Field Trial of the NoPig Inspection System

The NoPig system is an above ground metal-loss detection tool utilizing magnetics. Sensors at ground level detect disturbances in the magnetic field around the pipeline generated by impressed alternating current (AC) signals. This tool is intended for use on segments of pipeline which are considered unpiggable. Previous field trials indicated the tool was capable of detecting metal-loss in small diameter seamless pipe. Trials on electric resistance weld (ERW) or double submerged arc weld (DSAW) pipe were inconclusive. Modifications have been made to the NoPig hardware and analysis software to correct for the non-uniform magnetic fields produced by seamed pipe and girth welds. The study reported in this paper is a field trial of the modified inspection system. Recently inline inspected pipelines of nominal pipe size (NPS) 12 and 16 were selected for survey. Pipeline segments where significant metal-loss was detected from Inline Inspection (ILI) were selected for the blind test. Eight hundred meter sections of pipeline were surveyed at each of these locations to ensure a range of pipe conditions were included. After all surveys were complete, significant features were excavated and actual measurements were obtained. This paper describes the field inspection program as well as the analysis process used to verify the detection capabilities of the modified NoPig system. The results will include discussion of the positional accuracy, detection capability and threshold of the system. This analysis will help determine if the NoPig system is suitable alternative for assessing the integrity of unpiggable pipeline segments.