Circumferential　guided　waves　are　used　for　scanning　detection　of　defects　in　thick　wall　pipes.　Wavelet　transform　coefficients　at　a　certain　frequency　point　are　extracted　for　imaging　defect　in　thick　wall　pipe　by　using　continuous　wavelet　transform.　In　experiments,　the　angle　beam　probe　is　used　to　scan　the　axial　defect　in　the　step　of　2　mm　in　the　axial　direction　and　inspection　signals　are　obtained　when　the　element　of　angle　beam　probe　covers　the　axial　defect　with　different　coverage　extents.　The　signals　containing　defect　echoes　and　circumferential　echoes　are　intercepted　and　their　continuous　wavelet　transform　coefficient　envelope　signals　at　500　kHz　are　extracted.　According　to　the　comparison　of　these　envelop　signals　and　dispersion　curves,　received　inspection　signals　are　confirmed　to　be　mainly　circumferential　Lamb　wave　mode　CL3.　Furthermore,　continuous　wavelet　transform　coefficient　envelopes　of　inspection　signals　at　different　scanning　points　are　used　for　amplitude　envelop　imaging.　The　defect　is　reconstructed　based　on　this　amplitude　envelope　image　and　its　axial　length　can　be　confirmed　efficiently.　The　signal　to　noise　ratio　of　amplitude　envelopes　at　a　certain　frequency　point　is　greatly　better　based　on　continuous　wavelet　transform　and　imaging　results　show　high　focus　performance.　Therefore,　amplitude　envelop　imaging　method　can　be　used　for　enhancing　inspection　signal　identification　and　defect　recognition　based　on　continuous　wavelet　transform.　©　2013　Journal　of　Mechanical　Engineering.