Application of titanium and titanium alloys in the ocean
Titanium is a material with excellent physical properties and stable chemical properties. Titanium and its alloys have high strength, small specific gravity, and resistance to seawater corrosion and marine atmosphere corrosion, which can well meet the requirements of people in offshore engineering applications. After years of efforts of titanium industry personnel and ocean engineering application researchers, titanium has been widely used in the fields of offshore oil and gas development, harbor construction, coastal power stations, seawater desalination, ships, marine fisheries and marine heat energy conversion. Now, titanium used in offshore engineering has become one of the main fields of titanium civil application. The ocean, which accounts for about 71% of the earth's surface area, contains rich resources. Developing and utilizing the ocean has become the source of our great wealth, which has become one of the directions that people have worked hard for years. However, seawater is corrosive because it contains about 3.5% salt. In addition, some biological pollution in the ocean also accelerated the corrosion of seawater.
Application status
1. Offshore oil and gas development
Oil is the economic lifeblood of a country. It is estimated that the world's recoverable oil reserves are 300 billion tons, of which the seabed oil reserves are about 130 billion tons. The development of undersea oil began in the early 20th century. Its development has gone through the process from offshore to offshore, from shallow sea to deep sea. Due to the limitation of technical conditions and material development, ZUI can only exploit oil and gas deposits that extend directly from the coast to the shallow sea at the beginning. Since the 1980s, stimulated by the energy crisis and technological progress, offshore oil exploration and development has developed rapidly, and offshore oil development has advanced rapidly to the continental shelf, gradually forming a new offshore oil industry sector. The offshore drilling platform is the work base for offshore oil and gas exploration and production, which marks the level of offshore oil and gas development technology.
Offshore oil production equipment mainly includes oil production platform and auxiliary equipment, including crude oil cooler, riser, pump, valve, joint and clamp. 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 offshore oil platform pillars made of titanium in its oil fields in the early 1970s, and made tubular heat exchangers and plate heat exchangers from titanium. The titanium tubular heat exchanger uses seawater as the cooling medium to cool the high-temperature steam/oil mixture extracted from the oil well. The titanium plate heat exchanger also uses seawater as the cooling medium to cool the fresh water cooling crude oil in the carbon steel heat exchanger. The United States has used about 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 DIYI titanium high-pressure riser shafts in the world, which are used in the Heidrum project of Conoco, Norway.
The service life of petroleum titanium alloy titanium drilling pipe is long, its weight is only half of that of stainless steel, while its service 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 drilling difficult near circular and deep oil wells. The combined drilling tool with titanium drilling pipe can greatly reduce the drilling time and the total drilling cost. GrantPrideco, RTI Energy Systems and Torch Drilling Services in the United States first used titanium drilling tubes for industrial applications in 2000. The titanium drilling pipe jointly produced and supplied by GrantPrideco and RTI Energy Systems is also equipped with steel tool joints provided by GrantPrideco Anti fatigue. The joint is light in weight and flexible in use, and can make the titanium drilling pipe firm.
Seawater pipeline system is an indispensable part of subsea oil exploitation. Because titanium has high corrosion resistance to seawater and its service life is 10 times that of steel system, the cost of titanium pipeline system is cost-effective compared with Cu Ni system. American Active Metal Company and Precision Tube Technology Company jointly established a titanium tube technology company to produce a large diameter titanium alloy tube. The alloy used for this pipe is Ti-3Al-2.5V alloy, with a diameter of 650mm, a wall thickness of 22-25mm, a length of 350m, and a pipe weight of 80-90t. It is planned to be used for subsea oil exploitation. Another company in the United States made nearly 500m long shaft pipe by extruding seamless titanium alloy pipe with length of 15m, outer diameter of 600mm and wall thickness of 25mm, which has been used in an offshore drilling platform. It is said that the weight of the shaft tube can be reduced by half, thus greatly reducing the cost of ballasting. In addition, it has high fracture toughness and long fatigue life.
According to data reports, in the North Sea oil field development project in the United States, the titanium consumption of floating body devices and seafloor fixed devices on ships has increased compared with that before. The demand of 24 floating body devices and 64 seafloor fixed devices for titanium materials is: 50~100t for safety protection devices, 50~100t for connecting devices, 400~1000t for general lifting equipment, and 1400~4200t for drill pipes. The corrosion of structural parts caused by biological pollution of offshore oil exploitation platform is quite serious. An American company used long casing made of titanium tube on the exploitation 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 enable oil drilling to enter deeper water areas and deeper oil wells, including higher temperatures and production environments with severe corrosion (i.e., salt rich).
