1. The application status and prospects of titanium alloys in ocean engineering
㈠、Introduction
The ocean, which accounts for about 71% of the earth’s surface area, contains rich resources. Exploiting and using the ocean, making the ocean the source of our immense wealth, has become one of the directions that people have worked hard for many years. However, since seawater contains about 3.5% salt content, seawater is corrosive. In addition, certain biological pollution in the ocean also accelerates the corrosion of seawater.
Titanium is a material with excellent physical properties and stable chemical properties. Titanium and its alloys have high strength, small specific gravity, resistance to seawater corrosion and marine atmosphere corrosion, and can well meet the requirements of people in marine engineering applications. After years of efforts by people in the titanium industry and marine engineering application researchers, titanium has been widely used in offshore oil and gas development, harbor construction, coastal power stations, seawater desalination, ships, marine fisheries, and ocean thermal energy conversion. Now, titanium for marine engineering has become one of the main areas of titanium civilian applications.
㈡, application status
2.1 Offshore oil and gas development
Oil is the economic lifeline of a country. It is estimated that the world's recoverable oil resource reserves are 300 billion tons, of which the submarine oil reserves are about 130 billion tons. The development of submarine oil began in the early 20th century. Its development has gone through the process from near sea to far sea, from shallow sea to deep sea. Restricted by technical conditions and material development, initially, only oil and natural gas deposits that extend directly from the coast to the shallow sea could be exploited. Since the 1980s, stimulated by the energy crisis and technological progress, offshore oil exploration and development have developed rapidly, and offshore oil development has rapidly advanced to the continental shelf, and a brand-new offshore oil industry sector has gradually formed. The offshore drilling platform is a work base for the implementation of subsea oil and gas exploration and exploitation, and it marks the level of subsea oil and gas development technology. Offshore oil extraction equipment mainly includes oil production platforms and ancillary equipment. The ancillary equipment includes crude oil coolers, oil risers, pumps, valves, joints, and fixtures. These equipment are in contact with sulfide, ammonia, chlorine, and other media in seawater and crude oil. Because titanium has excellent corrosion resistance in these media, the United States used titanium-made offshore oil platform pillars in its oil fields in the early 1970s, and at the same time used titanium to make tubular heat exchangers and plate-type heat exchangers. Heater. The titanium tubular heat exchanger uses seawater as the cooling medium to cool the high-temperature steam/oil mixture drawn from the oil well. The titanium plate heat exchanger also uses seawater as the cooling medium to cool the freshwater that cools the crude oil in the carbon steel heat exchanger. The United States uses approximately 100 titanium heat exchangers on drilling platforms in the North Sea oil field. The titanium components ordered by Hunting Oilfield Services in Aberdeen, Scotland, UK, are said to be the world's first titanium high-pressure riser shaft for use in Conoco's Heidrun project in Norway.
Petroleum titanium alloy titanium drill pipe has a long service life, its weight is only half of stainless steel, but its use flexibility is twice that of stainless steel, and its service life is 10 times that of steel. These excellent properties make titanium an excellent material for nearly circular and deep oil wells that are difficult to drill. The combined drilling tool containing the titanium drill pipe can greatly reduce the drilling time and reduce the total drilling cost. Grant Prideco, RTI Energy Systems, and Torch Drilling Services in the United States used titanium drill pipes for industrial applications for the first time in 2000. The titanium drill pipes jointly produced and supplied by GrantPrideco and RTI Energy Systems are also equipped with steel tool joints provided by GrantPrideco Anti-Fatigue. The joint is light in weight, flexible in use, and can make the titanium drill pipe sturdy.
The seawater pipeline system is an indispensable part of subsea oil exploitation. Because titanium has high corrosion resistance to seawater, its service life is 10 times longer than that of the steel system. Therefore, the cost of the titanium pipeline system is more cost-effective compared with the Cu-Ni system. The American Active Metals Corporation and Precision Tube Technology Corporation jointly established a titanium tube technology company to produce a large-diameter titanium alloy tube. The alloy used in this pipe is Ti-3Al-2.5V alloy, with a diameter of 650mm, a wall thickness of 22-25mm, and a length of 350m. A pipe weighs 80-90t. It is planned to be used for subsea oil exploration. Another American company used a seamless titanium alloy tube with a length of 15m, an outer diameter of 600mm, and a wall thickness of 25mm to make a vertical shaft pipe nearly 500m long by extrusion, which has been used on an offshore drilling platform. It is said that the weight of this vertical shaft pipe can be reduced by half, thereby greatly reducing the cost of ballast. In addition, it also has high fracture toughness and long fatigue life.
According to data, in the North Sea oil field development project in the United States, the amount of titanium used in the floating device on the ship and the fixed device on the seabed has increased compared with before. The demand for titanium for the 24 ships’ floating devices and 64 submarine fixtures is: safety protection devices 50-100t, connecting devices 50-100t, general lifting equipment 400-1000t, drill pipes 1400-4200t. The corrosion of structural parts caused by biological contamination of offshore oil mining platforms is quite serious. A US company used a long casing made of titanium pipes on the mining platform to protect the parts on the platform.
