crack laws 1986 Reliable detection of corrosion at pipe supports and other features is difficult because the most likely corrosion location, at the support itself, is inaccessible for thickness gauging. Long range guided wave inspection can be used but the support itself gives a reflection at the frequencies typically used and this can give confusing results. Higher frequency guided waves can also be used but they are not sensitive to gradual thinning. A new method termed higher order mode cluster (HOMC) has been pioneered in India, but the approach but it is not well understood, nor has it been compared quantitatively with other methods e.g. A0/S0/SH wave testing at 100-300 kHz, 90° compression waves at MHz frequencies, CHIME and M-skip. This project will firstly understand how HOMC works, then look at reflection and transmission behaviour on different defect shapes and sizes, rough surfaces, supports, attenuative materials and liquid filled pipes, and then go on to compare the other methods on the same basis.