Applying Electrical Magnetic Coil and In-Pipe INS to Map Underground Pipeline Track

The accuracy of the current buried pipeline management geographic information system (GIS) is not adequate to serve as base information for road digging control and permit in Taiwan. The existing positioning system for buried pipelines does not offer satisfactorily accurate surveying results for all the scenarios because the positioning accurateness decreases with an increase in the pipeline depth. The costly excavation and direct survey of the exposed pipeline method can provide precise measurement at the designed arbitrary interval and then the discrete point is interpolated into the continuous track. The required traffic controls and excavation permits for roads are the most critical drawback of this technology. The method of in-pipe inertial navigation system (INS) can record the complete, continuous pipe tracks, but such measurement drifts with an increase in the survey length. We proposed a pipeline positioning system by radiating an extremely low-frequency (ELF) magnetic field from the electrical coil placed on the ground to constrain the locating measurement of in-pipe INS. The proposed system could easily expand the diameters or increasing turns of a ground-based coil device to enhance the magnetic field intensity for accurately positioning the deeper buried pipes. The field tests were performed using a ductile cast iron pipe (DIP), and the corresponding results revealed that for the overburden depth of 3.4–4.2 m, the average positioning errors were 0.12 and 1.6 m in the horizontal and vertical directions, respectively. This approach is only plausible for an empty pipeline, and access to both ends of the pipe is required. A four-person crew handled the proposed system to locate the track of a 5-km-long buried pipeline in an 8-h-long working day when the pipeline was unfilled.

Any pipeline with diameter larger than 10 cm (4 in.) could apply this system to locate the continuous track with the requirement of accessibility at both ends of the empty pipe. With 1.45-m coil, the maximum detectable buried depth is 15 m, and locating error is less than 20 cm at both directions for the cases with buried depth less than 5 m. Two people need to move and operate the magnetic coil at the ground and another two people must hoist the in-pipe unit at each end of the pipe simultaneously. With this arrangement, the continuous track of buried empty pipe could surveyed for 5 km in length within an 8-h working day.