This paper reports the use of dispersive Higher Order Modes Guided Waves (HOM-GW) and non-dispersive Higher Order Modes Cluster Guided Waves (HOMC-GW) for the detection and sizing of corrosion defects in pipes and tank floors. Pin-hole and wall thinning defects of different sizes were artificially generated on the pipe and the tank floor specimens in order to simulate corrosion pits under pipe supports and tank floor annular plate regions respectively. Since, the nature of loss of material differs in each type of corrosion; the same mode excited cannot be effective in characterizing all the defect types, although they all may indicate the presence of defect. The effective modes are identified for each type of corrosion and their defect characterizing sensitivity was studied. The validity of this technique was tested with field samples. © 2008 American Institute of Physics.