This Little Pig Clears the Oil Pipes

Of all the technologies available to maintain the nation’s 2 million miles of pipelines, one of the most critical devices evokes images of a muddy farm animal -- the pig.

Now erase the image.

The earliest, primitive pipeline pigs may have squealed as they scraped wax, mineral deposits, sand or other corrosion-causing debris from the insides of the nation’s energy highways, but even that similarity is gone.

The importance of so-called pigging leaped to center stage last week after oil giant BP shut down part of the Prudhoe Bay oil field on Alaska’s North Slope. The closure raised questions about the integrity of the nation’s pipelines and about how pipeline operators -- there are more than 3,000 -- keep the oil flowing.

Pigs can be made of metal, foam, plastic or gel. They range in size from a few inches to 7 feet tall and as wide as a tree -- or however big they have to be to fit snugly inside a pipe. Some are simple scrapers. Others, known as “porcupine pigs,” sport wire scrubbing brushes.

Propelled by the pressure of oil or other pipeline contents, these devices dislodge debris and clean the interior pipe walls.

More sophisticated “smart pigs” carry instruments that gather images and other data inside the pipeline so operators can pinpoint trouble spots.

“I’ve heard so many people say, ‘If you could make one for arteries, you’d be rich,’ ” said Gary Smith, president of Inline Services Inc., a Houston-based pig manufacturer and distributor.

BP ordered the Prudhoe Bay shutdown after discovering a leak and severe corrosion in 16 miles of aging transit pipes that feed into the 800-mile Trans Alaska Pipeline System.

The company acknowledged those lines had not been pigged in years. Instead, BP had relied mostly on exterior ultrasound technology to monitor the pipes’ integrity. It had considered the risk of corrosion low because the pipes carried market-ready crude or processed oil that had been stripped of harmful water, gas and solids.

BP now says it will use pigs to maintain and inspect all of its transit lines.

Even pipes that sit unused will corrode, said Steve Arrington, global operations manager of the pipeline and process services group for Houston-based oil-services conglomerate Halliburton Co.

“Corrosion is just a fact of life. Corrosion of metal alloys occurs all the time. All that man can do is minimize that or reduce it, but we cannot stop it completely,” Arrington said.

Legend has it that early pigs, made of stuffed burlap bags or other materials, earned their name because they would squeal as they scraped through a pipe. But Smith says the name is an acronym for “pipeline inspection gauge.”

Smith said all kinds of debris could build up in a pipeline, such as sand left from the pipe’s fabrication or condensation from natural gas and saltwater from oil extracted offshore. Even simple bacteria can corrode the metal, he said.

However, many operators resort to pigging only when a problem is apparent. By then, the pipe usually is already damaged, which can cause safety and environmental risks as well as jeopardize a multimillion-dollar pipeline.

Other technologies help assess pipe integrity, such as measuring the flow of an electrical current, said Tom Miesner, a Houston-based pipeline consultant. Increased resistance means the pipeline wall is thinning.