INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 18, No. 2, pp. 145-153 FEBRUARY 2017 / 145 © KSPE and Springer 2017 Development of RFECT System for In-Line Inspection Robot Considering Extendibility of Receiving Sensors based on Parallel Lock-in Amplifier Jae-Ha Park , Hui-Ryong Yoo , Dae-Kwang Kim , Hak-Joon Kim , Sung-Ho Cho , Sung-Jin Song , Hui-Min Kim , Gwan-Soo Park , and Yong-Woo Rho 1 School of Mechanical Engineering, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon-si, Gyeonggi-do, 16419, South Korea 2 KOGAS Research Institute, 960, Incheonsinhang-daero, Yeonsu-gu, Incheon, 21993, South Korea 3 School of Electrical and Computer Engineering, Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan, 46241, South Korea # Corresponding Author / E-mail: sjsong@skku.edu, TEL: +82-31-290-7451, FAX: +82-31-299-5276 KEYWORDS: Remote-field eddy current, Lock-in amplifier, In-line inspection robot, Nondestructive testing This paper proposes a new and effective approach to design a remote-field eddy current testing (RFECT) system equipped with a large number of sensors in order to provide full circumferential coverage of pipelines larger than 6 inches. By developing a parallel digital lock-in amplifier (LIA), the extendibility of receiving sensors can be achieved, and therefore, the modification of RFECT systems, which should be accompanied by sufficiently securing the receiving sensors whose number increases with the pipeline size, can be minimized. Using the design method for an RFECT system based on a parallel digital LIA, a new non-destructive testing (NDT) platform that can be applied to RFECT systems of various sizes without modifying the system architecture is developed. It is then applied to an RFECT system that can be mated with an in-line inspection (ILI) robot and has 36 receiving sensors to inspect unpiggable gas pipelines. The performance of the RFECT system is verified with respect to the sensitivity and the accuracy of defect characterization though the pull-rig test having a number of artificial defects. Manuscript received: February 26, 2016 / Revised: August 15, 2016 / Accepted: September 8, 2016 1. Introduction In-line inspection (ILI) technology has been a cornerstone for sustaining the integrity of pipelines in global infrastructures and has utilized several kinds of useful non-destructive testing (NDT) systems, such as magnetic flux leakage (MFL), ultrasonic testing (UT), and electromagnetic acoustic transducer (EMAT). As the conventional ILI tools referred to as “smart pigs” are propelled by the differential pressure between the front and rear of the tool body, the pressure of pipelines should be kept above a specified pressure. In the case of natural gas pipelines, the operating pressure should be maintained above 20 kgf/cm , and a special launching and receiving trap must be installed in order to stably deploy the conventional ILI tools to the pipeline. Pipelines that satisfy the above-mentioned conditions and for which the deployment of conventional smart pigs is possible are called “piggable” pipelines. Conversely, pipelines that cannot be inspected by smart pigs due to internal obstacles that exist in the itinerary of smart pigs in the pipeline and/or insufficient pressure are deemed “unpiggable” pipelines. Distribution mains mostly classified as unpiggable pipelines are buried in highly congested areas worldwide and are about three times longer than trunk pipelines, piggable pipelines that connect metropolitan cities. Thus, the need to inspect the unpiggable pipelines moving along in the interior of pipeline has arisen in the gas industry and necessitated ILI robots able to self-propel and negotiate obstacles. In order to develop an ILI robot for unpiggable pipelines, the selection of NDT technology suitable for the operating environment in unpiggable pipelines and the general limitations of ILI robots are very important. As the untethered type of ILI robot usually designed for long-range inspection is battery operated, NDT technology able to supply high performance in terms of sensitivity, detectability, and accuracy of defect sizing as well as minimize power consumption is preferred. Among the several common NDT technologies prevalent in the conventional ILI tools for piggable pipelines that are applicable to ILI robots, remote-field eddy current testing (RFECT) technology is considered the optimal NDT technology. The advantages of RFECT DOI: 10.1007/s12541-017-0020-9 ISSN 2234-7593 (Print) / ISSN 2005-4602 (Online)