Analysis of titanium welded pipe in salt making equipment and its application background
Titanium has the advantages of low density, high yield ratio, good heat resistance, low temperature resistance and heat transfer performance, especially good corrosion resistance in neutral and oxidizing media. It is widely used in many fields such as seawater desalination, electric power industry, petrochemical industry, aviation, aerospace industry, shipbuilding industry, military industry and so on It has a history of more than 40 years. At present, the world’s technologically advanced countries have basically replaced the titanium seamless pipe with titanium welded pipe, while in China, the titanium seamless pipe is still the main one. For a long time, due to the constraints of titanium strip production, pipe forming technology and welding technology, all titanium welded pipes rely on import. Due to the high price, the application field of titanium welded pipe is greatly limited. In recent years, in order to break the technical monopoly of foreign manufacturers on titanium welded pipe, a number of domestic powerful titanium production enterprises have invested a lot of capital and manpower in R&D, introduction and absorption, and conquered the production technology of titanium welded pipe. Now domestic titanium welded pipe has been gradually applied in various fields of national economy.
Comparison of technical indexes between titanium welded pipe and titanium seamless pipe
According to ASTM B338 standard of USA and GB/T 3625 standard of China.
(1) Chemical composition index (taking industrial pure titanium as an example, the same below): the comparison results are shown in Table 1. The chemical composition requirements of titanium welded pipe and titanium seamless pipe are the same.
Table 1 Comparison of chemical constituents
| Other elements | ||||||||||
| Type | Reference standard | Grade | C | O | N | H | Fe | Single | Total | Ti |
| Titanium welded pipe | ASTM B338 | Gr.2 | 0.08 | 0.25 | 0.03 | 0.015 | 0.3 | 0.1 | 0.4 | Allowance |
| Titanium seamless pipe | GB/T 3625 | TA2 | 0.08 | 0.25 | 0.03 | 0.015 | 0.3 | 0.1 | 0.4 | Allowance |
(2) Mechanical property index:
The comparison results are shown in Table 2. In addition to different tensile strength requirements, other indexes of titanium welded pipe and titanium seamless pipe are the same. The tensile strength of the products provided by the actual titanium welded pipe manufacturer is more than 400MPa.
Table.2 Comparison of mechanical properties
| Mechanical property index | |||||
| Type | Reference standard | Grade | Tensile strength (Mpa) | 0.2% residual deformation yield strength (Mpa) | 50 mm elongation (％) |
| Titanium welded pipe | ASTM B338 | Gr.2 | ≥345 | 275-450 | 20 |
| Titanium seamless pipe | GB/T 3625 | TA2 | ≥400 | 275-450 | 20 |
(3) Process performance index:
The flattening test requirements of titanium welded pipe and iron welded pipe are the same, the flaring rate is the same, and the air pressure test requirements are basically the same.
In addition to the external diameter (d = 2R0) and wall thickness of the pipe, the constant e is slightly different. E is 0.85 for welded pipe and 1.0 for seamless pipe. However, both welded pipe and seamless pipe have the same maximum hydraulic pressure requirement. When the pipe diameter is not more than 76mm, the maximum pressure of hydrostatic test is not more than 17.2mpa; When the pipe diameter is greater than 76mm, the maximum pressure of water pressure is no more than 19.3mpa.
(4) Comparison of metallographic and performance indexes between weld and base metal of titanium welded pipe:
① The metallographic structure of the weld of titanium welded pipe is different from that of the base metal. The structure of industrial pure titanium is. The grain size of the base metal is uniform. The microstructure of weld is dendrite. The grain size of the base metal is larger than that of the base metal.
② Performance comparison between weld and base metal:
- a. The strength coefficient of welded joint is close to 100%, sometimes the weld strength is slightly higher than the base metal.
- b. There is hardness difference between weld and base metal. The hardness of weld and HAZ is slightly higher than that of base metal.
- c. After welding, the on-line heat treatment process is adopted. By optimizing the annealing parameters, the metallographic structure of the base metal, weld and heat affected zone is basically similar; through annealing treatment, the welding stress is eliminated, and the weld microstructure is homogenized, and the hardness is close to that of the base metal.
Comparison of economic indexes between titanium welded pipe and titanium seamless pipe
In order to produce the products of the same specification by three high cold rolling mill, at least two or more times of reciprocating rolling are required to meet the process requirements. Moreover, the surface of the tube needs to be degreased and pickled every time. The production process is complex and can not realize automatic continuous production. There are many transfer processes, which will damage the pipe greatly, yield and production Low efficiency, unable to achieve mass production, production cycle is relatively long.
Due to the degreasing and pickling process involved in the production process of titanium seamless pipe, the environment is seriously polluted. Undoubtedly, additional equipment and protective measures should be added in environmental protection, which is bound to increase capital investment and increase production cost. The cost of single tube is too high when the super large seamless pipe manufacturer produces small batch orders. Therefore, there is a big difference between the cost and delivery time between titanium welded pipe and titanium seamless pipe. The price of titanium seamless pipe is high and the supply time is long.
