Application Of Titanium And Titanium Alloys in Marine Equipment
Titanium is the most ideal material in the marine environment. The use of titanium can greatly improve the combat effectiveness of naval ships and equipment, reduce maintenance costs, extend service life, and improve concealment. The Russian, American, and Chinese navies have widely used titanium in pressure hulls, seawater pipeline systems, superstructures and other components of submersibles, underwater submarines, surface ships, ships and other equipment.
1. Pressure hull
The titanium grades used for manned spheres of deep-sea submersibles at home and abroad are mainly Ti-6Al-4V and Ti-6Al-4VELI (corresponding to domestic grades TC4 and TC4ELI). Many manned spheres of deep-sea submersibles were made of steel in the early stage, but titanium was used instead in the later stage, which can reduce weight, increase diving depth, and improve service life. For example: ① The American Alvin submersible was built in 1964 using HYl00 high-strength steel (plate thickness 33.8 mm) with a diving depth of 2000 m. When it was rebuilt in 1973, the pressure hull was replaced with titanium alloy (plate thickness 49 mm), and the diving depth increased to 3600 m. Its auxiliary box and high-pressure gas generator also used Ti-6Al-4VELI; ② Japan's "Deepsea 2000" manned spherical shell was made of steel, and titanium was used to prepare the manned spherical shell when the "Deepsea 6500" was built to increase the diving depth.
In terms of the application of submarine pressure hulls, Russia was the first to use titanium. It is currently the country with the most advanced and mature technology in the world to use titanium to manufacture pressure hulls. The only titanium grade used in its all-titanium nuclear submarine manufacturing is IIT-3B titanium alloy (corresponding to the domestic grade TA17). In recent years, China has also preferred to use titanium materials when building submarines, and the grades are mainly concentrated in TA17, TC4, TC4ELI, TC11, pure titanium, etc.
In addition, many countries are currently building deep-sea manned submersibles and deep-sea all-titanium weapons and equipment. The "Struggler" full-sea manned submersible built in China successfully challenged the deepest part of the world's ocean-the Mariana Trench on November 10, 2020, with a depth of 10,909 m, realizing the Chinese people's deep-sea dream. The manned spherical shell material of the submersible is a high-strength, high-toughness damage-tolerant titanium alloy manufactured by Baoti Co., Ltd.; China has begun to build all-titanium deep-sea equipment.
2. Seawater pipeline system
The seawater pipeline system is complex and has many diameter specifications. The selected materials are required to have the characteristics of seawater corrosion resistance, high strength, and good fatigue performance. Titanium can meet all of these requirements. Pipes made of titanium alloy have significant advantages over traditional materials (carbon steel, stainless steel, copper alloy).
(1) Improve service life, to the same life as the ship itself. Russia compared the service life of pipeline systems made of traditional materials and titanium. The results show that titanium has the same service life as the ship, only needs to be invested once, and only requires simple maintenance during use; the service life of traditional materials is about 2 to 10 years, and must be regularly repaired or even replaced during the service life, especially under the influence of high-speed driving environment, various joints will produce local corrosion. According to the application data of US Navy ships, the service life of titanium piping is 40 years, and the service life of copper-nickel alloy piping is only 6 to 8 years.
China has carried out verification and assessment tests on the use of "titanium alloy" to replace "copper alloy" to manufacture seawater pipeline systems. After the TA2 titanium seamless pipes, supporting pipe fittings and titanium flanges provided by Baoti were run for nearly 3 years, the pipelines and supporting materials were disassembled and inspected, and no abnormal conditions such as cracks, holes and corrosion were found.
(2) Reduce costs. Although the one-time investment cost of titanium alloy parts is higher, the one-time investment can meet the full life use, and only simple maintenance is required during use, which greatly saves repair and maintenance costs. The copper-nickel alloy tubes used in the heat exchangers of the US Navy ships need to be replaced about 97 km per year, while Gr.2 pure titanium tubes are selected for the two main seawater piping systems of the LPD17 amphibious dock transport ship, with about 1,000 pipes and a total length of more than 3,350 m, saving up to $17 million in costs over the entire life cycle. In summary, the use of titanium in piping systems can not only reduce weight, but also achieve the same lifespan as the main body, while reducing costs. In recent years, it has been applied in batches on many types of marine equipment such as the 022 boat in China.
3. Superstructure
At present, there are also examples of titanium application in the superstructure of domestic ships, such as Ti70 (TA23) for masts, TA5 and TA7 bars for radar antennas, and TA2 and TA5 plates for hangar skins and frame structures. The US Navy also used a large amount of titanium in the key superstructure area of the LPD17 amphibious dock transport ship, which reduced its mass by about 50% and greatly improved the stability of the ship.
4. Application in other fields
In addition to the above-mentioned pressure hulls, piping systems and superstructures that use a large amount of titanium, there are other parts of domestic and foreign marine equipment that also use titanium.
