Application Status And Prospects Of Titanium Alloys in Ocean Engineering

(I) 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 a source of our great wealth, has become one of the directions that people have worked hard for 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 fields such as 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 for civilian applications.

(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 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, 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 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 equipments 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 manufacture 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 fresh water that cools the crude oil in the carbon steel heat exchanger.

Petroleum titanium alloy titanium drill pipe has a long service life, its weight is only half of stainless steel, but its 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.

According to data reports, 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 materials for 24 ships' floating devices and 64 submarine fixtures is: safety protection devices 50-100t, connecting devices 50-100t, general lifting equipment 400-1000t, and 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 use 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 type 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 that of steel systems. Therefore, the cost of titanium piping systems is cost-effective compared with Cu-Ni systems. of.

The most commonly used components include seaside drilling hoists, drill pipes, tapered stress joints (TSJ) and titanium/steel hybrid hoists

Small titanium parts such as titanium pumps, valves, joints, fasteners, fixtures and spare 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 logging instruments abroad.

2.2 Harbor construction

There is an oxide film on the surface of titanium with a thickness of no more than 10nm. It is very stable in corrosive environments and has excellent corrosion resistance to air, sea water 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 Ministry of Construction and the Iron and Steel Club of Japan on the Oigawa surface, and the various anticorrosion exposure tests conducted by the Ministry of Transportation and the Steel Pipe Pile Association on the Haosaki Floating Sand Trestle 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, 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 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 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 sea water to vaporize it, and then condense the steam to obtain fresh water. The latter is to pressurize the sea water, make the fresh water 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 fresh water.

2.5 Ship

Titanium and its alloys are corrosion-resistant in seawater and ocean atmospheres, and have light specific gravity, high strength, impact resistance, no magnetism, sound permeability, and low 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 structures, deep-sea survey ships and submarine pressure hulls, pipes, valves, rudders, shaft brackets, accessories, propellers and propellers in power drive devices Shafts, heat exchangers, coolers, hull sonar shrouds, etc.

The first application of titanium to ship hulls 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. 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.

2.6 Marine fisheries

According to reports, Japanese fisheries have changed from fishing to fish farming, and artificial farming of lionfish, flounder and eel has been realized. 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 areas 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. The thermoelectric power generation and tidal power generation projects have been researched and developed. The principle of thermoelectric power generation is to vaporize ammonia or freon by seawater with a higher ocean surface temperature to drive the turbine to rotate for power generation, and then cool the vaporized ammonia or freon with low-temperature seawater deep in the ocean to form a continuous cycle heat engine system.

The main equipment for thermoelectric power generation is evaporator, condenser, seawater suction pipe, loop, 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, It is also resistant to corrosion by ammonia and fluorine, so titanium is the most ideal material.

(Iii) Prospects

As an emerging civilian market for titanium, offshore engineering has developed rapidly in recent years. With the further intensification of the world energy crisis, countries in the world will invest a large amount of manpower and material resources in the exploitation of seabed petroleum resources and other mineral resources; in the trend of increasing shortage of global fresh water, all coastal countries will use sea water to produce fresh water; 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.