The ship is the most important equipment of the navy, and it is a platform for maritime transportation and combat. The materials used to build the ship must be able to withstand the corrosion of sea water and the marine atmosphere. Due to the complex structure of the ship, the amount of materials used is large, and there are many varieties and specifications. Selecting materials with excellent performance to make warships is the basis for ensuring the integrity and advancement of naval equipment.
The application of titanium alloys on ships is mainly based on the following characteristics of titanium alloys: wide strength range, excellent mechanical properties, unique physical properties (including magnetic properties), high specific strength and structural effectiveness, excellent Corrosion resistance and erosion resistance, excellent impact resistance, good machinability and weldability, reasonable cost and effectiveness. A lot of experience in the use of marine piping materials has confirmed that the service life of traditional materials in the pipeline system is limited. Among them, the steel pipe system will corrode after 1.2 to 2 years, and the service life of the CuNi pipeline system is 6 to 8 years. And the pipes, pumps, valves, heat exchangers and other equipment in the titanium alloy piping system can be used for more than 40 years. Because marine titanium alloys need to be in service in the marine environment for a long time, the strength, stress corrosion fracture toughness, weldability, etc. of the alloy must be considered when designing the marine titanium alloy.
Russia is the earliest country in the world to develop and use marine titanium alloys, and it is also the country with the widest range and the largest number of marine titanium alloys. It mainly includes PT-7M, PT-1M, PT-3V, 37, 5V titanium alloy and its corresponding welding wire, and has formed marine titanium alloy products with different strength levels such as 490, 585, 686, and 785 MPa. , Titanium alloy has been successfully used in the following components and equipment on ships: deepwater risers, supply pipes, pumps, filters, sea pipelines, drinking water pipes, drilling pipes and groundwater pipes, heat exchangers, diesel engines Independent fire pumps and fire extinguishing systems, deep water equipment shells, flexible pipes for external well systems, pressure vessels, high-strength flexible tensile parts for platform fastening joints, piping and containers for process solutions, etc. "Lenin", "Arctic", "Russian", "Soviet" and other types of ships. The titanium steam generators on the nuclear icebreakers of the former Soviet Union series have been used safely for 20 to 40 years, and No serious damage occurred.
3Mo-0. 8Ni The American marine titanium alloy is mainly based on the aerospace titanium alloy, and has selected titanium alloys with corrosion resistance, weldability and stress corrosion resistance in seawater corrosion environments, including pure titanium, Ti-0. 3Mo-0. 8Ni , Ti-3Al-2. 5V, Ti-6Al-4V, Ti-6Al-4V ELI, Ti-3Al-8V-6Cr-4Mo-4Zr. In addition, for the characteristics of marine titanium alloys, Ti-5Al-1Zr-1Sn-1V-0. 8Mo-0. 1Si, Ti-6Al-2Nb-1Ta-0. 8Mo and other marine titanium alloys have also been developed. The use of high-performance titanium alloys on ships has a significant effect on improving the mobility, stability, and effectiveness of ships, and reducing the hull quality. In the 1990s, the US Navy conducted certification assessments on the following ships, including: nuclear-powered aircraft carriers (CVN), missile cruisers (CG-47), missile frigates (FFG-7), detection ships (MCM), and amphibious landing craft (LSD41CV), landing ship, hovercraft (LVCA), amphibious assault landing ship (LHD), rapid combat munitions supply ship (AOE-6), double-hull surveillance ship (SWATH T-AGOS19), coastal detection ship (MHC-51), missile destroyer (DDG-51). These ships' seawater cooling systems, seawater systems and fire extinguishing systems, structural parts, propellers, sewage treatment systems, electrical components, fasteners, etc., have all used or are about to use high-performance titanium alloys.
The research and application of China's marine titanium alloy began in the 1960s. After decades of development, it has formed a relatively complete marine titanium alloy system that can meet the requirements of ships, submarines and deep submersibles for different strength levels. The application field involves hull structure, propulsion system, power system, electronic information system, auxiliary system, special equipment, etc. According to the yield strength level, that is, the yield strength is below 490 MPa is a low-strength titanium alloy with excellent plasticity; 490 ~ 790 MPa is a medium-strength titanium alloy, higher than 790 MPa is a high-strength titanium alloy, mainly used in marine power engineering Heat-resistant and corrosion-resistant parts and marine special machinery.
