Application Status and Prospect of Titanium Alloys in Ocean Engineering

(1) Introduction

The ocean, which accounts for about 71% of the earth's surface, contains abundant resources. It has become one of the directions of people's efforts for many years to develop and utilize the ocean to make the ocean the source of our huge wealth. However, seawater is corrosive due to its salt content of approximately 3.5%. In addition, some 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, and are resistant to seawater corrosion and marine atmosphere corrosion, which can well meet the requirements of people's applications in marine engineering. After years of hard work by people in the titanium industry and ocean engineering application researchers, titanium has been widely used in the fields of offshore oil and gas development, seaport construction, coastal power stations, seawater desalination, ships, marine fisheries and marine thermal energy conversion. Now, titanium for marine engineering has become one of the main fields of titanium civil application.

(2) 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 reserves are 300 billion tons, of which seabed 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 offshore to far sea, from shallow sea to deep sea. Restricted by technical conditions and material development, initially only oil and natural gas deposits extending 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, gradually forming a new offshore oil industry sector. The offshore drilling platform is the work base for the exploration and exploitation of subsea oil and gas, and it marks the level of subsea oil and gas development technology. Offshore oil production equipment mainly includes oil production platforms and auxiliary equipment, such as crude oil coolers, oil risers, pumps, valves, joints and fixtures. These devices are in contact with sulfide, ammonia, chlorine and other media in seawater and crude oil. Due to the excellent corrosion resistance of titanium in these media, the United States used titanium-made offshore oil platform pillars in its oil fields in the early 1970s, and used titanium to make tube heat exchangers and plate heat exchangers. Heater. The titanium shell and tube heat exchanger uses seawater as a cooling medium to cool the high temperature steam/oil mixture pumped from the oil well. The titanium plate heat exchanger also uses seawater as a cooling medium to cool the fresh water that cools the crude oil in the carbon steel heat exchanger. The United States uses about 100 titanium heat exchangers on oil rigs in the North Sea. The titanium component ordered by Hunting Oilfield Services in Aberdeen, Scotland, UK, is said to be the world's first titanium high pressure riser shaft for Conoco's Heidrum project in Norway. Petroleum titanium alloy titanium drill pipe has a long service life, its weight is only half of that 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 drilling difficult near-circular, deep wells. Combination drilling tools including titanium drill pipes can greatly reduce drilling time and reduce overall drilling costs. In 2000, GrantPrideco, RTI Energy Systems and Torch Drilling Services in the United States first used titanium drill pipes for industrial applications. Titanium drill pipe, produced and supplied by GrantPrideco and RTI Energy Systems, also features steel tool joints from GrantPrideco Anti-Fatigue. The joints are light in weight, flexible in use, and make titanium drill pipes sturdy and strong. Seawater pipeline system is an indispensable part of subsea oil exploitation. Since titanium has high corrosion resistance to seawater, its service life is 10 times that of steel system. Therefore, the cost of titanium pipeline system is cost-effective compared with Cu-Ni system. of. Active Metals of America and Precision Tube Technology have 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, the diameter is 650mm, the wall thickness is 22-25mm, and the length is 350m. Another company in the United States used seamless titanium alloy pipes with a length of 15m, an outer diameter of 600mm and a wall thickness of 25mm to make a nearly 500m long riser pipe by extrusion, which has been used in an offshore drilling platform. It is said that the weight of the riser tube can be reduced by half, which can greatly reduce the cost of ballast, in addition, it also has high fracture toughness and long fatigue life. According to reports, in the North Sea oil field development project in the United States, the amount of titanium used in the floating body device and the fixed device on the seabed has increased compared with the previous one. The demand for titanium materials for 24 floating body devices and 64 subsea fixed devices 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 fouling of offshore oil exploration platforms is quite serious. A company in the United States uses long casings made of titanium pipes on the mining platforms to protect the parts on the platform. The past few years have seen a marked increase in the use of titanium alloy components in oil drilling and offshore production operations. Titanium alloy components allow oil drilling to access deeper waters and deeper wells, including higher temperatures and highly corrosive (ie, salty) production environments. For this type of application, TC4 titanium rod (Ti-6Al-4V) based alloy is the most suitable and the lowest cost in terms of overall performance. Seawater pipeline system is an indispensable part of subsea oil exploitation. Since titanium has high corrosion resistance to seawater, its service life is 10 times that of steel system. Therefore, the cost of titanium pipeline system is more cost-effective than that of Cu-Ni system. of. Active Metals of America and Precision Tube Technology have 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 weighing 80-90t, which is planned to be used for subsea oil exploration . Another company in the United States used seamless titanium alloy pipes with a length of 15m, an outer diameter of 600mm and a wall thickness of 25mm to make a nearly 500m long riser pipe by extrusion, which has been used in an offshore drilling platform. It is said that the weight of the riser tube can be reduced by half, which can greatly reduce the cost of ballast, in addition, it also has high fracture toughness and long fatigue life. 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 Gr.5 alloys with particularly low interstitial elements are suitable for For more critical dynamic lifting devices. When the operating temperature exceeds 75 ~ 80 ℃, in order to prevent crevice corrosion or stress corrosion, a ruthenium-containing Gr29 alloy is used. The most commonly used components include offshore drilling hoists, drill pipes, conical stress joints (TSJs) and titanium/steel hybrid hoists. Small titanium components such as titanium pumps, valves, joints, fasteners, clamps and spare parts are already widely used on oil drilling platforms. Titanium alloys are also widely used on the shells of offshore oil exploration logging instruments abroad.

