Visual inspection and nondestructive evaluation (NDE) of natural gas distribution mains is an important future maintenance cost-planning step for the nation's gas utilities. These data need to be gathered at an affordable cost with the fewest excavations and maximum linear feet inspected for each deployment, with minimal to no disruption in service. Current methods (sniffing, direct assessment) are either postleak reactive or too unreliable to offer a viable and Department of Transportation-acceptable approach as a whole. Toward achieving the above goal, a consortium of federal and commercial sponsors funded the development of Explorer TM . Explorer TM is a long-range, untethered, self-powered, and wirelessly controlled modular inspection robot for the visual inspection and NDE of 6-and 8-in. natural gas distribution pipelines/mains. The robot is launched into the pipeline under live (pressurized flow) conditions and can negotiate diameter changes, 45-and 90-deg bends and tees, as well as inclined and vertical sections of the piping network. The modular design of the system allows it to be expanded to include additional inspection and/or repair tools. The range of the robot is an order of magnitude higher (thousands of feet) than present state-of-the-art inspection systems and will improve the way gas utilities maintain and manage their systems. Two prototypes, Explorer-I and -II (X-I and X-II), were developed and field-tested over a 3-year period. X-I is capable of visual inspection only and was field-tested in 2004 and 2005. The next-generation X-II, capable of visual and NDE inspection [remote field eddy current (RFEC) and magnetic flux leakage (MFL)] was developed thereafter and had field trials in 2006 and late 2007. It was successfully deployed into low-pressure (<125 psig) and high-pressure (>500 psig) distribution and transmission natural gas mains, with multi-1,000-ft inspection runs under live conditions from a single excavation. This paper will describe the overall engineering design and functionality of the Explorer TM family of robots, as well as the results of the field trials for both platforms. It will highlight the importance of the various design and safety features of the in-pipe crawler and showcase the value of data types and position-tagged visual/NDE data collected in working pipelines under live flow conditions. C

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