Abstract: Based on the principle of articulated serial robots, an articulated external pipe walking robot was designed, a kinematic model of the robot was established, and the inverse kinematic solution for the robot to traverse typical obstacles outside the pipe was given. This model provides the theoretical basis for structural design and trajectory planning. Keywords: External pipe robot, articulated robot, kinematic synthesis Introduction When pipelines transport high-temperature, high-pressure, or highly toxic fluid media, it is necessary to regularly inspect or monitor the pipeline's operation in real time for safety. In-pipe robots are not suitable for this task, while external pipe robots show significant superior performance. Since the 1970s, foreign scholars have conducted research on external pipe walking robots and have developed various external pipe walking robots [113]. Later, Spanish scholars developed a climbing robot using the Stewart-Cough parallel mechanism, which can climb not only horizontal pipes but also vertical pipes. In 2000, Envision L51 in the United States designed and launched some small external axial walking mechanisms using magnetic wheel structures. And a circumferential crawler, which uses a metal soft belt tightly clamped on the pipe as a track, and the walking wheels drive the vehicle body to walk along it to drive the instrument to rotate. Reference [6] proposes to use a special chain drive based on flexible body friction transmission to realize the circumferential motion outside the pipe. However, there are various obstacles on the pipe, such as T-shaped and L-shaped pipes, parallel pipes and flanges, etc., so the robot outside the pipe is required to have the ability to flexibly cross these obstacles. In response to this requirement, this paper proposes an articulated robot outside the pipe, which is an application of articulated serial robot on the pipe and has the ability to cross these obstacles. The following focuses on the kinematic model of the articulated robot and the inverse kinematic solution when crossing typical obstacles. [Click for details]