For such applications, TC4 titanium rod (Ti-6Al-4V) based alloy is suitable for ZUI in terms of comprehensive performance, and its cost is low. Seawater pipeline system is an indispensable part of subsea oil exploitation. Because titanium has high corrosion resistance to seawater and its service life is 10 times that of steel system, the cost of titanium pipeline system is cost-effective compared with Cu Ni system. American Active Metal Company and Precision Tube Technology Company jointly established a titanium tube technology company to produce a large diameter titanium alloy tube. The alloy used for 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 weight of 80-90t. It is planned to be used for offshore oil exploitation. Another company in the United States made nearly 500m long shaft pipe by extruding seamless titanium alloy pipe with length of 15m, outer diameter of 600mm and wall thickness of 25mm, which has been used in an offshore drilling platform. It is said that the weight of the shaft tube can be reduced by half, thus greatly reducing the cost of ballasting. In addition, it has high fracture toughness and long fatigue life.
Practice has proved that Ti-6Al-4V (Gr.5_TC4) alloy is a good ZUI material for drilling pipes. As a drilling application, yield strength and fatigue strength are important for ZUI. Therefore, two kinds of Gr 5 alloy is suitable for key dynamic lifting devices. When the service temperature exceeds 75~80 ℃, Gr29 alloy containing ruthenium is used to prevent crevice corrosion or stress corrosion.
The common components of ZUI include offshore drilling lifting device, drilling pipe, tapered stress joint (TSJ) and titanium/steel mixed lifting device.
Small titanium parts such as titanium pumps, valves, joints, fasteners, clamps and spare parts have been widely used on oil exploitation platforms. Titanium alloy is also widely used on the casing of offshore oil exploration logging tools abroad.
2. Harbor building
There is an oxide film with a thickness of no more than 10nm on the surface of titanium material. It is very stable in the corrosive environment and has excellent corrosion resistance to air, sea water and marine environment. It is a raw material that can adapt to various marine environments at present. Japan vigorously carries out marine development, such as the bridge from Honshu to Siguo, the cross road of Tokyo Bay, Kansai Airport, floating oil storage base, etc. The investigation reports on the exposure tests conducted by Japan's Ministry of Construction and the Steel Club on the sea surface of Otsuikawa, as well as various anti-corrosion exposure tests conducted by the Ministry of Transport and the Steel Pipe Pile Association on the floating sand trestle in Bozaki, also show that titanium is a suitable material for ZUI. In addition to excellent corrosion resistance, titanium also has the advantages of few dissolved ions in seawater environment, non-toxic, and no need to worry about environmental pollution. Japan has also built a super large floating ocean building, which uses titanium steel composite materials at the sea water scouring place; In the construction of Tokyo Bay cross highway, titanium materials are used as the splash proof torso of piers, and the titanium consumption of each pier is 0.9t. Large floating ocean buildings that have been used or are planned include airports, harbor logistics bases, sports facilities, etc.
3. Duyen Hai Power Station
The comprehensive utilization of seawater is one of the important projects in ocean engineering. The condenser of coastal power station is the equipment that uses large amount of seawater. The titanium used in coastal power plants is mainly used in condensers. Because the condenser uses seawater as cooling water, and the seawater contains a large amount of silt, suspended substances, marine organisms and various corrosive substances, the situation is more serious in the brackish water with alternating changes of seawater and river water. The traditional condenser is made of copper alloy tubes, which are often severely damaged due to various corrosion in seawater. Titanium has good corrosion resistance in seawater, especially in polluted seawater, and its corrosion resistance against high-speed erosion of seawater is particularly outstanding.
4. Seawater desalination unit
"Water is the source of life". At present, the lack of water resources has become a worldwide problem. About 25 per cent of the world's population does not have adequate drinking water resources. The land rivers and groundwater resources in the world are far from meeting the needs of industrial development. Therefore, in the future, seawater desalination will be an effective way to solve the problem of freshwater resources.
