Trans Alaska Pipeline "Pig"

Pipeline devices called pigs are routinely used around the world. The earliest pigs cleaned the inside walls of small-diameter lines, and their short, squat shape gave them the name, which remained in use even as later designs no longer resembled the animal. In the trans Alaska pipeline, scraper pigs remove wax deposits that form as crude oil enters at about 125 degrees Fahrenheit at Prudhoe Bay and gradually cools while flowing through the line. If the wax were allowed to build up on the inner walls, oil flow would be reduced, so scraper pigs are launched periodically and travel with the oil at an average rate of 6-7 miles an hour before being removed at retrieval sites called traps, then cleaned and repaired for reuse. Traditional scraper pigs were constructed primarily of steel with molded urethane cups and urethane scrapers, while a newer all-urethane scraper pig is more resilient and flexes as it passes pipeline valves, placing minimum strain on the pipeline. More complex instrument pigs also move through the pipeline with the oil and are launched and retrieved in the same way, but they electronically monitor the line for early signs of pipe deformation and internal or external corrosion. Fitted with a tape recorder to continuously log the pipe's condition as they pass through, these instrument pigs help permit preventive maintenance before problems develop, and several types are used frequently each year to inspect the pipeline.

Delta Junction, Alaska · United States