The Titanic, famously known as the "unsinkable" ship, was a British luxury ocean liner considered a marvel of engineering at the time that sank on its maiden voyage, from Southampton to New York City, in April 1912. On April 14, 1912, the Titanic struck an iceberg in the North Atlantic Ocean, resulting in the loss of more than 1,500 lives -- one of the deadliest commercial peacetime maritime disasters in modern history. A combination of factors contributing to the sinking, including inadequate safety measures, a shortage of lifeboats, and the high speed the ship was maintaining in icy waters. The wreckage of the Titanic rests at a depth of approximately 12,500 feet (3,800 meters) on the ocean floor, about 370 miles (600 kilometers) southeast of Newfoundland. While the sinking of the Titanic has had a lasting impact on maritime safety regulations, exploration of the Titanic wreckage for numerous books, films, and television documentaries has grown its broader cultural impact.
The world witnessed the inherent and continuing danger of ocean exploration and voyage with this past week’s loss of the OceanGate Titan submersible. The Titan submersible, built by OceanGate Expeditions, launched in 2018. According to its design specifications, the Titan was capable of diving to a depth of 13,123 feet (4,000 meters), or slightly deeper than the Titanic. The Titan was the first submersible to be constructed from carbon fiber and titanium, making it much lighter than traditional submersibles.
Why Carbon Fiber?
Carbon fiber is strong and lightweight, resistant to corrosion, and generally unaffected by water, making it ideal for underwater applications. Indeed, carbon fiber is much stronger than steel in both tension and compression. The tensile strength of carbon fiber is between 3-7 GPa (gigapascals) compared to 0.2-1.2 GPa for steel, or between 6 to 15 times as strong. Despite its tensile strength, carbon fiber is poor in high compression environments like deep underwater. This is because carbon fiber is anisotropic, meaning that its properties vary depending on the direction of the force being applied. Because the carbon fibers are arranged in parallel bundles, in compression those bundles tend to buckle. At the depth of 12,500 feet, where the Titanic wreckage is located, is between 375 to 400 atmospheres, which is equivalent to about 5,500 to 6,500 pounds per square inch (PSI). This is about 400 times more than the pressure at sea level. Indeed, 375 to 400 atmospheres is equivalent to 3.75 to 4 GPa, which exceeds the compression strength of some carbon fiber.
Moreover, carbon fiber can degrade with multiple exposures to high compressive force environments. This is because the carbon fibers themselves are not very strong in compression. The strength of carbon fiber composites comes from the way the fibers are aligned and the resin that holds them together. When carbon fiber composites are subjected to high compressive forces, the fibers can start to buckle and break. This can cause the composite to lose its strength and stiffness. In addition, the resin can start to crack and delaminate, which can further weaken the composite. The amount of degradation that occurs will depend on the severity of the compressive forces and the number of exposures. However, even a few exposures to high compressive forces can significantly weaken a carbon fiber composite.
Not the Titan’s First Rodeo
While designed to make up to thirty deep water dives, between 2018 and 2022, the Titan had apparently already made 22 dives, which means it had undergone repeated and significant exposure to the high compressive strength environment found deep in the sea. Titan’s previous dives were not without incident. In 2021, the Titan experienced a battery issue during a dive and had to be manually reattached to its lifting platform. In 2022, it suffered a hydraulic leak that caused it to lose buoyancy. Perhaps more important, the same year, the Titan was involved in a collision with its launch and research vessel, the Polar Prince, which cracked the submersible's acrylic viewport and dented the hull. Surprising in hindsight, engineers determined that the damage to the Titan was not serious enough to prevent it from continuing the dive. The Titan was then cleared to continue the dive to the Titanic wreckage, which it completed without further incident.
Design & Safety Testing and Transparency
The issue that Titan and Oceangate will face is the adequacy of the testing of the design of the Titan, the testing of the structural design of the vessel, and the pre-deployment testing of the actual vessel. The company releases very little of that data and in the wake of such a catastrophic failure, the optics of the lack of transparency are even more damaging. Any particular GE jet engine typically undergoes 150 hours of testing before it is ready for commercial passenger use. This testing is conducted in a variety of environments, including static testing, ground testing, and flight testing and comes after years of design testing. By contrast, according to the OceanGate Expeditions website, the OceanGate Titan was tested for just over 50 hours before its first dive. There is even less data on the design testing of the relatively inexpensive components used – such as the standard PlayStation controller OceanGate Expeditions implemented to pilot the Titan submersible. The use of a PlayStation controller was, of course, a cost-saving measure. It is unclear if cost considerations also played a factor in the structural monitoring of the vessel or the analysis of the condition of its carbon fiber and other critical structural components.
Conclusion
As mentioned above, while it is too early to reach definitive conclusions regarding the cause of the catastrophic failure of Oceangate’s Titan submersible vessel, many potential sources of failure exist. A more rigorous and attentive design and testing program could have averted the failures that ultimately caused the implosion of the Titan vessel and caused the death of those who died aboard. We continue to study and better understand the specific cause of failure as we urge designers of innovative projects to subject their designs to rigorous and transparent testing protocols.
BOSTON ● June 24, 2023
About the Author
Dr. Mukti L. Das, Senior Technical Advisor
Dr. Mukti L. Das is Senior Technical Advisor to Troca Global Advisors. As a Fellow of the American Society of Civil Engineers, an honor bestowed upon less than three percent of American civil engineers, Mukti has more than 40 years of engineering experience on nuclear, fossil and hydroelectric power plants, pulp and paper manufacturing facilities, underground structures, road and railroad bridges, high-rise structures and other industrial facilities. Mukti currently serves as the Chairman of the American Concrete Institute Subcommittee on Foundations for Dynamic Equipment.
A leading global structural expert, Mukti serves Troca Global Advisors and its clients for all engineering related issues, including structural forensic engagements, investigating and determining the causes of structural failures of buildings, bridges and other facilities. Mukti renders opinions and provides testimony in court and other judicial proceedings.
Formerly a Principal Civil Engineer at Bechtel Power Corporation and a member of the accreditation board for ABET, Mukti holds a Ph.D. and M.S. from the University of Massachusetts, Amherst and a B.S. from the University of Calcutta. He’s also our German expert (he lived in Germany for years, is fluent in German, and savors his beloved Franziskaner-Bräu).
About Troca Global
Troca Global and its affiliated companies provides high value advisory services to clients across disciplines and around the world who seek solutions to critical, interesting and often complex issues. The firm is dedicated to achieving pragmatic and efficient results for our clients based on years of multi-disciplinary experience. The exceptionally broad expertise of our network allows us to advise our clients in a large array of disciplines.
Our Structural Services Team, led by Dr. Das, provides guidance to owners and managers of buildings, bridges, roadways, and facilities regarding a wide array of structural stability, health and safety issues. If you have structural engineering or structural forensic needs, please contact us.