As a Material of Choice, Titanium Allows Submersible to Reach ‘Full-Ocean Depth’

By Michael C. Gabriele

In business, when individuals or companies achieve major milestones or stellar accomplishments, they’re praised for having reached great heights of success. However, in contrast to this lofty description, Triton Submarines LLC, Sebastian, FL, has have been lauded for its great depth of success.

How deep? Triton’s 36000/2 titanium submersible reached a depth of 35,853 feet or “full-ocean depth” (nearly seven miles) in the Pacific Ocean’s “Challenger Deep” region within the Mariana Trench near the island of Guam—the lowest-known point on the Earth’s ocean floor. By way of comparison, the peak of Mount Everest is the highest point on the Earth’s surface at 29,000 feet.

Jarl Stromer, Triton’s manager of class and regulatory compliance, said his company designed, built and delivered the titanium submersible in 2019 to accommodate explorer Victor Vescovo and his “Five Deeps Expedition” to journey to the deepest points in the world’s oceans. Stromer explained that Pittsburgh-based Allegheny Technologies Inc. (ATI) served as Triton’s “most-important vendor” and strategic partner in the project. ATI produced a titanium Grade 5 ingot at its Specialty Materials facility in Monroe, NC, and then created the two interlocking hemispheres of the Triton 36000/2 submersible at its Forged Products plant in Cudahy, WI.

Initially, Triton and ATI considered using nickel steels, Inconnel 718 nickel-based super alloy, aluminum alloys, and titanium Grade 23 to build the Triton sub, but eventually selected titanium Grade 5 (Ti 6Al-4V), the workhorse aerospace alloy. Grades 23 and 5 are similar, with Grade 23 offering higher ductility and fracture toughness. Stromer said ATI’s titanium Grade 5 prevailed because of its mostfavorable combination of properties, including strength-to-weight ratio and excellent corrosion resistance to seawater.

Stromer said the decision was made not to weld the two 36000/2 titanium square-shaped hemispheres, but rather have them interlocked with “O” rings and utilize the enormous deep-sea pressures to keep the unit watertight. The sub was designed for multiple trips to the ocean’s depths. So far Trion has built only one 36000/2 (a sub designed to reach 36,000 feet and carry two passengers). Triton has also built two 1000/2 units and 10 3300/3 submersibles. Triton also builds submersibles with acrylic hulls.

While the submersible represents a specialty “showcase” project, it does demonstrate the capabilities of titanium design and manufacturing, as well as survive extreme environments—perhaps opening doors for similar undersea projects or even applications for deep-water oil and gas drilling platforms. ATI, in an article posted on the “newsroom” section of its website (https://www. atimetals.com/newsroom), titled “The Perfect (Hemi) Sphere,” reviewed the production technology details of the Triton project from the perspective of the titanium industry.

According to its newsroom article, ATI began its partnership with Triton years before the 36,000/2 project, with extensive research, development and trial runs that resulted in ATI helping Triton “to transform titanium into the perfect hemispherical shape that would withstand full-ocean depth pressure.” The challenge to engineer the Triton sub involved “forging a 90mm-thick pressure hull out of titanium within 0.1 percent of perfect sphericity necessary to ensure the homogenous microstructure and consistent mechanical properties enabling equal distribution of weight while maintaining integrity of the shape.”

ATI used its 15,000-ton hydraulic press in Cudahy to forge the titanium hulls. “Relying on modeling and predictive technologies, each intermittent target shape was carefully engineered to refine the structure until a flat disc or ‘pancake’ was formed. This process was repeated to produce a second pancake with the same properties.” The two titanium pancakes were converted to a dome shape through precise control of the 20,000-pound open dies against the gravity of 15,000 tons of force.

Triton is one of just a handful of submersibles to reach full-ocean depth, but it’s only the first to be fully certified by DNV-GL and the first to reach full-ocean depth multiple times. (DNV GL, formed in 2013 through the merger of Det Norske Veritas (DNV) and Germanischer Lloyd (GL), is involved in maritime risk assessment and certification, according to the website Dolphin Charger: www.dolphin-charger.com/ news/dnv-gl-certification).

Celebrated Hollywood filmmaker James Cameron made a dive in March 2012. A Navy expedition occurred in 1960. As stated on the Triton website (https://Tritonsubs. com), the 36000/2 “opens up to repeatable exploration the 70-percent of the world’s oceans hitherto beyond the reach of mankind. Equipped with a full science suite and ultrahigh definition filming capabilities, the 36000/2 is helping scientists and explorers uncover the mysteries of the most unexplored region on Earth— the ultra-deep. Reliable and repeatable exploration to full-ocean depth affords scientists the opportunity to compare rich data-sets spanning the full gradients of depth, temperature, salinity and other factors.”

“In order to protect our oceans, we must first understand them. The key to understanding their global impact lies in the gathering, interrogation and interpretation of quality, scientific data. The challenge presented to Triton was to build a craft that would match these forebearers for depth, but be able to repeat the dive hundreds, if not thousands, of times. Such a vessel must serve a meaningful purpose; to exist not simply to set records, but to further human understanding through serious scientific research and to inspire a passion for our oceans.”

Stromer said it’s expected that the Triton sub fleet will continue to explore the ocean’s depths in the coming years, looking to map the sea floor and document discoveries of never-before-seen aquatic life.

Profile of an Explorer

The New Yorker magazine, in its May 10, 2020 edition, published an article (“Thirty-Six Thousand Feet Under the Sea”) that described Victor Vescovo’s undersea adventures in the 36000/2, which resembled “a bulging briefcase, with a protruding bulb at the bottom. This was the pressure hull—a titanium sphere, five feet in diameter.” In September 2014 Vescovo first contacted Triton Submarines and outlined his plan for the Five Deeps Expedition. The article described Vescovo as a former a jet and helicopter pilot, “familiar with the procedure-driven piloting of complex craft,” who made his fortune as a private equity investor.

“It was the middle of summer, 2018, in South Florida, and Triton’s technicians were working 15 hours a day. Every major component of Vescovo’s submarine had to be developed from scratch.”

The article also recounted a vivid description of the dive. “After thirtyfive thousand feet, he began releasing a series of weights, to slow his descent. Nearly seven miles of water was pressing on the titanium sphere. If there were any imperfections, it could instantly implode.” The submarine touched the silty bottom, and the pilot, a fifty-three-year-old Texan named (Vescovo) became the first living creature with blood and bones to reach the deepest point in the Tonga Trench” (the second-deepest undersea trench, located in in the southwestern Pacific Ocean, and one of the target sites in the Five Deeps Expedition)

Courtesy of Triton Subs