The　conductivity　of　metal　pipeline　is　crucial　for　assessing　material　properties,　ensuring　industrial　safety,　and　conducting　quality　control.　In　order　to　accurately　measure　the　conductivity　of　pipes,　this　article　proposes　a　dual-frequency　eddy　current　(EC)　testing　method.　The　EC　analytical　model　of　a　cone-shaped　solenoid　coil　outside　a　conductive　pipe　is　derived　using　the　second-order　vector　potential　(SOVP)　of　the　magnetic　field,　and　the　effects　of　coil　parameters　on　the　signal　are　analyzed.　Based　on　the　theoretical　model,　a　quadratic　relationship　has　been　found　between　the　logarithm　of　the　probe　lift-off　and　the　inductance　change　of　pipe　at　high　frequency,　from　which　the　probe　lift-off　distance　can　be　estimated.　Then,　the　phase　signature　measured　at　low　frequency　is　used　to　determine　the　conductivity　of　the　pipe　through　the　Newton-Raphson　algorithm.　Numerical　simulations　and　experiments　have　been　conducted　to　evaluate　the　proposed　method　for　conductivity　estimation　with　various　pipe　materials　and　probe　lift-offs.　The　method　achieves　an　accurate　estimation　of　pipe　conductivity　with　a　relative　error　lower　than　3%.　©　1963-2012　IEEE.