Japanese marine titanium alloys are mainly pure titanium, Ti-6Al-4V, Ti-6Al-4V ELI, which are mainly used in the pressure-resistant shell of deep submersibles and various civilian cruise ships and fishing boats.
Problems and solutions in use 3.1 Crevice corrosion
Corrosion problems: There are small gaps in the detachable connectors (flanges, threaded connections, etc.) used in ships, and there will be aggressive high concentrations of chloride and fluoride ions in the gaps, which requires titanium alloys in seawater It has good resistance to high temperature crevice corrosion in the environment. In titanium alloy heat exchangers and seawater desalination equipment, the working environment is 90 ~ 250 ℃, the medium pH value is 1.5 ~ 4.0 (especially in salt and kerosene-like deposits), the crevice corrosion is very fatal.
Anti-corrosion measures:
(1) Adding Pd and Ru elements to the titanium alloy can effectively improve the crevice corrosion resistance of the titanium alloy.
(2) Perform Ru/Pd-containing surface treatment on the surface of the titanium alloy, for example, infiltrate Ru/Pd elements on the surface of the titanium alloy or perform micro-arc oxidation to form oxides containing Ru/Pd elements on the surface of the titanium alloy. In order to reduce the cost of surface treatment, a gradient coating containing Ru/Pd elements can also be prepared on the surface of the titanium alloy.
(3) When using cathodic protection technology to protect the steel structure, the potential is between -800 mV and -1050 mV to avoid hydrogen-induced oversaturation and hydrogen-induced cracking of the titanium alloy.
3. 2 Galvanic corrosion
Titanium is very prone to galvanic corrosion when it is connected to steel and copper. Protective measures include:
1. The pipe is thermally oxidized, micro-arc oxidized, and anodized to form an oxide layer or ceramic layer on the metal surface to achieve insulation. The titanium tube is oxidized to form an oxide film that can reduce the cathode polarization effect of the titanium alloy by 80% to 90%. The life of the oxide film is equivalent to the life of the titanium tube.
2. Use asphalt rubber (12910, 25.00, 0.19%) for insulation treatment at the interface between the pipe, valve mouth and steel and copper equipment;
3. Protect the middle flange between the titanium tube and the stainless steel nozzle.
3. 3 Welding corrosion of large structural parts
Protective measures include:
1. Large structural parts such as shells, high-pressure vessels and tensile parts used on ships need to use high-strength titanium alloys based on the pressure resistance requirements, and the connection of high-strength titanium alloy thick-walled welded parts must be excellent in seawater Operability, no heat treatment is required after welding.
2. TC4 titanium alloy and low-gap TC4 titanium alloy are used in the United States and Europe (oxygen content is controlled within 0.13%); the Russian Prometheus Central Research Institute of Structural Materials has developed PT-3V, 37, 5V marine titanium alloys; China has developed TA24 and TA31 titanium alloys.
3. For large structural parts, heat treatment cannot be performed after welding, and there is tensile stress on the surface, which greatly reduces the corrosion resistance and fatigue resistance of titanium alloy components. Ultrasonic impact treatment can be performed on the surface of the weldment to transform the tensile stress on the surface of the weldment into compressive stress, which is beneficial to the improvement of fatigue performance.
Prospects for the development of China's marine titanium alloy
For material research, China's marine titanium alloys also need to carry out titanium alloy performance research in the marine environment, including:
①Working environment (temperature, pH value, solution composition), stress mode (free state, reverse bending, torsion), alternating load on titanium alloy in air and sea water, corrosion fatigue, fatigue crack growth rate, stress corrosion fracture Research on the impact of toughness;
②The influence of processing technology on the texture type of titanium alloy pipe (radial texture, axial texture) and the type of texture on the performance of pipe processing technology (flaring, flattening, blasting);
③Pd, Ru trace elements on the corrosion resistance mechanism of titanium alloy in H2S, Cl- environment;
④Tensile and fatigue performance evaluation of titanium alloy under irradiation environment;
⑤Research on welding deformation control and correction of different welding forms of corrosion-resistant titanium alloy.
Baoji Hongyada Nonferrous Metal Material Co., Ltd.
Contact: Zhang Hongbin
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