New marine material: titanium alloy
The 21st century is called the century of the ocean. Marine space and resources have not only become an important field of increasingly fierce military and economic competition in the world, but also become a strategic space and base for human survival, social development and sustainable prosperity of coastal countries. In view of this, the coastal countries, especially the powerful naval powers, are taking the construction of sea power as the core, and vigorously develop the naval equipment, marine security equipment and marine engineering equipment in order to enhance the comprehensive sea control ability of controlling the ocean, safeguarding the marine rights and interests and territorial integrity, and developing and utilizing the marine space.
Materials for ocean engineering must have the characteristics of high strength, seawater hydrothermal corrosion resistance, sulfide corrosion resistance, microbial adhesion resistance and high toughness. Titanium is light, high-strength, corrosion-resistant, especially immune to salt water or sea water and marine atmospheric environment. It is a high-quality lightweight structural material, known as “marine metal”, and is an important strategic metal material. Titanium has a wide range of applications in marine engineering, especially suitable for light marine engineering equipment. It is one of the new key materials in the field of ocean engineering. Therefore, making full use of marine materials titanium and titanium alloy will contribute to the development of national marine strategy.
Application of titanium alloy in ocean
Table of Contents
Application of titanium alloy in ocean
- Application on ship
- Deep sea submersible
- Nuclear-powered submarine
- Deep sea space station
- Seawater desalination
- Offshore drilling platform
Application on ship
The application of titanium alloy in ship industry began in 1960s, about 10 years later than that in aviation industry. The United States, Russia, Japan and China are the first countries to engage in the research of titanium application in ship field.
Hull structural materials
Compared with fiber reinforced plastics, aluminum alloy, steel and other materials used before, titanium hull is light, can increase the effective loading weight, has a long service life, almost no maintenance, and is easy to remove marine organisms attached to the surface. For example, the titanium fishing vessels built by Japan iron and steel company, Toho technology company and ETO shipbuilding company are all made of titanium. The length of the “Titan express” speedboat made by Japan’s nissho Industrial Company is about 12m. The hull shape is a beautiful cubic curve, which can reduce the sailing resistance to the greatest extent.
The service life of pumps, valves and piping on warships is only 2-5 years because of the bad working conditions. Titanium has excellent corrosion resistance and erosion resistance, good yield strength and low density. Therefore, it can be used to make thin wall, small diameter pipeline, valve and other accessories. It can not only reduce the weight, but also significantly prolong the service life of the system and improve the reliability of the system. For example, the density of titanium condenser tube is reduced by 1 / 2 compared with B30 condenser tube. The experience of using titanium alloy pipes and equipment in warships shows that titanium alloy materials have high reliability in terms of mechanical strength and seawater corrosion resistance. The corrosion life of titanium alloy pipes, valves, pumps and other accessories shall not be less than 1.2 × 105h, and the service life shall not be less than 40 years. The service life of various pumps, valves and pipes made of titanium alloy is much longer than that of copper or stainless steel products.
The propeller and propeller shaft made of titanium alloy can improve the propulsion speed and prolong the service life. Titanium alloy propellers have been used on a variety of ships in the United States. For example, the hydrofoil in the United States has used the super cavitation titanium alloy propeller with a diameter of 1500mm and four blades. Titanium alloy is also an excellent material for marine water jet propulsion equipment. The Japanese torpedo boat pt-10 adopts Ti-6Al-4V alloy water jet propulsion device. The shaft diameter is reduced from 95mm to 75mm and the weight is reduced by 600kg under the condition of constant speed. The power plant of the Russian made atomic icebreaker also uses titanium steam engines. The service life of the engine can be prolonged more than 10 times by using titanium alloy. In addition, a large number of titanium alloy materials are used in marine engine parts such as engine disk and rotor blade. The use of titanium alloy power propulsion device can also overcome the defects of using copper alloy to cut the earth’s magnetic line of force while sailing, which is not conducive to the removal of magnetic mines.
