Conventional inspection procedures using industrial endoscope cameras find it challenging to inspect narrow pipes because the endoscope cannot be inserted in the pipes due to the increasing friction and complex pipe structure. Active propulsion techniques can help improve inspection efficiency; however, the locomotion mechanism in such a narrow space is challenging because of the pipe’s geometrical configuration. In this study, a novel flexible propulsion module is proposed for narrow pipe inspection. The module is designed based on a newly proposed hollow-type duplex-chambered inchworm mechanism, which achieves smooth inchworm locomotion using only two air supply lines. With a simple attachable module design, the inspection operator can easily add active propulsion capabilities onto the regular industrial endoscope camera with a maximum diameter of 7 mm. The concept of the system and the structure of the mechanism are presented herein. Various experiments and simulations were performed to reveal the characteristics of the mechanism, and the results are discussed in terms of operating pressure, generated force, and locomotion speed, among other parameters. A prototype demonstrated smooth locomotion through 31-mm pipes at 26.6, 22.1, and 51.1 mm/s for horizontal locomotion, vertical climbing, and vertical descent, respectively, and performed well through a bending pipe.