This is done without stopping the flow of the product in the pipeline. In pipeline transportation, pigging is the practice of using pipeline inspection gauges or gadgets, devices generally referred to as pigs or scrapers, to perform various maintenance operations. A scraper pig shown at the Trans-Alaska Pipeline System Visitors Center The wire brush encircles the shaft and scours the interior of the pipeline. A cleaning pig for a 150-millimetre (6 in) oil pipeline. The black rectangles at the top and the circular disks in the center are magnets to attract and remove any loose metal objects in the pipe. The blue plastic disks seal against the inside of the pipe to propel the device and to remove loose sedimentation or scale buildup. A cleaning pig for a 710-millimetre (28 in) oil pipeline.
