Coatings, Cathodic Protection Check Cold-Climate Corrosion.

• Author: KANE, ROGER

Rusty steel, blistered sheet metal, deteriorating concrete-- the effects of corrosion are not hard to find, but they can be difficult to combat. From coastal Southeast out to the Aleutian Islands up to the North Slope and throughout the Interior, engineers are engaged in a costly battle with corrosion on two fronts: internal environments and external environments.

Corrosion is the deterioration of a material or its properties, caused by a reaction within its environment. Wood, plastics, ceramics and metals are substances gradually destroyed by corrosion, which is measured by changes in weight, dimension or mechanical properties, such as tensile strength( the greatest longitudinal stress a substance can bear without tearing apart) or ductility (capability to be molded into a new form).

Corrosion causes about $1 billion a year in damages in Alaska, according to Lyle Perrigo, director of the U.S. Arctic Research Commission's Alaska Office. That cost could be as high as 6 percent of the value of goods and services produced in Alaska, but Perrigo said there are ways to cut losses.

"About 1 percent could be saved by using cathodic protection, by using the right kind of building materials or by using the right kinds of inhibitors. Just because you have high (corrosion rates, that doesn't mean you can't cope with it (corrosion)," Perrigo said. "We can paint more frequently, use better coatings, better designs--these are not insurmountable problems. We do not need to reinvent the wheel. We just need to figure out where it is going."

Internal Environments

Internal environments include the interiors of oil and water pipelines, and mechanical systems. Fluids transported, or carried for lubrication, in these systems are corrosive, but corrosion in these environments can be controlled using proper materials, designs and chemical inhibitors.

"Internal corrosion is big business," according to Christopher Dash, a corrosion engineer with Phillips Alaska Inc. "Oil, water, gas and solids can eat pipes at phenomenal rates. With unprotected pipes, we're talking inches a year. And most pipes are not inches thick."

The pipes Dash is concerned about carry crude oil from drill sites to gathering sites and ultimately into the trans-Alaska oil pipeline. The pipes are 24 inches in diameter and have walls three-eighths-of-an-inch thick. They carry crude mixed with seawater (which is pumped into oil-rich reservoirs to build pressure and force the oil out of the ground)...