In China, propeller research was carried out in the 1960s. Hydrofoil speedboat propeller was developed in 1972. Up to now, various titanium alloy propellers with diameter of 450-1100mm have been produced. The maximum diameter of fixed titanium alloy propeller is 1200mm and the mass is 130kg. Titanium alloy is used to replace ak-27 steel and copper alloy for the 25 Type torpedo speedboat developed in China. The weight is reduced by 30% – 40%, and the service life is increased several times. There is no need for surface coating. Marine organisms are easy to clean and maintain.
Heat exchanger, condenser, cooler, evaporator
The pipeline system and valve of heat exchanger, condenser, cooler and evaporator can be made of titanium. The maintenance free service life of the equipment made of titanium can reach more than 100000 hours, and it will not release harmful substances, which is environmentally friendly. However, copper based alloy will release harmful copper ions to the environment due to corrosion. In October 2016, the national key R & D project “development and application of manufacturing technology for low cost and high corrosion resistant titanium and titanium alloy pipes and high-quality titanium belts” was launched in Kunming. The project was led by Yunnan Titanium Industry Co., Ltd., a subsidiary of Kunming Iron and steel Holding Co., Ltd. In order to meet the national strategic needs, the project takes offshore oil drilling platform, seawater desalination, large-scale ship engineering and other major projects as the application background. In view of the gap between China and foreign countries in the development and application of titanium and titanium alloy pipes, as well as the relevant manufacturing technologies that need to be breakthrough urgently, the project is applied through R & D.
In seawater, the attenuation of light wave or radio wave is much greater than that of sound wave. Therefore, in the development and utilization of the ocean, sonar is widely used in the search and detection of underwater targets by ships and torpedoes. In sonar equipment, different kinds of acoustic materials are needed. Among them, the sonar dome of warship and torpedo and the shell of high-pressure sound transmission container are made of underwater sound transmission structural materials.
In general, the purpose of installing streamlined sonar dome outside the sonar transducer is to reduce the hydrodynamic noise generated by ship motion, ensure the effective and normal operation of underwater acoustic equipment, and improve the operating distance of sonar. The sonar dome must have good sound transmission performance, so that the underwater acoustic signal can pass through with little loss and distortion. According to the different requirements of underwater and surface application, there are two kinds of sound transmission data for sonar dome of naval vessels in service in China, one is stainless steel, the other is fiber reinforced FRP. In the past, Russia also used FRP, but later mostly used titanium alloy. Because of its good sound transmission performance, many foreign large-scale combat ships, such as Russia modern class, are made of titanium alloy and used in the sonar system of Russian aircraft carrier “Kursk”, “titanium plate Minsk” and “Kiev”.
Deep sea submersible
As a major special project of China’s “863” plan, the 7000 meter submersible developed by 702 Research Institute of China Shipbuilding Industry Group Corporation is 8 meters long, 3.4 meters high and 3 meters wide. It is made of special titanium alloy materials. It can withstand 710 tons of heavy pressure in the deep sea of 7000 meters. It uses the most advanced high-tech in the world to realize the integration of carrier performance and operation requirements The shell is the most special and important part of the deep submersibles. The titanium alloy manned spherical shell, which is located in the front of the deep submersibles and can seat three people, can bear 700 atmospheric pressures, and realize the same life support system as spaceflight.
According to UNESCO publications, the world’s total marine energy is 76.6 billion kw. The condenser is an important large-scale equipment in coastal power station and nuclear power station, and the cooling medium is seawater. Steel and copper alloy materials are traditionally used, but the corrosion resistance of seawater is poor and the service life is short. In seawater, especially under the action of polluted seawater, copper alloy condenser is prone to pitting corrosion, pitting corrosion, stress corrosion and fatigue corrosion, which leads to equipment leakage and causes significant economic losses. The practice at home and abroad has proved that titanium material is the most suitable material for condenser of power station. The total installed capacity of power stations in the world is about 2 × 107mw. There are more than 5000 thermal power stations and hydropower stations. Titanium condensers account for 3% – 4%. There are more than 380 nuclear power plants with titanium condensers accounting for 30%. Titanium condensers are widely used in power stations in Europe, the United States and Japan. All titanium condensers are used in Taizhou Power Plant, Zhenhai Power Plant, Qinshan nuclear power station and Daya Bay nuclear power station. The titanium condenser used in coastal power station has many advantages: it can use seawater as cooling medium on site; it has good corrosion resistance and long service life; it has high heat exchange efficiency and good economic benefit; it has high safety performance, reduces power outage maintenance time, and has low production efficiency.
