Subsurface defects can be detected by flash thermography by evaluating the temperature response at the surface. Many techniques have been developed in the past to localize a defect and also to estimate its depth and size. Two of the most established methods are TSR and PPT, whereby TSR analyzes the data in the time domain, and PPT evaluates the signal in the frequency domain. In order to get the data in the frequency domain, Fourier transformation, especially FFT is used to calculate the phase shift for the different frequencies. The usage of FFT assumes a periodical signal or a temporal signal which is limited in the time. As this is not the case for the temperature signal after a short pulse heating, the transformation to the frequency domain generates some errors. Therefore parameters as sampling frequency and duration of evaluation have to be selected carefully. Even if many publications have been already dealing with this topic, in this paper a new approach is attempted by comparing the temporal behavior as it is handled by the TSR technique with the frequency behavior calculated by PPT. The results are interpreted with the help of simulation models of flat bottom hole samples.

Date Published: 11 May 2016
PDF: 13 pages
Proc. SPIE 9861, Thermosense: Thermal Infrared Applications XXXVIII, 98610P (11 May 2016); doi: 10.1117/12.2228864

Published in SPIE Proceedings Vol. 9861:
Thermosense: Thermal Infrared Applications XXXVIII
Joseph N. Zalameda; Paolo Bison, Editor(s)