The feeder pipes in a pressurized heavy water reactor (PHWR) suffer from flow-assisted corrosion (FAC), which makes the wall thickness of the pipes thin. This effect is a well-known degradation mechanism of a carbon pipe with high pressure and high flow rate. Therefore, the weak parts of the pipe should be measured to guarantee the safety. This paper describes a mobile out-pipe inspection robot with an automatic pipe tracking system for a feeder pipe inspection in a PHWR. The robot is composed of dual inch worm mechanisms. One is for a longitudinal motion along a pipe, and the other is for a rotational motion in a circumferential direction to access all of the outer surfaces of a pipe. A design method for a gripper actuator is proposed by using a kinematic and force analysis. The proposed mechanism shows a more stable gripping capability than the conventional ones. An automatic pipe tracking system is proposed based on machine vision techniques to make the mobile robot follow the exact outer circumference of a curved feeder pipe as closely as possible, which is one of the requirements of a thickness measurement system for a feeder pipe. The proposed sensing technique is analyzed to verify its feasibility and to develop a calibration method for an accurate measurement. A mobile robot and control system are developed, and the automatic pipe tracking system is tested in a mockup of a feeder pipe.