Application of Titanium materials in marine engineering

In 1965, the United States Harvey Aluminum Company in the construction of a desalination plant in the Virgin Islands, its thermal conductivity tube all use 0.7mm seamless titanium tube wall thickness, a total length of 1.85 million meters, about 24t, the daily processing capacity of 1.84 million cubic meters. In 1967, Japan's Matsushima Carbon Mining Co., Ltd. built a 2650t/d seawater desalination plant. Due to the corrosion of bromine (Br) in seawater, the heat transfer tube and tube plate of the ventilating condenser and jet compressor of this device cannot be used in copper alloy. After the replacement of titanium, no failure caused by corrosion has occurred.

Fresh water accounts for about 3% of the Earth's water resources, and obtaining water through desalination is a new trend, especially in the Middle East, where water shortages are severe. Desalination was used to obtain fresh water as early as the 1950s, and 1,468 desalination units were built around the world in 1979, and 9,014 desalination units were built in 5,738 locations around the world by 1993. In 2004 there were 15,000 desalination plants under construction around the world.

The main methods of seawater desalination are as follows.

① Evaporation method single-stage flash method, multi-stage flash method, vertical multi-method, horizontal multi-method, immersion tube method, steam compression method; ② diaphragm electrodialysis method, reverse immersion method; ③ Compound law. Among them, evaporation method is used, followed by reverse immersion method, and electrodialysis method is less used.

Application of titanium in Marine civil construction industry:

The main problem facing Marine buildings is the serious corrosion of seawater and sea salt particles, titanium material because of its excellent corrosion resistance has become the preferred material for Marine buildings, Marine construction field, titanium applications are mainly divided into three categories: ① steel structural corrosion prevention; ② Corrosion resistant structural parts; ③ Corrosion prevention of concrete structural parts. Titanium has become the first choice of Marine structures, It has two roles : The first is use titanium sheet to cover the corrosion-prone parts; The second is the titanium steel composite plate for the perishable part of Marine structures.

Fresh water accounts for about 3% of the earth's water resources, through seawater desalination to obtain new fresh water resources is a major trend of international water use in the future. Now Desalination is main way to obtain water in water-scarce regions like the Middle East.

1. International seawater desalination situation

By 1993, the international countries in 5738 regions of the seawater desalination equipment a total of 9014 units, the total capacity of 1.624X107m3 / d, only the Middle East region of the total capacity of 8.91 *106m3 / d, accounting for 55%, the United States is 2.37*106m3 / d, accounting for 5% of the weight.

As early as the 1950s, seawater desalination has been used to produce fresh water. The main methods of seawater desalination are : (1) transpiration method: multi-stage flash method, single-stage flash method, vertical multi-method, horizontal multi-method, immersion tube method, steam contraction method; ② : electrodialysis, reverse osmosis; ③ Compound law. Among them, transpiration method accounted for 60%, reverse osmosis method accounted for 33%, electrodialysis method accounted for 5.5%. Table 1 shows the main desalination methods used in Japan and their useful share.

2, the use of titanium in seawater desalination equipment

2.1 Heat conduction tube in seawater desalination equipment

The original seawater desalination equipment thermal conductivity pipe is mainly used copper alloy pipe, because there are many lack of copper alloy pipe, has been replaced by high reliability and maintenance free titanium pipe.

(1) The wall thickness of the titanium tube is determined by the application conditions, the tube plate material, the construction talent of the tube expansion operation, the welding skills of the tube end, etc., because the diameter of the thermal tube is small and the strength requirement is not high, so the pipe with thinner wall thickness is selected in practice. Generally, the wall thickness of the copper alloy tube is 0.9mm-1.2mm; Instead of titanium tubes, thin wall welded tubes with a wall thickness of 0.3mm can be used in places with little corrosion.

(2) The thermal conductivity of titanium tube Because the raw materials of the thermal conductivity tube are different, the thermal conductivity is also different, such as titanium is 17W/(m•k), aluminum brass is lOOW/ (m•k), 90/10 white copper is 47W (m•k), 70/30 white copper is 29W/(m•k), therefore, the thermal conductivity of the thermal conductivity tube can be controlled by changing the wall thickness. Among the above materials, titanium has the smallest thermal conductivity. Such as the use of thin-walled titanium welded pipes, although the thermal conductivity is worse than aluminum brass, it is appropriate with 90/10 white copper, which is better than 70/30 white copper.

