Determination of the Velocity of a Torsional Wave Based on the Spectrum of an Acoustic Echogram of a Series of Multiple Reflections

Modern technical means, including those using computerized components, provide new signal processing capabilities using spectral analysis. A method for calculating the velocity of an acoustic wave С from the spectrum of an echogram containing multiple reflections of acoustic pulses is described. The method is based on the detection of spectral lines spaced from each other along the frequency axis by Δ f , corresponding to the pulse repetition rate repeatedly reflected from the testing object’s end. The velocity С is calculated as the average value С = L Δ f , where L is the length of the acoustic axis. The search for spectral lines is carried out in the frequency domain corresponding to the working area of the input path of the registration system. To accurately determine the position of the maximum of the spectral line, it is approximated by a parabola. The velocity of the torsional wave was calculated in a batch of pipes – blanks of a plunger of a deep rod pump with lengths from 5.245 to 5.248 m, a diameter of 59 mm and a wall thickness of 13.75 mm, in the amount of 20 pieces. The sounding is performed using an electromagnetic acoustic sensor mounted on the outer surface of the pipe next to the end face. The measurement was performed with an ADNSH-P flaw detector with a receiving path bandwidth from 9.5 to 63 kHz at a level of -6 dB. The echograms were obtained at a sampling frequency of 3.75 MHz and contain 10 reflections. The torsional wave velocities of the pipes in the batch range from 3294 to 3298 m/s