained voltage signal due to defect can form a Lissajous pattern in the impedance plane and can be used for defect evaluation. The results showed that the proposed encircling RFEC technique is capable of detecting outer wall defects of both orientations, and determining the circumferential location of the defect.

23.02.2022