Russia is in the leading position in the world in building titanium alloy nuclear submarine technology, and is also the first country to build pressure hull with titanium alloy. Since the 1960s, Russia has developed four generations of nuclear submarines. The world’s first all titanium nuclear submarine, k162, was launched in December 1968. It has been in operation for more than 30 years. It has been in various oceans and seas, and has undergone different loads and environmental assessments. There has never been any accident. Russia built the first “Alfa” class nuclear submarine in 1970, and six more were built successively from 1970s to 1980s, each of which used about 3000t titanium, and the maximum diving depth was 914m, which was light, fast and with good maneuverability. A typical example of titanium used in ships is the Russian typhoon class nuclear submarine. It has a titanium shell. Due to military needs, it adopts double shell structure. Its double shell shell uses titanium 9000t, which makes it have the advantages of non-magnetic, deep diving, fast speed, low noise and less maintenance times.
The hull of a manned deep-sea submarine, manufactured by the Southwest Research Institute (SwRI), is made by eliti-64. The inner diameter of the new submarine sphere is 2.1 meters, the working space is large, it can accommodate three people, and the maximum working depth in the sea water can reach 6500 meters.
Deep sea space station
Deep sea mobile space station will be mainly used for marine scientific exploration, known as “Tiangong-1” in the ocean. Since the 1960s, the United States and the former Soviet Union have successively improved the deep-sea space station system. In 2000, Russia announced the civil construction of its deep-sea space station, which was targeted at oil exploration in the Arctic Ocean. China put forward the concept of deep sea space station in the 1990s, aiming at the peaceful development and utilization of marine resources. The test craft of deep sea space station that has been built and the small deep sea mobile workstation under construction are all independently developed by China. The establishment of deep-sea space station is inseparable from the support of titanium and titanium alloy key materials. In the “13th five year plan” of national science and technology innovation plan, the deep sea space station of “science and technology innovation 2030 major project” was put forward again, and the project was definitely approved. The main construction material of the space station is titanium alloy. It is preliminarily estimated that the construction of a main station will consume more than 4000 tons of raw materials.
Seawater desalination has become the main way to obtain fresh water in the Middle East and other water deficient areas. Among the production methods of seawater desalination, multistage flash evaporation is the most reliable and widely used method. The equipment of this method is mainly composed of seawater heating, condenser of heat recovery section, condenser of heat output part, ventilation condenser and jet compressor. A large number of heat transfer tubes are used in heat exchange part. The original copper alloy tube has been replaced by titanium tube due to its non corrosion resistance Instead.
The evaporator in the desalination unit contacts with high temperature seawater, and the salinity increases after evaporation. Titanium alloy is resistant to high temperature ion corrosion and can be widely used in evaporator of seawater desalination unit. Meanwhile, titanium has strong corrosion resistance to chlorine, so it is the preferred material for heat exchanger of seawater desalination equipment. With the rapid development of petrochemical industry and electric power industry in coastal areas, seawater instead of fresh water as industrial cooling medium can save a lot of fresh water resources and obtain significant economic and social benefits. However, due to the strong corrosion of seawater, when the ordinary carbon steel or stainless steel is used as the cooling medium, seawater will cause serious corrosion to the tube bundle, significantly reducing the service life of the heat exchanger, not only increasing the number of equipment replacement, but also causing the device shutdown too frequently due to equipment failure, thus reducing the economic benefits. In general, in order to solve this problem, it is necessary to upgrade the material of the tube, which is commonly used in titanium tube.
In the aspect of titanium material selection, industrial pure titanium ASTM grade 2 is the most widely used. The fact shows that grade 1 and grade 2 have special ability to resist stress corrosion cracking in natural water, sea water and various chlorides; while grade 7 or grade 12, grade 16 (ti-0.5% PD), are used for seawater heaters with higher temperature It has higher corrosion resistance, but the cost is more expensive. In addition, the fouling factor of titanium heat exchanger is about 0.95-0.99.
