Application of titanium on ships

In Russia, the shipboard acoustic flow shroud used to be made of glass fiber reinforced plastic (FRP), and later most of them were made of titanium alloy. It has been proved that titanium alloy acoustic flow shroud has excellent comprehensive performance, and the "Kursk" sonar system produced by them is made of titanium. The sonar shields of the K877, K636, 956 and Liaoning aircraft carrier purchased by China are all made of titanium alloy. According to the different requirements of underwater and surface applications, some of the naval vessel sonar shrouds built in China in the early years are made of stainless steel and some of glass fiber reinforced plastics. During the ninth Five-Year Plan period, thorough and comprehensive research has been made on titanium alloy shrouds and fruitful results have been obtained. Now titanium alloy is gradually used. The life of titanium spiral is more than 5 times longer than that of copper alloy.

The requirements of materials for ship propellers are: high strength, strong fatigue resistance to seawater, erosion resistance and cavitation corrosion. In terms of existing materials, titanium alloy is the first choice to meet these requirements. The US Navy pioneered the use of a 1500mm diameter, four-blade detachable supercavitation titanium alloy propeller on hydrofoil craft. In 1972, China developed titanium alloy propellers for hydrofoil speed boats. By 2014, it is estimated that about 800 pieces of various propellers with diameters ranging from 450mm to 1500mm have been produced, with the largest mass exceeding 160kg. However, the long-term use and operation show that the advantages of titanium alloy propellers and their shafts in the manufacturing cost have not been fully manifested, so the application of titanium alloy propellers has not reached the stage of universal practicality, and it needs to be further developed and promoted. The titanium propeller parts also include rudder and bearing seat, etc. Engine exhaust cooling pipe and muffler.

On the one hand, it needs to pass through the pipe (double cooling pipe) to cool the sea water and cool the exhaust gas. On the other hand, it needs to install silencers to reduce the exhaust noise to less than 60dB. Titanium is a good material for manufacturing the muffler: The durability at high temperature is stronger and longer than that of aluminum alloy, the density is lower than that of stainless steel, and the sound elimination effect is good.

Most of the frequency converters (mixer Minxing) in The Japanese muffler have been replaced with titanium. The reason for choosing titanium material to make the mixer is that the temperature of the high temperature end is up to 500℃, and the material is required to have good high temperature lasting strength; Although the temperature of the low temperature is not high, around 100℃, but contact with seawater, need to have high corrosion resistance. At present, the frequency conversion devices of medium and high speed ships are mostly made of aluminum, but the high temperature performance of aluminum is not good, it is easy to crack in the weld and heat affected zone, and the low temperature end is easy to be corroded by seawater. Stress corrosion cracking may occur in the welded parts if stainless steel is used. Their service life is from 5a to 10a, during which they need to be repaired several times. Titanium is stronger than aluminum, and at the same strength, the thickness of titanium is much thinner than aluminum, about 40% thinner than stainless steel. In addition, the price of titanium products is about twice that of aluminum and stainless steel products. Considering the cost of maintenance and replacement parts, it is undoubtedly much more economical to use titanium parts. Japan's Coast guard proposed in 2002 that all seawater and exhaust mixing devices on ships be made of titanium.

Ships on pumps, valves, piping, such as engine cooling water and fire water piping system working conditions is very bad, the past is made of copper, is also useful in anti-corrosion coat of steel pipe and stainless steel pipe manufacturing, but their service period is not long, only 2 a ~ 5 a, if use titanium pump, titanium tube, titanium valve life for 25 ~ 30 a, Not only the total cost is greatly reduced, but also it is safe and reliable during operation, without corrosion, leakage and other safety accidents. According to the standard of the former Soviet Union and Russia, the life of titanium pipeline is 3 years: the first life is 8A ~ 9A, from the launching to the first docking maintenance; Second service life should not be less than 15A; The third time is 5a to 10a. It is required that ships of the class used should operate reliably during 25A ~ 30A. At present, only titanium and titanium alloy can meet this requirement among all structural materials, and they are also the most cost-effective materials.