Flowing with Questions about the Trans-Alaska Pipeline

While driving your relatives over Alaska's highways this summer, you'll no doubt be inundated with questions about furry things, leafy things, andóif you're traveling the Richardson, Steese, Elliott, or Dalton highways — the trans-Alaska oil pipeline.

With the aid of Alyeska Pipeline Service Company's Elden Johnson, I gathered some facts that might be helpful when your brother-in-law from Georgia lobs pipeline questions at you. Johnson, a corrosion engineer with Alyeska, has worked on the design, construction and maintenance of the pipeline since 1973.

Completed in 1977, the pipeline covers 800 miles of mountain, muskeg and river valleys in its span from Prudhoe Bay to Valdez. Stretch the pipeline over the Lower 48 and it would reach from Los Angeles to Denver.

The pipe is a tube of 1/2-inch thick steel with a diameter of 48 inches. It looks thicker from the highway because the steel pipe is wrapped with four inches of fiberglass insulation. The shiny wrapping we see is a coat of aluminum sheet metal.

The closer oil is to the molten core of the earth, the hotter it is when oil companies pull it to the surface. Oil pumped from the Prudhoe Bay field, which is 10,000-to-20,000 feet deep, is about 145 to 180 degrees Fahrenheit. Using heat exchangers that work like a car's radiator, the oil companies cool the oil to about 120 degrees before it enters the pipeline.

If the flowing oil was cold, the pipeline wouldn't inspire nearly as much highway conversation. Engineers would have buried the entire pipeline had it not been for permafrost — permanently-frozen soil lying in sheets and wedges beneath the ground surface. The pipeline couldn't be buried in permafrost because the heat of the oil would cause the icy soil to melt. The pipe would then sag, and possibly leak. Because much of Alaska is underlain with permafrost, Alyeska routed just over half the pipeline above ground.

Where it snakes over land, the pipeline is supported by posts designed to keep permafrost frozen. Topped with fan-like aluminum radiators, the posts absorb cold from the winter air and transfer it to the soil. When the air temperature is 40 below, for example, the posts cool down to 40 below and take away heat from the soil, assuring the ground stays frozen.

The pipeline was built in a zigzag pattern to allow the pipe to expand and contract. Because workers welded much of the pipeline at temperatures well below zero, engineers anticipated that the metal would expand once hot oil began flowing through.

The zigzag also allows the pipeline to flex during earthquakes; it slides over H-shaped supports with the aid of Teflon-coated "shoes" that stand on the crossbar between the posts holding up the pipeline. Where the pipeline crosses seismic faults — weak areas of rock that rupture during earthquakes when the plates of the earth grind against one another — it sits on rails. Near the Denali Fault south of Delta Junction, the pipeline rests on 20-foot steel bars that allow it to move side-to-side should an earthquake cause the earth's crust to slip laterally along a fault line.

The temperature within the pipeline is relatively constant despite ambient temperatures along the line that can range from nearly 100 above to 80 below, which is the Alaska record cold temperature set on Jan. 23, 1971 at Prospect Creek Camp on the Dalton Highway. The four inches of fiberglass insulation that surrounds the above-ground pipeline keeps oil warm enough to flow even on the coldest winter days. If the pipeline had to be shut down in the winter, the oil within could sit for several months before congealing.

Powered by the heartbeat of 10 pump stations, oil flows through the pipeline at about the speed the Yukon River carries a raftóabout 5 to 7 miles per hour. At that rate, it takes about five-and-one-half days for oil to complete the journey from Prudhoe Bay to Valdez. Hopefully, you'll spend less time than that in the car with your brother-in-law this summer.