The TA1 seamless tube of industrial pure titanium is selected as the condensing tube of flash evaporator and the heat exchange tube of brine heater. TA1 + 16MnR + 316L double-sided titanium composite steel plate is selected for tube plate. This is because titanium is light, corrosion-resistant and has high strength. It is a good seawater corrosion resistant material with high reliability. Secondly, the use of titanium composite steel plate can reduce the use of titanium, and can meet the use requirements Low installation cost.
A series of corrosion-resistant titanium alloys for offshore engineering, such as Ti75, Ti31 and ti631, have been developed by Northwest Institute of nonferrous metals and Beijing General Institute of nonferrous metals.
Offshore drilling platform
Titanium alloy has high strength, low density, excellent corrosion resistance and good toughness, so it is the best choice for offshore drilling system equipment such as riser, drill pipe and cone stress joint. In more cases, the composite application of titanium and steel has a great contribution to the cost reduction and efficiency improvement of offshore drilling system.
In the past few years, the application of titanium alloy components in offshore oil drilling system has increased significantly. Titanium alloys allow drilling equipment to enter deeper water and wells, including hotter and more corrosive environments. Ti-6Al-4V based titanium alloy has the best physical, mechanical and corrosion properties, which is more attractive for offshore drilling components.
Ti-6Al-4V alloy is mainly used in offshore drilling system
- (1) In addition to weight reduction, titanium alloy is used for drilling riser in offshore drilling, which has good damage tolerance and is easy to be inspected by traditional technology. Beihai oilfield is the first time that titanium alloy drilling risers are widely used at sea. Although the use of titanium in risers has been very successful, the market for all titanium risers is very limited. Due to economic reasons, stainless steel / titanium or composite / titanium risers will be widely used.
- (2) Rotary fatigue and physical wear of traditional stainless steel pipe appear prematurely in short distance drilling (radius of curvature less than 18m). Therefore, RTI titanium company of the United States has developed a drill pipe made of grade 5 alloy and standard Cr Mo steel joint. This design avoids the tool jamming and wear, and ensures its toughness and fatigue life. In 1999, ten wells with radius of curvature of 18m were successfully drilled with titanium alloy pipes with an outer diameter of 73 mm. Recently, titanium alloy drill pipe with outer diameter of 63.5 mm has been used to drill oil wells with radius of curvature of 12m-15m. In addition, the nonmagnetism of titanium alloy is also attractive, which makes oil well exploration not affected by magnetism. In long-distance drilling, the drilling depth of steel pipe is only 6.1km in vertical direction and 7.1km-9.1km in horizontal direction, while titanium pipe can reach 9.1km in vertical direction. With the use of large diameter titanium pipe, the lifting force and torque of drilling tool are reduced by about 30% and 30% ～ 40% respectively, and the limitation of hydraulic transmission device is overcome.
- (3) Compared with flexible joints such as rubber / copper, titanium conical stress joint is compact in design, easy to check, good air tightness, and can be used at high temperature. TITANIUM CONE stress joint is only 1 / 3 of steel, and its cost is similar to or even lower than that of steel. RTI has designed and manufactured grade 23 and grade 29 alloy stress joints, which have been installed on drilling platforms in the Gulf of Mexico and the North Sea. Due to the relatively low cost and successful application examples, the titanium stress joint market shows a continuous growth trend.
Titanium and titanium alloy have many advantages, but for the application in ship and offshore engineering equipment, it is also a new material. In order to promote the further development of titanium and titanium alloy in the future, in 2016, titanium for offshore engineering was included in the national key project for development of new materials, and a platform for research, application research and evaluation of titanium alloy materials and technology for offshore engineering was established, which can greatly promote the leapfrog development of titanium materials for offshore engineering and upgrade and develop the technical level of China’s marine engineering equipment At the two sessions of the meeting, the representatives of the meeting once again proposed to vigorously develop titanium alloy materials for marine engineering, so as to promote the design criteria, technical system, application technical standards and specifications of marine engineering, especially the titanium equipment for ships at the national level; vigorously develop the low-cost production technology of titanium alloy, optimize and improve the titanium alloy system for marine use in China, and establish the performance database of marine titanium alloy It provides abundant data support for the material selection of titanium and titanium alloy for offshore engineering.
Source: Network Arrangement – China Titanium Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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