A Novel Method of Estimating the Aspect Ratio of Pipe Wall Thickness to Diameter Utilizing the Characteristics of a Hollow Cylindrical Guided Wave
We have developed a method of estimating the aspect ratio of a pipe wall thickness to diameter (t/d) using a hollow cylindrical guided wave (HCGW). The HCGW is an ultrasonic guided wave in a pipe. The method is very useful for onsite and nondestructive estimation of pipe wall thickness. It is based on the change of the dispersion relation of the HCGW as a function of t/d. The group velocity of the primary wave (first arriving wave packet from an impulse source) of the HCGW ranges from the bar velocity to the sheet velocity as a function of t/d. The bar velocity is the velocity of the DC component of the guided wave propagating in a solid cylinder; the sheet velocity is that of the S0 mode Lamb wave. The first part of the paper describes the principle of the method. In the last part, a laser ultrasonic method was employed to verify the method in both time- and time-frequency domains. The experimental results for aluminum pipes with various t/d’s were in good agreement with the theory.