The application status and Prospect f titanium alloy in ocean engineering
(i) introduction
The oceans, which cover about 71% of the earth's surface, are rich in resources. This has been a source of wealth for many years. However, seawater is corrosive because it contains about 3.5% salt. In addition, the corrosion of seawater is accelerated by certain biological pollution in the ocean.Titanium is a material with excellent physical properties and stable chemical properties. Titanium and its alloys have high strength, low specific gravity, and are resistant to seawater corrosion and corrosion of the marine atmosphere, which can well meet the needs of people in marine engineering. Titanium has been used for many years in offshore oil and gas development, harbor construction, and coastal engineering applications. After years of hard work by titanium industry professionals and researchers in offshore applications, titanium has been used in offshore oil and gas development, seaport construction, coastal engineering, and marine construction. Power plants, seawater desalination, ships, marine fisheries and ocean thermal energy conversion and other fields have achieved extensive applications. Nowadays, titanium for marine engineering has become one of the main fields of titanium civil applications.
(ii) Application status
2.1 Offshore oil and gas development
Oil is the lifeblood of a country's economy. It is estimated that there are 300 billion tons of recoverable oil resources in the world, of which about 130 billion tons are under the seabed. The development of the seabed began at the beginning of the 20th century. The development of subsea oil began at the beginning of the 20th century. Its development went from offshore to distant sea and from shallow to deep sea, and was limited by the technical conditions and material development. Due to limitations in technology and materials development, initially only oil and gas deposits extending directly from the coast to the shallow sea could be exploited. Since the 1980s, spurred by the energy crisis and technological advances, offshore oil exploration and development has developed rapidly, and offshore oil and gas exploration and development has become a major part of the economy. The rapid advance of oil development on the continental shelf has gradually led to the formation of a new offshore oil industry sector. The offshore drilling platform is the working base for the implementation of subsea oil and gas exploration and exploitation, which marks the level of technology of subsea oil and gas development. The offshore oil production equipment mainly includes oil production platforms and ancillary equipment, such as crude oil coolers, riser pipes, pumps, valves. Fittings, clamps, etc. These devices come into contact with seawater and crude oil in media such as sulfides, ammonia and chlorine. Because of the excellent corrosion resistance of titanium in these media, the United States has been using titanium in its oil fields since the early 1970s. Titanium is used to manufacture both tubular and plate heat exchangers for the offshore oil platform columns. The titanium tube and tube heat exchanger uses seawater as the cooling medium to cool the high temperature steam/oil mixture pumped from the oil well. The titanium plate heat exchanger also uses seawater as the cooling medium to cool the fresh water used to cool the crude oil in the carbon steel heat exchanger. About 100 titanium heat exchangers are in use on oil rigs in the North Sea in the United States。Smaller titanium components such as titanium pumps, valves, fittings, fasteners, clamps and spare parts have been used extensively on oil production platforms. Titanium alloy is also used extensively on the casing of foreign offshore oil exploration and logging instruments.
2.2 Harbor construction
Titanium has a layer of oxide film with a thickness of 10 nm or less on its surface, which is very stable in corrosive environments. It is the material most suitable for various marine environments at present because of its excellent corrosion resistance. Japan is actively engaged in marine development, such as the Honshu-Shikoku Bridge, Tokyo Bay Crossing, Kansai Airport, and floating oil storage bases. The Ministry of Construction and the Steel Club of Japan have conducted exposure tests on the ocean surface of the Oigawa River, and the Ministry of Transport and the Steel Pile Association have conducted exposure tests on the sand drifting trestle bridge at the Wave School. Titanium has been shown to be the most suitable material for corrosion protection in a variety of studies such as corrosion exposure tests. In addition to its excellent anticorrosion properties, titanium has very few dissolved ions in seawater and is non-toxic, so there is no need to worry about contaminating the environment. advantages. Japan also built a mega-floating marine structure using titanium steel composite in the sea wash; the Tokyo Bay Trans-Highway at Titanium was used in the construction of the splash-proof trunks of the piers, with 0.9t of titanium used per pier. large scale, used or planned. Floating marine structures are airports, harbor logistics bases, sports facilities, etc.
2.3 Offshore power stations
The comprehensive utilization of seawater is one of the important projects in marine engineering, and the condenser of coastal power station is the equipment that utilizes large amount of seawater. Titanium for coastal power plants is mainly used for condensers. Since the condenser is made of seawater for cooling water, and seawater contains a large amount of mud, sand, suspended matter, sea creatures and various corrosive substances. The situation is even worse in brackish water, where seawater alternates with river water. Condensers are traditionally made of copper alloy tubes, which are often severely damaged in seawater due to various types of corrosion. Titanium has good corrosion resistance in seawater, especially in polluted seawater, and is particularly resistant to the high speed scouring corrosion of seawater.
2.4 Seawater desalination plant
"Water is the source of life". At present, the lack of water resources is a problem plaguing the whole world. About 25 per cent of the world's population does not have sufficient drinking water resources. The world's land rivers and groundwater resources are far from meeting the needs of industrial development, therefore, in the future, desalination of seawater will be one of the most important tasks of mankind. An effective method for solving freshwater resources.
