Serving Whitman County since 1877
Serving Whitman County since 1877
When they finish their work 160 feet below the surface if the Snake River, a new surface will be on the 31-year-old turbines at Lower Granite Dam.
Encased in a cylinder of wicket gates; the six giant propellers churn out electricity for the eastern Washington power grid.
Now, it is time for something major.
The 8–foot adjustable blades have turned since 1975 with only minor maintenance every six years.
It is called cavitation repair, and a seven-man crew from Tennessee began the months-long project in September.
The Bonneville Power Administration contract involves resurfacing of the turbine chamber walls and the six blades of each turbine.
Cavitation occurs as river water pushes through turbines, taking the pressure out to make electricity. The water pressure lowers enough to make it boil, taking it from liquid to a vapor and back again as the water goes from one side of the turbine blade to the other.
As the H2o flashes into vapor and back, it gives off a pop sound. These crackles cause scratches on the wall, causing the two-inch thick parent steel to erode.
“It’s much like a firecracker going off next to steel,” said Rob Lustig, Chief of Maintenance at Lower Granite Dam. “We’re pulling the potential energy out of the water.”
As a result, honeycomb marks bore into the steel.
After 31 years, some are as much as an inch deep.
The erosion of the walls which encase the turbine, or draft tube, is small to the eye. Just evident are patches of webbed and pocked gray, which are first marked with chalk for repair by the crews.
In August, the first of the special group arrived to begin the cavitation repairs.
On Wednesday, Oct. 5, Superintendent Mallory Davis led a crew of five as they climbed up and around Turbine No. 3 on scaffolding, metal and rope ladders, while drawing squares with yellow chalk. Their first weeks on the job were taken up by building the scaffolding.
Headlamps sent shadows up and out, everywhere.
“A Harvard education I got doing this,” said Davis, who spent five years in the Coast Guard before joining his uncle’s hydroelectric business in Hixson, Tenn. “It’s amazing what welding can do. It just fools you.”
In the 20 years since he started, Davis has done cavitation repairs on dams from Texas to Saskatchewan. All told, there are only five U.S. states he hasn’t worked in.
To get to their job site at the bottom of the turbine, the workers descend 15 feet down a single person-carrier cage through a four-foot wide corrugated pipe. At the bottom, the pipe drops into an open, towering cavern of cement, with three 70-foot high intake gates on one side. The gates when open let in 22,000 cubic feet of water per second.
When closed, they could be racquetball courts in Gotham City.
At the bottom center of the cavern is the wicket gates housing the turbine.
The giant propeller is 26 feet in diameter.
“You could drive a Volkswagen bug through those blades” said Lustig.
Once Davis and crew mark all the honeycombed cavitation spots and the draft tube is ready, they set up their patented milling machines, which rest on top of the plane of the turbine blades. Then the crew places and connects flumes for smoke, puts on respirators for a different kind of underwater breathing, and the lights go up. Welding torches flare, sparks fill the cylinder and smoke billows.
With two welding torches burning from each of the six turbine blades, the workers weld in rows of horizontal beads, 1/8-inch at a time.
They won’t stop until the project is done, working 24 hours a day, seven days a week, in shifts.
The final product is a coating of 1/4 inch of smooth stainless steel.
“The smoother you get it, the better the water flows over it and the less problems in the future,” said Davis.
The new surface will replace the original lining of mild, carbon steel, which was standard during the era of the dam’s construction.
Stainless steel withstands cavitation much better, lasting as much as 10 times longer.
Davis and his crew stay in a rented house in Pullman. They moved here from a job in Vermont.
One of the first things Davis does at each work site is to buy a printer.
“I’ve bought many printers in my life, I can tell you that,” he said. Since it’s a hassle to take a printer on airplanes, he just gives the one he has away at the end of each job and buys another one. This year he’s bought 14.
As a certified welding inspector for cavitation projects, he spends as many as 47 weeks away from home each year. It’s a job that only three or four people in the United States have.
He spends a lot of time in dark, tight spaces.
“I am claustrophobic, believe it or not,” he said. “I’ve had to blow out air just to get around in places, then I go to bed at night and it comes back to me, I start sweating.”
He enjoys it though, while it’s always nice to get home.
“I’ve got four kids and a wife that deserves better,” he said.
As for his current project, at Lower Granite, the BPA, the contract is for $6 million - $1.4 million per turbine. The contract is paid by square inches resurfaced.
Three years ago, two of the six Lower Granite turbines underwent cavitation repair. The remaining four will be done on this contract, with Davis and crew finishing two this fall, and two after spring runoff.
All six cylinders need to run during high water.
Until 10 years ago, the generator floor at the dam – which visitors can look over from the mezzanine level on guided tours - was clear and open. As the dam has aged, lately the floor has been populated with workers, machines and tools, including wrenches the size of sturgeon, and bolts as wide as cooking pots.
Garth Meyer is a former Whitman County Gazette reporter.
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