Application of titanium alloy to pressure hull structure of submersible

The submersible consists of three parts: pressure structure, attachment structure and internal frame platform structure. The pressure-resistant structure is the core component of submersible, which is resistant to seawater pressure, provides stable operating environment for internal instruments and equipment, and provides reliable working and living space for personnel.

Alloy steel has high strength and high density at the same time, resulting in the structure of pressure hull made of alloy steel is usually thick and heavy, especially in the case of large depth, due to the structural weight and steel plate thickness, the submersible can provide insufficient payload and space, which is not conducive to the arrangement of equipment and personnel activities.

The appearance of titanium alloy solves this problem to some extent. Although the strength of titanium alloy is slightly weaker than that of alloy steel, its density is only about 1/2 of that of alloy steel, and it has a higher specific strength. At the same time, titanium alloy has excellent resistance to Marine environment and can well meet the needs of underwater equipment. It is the most popular metal material in underwater equipment at present. Almost all submersible pressure hull structures in service are made of titanium alloy material. The pressure hull structure of France's Nautile, Japan's Shinkai6500 and the domestically developed submersible Jiaolong, Deep Sea Warrior and Struggler are all made of titanium alloy.

Alvin was built in 1964. It initially used alloy steel as a circular pressure hull structure material, with a maximum depth of 1,868m. In 1972, the pressure hull material was replaced by titanium metal and the working depth was increased to 4,500 m. During another refit in 2012, the pressure hull structure was reconstructed using titanium alloy and the inner diameter of the shell was increased. The payload was increased and the design depth was further increased to 6000 m.

Built in 1989, Shinkai 6500 measures 9.7 m×2.8 m×4.1m in length × width × height. The pressure ball shell has an inner diameter of 2.0 m and is made of 73.5 mm thick titanium alloy. Shinkai6500 was designed to go to a depth of 6500m, with the actual maximum dive of 6,527m, setting a record for manned submersitions at the time