2.2 There is an oxide film with a thickness of no more than 10nm on the surface of the titanium material for seaport buildings. 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 Honsu to Shikoku, the bridge across Tokyo Bay, the Kansai Airport, and the floating oil storage base. The exposure test conducted by the Ministry of Construction and the Iron and Steel Club of Japan on the ocean surface of the Oigawa River and the investigation reports of various anticorrosion exposure tests conducted by the Ministry of Transport and the Steel Pipe Pile Association on the Bosaki floating sand trestle also showed that titanium is the most suitable material. In addition to its excellent anti-corrosion properties, titanium also has the advantages of very few dissolved ions in the seawater environment, no toxicity, and no need to worry about polluting the environment. Japan has also built a super-large floating marine structure, using titanium-steel composite materials in the seawater scour; in the construction of the Tokyo Bay spanning highway, titanium materials have been used as the splash-proof torso of the bridge piers, and the titanium-steel composite materials of each bridge pier are The amount is 0.9t. Large floating marine structures already in use or planned include airports, harbor logistics bases, sports facilities, and more.

2.3 The comprehensive utilization of seawater in coastal power stations is one of the important projects in marine engineering. The condensers in coastal power stations are equipment that utilizes a large amount of seawater. The titanium used in coastal power stations is mainly titanium used in condensers. Since the condenser uses seawater as the 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 fresh brine where the seawater and the river water alternate. 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 corrosion resistance is particularly outstanding.

2.4 Desalination plant "Water is the source of life". Currently, water scarcity has become a problem plaguing the world. About 25% of the world's population does not have adequate sources of drinking water. The world's terrestrial rivers and groundwater resources are far from meeting the needs of industrial development. Therefore, desalination of seawater will be an effective method for human beings to solve freshwater resources in the future. 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 it, and then condense the steam to obtain fresh water. The latter is to pressurize sea water, so that the fresh water in it passes through a special membrane and retains the salt to obtain fresh water. The early seawater desalination devices used copper alloys, 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 the desalination plant. The major producers of desalination plants are the United States and Japan. By 2004, there were more than 15,000 desalination plants built or under construction in the world, with a daily output of about 32 million tons of fresh water. The Japanese company built 10 distillation units for Saudi Arabia with a daily output of 30,000 tons of fresh water, using 3,200 tons of titanium tubes, and an average daily output of 10,000 tons, requiring 107 tons of titanium. my country's Tianjin, Shandong and other places have built or are building seawater desalination plants. For example, the preliminary plan for seawater desalination in Tianjin is to produce 500,000 tons of fresh water per day by 2007 and 700,000 tons by 2010. It is estimated that about 250 tons of titanium will be used in seawater desalination projects in Tianjin and Shandong.

2.5 Ship titanium and its alloys are corrosion-resistant in seawater and marine atmosphere, and are considered to be good ship materials because of their light specific gravity, high strength, impact resistance, non-magnetic, sound transmission and small expansion coefficient. In recent years, the application of titanium in ships has attracted much attention. The navies and shipbuilding industries of various countries also attach great importance to the application of titanium on ships, and have developed many grades of marine titanium alloys. Titanium and its alloys are widely used in ships, such as hull structures, deep-sea survey vessels and submarine pressure hulls, pipes, valves, rudders, shaft brackets, accessories, propellers and thrusters in power drives Shafts, heat exchangers, coolers, hull sonar shrouds, and more. The first application of titanium on 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 hull structure can not only reduce the weight of the hull itself, increase the effective load weight, but also reduce maintenance and prolong the service life of the ship. Aluminum alloy, mild steel and other hull structural materials generally require maintenance within 10 years, while titanium materials hardly require maintenance and repairs, and their lifespan can be extended from the usual 20 years to 30 to 40 years. Japan's research on titanium alloys for deep-sea survey ships has been fruitful. Almost all of the "Deep-Sea 6500" pressure chambers that can accommodate 3 operators use titanium alloys. This is the result of long-term efforts at Mitsubishi Heavy Industries Kobe Shipyard. Submarines use a large amount of titanium. For example, a nuclear submarine with a diving depth of 900m uses up to 3500t of titanium.

2.6 Marine fishery It is reported that Japan's fishery has changed from fishing to fish farming, and lionfish, flounder, eel, etc. have been artificially cultured. In artificial breeding technology, titanium metal mesh and titanium tube heat exchanger to maintain a certain seawater temperature are widely used. The artificial culture of grouper has been realized in the coastal areas of Fujian in my country, and the titanium plate type culture basket used has brought excellent benefits to the culture of grouper.

2.7 Ocean thermal energy conversion There is a huge amount of energy in the ocean, such as tidal energy, wave energy, temperature difference energy, ocean current energy and salt difference energy and so on. With the increasing shortage of energy in the world, people will be more interested in the development and utilization of ocean energy. Thermoelectric and tidal power generation projects have been researched and developed. The principle of thermoelectric power generation is to use the seawater with high temperature on the ocean surface to vaporize ammonia or freon to drive the turbine to rotate and generate electricity, and then use the low-temperature seawater in the deep ocean 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., which require not only corrosion resistance, but also ammonia and fluorine corrosion resistance. Titanium and its alloys not only have good seawater corrosion resistance, It is also resistant to corrosion by ammonia and fluorine, so titanium is the most ideal material. Titanium tube evaporators and condensers have been used in thermoelectric power stations in the United States and Japan, and good results have been achieved.

(3) Prospects

As an emerging civil market of titanium, marine engineering has developed rapidly in recent years. With the further aggravation of the world energy crisis, all countries in the world will invest a lot of manpower and material resources to exploit seabed oil resources and other mineral resources; in the trend of global shortage of fresh water, all coastal countries will use seawater to produce fresh water; The increasingly fierce competition of naval equipment of various military powers is inseparable from titanium and titanium alloy materials. Therefore, the application of titanium and its alloys in marine engineering will become more and more extensive. It is expected that titanium for marine engineering is expected to become a larger application market for titanium materials.