Million Dollar Bridge - Portland, Maine

When a runaway barge Slammed into the Million Dollar Bridge in Portland, Maine, in 1986, it damaged a bridge support and halted drawbridge traffic for weeks. This prompted the Maine Department of Transportation, which has been planning to replace the bridge for decades, to revise its bridge design to prevent future damage. The DOT now plans to sink 38 fenders into the bay floor around the bridge supports. (Bridge construction, which will cost $165 million, began earlier this year.) The fenders are 1/2-inch-thick steel pipes, 36 inches in diameter and 109 feet long. To protect the steel from corrosion, bridge engineers specified a functional thermoset powder coating.

For that, they turned to Lane Technical Coatings, Carlisle, PA. A one-time division of Bethlehem Steel, Lane has powder coated concrete reinforcing bar, or rebar, for nearly 20 years. When managers bought the coating division from Bethlehem 9 years ago, they added a custom coating plant to handle large jobs, such as the pipes. At 21,000 pounds each, the pipes are the most massive objects ever handled at the plant, said Gregg Weaver, vice president of Lane Enterprises and general manager of the coatings division. The coating job also included several smaller pieces of structural steel.

To begin the coating process, a crane transferred the pipes from railroad cars to rail-guided steel carts. Moving at 3 to 4 feet per minute, the carts first carried the pipes through a 16-wheel in-line shot blaster. The pipes bypassed the plant's five-stage surface preparation system because they were too big. Besides, the DOT had only specified a near-white, shot-blasted surface, which generally is all that structural steel requires, Weaver said.

Next, the pipes entered the preheat oven, a combination of infrared and convection units stretching 100 feet. As the pipes emerged from the preheat oven, they entered a 20-foot long automatic spray booth, where 16 coronacharging spray guns applied 18 mils of gray epoxy powder to the hot surface. The pipes then entered a 170-foot-long convection oven for final curing. The whole process took 1 1/2 hours. In the final step before shipping, workers used a holiday detector to check for holidays, or pinholes, in the coating. When the job requires it, Lane also conducts salt-spray and cathodic disbondment tests on the coatings.

By Matthew Knopp,
Associate Editor
Powder Coating - November 1995