Compared with titanium seamless pipe, titanium welded pipe has the following advantages in economy:
- (1) High yield: titanium seamless pipe from sponge titanium to pipe, through rolling or drawing, the yield is only about 50%. In the process of rolling or drawing, the raw materials are wasted, so the material utilization rate is quite low and the production cost is high; while for the production of titanium welded pipe, the material utilization rate is usually about 80% from sponge titanium to welded pipe. If titanium strip is used as raw material, the material utilization rate is relatively low The utilization rate can reach more than 95%, the material utilization rate can be greatly improved, and the production cost is relatively reduced.
- (2) Thin wall and uniform wall thickness: after rolling or drawing process, it is difficult to achieve wall thickness less than 1 mm for Qinzhou seamless pipe, while wall thickness of 0.5 mm and less can be achieved for Qinzhou welded pipe, which saves a lot of materials and costs; moreover, titanium seamless pipe is difficult to achieve uniform wall thickness and poor concentricity, while cold rolled titanium strip is used for titanium welded pipe, and the difference between the same plate is very small, the wall thickness of the product is uniform and the concentricity is good.
- (3) Superior performance: with the continuous development of welding technology, the mechanical properties of titanium welded pipe have fully met the requirements of seamless pipe, and the weld strength and corrosion resistance have exceeded the performance level of base metal.
- (4) Good heat transfer effect: titanium welded pipe can achieve wall thickness of 0.5mm and below. Due to its thin wall, titanium welded pipe can obtain higher heat transfer coefficient than titanium seamless pipe, and its heat transfer effect is better under the same heat exchange area.
Application of titanium welded pipe
In the 1960s and 1970s, the United States, Japan, France, Russia and other countries have successively used titanium welded pipe in seawater desalination, electric power, chemical industry, salt making and other equipment. At present, foreign large-scale welded pipe companies mainly include Japanese steel company and Kobe Steel Company, France’s valtimet company, Russia’s vsmpo company; domestic large-scale welded pipe companies mainly include Xi’an BaoTi Meite Farino Welding Pipe Co., Ltd. (a Sino foreign joint venture company) controlled by Baoji Titanium Industry Co., Ltd., Hunan Xiangtou Jintian new materials Co., Ltd. (wholly owned by China), Chang’an State valino Welding Pipe Co., Ltd. (wholly owned by France), etc. These enterprises almost monopolized the titanium welded pipe market in China. In particular, Hunan Xiangtou Jintian New Material Co., Ltd., the largest domestic manufacturer of high-performance titanium welded pipe with an annual output of 5000 tons, has formed an adult production capacity of 2500 tons of titanium welded pipe, and provided more than 500 tons of products to the market last year alone. Now the domestic titanium welded pipe industry has become a vigorous development trend.
(1) Application of titanium welded pipe in seawater desalination
At present, distillation is the main method of seawater desalination in the world. Due to the pollution of seawater, the water quality is getting worse, so many countries and regions have adopted titanium welded pipe with strong corrosion resistance and long service life to replace stainless steel pipe. In the Middle East countries where the main project area is located, titanium welded pipes are almost all used for evaporator and heat exchanger of seawater desalination equipment. For example, in 2010, the 800000 tons of seawater desalination project in yanbu phase III of Saudi Arabia, Doushan of South Korea and fisia of Italy adopted titanium welded pipe with the specification of above medium 40, wall thickness of 0.7, length of more than 25 meters, and the total consumption of more than 6600 tons; the design of French SIDEM used titanium welded pipe with a thickness of 0.7.
The specifications are Φ19×0.7 and Φ22×0.7, and the consumption is more than 3000 tons. The history shows that Japan is one of the earliest countries to develop and apply thin-walled titanium welded pipe for seawater desalination. Only from 1967 to 1994, the production system of thin-walled titanium welded pipe was developed correspondingly. A desalination plant with a daily output of 100 tons of pure water needs 60000 titanium welded pipes. Since the use of titanium welded pipes, the relevant manufacturers of seawater desalination plants in Japan have used a total thousands of tons of titanium welded pipe.
(2) Application of titanium welded pipe in electric power industry
In the world power industry, Europe, America, Japan and other countries, when building coastal power plants in the 1970s, titanium welded tubes were used in the condenser equipment. Titanium condenser was used in China’s electric power industry since 1980s. In 1983, China began to develop thin-walled welded titanium tube condenser. In recent years, with the development of coastal economy in China, the construction of coastal thermal power station is speeding up, and the consumption of all titanium condenser is also increasing. Taking 200MW unit as an example, each unit uses about 28T titanium welded pipe. By the end of 1999, 27 domestic appliance plants and 96 units have used titanium condenser, with an installed capacity of 2.95x107kw and a total of 3100 tons of titanium welded pipe are used. The state has also clearly stipulated in the “Eleventh Five Year” electric power reform plan that the newly built coastal thermal power plant uses titanium welded pipe as the main raw material. Nuclear power is the key development area of China’s energy industry. As a kind of clean and environmental protection, it conforms to the national industrial policy and the direction of future energy development. Nuclear power plants are generally built in the sea, using sea water as the cooling medium. At present, titanium welded pipe is basically used as cooling pipe. Titanium welded pipes are generally thin-walled tubes with a wall thickness of 0.5-0.7mm.
