Trans Alaska Pipeline "Pig"

Trans Alaska Pipeline "Pig". . , Devices called "pigs" are routinely used in pipelines around the world. The first pigs, used to clean the inside walls of early small-diameter lines, were short and squat, suggesting the shape of the common barnyard animal. The name was applied by some early pipeliner, and the description stuck. It persists today, although the modern device retains little of the original pig-like contours. Pigs used to clean pipelines by scraping away interior deposits are called "scraper" pigs. Later pipeline engineers developed additional uses for the internal devices, but even the most sophisticated of these is called a pig., URETHANE SCRAPER PIG , The urethane scraper pig pictured above is the ty[?, probably "typical"] [marker broken] trans Alaska pipeline. , Its predecessor was the urethane-and-steel device sta[?] display. The all-urethane pig is more resilient and flexes as it [?] the pipeline valves. This design places minimum strain on the p[?, probably "pipeline"], WHY ARE SCRAPER PIGS REQUIRED? , Crude oil enters the trans Alaska pipeline at about 125 degrees Fahrenheit at Prudhoe Bay. As the oil flows through the line it gradually cools, and wax occurring naturally in the oil may be deposited in the line. This wax adheres to the inner walls of the pipe, and if the build-up was allowed to continue, the oil flow would be reduced. Therefore, scraper pigs are launched into the pipeline periodically to scrape away these deposits. The pigs move through the line at the average oil flow rate of 6-7 miles an hour. They are taken out of the line at pig retrieval sites, called "traps.” After a pig is removed from the line, it is cleaned and repaired for re-use., TRADITIONAL SCRAPER PIG , Traditional scraper pigs like the one in this display were constructed primarily of steel, but employed urethane in the molded cups that are used to push it through the line by the flowing oil. The scrapers used to clean the deposits from the interior pipe walls were also made of urethane., ["Pig" Diagram, left to right, reads] , Bumper Nose . Support/Drive Cup . 255 Ultrasonic Transducers . Pig Location Transmitter, INSTRUMENT PIG , This tool is more complex than the scraper pigs. The instrument pig moves through the pipeline with the oil and is launched and retrieved just like the scraper pig. This device serves another function. The instrument pig electronically monitors the pipeline for early indications of potential problems, such as pipe deformation and internal or external corrosion. Early detection of these conditions permits preventive maintenance before problems can develop. The instrument pig is fitted with a tape recorder to continuously log, note and register the condition of the pipe as the pig passes through. The taped record is inspected at the end of each run through the line. Several different types of instrument pigs are frequently used to inspect the pipeline each year.