(3) Titanium tube economic titanium tube unit mass offer is 2 to 6 times more expensive than copper alloy, but from the cost-effective consideration, titanium tube offer can compete with copper alloy tube, because titanium density is low, wall thickness together, equal length of titanium tube quality is only 50% of copper alloy tube, when titanium tube wall thickness is 50% of copper alloy tube, The mass of titanium tube with the same heat transfer area is only 1/4 of that of copper alloy tube. According to the current quotation level, the selection of thin-wall titanium welded pipe is the same as the aluminum copper pipe, which is cheaper than the white copper pipe. It can be seen that titanium tubes are competitive in terms of quotation.

2.2 Development and application of thin-wall titanium welded pipe in Japan

The successful development of titanium strip rolling skills has become the basis of the mass producer of titanium welded pipes. In the 1960s, in the production of electrolytic caustic soda, Japan chose titanium wire; In the early 1990s, in order to avoid pollution, the caustic soda production process has been improved, with the choice of separation method, more than 700 tons of titanium strips can be used, as the key, Japan has developed the continuous production of hot-rolled and cold-rolled titanium coil skills, the establishment of seawater desalination and power station condenser titanium thin-wall welding pipe coil mass production system, The production skills of thin wall welded pipe are developed accordingly. Power station condensers made by Hitachi, Mitsubishi and Toshiba are use titanium welded tubes with a thickness of 0.5mm, and seawater desalination equipment made by Mitsubishi, Kawasaki, Hitachi, Mitsui and Kobe Steel uses titanium welded tubes with a thickness of 0.5mm-0.7mm. Mainly used in power stations, titanium welded pipes have been widely used as heat transfer tubes in the fields of seawater desalination, ironmaking, ships, cleaning, chemical industry and so on. By 1983, in 16 years, Japan produced 4038t thin-wall titanium welded pipe used in seawater desalination equipment around the world, and has not been damaged by seawater corrosion.

(1) Ventilation coagulators and eruption compressors The real desalination equipment in Japan is the 2650t/d desalination equipment built by Matsushima Carbon Mine Co., LTD., in 1967. The heat transfer tube and tube plate of the ventilation condenser and the eruption compressor of the equipment can’t use copper alloy because of the corrosion of BR-in seawater. After replacing it with titanium, don’t have problems that caused by corrosion .

(2) Multi-stage flash condenser is to use seawater as cooling water to cool the water vapor in the flash chamber at all levels, because seawater is often mixed with sediment and sea life, which are attached to the heat transfer tube and the end of the tube and corrodes the copper alloy tube. Therefore, titanium tubes are now used on the heat transfer condenser of almost all MSF desalination equipment. Especially in order to bacteria in dead seawater, oxygen has to be injected, and titanium tubes with good corrosion resistance need to be used.

(3) The heat transfer area of the condenser in the heat recovery part is large. Because of economic reasons, copper alloy tubes are generally used, and titanium tubes are only used in special occasions, such as the intense corrosion of copper alloys by media containing or other pollutants. In 1977, the 3600t/d MSF desalination equipment exported to Germany, because it is an accessory equipment, can not use copper alloy, and chose titanium; Because of the corrosion of oxygen sulfide, the 3120t/dMSP desalination equipment in Peru corroded the aluminum brass tube after 1 year of use, and eventually replaced all the heat transfer tubes with titanium tubes. According to public information, there are 60,000 titanium tubes for 100 tons of seawater desalination equipment per day. From 1967 to 1994, in nearly 30 years, a total of 52 sets of condensers originally used in energy level thermal power generation and 7 sets of seawater desalination equipment were produced, with a total of 11000t titanium welded pipes.

3. Problems that should be pay attention to when using

(1) galvanic corrosion titanium has a positive potential in seawater, and when touched with other metals, it can promote the corrosion of other metals. Avoidance methods include the use of titanium in both the heat transfer tube and the tube plate, or the method of dedicating the anode. Above 80℃, in order to avoid hydrogen absorption, Fe-90% Ni alloy is used as the dedication anode; Below 80℃, use coating or rubber lining steel plate.

(2) Void corrosion titanium tube is installed on the titanium tube plate by expanding the tube method, and void corrosion can occur in seawater with a pH value of 100 ° C and 8. However, in practice, copper alloy is used in the water chamber, and even if the sea temperature reaches 120℃ , void corrosion will not happen. In practice, in order to improve the reliability of the equipment, pipe end welding is used more than 100℃ to avoid void corrosion.

(3) Hydrogen absorption in seawater above 80℃; Titanium may absorb hydrogen; When cathode maintenance is applied, overmaintenance can cause hydrogen uptake. If Fe-9% Nq alloy is used as a dedicated anode plate, titanium hydrogen absorption will not occur.

(4) Oscillation Because the titanium tube wall is thin, when replacing the copper alloy tube, you should also pay attention to the damage caused by the oscillation of the tube. This problem can be solved by using a method that is smaller than the distance of the tube support plate of the copper alloy tube.