Detection of axial crack in the bend region of a pipe by high frequency electromagnetic waves

Abstract

High frequency electromagnetic guided waves are used to detect axial narrow slit or crack in bend-section of the U-shape pipe. In the previous studies performed by the authors, electromagnetic waves (EM-waves) of TM 01- and TE 11-modes have used to detect circumferential and axial crack in straight section of a pipe, appropriately. In this paper to show potential of this technique for detection of any shape of piping system, especially bend-section of the steam generator (SG) and feeder pipe of pressurized water reactor (PWR), axial crack in bend-section is investigated. Due to axial orientation of the crack, TE 11-mode, a suitable mode for detection of axial crack is implied for this purpose. To excite TE 11-mode in the test pipe, microwave signals generated by the network analyzer, are sent to the inspected pipe by a coaxial line and a mode converter. Presence of the crack causes change in the reflection coefficient of the reflected signals from the crack. The behavior of the crack characteristic signals as a function of time is studied to estimate time of flight of the reflected wave and consequently crack position. Suitable frequency range is chosen in order to generate only TE 11-mode in the test pipe. To show effect of frequency range of the electromagnetic waves to the crack, crack positions are also evaluated for several smaller frequency ranges. Two crack positions were examined and comparisons of measurement results with theoretical calculations indicate that the microwave guided waves technique has high capability to detect defect in bend-section of a piping systems.