(Photo by Tom Kleindinst, Woods Hole Oceanographic Institution) [ Hide caption ]
From the beginning of 2011 to May 2013, Alvin, the U.S. science community’s only human-occupied submersible dedicated to deep-sea research, underwent a major upgrade and overhaul to greatly enhance its capabilities. In the end, the iconic sub was disassembled, redesigned and rebuilt, piece by piece, by a one-of-a-kind team of engineers, technicians, and pilots at WHOI.
Here, Kurt Uetz, project manager for the upgrade, describes the long and winding path taken by Alvin’s new personnel sphere during its fabrication and assembly:
This picture was taken the day the new personnel sphere arrived at WHOI, in June of 2012. We took 41,000 pounds of titanium and built an 11,000-pound sphere, and left shavings all over the U.S.
The process began with three ingots from a mill in Pennsylvania, two at 17,000 pounds each and one at 7,000 pounds. The two larger ones were sent to Milwaukee for forging. They literally beat the ingots into disks about 140 inches across and 4 inches thick. They heated them up and pressed them down, heated them up, pressed them down. Then they built a massive round mold and pressed each heated disk into the mold to make two hemispheres.
Those went to a company in Los Angeles for annealing. They were heated in an oven, in a specific atmosphere of oxygen and other elements, and quenched in water within 60 seconds of coming out of the oven. Annealing captures the metal’s material properties to give it what they call ‘material toughness’ so it can be machined, yet be strong enough to absorb the stress of going to ocean depths at 10,000 pounds per square inch.
From there, the two hemispheres went to Anaheim, where they were machined to their current thickness of 2.81 inches, almost perfectly shaped. The greatest out-of-roundness is about 30 one-thousandths of an inch. They used an electron-beam weld to weld the two hemispheres together without any filler metal. It was done in extreme vacuum, greater than the vacuum of space, to reduce any molecules of air that could affect the weld. Then they machined openings in the sphere for the windows, the hatch, and two parts on the back called penetrator plates. With the smaller ingot they made fluted inserts for the holes. Those were also electron-beam welded into place.
When you weld, the metal close to the weld expands and then shrinks. That leaves stress in the metal. So the sphere was shipped to Ohio, where it was heated slowly in a vacuum oven and then cooled to relieve the stress from all the welding.
Then it went back to Anaheim for more machining and some minor welds. From there it went to San Antonio, where the primary contractor for the sphere, Southwest Research Institute, installed the hatch and windows. The windows are made of a very high-grade optical acrylic.
Next, the sphere went to Annapolis for hydrostatic tests. For the pressure test, both the chamber and the sphere are filled with water because if the sphere is empty and it fails, it implodes, and you could get shrapnel flying about. The test is performed in stages of increasing depths and held there for specified amounts of time. The sphere was tested to 8,000 meters, nearly 12,000 psi, which is about 24 percent deeper than Alvin’s eventual maximum operating depth of 6,500 meters. It passed all the tests.
Then it was delivered to WHOI, where we began assembling it into the vehicle.
As a career Navy officer, I drove surface ships and worked in shipyards as a project manager for shipbuilding and ship repair.
I came here three years ago, just for this project. I often said, ‘I’ve got the best job at Woods Hole.’ The last eight months of the project were pretty hectic and stressful on everybody, but I think the vehicle is going to provide an ‘Aha!’ moment in the deep ocean for all of us.
Alvin is owned by the U.S. Navy and operated by WHOI. The current upgrade has been funded largely by the National Science Foundation, with support from private donations to WHOI.