Abstract: The non-excavation external detection technology can directly detect the defects of in-service pipeline on surface. This paper introduces three kinds of non-excavation external detection technologies suitable for the in-service pipelines, including TEM (transient electromagnetic), MTM (magnetic tomography method) and NoPig. Their basic principles of pipeline corrosion detection are analyzed and the composition and working process of each intelligent device is explained. Besides, this paper also introduces the engineering application of those technologies and systematically analyzes the applicability and limitations. TEM, MTM and NoPig use the electromagnetic principle to detect the metal pipeline on surface which all has the remarkable advantages like non-excavation, no destruction on the external anticorrosive coating and no influence on the operation of the pipelines. But the application status indicates that more practical experience is needed in the aspects like anti-interference of the complex field environment and reliability of the data results.