Pulsed eddy current testing for gap measurement of metal casing

Abstract

A pulsed eddy current testing (PECT) method is proposed to measure the gap of non-ferromagnetic metal casing. Firstly, the detection sensitivity to the casing gap of the voltage signal induced respectively by time-harmonic excitation current and by pulsed excitation current are calculated theoretically and compared. Then the advantages of PECT method for gap measurement are discussed. Secondly, the difference curve of the time-domain induced voltage signal between two gaps near the nominal value is presented. And the value of the induced voltage signal corresponding to the peak time of the difference curve is extracted to serve as the signal characteristic. Furthermore, using a calibrated casing, the function relationship between the signal characteristic and the casing gap is derived by curve fitting. Finally, the casing gap can be determined rapidly through the induced voltage at the peak time. This paper provides a reliable non-destructive testing method for the casing gap measurement, and compared with the existing sinusoidal eddy current testing method, the PECT method can significantly improve the signal-to-noise ratio and the detection sensitivity to the casing gap.

Circular-arc array for the pulsed eddy current inspection of thermally insulated pipelines

“…This is because CUI can result in sudden and hazardous leaks, as well as plant shutdowns with a significant decrease in production volumes [1][2][3][4]. Several techniques have been developed for detecting various defects in pipelines, such as the visual method [5], radiography [6], ultrasonic guided waves [7,8], microwaves [9,10], and eddy current testing [11][12][13][14]. Among them, pulsed eddy current (PEC) testing [13,14], a different form of the eddy current-based technique, is well-known and widely accepted for its noncontact characteristic and potentially large lift-off distance.…”