Method for determining average wall thickness for pipes and tubes using guided waves

A method for measuring changes in an average wall thickness for a longitudinal section of pipe from a single location comprising the steps of:

• directing interrogating mechanical waves into a wall of said pipe at said single location;
• receiving a multifrequency return signal, said multifrequency return signal resulting from a dispersion of said interrogating mechanical waves throughout said longitudinal section of pipe;
• analyzing said return signal by determining the ratio of wave group velocity at a first selected frequency to wave group velocity at a second selected frequency, said first and second selected frequencies being discrete frequencies offset from a cut-off frequency, said cut-off frequency being a frequency range over which said return signal is significantly attenuated due to the original geometry of said pipe;
• comparing said ratio of wave group velocities with a baseline ratio for said pipe;
• and
• correlating a change in said ratio with a respective change in said average wall thickness for said longitudinal section of pipe.