Remote-Field Eddy Current Inspection Tool for Small-Diameter Unpiggable Pipelines

Inspection of natural gas pipelines is necessary to ensure their integrity. Considerable pipeline mileage exists where the lines, particularly those in the smaller-diameter range, have internal restrictions and/or low pressure/flow rates. Conventional magnetic flux leakage (MFL) inspection pigs cannot be used because the product flow and pressure is not sufficient to propel the pig, and the large MFL magnets cannot readily move through restricted areas. To overcome these problems, an untethered, self-powered tool was developed that can adjust to inspect different pipe sizes and can retract to pass through obstructions such as elbows and tees. Southwest Research Institute developed a remote-field eddy current (RFEC) inspection system for detecting and characterizing pipe wall loss, and this system was integrated with Explorer II, a robotic transport device developed by Carnegie Mellon. The resulting tool has the capability to inspect 6- to 8-inch-diameter pipelines containing tight bends and tees, and can be launched, operated, and retrieved with the pipeline in service. This paper describes the RFEC inspection technology, the RFEC system modules developed for Explorer II, and preliminary test results.