From the point of view of the development of seawater desalination at home and abroad, mainly by two methods: distillation and reverse osmosis. The former is to heat the seawater to make it vaporized, and then the steam condensed to obtain fresh water. The latter is to pressurize seawater, so that the freshwater through a special membrane and the salt will be intercepted to obtain freshwater. Early desalination plants used materials such as copper alloys and carbon steel, which were not resistant to seawater corrosion and were inefficiently productive. It was soon replaced by titanium, which has excellent corrosion resistance to seawater. The main application of titanium in seawater desalination is the heat transfer tube of the desalination plant heater. The main producers of seawater desalination plants are the United States and Japan. By 2004, there were more than 15,000 desalination plants built or under construction worldwide, producing about 3,200 tons of fresh water per day. (b) The production capacity of the distillation plant for Saudi Arabia is 30,000 tons per day. The Japanese company constructed 10 distillation plants for Saudi Arabia with a daily production capacity of 30,000 tons of fresh water and 3,200 tons of titanium tubes for an average daily production capacity of 3,000 tons. The 10,000-tonne desalination plant requires 107 tonnes of titanium.
2.5 Ships
Titanium and its alloys are resistant to corrosion in seawater and marine atmosphere, and have light weight, high strength, impact resistance, non-magnetic, sound permeability and low expansion coefficient. and is considered a good material for ships. In recent years, the application of titanium in ships has attracted people's attention. The navy and shipbuilding industry of various countries also attach great importance to the research on the application of titanium in ships, and have developed many grades of titanium alloys for ships. Titanium and its alloys are widely used in ships, such as hull structures, pressure-resistant shells of deep-sea survey ships and submarines, pipelines, valves, and other alloys. Rudder, shaft brackets, accessories, propellers and propeller shafts in power drives, heat exchangers, coolers, hull sonar deflectors And so on.
The first application of titanium on the hull of a ship was the Soviet Union's alpha class submarine. Subsequently, titanium was used for artificial and unmanned deep-sea research and deep-sea assistance submarines. Titanium is used in industrial titanium for general structural parts and Ti-6Al-4V alloy for pressure vessels. It is reported that titanium for hull construction not only reduces the weight of the hull itself, but also increases the effective loading weight, and reduces the number of tons of fuel in the submarine. Maintenance and prolong the service life of ships. Aluminum alloy, mild steel and other hull structural materials generally require maintenance for 10 years, while titanium requires almost no maintenance and has a long service life. This can be extended from the usual 20 years to 30 to 40 years.
Japan's research in titanium alloys for deep-sea research vessels has been very successful. Titanium alloys are used almost exclusively in pressure-resistant silos. This is the result of long-standing efforts by Mitsubishi Heavy Industries Kobe Shipyard. The amount of titanium used in submarines is large, for example, a nuclear submarine with a diving depth of 900m uses up to 3500t of titanium.
2.6 Marine fishery
It has been reported that Japanese fisheries have shifted from fishing to fish farming, and lionfish, halibut, eels, and other fish have been artificially farmed. Titanium nets and titanium tubular heat exchangers that maintain a certain seawater temperature have been used extensively in artificial culture techniques. In China, the artificial culture of grouper has been realized in the coastal area of Fujian Province, and the titanium plate culture baskets have brought excellent results for the culture of grouper. Benefits.
2.7 Ocean thermal energy conversion
The oceans contain enormous amounts of energy, such as tidal, wave, temperature, current and salinity energy. As the world's energy resources become increasingly scarce, there will be greater interest in the development and utilization of ocean energy. The thermoelectric and tidal power projects have been researched and developed. The principle of thermoelectric power generation is based on the vaporization of ammonia or Freon by seawater at the higher surface temperature of the ocean to drive a turbine to generate electricity. Then the low-temperature seawater in the ocean depths will be used to cool the vaporized ammonia or Freon to form a continuous circulation heat engine system.
The main equipment of thermoelectric power generation is evaporator, condenser and seawater suction pipe, loop, etc. It requires equipment not only to resist corrosion, but also to resist the corrosion of ammonia and fluorine, titanium and its alloy not only have good corrosion resistance to seawater, but also resist the corrosion of ammonia and fluorine, so titanium is the most ideal material.
The United States, Japan's thermoelectric power plant have used the titanium tube evaporator and condenser, and achieved good results.
(iii) Prospect
Marine engineering, the emerging civilian market for titanium, has grown rapidly in recent years. As the world's energy crisis further intensifies, countries around the world will invest heavily in the exploitation of seabed oil and other Mineral resources; in a global trend of increasing freshwater scarcity, coastal countries will use seawater for freshwater production; furthermore, seawater will be used as a source of freshwater. Titanium and titanium alloys are indispensable for the naval equipment of major military powers, which is becoming more and more competitive, and for this reason, titanium and titanium alloys are becoming more and more widely used in marine engineering. Therefore, titanium and its alloys are expected to be used more and more extensively in marine engineering. It is expected that titanium in marine engineering is expected to become a large market for titanium materials.
Amy.Qin
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