U.S. gas utilities maintain an underground distribution network of over 1 million miles. Underground steel gas mains often corrode or crack causing the gas to leak. Gas leaks can produce catastrophic explosions particularly in urban and residential areas. Gas utilities use a costly and cumbersome approach to gas line repair requiring sensitive leak detectors and sometimes digging multiple holes in the street before locating and repairing the leak. Utility gas leak repair costs exceed several hundred million dollars annually nationwide.
GRI and NASA are funding a program to reduce the cost of repairing gas distribution mains using advanced robotics technology. Over a three-year program, researchers expect to develop a robotic repair system, which can travel a thousand feet in either direction from a single excavation to enable multiple repairs of corroded and leaking pipe joints in live gas mains. GRI expects that the system could provide up to 50% cost savings over conventional repair methods.
The NREC is teamed with Maurer Engineering, Inc. (MEI) to develop a live distribution gasline inspection and repair system with minimal live-access requirements. NREC will utilize MEI’s live-pipe access and coiled-tubing deployment system to deploy GRISLEE, a remotely controllable, modular leak-detection, imaging and repair robot system for the real-time in-situ inspection and repair of live distribution, 4-inch diameter gas mains. The intention will be to access live gas mains, insert GRISLEE through use of MEI’s coiled-tubing system, and “push-pull” it through the gas main. First a magnetic flux leakage flaw-detection head will be inserted to detect wall thinning and/or leaks in the pipe wall due to outside in corrosion or leaking joints. Then a repair head is inserted to prepare the affected pipe area followed by emplacement of an expandable metallized epoxy sleeve to reinforce and/or seal and plug the leak under live gas pressure and without affecting the continued gas flow inside the main line.
In the first year’s effort, several modules were developed and a facility for testing the system was built. The system performance was successfully demonstrated in the laboratory environment on a clean but leaky plastic pipe. Next year’s effort will include improving and completing all modules, expanding the testing facility, and conducting tests with real world pipes and joints. Upon successful completion, the third year’s effort will be devoted to field trials with participating gas utilities and to identify a commercial organization to market the system.
