Lamination　defect　is　one　of　the　common　defects　in　the　manufacturing　process　of　seamless　pipes.　In　this　paper,　the　quantitative　detection　of　a　lamination　defect　in　thin-walled　metallic　pipe　using　circumferential　Lamb　waves　is　studied.　To　interpret　the　received　time-domain　signals　and　extract　useful　information　about　the　lamination　defect,　wavenumber　analysis　is　performed　on　these　signals.　A　three-dimensional　finite-element　model　is　established　using　Matiab　and　ABAQUS　commercial　software.　Owing　to　the　processing　technique,　an　aluminum　ring　structure　with　a　three-quarters　circumference　is　considered　to　represent　the　metallic　pipe.　The　lamination　defect　constructed　in　the　model　is　a　＂zero-volume＂　crack,　which　stretches　from　theta　=　180　degrees　to　270　degrees　and　locates　in　the　mid　plane　of　the　wall.　A　five-cycle　0.41-MHz　sinusoidal　tone-burst　signal　modulated　by　a　Flaming　window　is　carefully　chosen　to　generate　the　appropriate　excitation　wave,　in　CL0　mode.　According　to　the　received　signals,　the　conclusion　that　the　incident　CL0　mode　interacts　with　the　lamination　defect　for　numbers　of　times　can　be　obtained.　The　space-amplitude　curve　of　incident　waves　is　also　depicted　to　reveal　the　amplitude　distribution　of　incident　waves.　A　fully　non-contact　experimental　platform　that　adopts　an　electromagnetic　acoustic　transducer　as　a　transmitter　and　a　laser　ultrasonic　inspection　system　as　a　receiver　is　set　up　to　verify　the　finite-element　model.　Three　different　wavenumber　analysis　methods　are　performed　on　the　wavefield　signals　to　explain　the　detect　ability　of　the　lamination　defect　separately　through　both　numerical　and　experimental　studies.　It　can　be　concluded　that,　from　the　variation　of　wavenumber,　the　continuity　of　structure　can　be　deduced.　Not　only　can　the　location　be　calculated　with　an　error　of　less　than　10%,　but　the　profile　of　the　lamination　defect　can　also　be　imaged.　It　is　also　found　that　very　good　consistency　exists　between　numerical　and　experimental　results.