Robot Explores Gas Mains in New York
Anne L. Fischer
A self-propelled robot may be coming to the rescue of old, decaying gas lines running under New York and surrounding areas. With some pipes dating to the late 1800s, maintenance is a challenge made even more difficult by the city's web of underground copper, fiber optics, steel and plastics that move water, gas, electricity and communications.
Repairs have become so cumbersome that they are made on an as-needed basis, and preventive maintenance is virtually unheard of. To attend to problems, workers use ancient maps to locate the main and, with a general idea of where to excavate, drill down, tap into the main and drop a push-rod camera to search for the source.
Figure 1. Explorer is a sausagelike train made up of seven links that recently explored the gas mains under Yonkers, N.Y., looking for corrosion, thinning walls and other signs of wear.
The "cameras on a stick," as Phil Fowles, senior engineer at Consolidated Edison calls them, slog through the buildup of debris and water at the bottom of the pipe, creating friction as they go. The cameras are tethered to cable that provides power and lights. Under good conditions, their visibility is 100 to 130 feet down a pipe, but the cable often snakes around in the pipes and binds up, limiting the distance and impeding progress. They also can't be centered within the pipe, and frequently survey only the bottom part, according to Fowles.
Some high-pressure natural gas pipelines can be inspected by "smart pigs," which have been around the industry for many years. They rely on magnetic flux leakage to detect anomalies in the pipe walls, a technique that uses strong magnets on the walls. Sensors are used to measure variations in the wall thickness, indicating thinness caused by external corrosion.
The "pig" is a cylindrical object that is dropped into the pipe, and gas pressure blows it through the pipe, sometimes tens of miles. The pig can detect decaying pipes, but there are drawbacks. One, it has to be retrieved from the main, and its length of travel is not always known, so gas line workers can't be certain of its location. The other problem is that bends, plug valves, and inconsistent flow rates and pressures may prevent the pig from traveling through the pipe at all.
Figure 2. The untethered robot can be used to inspect the insides of 6- to 8-inch-diameter gas mains, capturing real-time video and sending data wirelessly to the operator.
The tide may have turned, however. Consolidated Edison recently deployed a robot under the streets of Yonkers, N.Y., where it inspected hundreds of feet of gas main. The patent-pending Explorer robot was built as a project launched by the Northeast Gas Association, the National Robotics Engineering Consortium at Carnegie Mellon University in Pittsburgh, NASA and the US Department of Energy (DoE). The goal was to build a teleoperated, long-range, untethered robot that uses video to inspect live gas mains. The Explorer can drive itself through 6- and 8-inch mains for hundreds of feet, resulting in fewer excavations per mile and a cost savings for the gas company.
The robot is a tiny train of seven links or modules: two drive modules (one on each end); two battery modules; two support modules for centering; and one with a central computer. Each is separated by active-gear, motor-driven steering joints, which allow the train to launch, to handle sharp bends and to navigate the pipe. Each drive module has a custom-made digital 640 × 480-pixel CMOS-based camera with a fish-eye lens mounted for pipe viewing and locomotion assistance.
The battery is a nickel-metal hydride, but Hagen Schempf, principal systems scientist at Carnegie Mellon's Robotics Institute, said the next generation will be lithium ion, which has increased capacity at the same size and weight. The lights on the Explorer are bright-white infrared LEDs that illuminate up to 3 feet ahead or as much as 20 feet with high-reflectivity targets in place.
Explorer's camera is perfectly centered in the pipe with a 190° field of view, allowing it to see the pipe wall perpendicular to the camera. It takes real-time video, looking for corrosion, gouging, denting and cracking pipes. Data is transmitted wirelessly to an operator in a van at the point of access, who controls the console. The Explorer uses a proprietary combination of software and hardware developed at Carnegie Mellon to provide long-range communication at high bandwidth.
Plans for the robot
According to Fowles, the length of pipe that the robot can inspect is limited only by the ability of wireless communications and battery life, making these the areas that need improvement. He'd like to see it capable of communicating at a greater distance, so that it can travel even farther.
Tethered robots have been in use in sewers for some time, Schempf said, but the Explorer opens up a range of possibilities for performing various types of underground inspections. His group is working to add nondestructive evaluation sensors that will help utilities perform preventive maintenance by analyzing the levels of corrosion and degradation of their steel infrastructure. He also would like to increase the battery power, transmission range and ruggedness of tomorrow's underground Explorer to enhance its usability, to lower its cost per mile and to ensure that it will survive the rigors of field use.
Rodney J. Anderson, a technology manager at the DoE's National Energy Technology Laboratory, sees the day when advanced sensors will allow inspection of pipes from aboveground. These tools are not yet available, but he expects that by focusing on placing advanced sensors on robots such as the Explorer, aboveground inspection is just on the horizon.
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