U.S. Navy: The Business Case for a Titanium Ship
Participants at a workshop exploring the use of titanium structure for ships found that it is not only possible to construct a ship hull from titanium-or Ti, it could be cost effective.
The workshop was sponsored by the Office of Naval Research and hosted by the University of New orleans, where an ONR research program on titanium ship structures is being conducted. Representatives of the shipbuilding industry, titanium suppliers, Navy, Coast Guard and Air Force labs, and academia discussed and examined materials, processes and applications.
Most ships today are primarily made from steel. Alternative materials include aluminum and composites. But the consensus of the workshop attendees was that titanium-while more expensive than other materials on a pound for pound basis-has many positive properties that contribute to lower total ownership costs (TOC) throughout the life of the ship.
Because titanium has more strength for its weight than steel-Ti offers a 40% weight savings compared to steel-lightweight designs can be achieved that offer increased payload capacity, reduced fuel consumption and reduced carbon emissions. It has a low magnetic signature, which means you can reduce heavy and power-consuming degaussing coils to protect against magnetic influence mines. It has temperature resistance, so it’s safer for structures like gas turbine exhaust systems. And Ti is virtually corrosion-free in seawater, so it can be cost effective for sea water piping systems such as cooling water and firemain.
However, more research is needed to develop high-productivity Ti welding processes for ship construction. Although well established, the existing titanium welding processes are too slow for ship hull construction which typically requires miles of welds, according to Dr. Pingsha Dong, a professor at University of New orleans School of Naval Architecture and Marine Engineering, and director of UNO’s Welded Structures Laboratory. Through the UNO investigation, advanced metal inert gas (MIG) welding and friction stir welding showed their potential.
Chris Conrardy, chief technology officer at the Edison Welding Institute (EWI), says there are different techniques for welding titanium, including gas tungsten arc welding, electron beam welding, high-power laser welding, friction stir and hybrids of the different methods. "The optimum approach depends on the structure’s configuration, joint design, performance requirements, and economic considerations."
But in each case, quality control is paramount, and inert gas shielding is required to avoid contamination. "Avoidance of contamination is a primary concern with all titanium fusion welding processes," Conrardy says.
"Titanium is highly reactive at elevated temperatures and requires shielding of the molten metal during welding and cooling," says Jennifer Wolk, a materials engineer with Naval Surface Warfare Center (NSWC), Carderock Division specializing in welding and friction stir welding of non-ferrous materials.
"Most steel ships are scrapped because of corrosion of the hull, not problems with the machinery," says Rob Moore at Textron Marine & Land Systems (TM&LS). "TOC is reduced by using a titanium hull."
Aerospace grade titanium used in aircraft is about nine times more expensive than steel. But industry experts predict that "fit-for-purpose" ship hull or marine grades of titanium, as proposed by UNO, could be made less costly-perhaps only three times as expensive as steel -by changing the processing and finishing requirements. When weighed against its positive attributes, titanium may become even more cost effective.
Moore says Ti production is energy dependent and the cost of energy is not going to go down. But, he says, marine grade Ti will likely cost much less than commercially available aerospace grade Ti.
Marine specific Ti grades have been developed and used for some high strength naval applications, such as piping, but not for general structural applications. The cost of marine grade Ti would depend on the end use and properties needed for the application.
Colen Kennell of the Center for Innovation in Ship Design at NSWC Carderock says Ti offers a potentially ship-scale cost effective alternative to steel structures. "For faster ships, lightweight hulls are a critical enabling technology."
As a further benefit, when a vessel reaches the end of its service life, its scrap value is much higher than a steel ship.
"Old ships are a problem," says Kennell. "Ti scrap retains substantial value even at the end of a 30 or 40 –plus year ship life."
There are other alternatives to steel, such as aluminum and composites for ship structures. "If you want an all-composite ship, then you would need an all-composite shipyard. But Ti could be introduced in a steel yard," says Kennell.
Wolk adds that Ti fabrication currently exists in shipyards, but does require strict controls for fabrication.
There is also the possibility that building ships from titanium would create a demand that would drive the cost up for the metal. There is precedent, when there was an unexpected demand for Ti when Callaway introduced the Big Bertha golf club at about the same time that Boeing announced the start of construction of a new airplane. A spike in the titanium market could also disrupt the aerospace sector.
But suppliers at the conference said that even if the Navy decided to build three or four Ti ships a year, US Titanium capacity is not a constraint. The US has sufficient projected capacity looking at current demand signals, and steps can be taken to mitigate demand spikes.
Such a fabrication facility would require a significant investment, Kennel says, and without additional demand it might be unsustainable. "But there aren’t any show-stopper industrial or management issues."
Raymond M. Walker of Keystone Synergistic Enterprises in Port St. Lucie, Fla., says the workshop demonstrated that there are no engineering barriers or obstacles that prevent design or construction of a titanium naval ship. "Challenges, yes; but no barriers."
Walker, an expert in welding and joining of titanium and vessel fabrication, says it was valuable to have representation from many of the key players in the effort to manufacture with titanium: the titanium material providers, titanium processing and joining experts, ship designers, ship fabricators, as well as commercial interests. "It was helpful to get a consensus from this group as to the realities and methods needed for fabricating a titanium vessel."
Vessel life, fuel efficiency, reduced maintenance, and increased range/payload will drive the argument, Walker says. "No new technologies are required, only adaptation of existing titanium practices (primarily from aerospace) to the specifics of vessel design and fabrication."
"The Navy is challenging industry to produce an affordable solution and we all have to take that as an action item to deliver this package as soon as we can back up the numbers and corresponding data," says Booty Cancienne, production superintendent for Textron Marine and Land Systems (TM&LS) in Slidell, La.
Cancienne is production supervisor for the TM&LS shipyard with four decades of experience. He’s worked at TM&LS for 35 years, and five more at other yards. He is responsible for all marine construction at TM&LS, including development of all processes, materials and metals used, training of employees and schedule and cost for all programs. He has overseen the construction-and later the refurbishment-of dozens of Navy LCACs (landing craft air cushion). In his job, he makes recommendations for engineering changes to reduce cost and to improve construction fabrication. At the workshop, when it came to welding, his was the voice of experience.
Most recently, he has been involved in the TM&LS proposal for the T-Craft innovative naval prototype being investigated by ONR. TMLS has fabricated a T-Craft side-hull section of aluminum, and will build the same structure from titanium to provide comparison data.
Cancienne says a titanium hull is possible. "We in industry must make the fear of high cost go away. We have to develop some processes to reduce cost and turn everyone’s attention to the customers’ needs and how to meet commercial and Navy requirements."
DATE:2012.4.18
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