In the past few years, the application of titanium alloy components in oil drilling and coastal production operations has increased significantly. Titanium alloy components allow oil drilling to enter deeper waters and deeper oil wells, including higher temperatures and severely corrosive (ie, salty) production environments.
For this kind of application, considering the overall performance, TC4 titanium rod (Ti-6Al-4V)-based alloy is the most suitable and has the lowest cost. The seawater pipeline system is an indispensable part of subsea oil exploitation. Because titanium has high corrosion resistance to seawater, its service life is 10 times longer than that of the steel system. Therefore, the cost of the titanium pipeline system is more cost-effective compared with the Cu-Ni system. American Active Metals Corporation and Precision Tube Technology Corporation jointly established a titanium tube technology company to produce a large-diameter titanium alloy tube. The alloy used in this pipe is TA18 (Ti-3Al-2.5V) alloy, with a diameter of 650mm, a wall thickness of 22-25mm, a length of 350m, and a pipe weighing 80-90t. It is planned to be used for subsea oil exploration. . Another American company used a seamless titanium alloy tube with a length of 15m, an outer diameter of 600mm, and a wall thickness of 25mm to make a vertical shaft pipe nearly 500m long by extrusion, which has been used on an offshore drilling platform. It is said that the weight of this vertical shaft pipe can be reduced by half, thereby greatly reducing the cost of ballast. In addition, it also has high fracture toughness and long fatigue life.
The practice has proved that Ti-6Al-4V (Gr.5_TC4) alloy is the best material for drilling pipes. As drilling applications, yield strength and fatigue strength are the most important. Therefore, two special low-clearance elements of Gr.5 alloy are suitable For the more critical dynamic lifting device. When the operating temperature exceeds 75 ~ 80 ℃, in order to prevent crevice corrosion or stress corrosion, use the ruthenium-containing Gr29 alloy.
The most commonly used components include seashore drilling hoisting devices, drill pipes, tapered stress joints (TSJ), and titanium/steel hybrid hoisting devices.
Titanium pumps, valves, joints, fasteners, fixtures, and spare parts, and other small titanium parts have been widely used on oil mining platforms. A large number of titanium alloys are also used on the shells of offshore oil exploration and logging instruments abroad.
2.2 Harbour Building
There is an oxide film on the surface of titanium material with a thickness of no more than 10nm. It is very stable in corrosive environments and has excellent corrosion resistance to air, seawater, and marine environments. It is currently the most suitable raw material for various marine environments. Japan has vigorously carried out marine development, such as the bridge from Honshu to Shikoku, the road across the Tokyo Bay, the Kansai Airport, and the floating oil storage base. The exposure test conducted by the Japanese Ministry of Construction and the Iron and Steel Club on the ocean surface of Oigawa, and the investigation reports of various anticorrosion exposure tests on the Hazaki Floating Sand Trestle by the Ministry of Transportation and the Steel Pipe Pile Association also showed that titanium is the most suitable material. In addition to excellent anti-corrosion properties, titanium also has the advantages of very few ions dissolved in seawater, is non-toxic, and no need to worry about environmental pollution. Japan has also built a super large floating marine structure, using titanium steel composite materials in the seawater erosion; in the construction of the Tokyo Bay across the highway, titanium materials are used as the splash-proof trunks of the piers, and each pier is made of titanium The amount is 0.9t. The large floating marine buildings that have been used or planned include airports, harbor logistics bases, sports facilities, and so on.
2.3 Coastal power station
The comprehensive utilization of seawater is one of the important projects in marine engineering. The condenser of the coastal power station is a device that uses a large amount of seawater. Titanium used in coastal power stations is mainly titanium used in condensers. Since the condenser uses seawater as cooling water, and the seawater contains a large amount of mud, sand, suspended matter, marine organisms, and various corrosive substances, the situation is more serious in the alternately changing seawater and river water. Traditional condensers use copper alloy tubes, which are often severely damaged due to various corrosion in seawater. Titanium has good corrosion resistance in seawater, especially polluted seawater, and its high-speed erosion resistance to seawater is particularly outstanding.
2.4 Seawater desalination device
"Water is the source of life". At present, the lack of water resources has become a problem that plagues the world. About 25% of the world's population does not have sufficient drinking water resources. The world's terrestrial rivers and groundwater resources are far from meeting the needs of industrial development. Therefore, in the future, seawater desalination will be an effective way for mankind to solve freshwater resources.