From 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 it, and then condense the steam to obtain fresh water. The latter is to pressurize the sea water, so that the fresh water in it can pass through a special membrane and retain the salt to obtain fresh water. Early seawater desalination plants used copper alloy, carbon steel and other materials. Because these materials are not resistant to seawater corrosion and have low production efficiency, they were quickly replaced by titanium with excellent seawater corrosion resistance. In seawater desalination, the main application of titanium is the heater heat transfer tube of desalination device. The major producers of desalination plants are the United States and Japan. By 2004, more than 15,000 desalination units had been built or were under construction around the world, and the daily output of fresh water was about 32 million tons. Japanese companies built 10 distillation units with a daily output of 30000 tons of fresh water for Saudi Arabia, using 3200 tons of titanium tubes. The average daily output of 10000 tons of units requires 107 tons of titanium.
China's Tianjin, Shandong and other places have or are building desalination units. For example, Tianjin's preliminary plan for seawater desalination is to produce 500000 tons of fresh water per day by 2007 and 700000 tons by 2010. It is estimated that the amount of titanium used for seawater desalination projects in Tianjin and Shandong is about 250 tons.
5. Ship
Titanium and its alloys are corrosion-resistant in seawater and marine atmosphere, with light specific gravity, high strength, impact resistance, no magnetism, sound transmission and small expansion coefficient, and are considered as good ship materials. In recent years, the application of titanium in ships has attracted much attention. The navy and shipbuilding industry of various countries also attach great importance to the research on the application of titanium in ships, and many brands of marine titanium alloys have been developed. Titanium and its alloys are widely used in ships, such as hull structures, deep-sea survey ships and submarine pressure housings, pipes, valves, rudders, shaft brackets, accessories, thrusters and propeller shafts in power driven devices, heat exchangers, coolers, hull sonar fairings, etc.
The first application of titanium on ship hull was made in the former Soviet Union α Class A submarine. Subsequently, titanium was used for artificial or unmanned deep-sea research and deep-sea aid submarines. Industrial pure titanium is used for general structural parts, and Ti-6Al-4V alloy is used for pressure vessels. It is reported that titanium used for hull structure can not only reduce the weight of the hull itself, increase the effective loading weight, but also reduce maintenance and prolong the service life of the ship. Aluminum alloy, mild steel and other hull structural materials generally require 10 years of maintenance, while titanium materials almost do not require maintenance and repair, and their service life can also be extended from about 20 years to 30 to 40 years.
Japan has made great achievements in the research of titanium alloys for deep-sea survey ships. Almost all of the pressure chambers in the "deep-sea 6500" that can accommodate three operators have used titanium alloy materials. This is the result of long-term efforts of Mitsubishi Heavy Industries Kobe Shipyard. Submarines use a large amount of titanium, for example, a nuclear submarine with a depth of 900m uses 3500t of titanium.
6. Marine fishery
It is reported that Japan's fishery has changed from fishing to fish farming, and lionfish, flatfish, eels, etc. have been farmed artificially. In the artificial culture technology, titanium metal mesh and titanium tube heat exchanger are widely used to maintain a certain seawater temperature. The artificial cultivation of grouper has been realized in the coastal areas of Fujian Province in China, and the titanium plate aquaculture basket has brought great benefits to the cultivation of grouper.
Ocean thermal energy conversion
The ocean contains huge energy, such as tidal energy, wave energy, temperature difference energy, current energy and salt difference energy. With the increasing shortage of energy in the world, people will be more interested in the development and utilization of marine energy. Thermal power generation and tidal power generation projects have been studied and developed. The principle of thermoelectric power generation is to use the seawater with higher ocean surface temperature to vaporize ammonia or freon to drive the turbine to rotate for power generation, and then use the low-temperature seawater in the deep ocean to cool the vaporized ammonia or freon to form a continuously circulating heat engine system.
The main equipment of thermoelectric power generation is evaporator, condenser, seawater suction pipe, loop, etc. The equipment is required to be resistant not only to corrosion, but also to ammonia and fluoride. Titanium and its alloys not only have good seawater corrosion resistance, but also to ammonia and fluoride corrosion, so titanium is an ideal material for ZUI.
Titanium tube evaporators and condensers have been used in thermal power plants in the United States and Japan, and good results have been achieved.
Outlook
As a new civil market of titanium, offshore engineering has developed rapidly in recent years. With the further aggravation of the world energy crisis, countries around the world will invest a lot of manpower and material resources to exploit submarine oil resources and other mineral resources; In the trend of the global shortage of fresh water, all coastal countries will use seawater to produce fresh water; Moreover, the naval equipment competition among military powers is increasingly fierce, which is inseparable from titanium and titanium alloy materials. Therefore, titanium and its alloys will be more and more widely used in offshore engineering. It is expected that titanium for offshore engineering is expected to become a large application market of titanium materials.
