Application and development of large diameter titanium pipe and titanium alloy pipe for Marine applications

In recent years, China has carried out a large number of major projects such as the construction of offshore ships, offshore oil drilling platforms, seawater desalination, artificial islands and reefs, and the demand for various types of high-strength corrosion-resistant metal pipes used in medium and large-scale equipment in the above fields has shown a substantial growth trend. Because metal pipes need to be applied in complex and harsh Marine environments (strong corrosion, typhoon, strong convection, high temperature, high pressure, biological adhesion), there are extremely high requirements for their corrosion resistance. Titanium and titanium alloys have unique advantages such as high strength and toughness, no magnetic, low density and excellent corrosion resistance, and become the most ideal materials for large-scale equipment in the above fields. Titanium has the characteristics of high strength, high toughness, high specific strength, light weight, no magnetism, corrosion resistance to seawater and Marine atmosphere, etc. The corrosion life of titanium and titanium alloy pipeline is more than 120,000 hours, and the service life is more than 60 years. Under the harsh Marine working conditions, the whole life of titanium alloy material is incomparable to other metal materials. At the end of the life of the equipment can be 100 percent harmless recovery. Therefore, it is the best material for Marine equipment.

1. Characteristics of Marine equipment

(1) Marine equipment is a large metal building with large tonnage, high investment cost and great damage loss.

(2) The system has complex structure, complete functions, complex and harsh working conditions, high reliability requirements, and great difficulty in construction technology.

(3) Material life extension is of great significance to ensure the integrity, reliability and safety of Marine equipment and structures, and promote resource protection and sustainable development.

(4) Improving the performance of Marine equipment mainly involves improving the application of corrosion-resistant, lightweight, high-strength and high-toughness materials, reliability and life-cycle product economy.

2. Advantages of titanium alloy pipe

Titanium alloy has high melting point, low density, high strength, corrosion resistance, superconductivity, shape memory and hydrogen storage and a series of important characteristics, widely used in aviation, aerospace, ships, nuclear power, medical, chemical, metallurgy, electronics, sports and leisure, construction and other fields, known as the "third metal", "air metal" and "ocean metal". The pipe is used in the transmission channel of gaseous and liquid medium, which is the basic product of various fields of the national economy. Because of its excellent characteristics of light weight and good corrosion resistance, titanium alloy pipe has a wide range of applications in aviation engines, aerospace vehicles, petroleum transmission pipelines, chemical equipment, Marine environment construction and various offshore operation platforms. Such as coastal power stations, offshore oil and gas exploitation and transportation, seawater desalination, Marine chemical production, alkali and salt production, oil refining equipment, etc., the prospect is very broad.

Popularizing and applying titanium materials is one of the most important technical development directions of ship and ocean engineering equipment. Titanium alloy pipe has been widely used in ship and ocean engineering equipment by developed countries. A large number of titanium materials are used to improve the safety and reliability of the equipment, reduce the volume and quality of the equipment, reduce the number of equipment damage accidents and maintenance significantly, and greatly extend the service life.

3. Machining performance characteristics of titanium alloy pipe

Titanium alloy has low plasticity and high deformation resistance at room temperature, but it has good plasticity and low deformation resistance in α+β two-phase zone and β phase zone. Therefore, the forming and manufacturing of titanium alloy materials or the preparation of various profiles (plate, rod, tube, etc.) need to be heated to the phase transition point.

Because titanium alloy is easy to react with oxygen, nitrogen, carbon and other chemical reactions at high temperature and easy to absorb hydrogen, resulting in a sharp decline in the deformation performance of titanium alloy and affect the service performance of materials, coupled with low thermal conductivity of titanium alloy, large billet heating, often lead to large temperature difference between sections, easy to lead to cracking in the deformation process; In addition, the deformation zone of titanium alloy has a narrow temperature range and is sensitive to strain rate, which requires deformation at a lower rate. At the same time, since the cooling rate after deformation directly affects the room temperature equilibrium structure and the service performance of the component, it is necessary to keep the deformation temperature constant or take measures to reduce the temperature drop rate in the process of deformation to make it have enough plasticity.

At present, titanium equipment used in domestic ships mainly includes: main condenser of submarine, titanium alloy torpedo launching water cylinder, emergency cooler of nuclear power pressurized water reactor primary system, sonar deflector, titanium alloy propeller, diesel engine smoke exhaust pipe and sea piping system, related piping and pump valve system, deep submersible pressure hull and auxiliary system. Typical specifications of seawater pipeline :OD308xwtk4mm, OD285xWTK5mm; Ship main sea water piping system :OD12.7~OD304.8mm.

Due to the low density of titanium and titanium alloy, corrosion resistance, high strength, can greatly reduce the weight of the equipment, so although from the unit price, titanium and titanium alloy will be more expensive, but the overall weight of the equipment is reduced, titanium and titanium one-time input will not be higher than other materials, or even lower than other materials. Titanium and titanium alloy tubes have a huge application prospect. With the maturity and promotion of high efficiency, short flow and low cost production technology, many applications of copper and copper alloy tubes can be replaced by titanium and titanium alloy tubes.

Along with the gradual deepening of Marine power strategy, the demand for large diameter pipe with high strength and corrosion resistance is increasing in Marine equipment, exploration and development of Marine oil and gas fields, ships and other fields. The large-scale production of large diameter titanium alloy tube and the industrialization popularization and application of high efficiency, short process and low cost preparation technology will further meet the market demand for titanium and titanium alloy products at low cost. At the same time, the concentration of titanium industry is not high at present, so manufacturers should actively cooperate with national standard formulation and design units, colleges and universities, downstream users and other related equipment manufacturers to establish a national titanium technical and economic network service platform, form a joint force, and jointly promote the market development of titanium alloy.