From the perspective of the development of seawater desalination at home and abroad, there are mainly two methods: distillation and reverse osmosis. The former is to heat seawater to vaporize and then condense the steam to obtain fresh water. The latter is to pressurize the seawater, make the freshwater pass through a special membrane and intercept the salt to obtain fresh water. Early seawater desalination devices used copper alloys, carbon steel, and other materials. Because these materials were not resistant to seawater corrosion and had low production efficiency, they were quickly replaced by titanium with excellent seawater corrosion resistance. In the desalination of seawater, the main application of titanium is the heat transfer tube of the heater of the desalination device. The main producers of desalination plants are the United States and Japan. By 2004, there were more than 15,000 seawater desalination plants built and under construction in the world, with a daily output of about 32 million tons of freshwater. The Japanese company built 10 distillation units with a daily output of 30,000 tons of freshwater for Saudi Arabia, using 3,200 tons of titanium pipes, and an average daily output of 10,000 tons requires 107 tons of titanium.
my country's Tianjin, Shandong, and other places have built or are under construction of seawater desalination equipment. For example, the preliminary plan for seawater desalination in Tianjin is to produce 500,000 tons of freshwater per day by 2007 and 700,000 tons by 2010. It is estimated that the amount of titanium used in seawater desalination projects in Tianjin and Shandong is about 250 tons.
2.5 Ship
Titanium and its alloys are resistant to corrosion in seawater and ocean-atmosphere and have light specific gravity, high strength, impact resistance, no magnetism, sound permeability, and small expansion coefficient. They are considered good ship materials. In recent years, the application of titanium on ships has attracted much attention. The navies and shipbuilding industries of various countries also attach great importance to the research on the application of titanium on ships, and many brands of marine titanium alloys have been developed. Titanium and its alloys are widely used in ships, such as hull structural parts, deep-sea survey ships and submarine pressure hulls, pipelines, valves, rudders, shaft brackets, accessories, and power drive devices. Shafts, heat exchangers, coolers, hull sonar shrouds, etc.
The first application of titanium to the hull of a ship was the alpha-class submarine of the former Soviet Union. Subsequently, titanium was used in artificial or unmanned deep-sea research and deep-sea assistance submarines. Industrial pure titanium is used for general structural parts, and Ti-6Al-4V alloy is used for pressure vessels. According to reports, the use of titanium in the hull structure can not only reduce the weight of the hull itself, increase the effective loading weight, but also reduce maintenance and extend the life of the ship. The hull structural materials such as aluminum alloy and mild steel generally require maintenance in 10 years, while titanium materials require almost no maintenance and repair, and their lifespan can be extended from the usual 20 years to 30-40 years.
Japan’s research on titanium alloys for deep-sea survey ships is fruitful. Almost all titanium alloy materials are used in the pressure chamber of the “Deep Sea 6500” that can accommodate 3 operators. This is the result of long-term efforts by Mitsubishi Heavy Industries Kobe Shipyard. Submarines use a large amount of titanium. For example, a nuclear submarine with a dive depth of 900m uses up to 3,500 tons of titanium.
2.6 Marine fisheries
According to reports, Japanese fisheries have changed from fishing to fish farming, and lionfish, flounder, eel, etc. have been cultivated artificially. In artificial breeding technology, a large number of titanium metal meshes and titanium tube heat exchangers that maintain a certain seawater temperature are used. The artificial cultivation of grouper has been realized in the coastal area of Fujian, my country, and the titanium plate type breeding basket used has brought excellent benefits to the cultivation of grouper.
2.7 Ocean thermal energy conversion
The ocean contains huge energy, such as tidal energy, wave energy, temperature difference energy, ocean current energy, and salt difference energy. As the world's energy resources become increasingly scarce, people will be more interested in the development and utilization of marine energy. Has researched and developed thermoelectric power generation and tidal power generation projects. The principle of thermoelectric power generation is to vaporize ammonia or freon using seawater with a higher ocean surface temperature to drive turbines to rotate for power generation, and then use deep ocean low-temperature seawater to cool the vaporized ammonia or freon to form a continuous cycle heat engine system.
The main equipment for thermoelectric power generation are evaporators, condensers, seawater suction pipes, loops, etc. The equipment is required not only to be corrosion resistant but also resistant to ammonia and fluorine. Titanium and its alloys not only have good seawater corrosion resistance, but It is also resistant to corrosion by ammonia and fluorine, so titanium is the most ideal material.
Titanium tube evaporators and condensers are used in thermoelectric power plants in the United States and Japan, which have achieved good results.
Iii, Outlook
As the emerging civilian market of titanium, offshore engineering has developed rapidly in recent years. As the world energy crisis further intensifies, countries in the world will invest a lot of manpower and material resources to exploit seabed petroleum resources and other mineral resources; in the trend of an increasing shortage of global freshwater, all coastal countries will use seawater to produce freshwater; moreover, The increasingly fierce competition for naval equipment of various military powers, etc., are inseparable from titanium and titanium alloy materials. Therefore, the application of titanium and its alloys in marine engineering will become more and more extensive. Titanium for marine engineering is expected to become a larger application market for titanium materials.
2. The market situation of titanium alloy civilian health products
1. Current market conditions
At present, iron, aluminum, and stainless steel are widely used in tableware and cooking utensils at home and abroad, which will cause more or less damage to the human body during use.