(3) Petrochemical Industry
In the production process of petrochemical plants, a large number of heat exchange devices are needed, such as normal pressure test device, nitrogen cracking unit, heat exchanger of offshore oil platform, water treatment and water supply system, fire protection system, PVC heat exchanger, coil oxygen test and chlorination reactor, methanol synthesis reaction and other production devices. Because of the limitation of the corrosion resistance of stainless steel pipe, these devices use titanium welded pipe instead. Practice has proved that in petrochemical industry, the use of titanium welded pipe reduces the maintenance time and frequency, ensures the normal operation of equipment, and improves the competitiveness of enterprises. At present, the application of titanium welded pipe in petrochemical industry is gradually expanding.
(4) Application of titanium welded pipe in salt industry
Whether it is multi effect vacuum evaporation or hot pressed salt, a large number of tubular heat exchange equipment will be used, which is known as the heating chamber or preheater in the industry. Because of the strong corrosiveness of brine, in China, the carbon steel, stainless steel, red copper and copper nickel alloy heat exchange tubes used in the early stage have been replaced by titanium heat exchange tubes. Titanium heat exchange tubes have become the mainstream materials for designing heat exchange equipment in salt plants in China. According to the authoritative data released by China Salt Industry Association in March 2012, the production capacity of well and mineral salt area in 2011 was 46.45 million tons. If the area of heat exchange equipment corresponding to this capacity is converted into the consumption of titanium heat exchange tube, it is estimated that it should be more than 3000 tons. Due to the high recognition of China’s salt making industry to the domestic titanium seamless pipe led by Baoji industry, titanium welded pipe has not been applied. In contrast, titanium welded pipes have been used by salt factories in the United States, Europe and Japan. For example, in the sakaku plant of diamond Salt Co., Ltd., which was built in the mid-1970s, Φ42.7×0.7×7450 and Φ44.1×0.7×7450 titanium welded pipes were used as heat exchange tubes in heating chamber; in halingen salt plant in the Netherlands, which was built in the mid-1990s, Φ138.8xo.889×8580 titanium welded pipes were used as heat exchange tubes in heating chambers. The author believes that the root cause of this phenomenon is that the domestic salt industry lacks a comprehensive understanding of the new material, titanium welded pipe, and there are cognitive problems; moreover, titanium welded pipe is imported, which has only started domestic production in recent years, although the performance is excellent, the price does not occupy an advantage.
Titanium welded pipe is widely used. In addition to seawater desalination, electric power, petrochemical and salt making, it is also used in shipbuilding, aviation, aerospace industry, automobile industry, food hygiene, sports industry and military industry.
Conclusion
Titanium welded pipe adopts cold bending forming technology and welding technology. After environmental protection and energy-saving treatment, it has excellent characteristics that titanium seamless pipe can’t match
- (1) In terms of performance, there is no difference between titanium welded pipe and titanium seamless pipe.
- (2) In terms of appearance quality, titanium welded pipe is far better than titanium seamless pipe. Titanium welded pipe is welded by cold rolled titanium strip, with uniform wall thickness, good finish, and is not easy to scale in the pipe. Especially for thin-walled titanium pipe, seamless rolling process can not meet the requirements.
- (3) In terms of product length, the product length of titanium welded pipe is relatively unlimited, but the length of titanium seamless pipe is greatly limited due to the influence of rolling mill itself.
- (4) In terms of energy conservation and environmental protection, cold bending forming technology and welding technology are adopted for titanium welded pipe. There is no waste gas, waste water and other objects discharged in the production process. The production process is environmentally friendly and energy-saving. A large amount of lubricating oil is required in the rolling process of titanium seamless pipe, and degreasing and pickling are required after rolling, which will inevitably have a certain impact on the environment and operators.
In a word, titanium welded pipe has obvious advantages in aviation, aerospace, seawater desalination, petrochemical, salt making and power industry with high corrosion. In recent years, the price of titanium welded pipe has changed from much higher than that of titanium seamless pipe to nearly close to that of titanium seamless pipe. Now, China’s professional titanium welded pipe production has formed an annual capacity of about 6000 tons. We have reason to believe that with the progress and maturity of titanium welding technology, titanium welded pipe will gradually replace titanium seamless rolling pipe, and it is inevitable to realize the production of titanium welded pipe in large quantity, high efficiency, high precision and low cost. The titanium welded pipe with high quality and low price will be accepted by the majority of Chinese salt industry users.
Author: Zeng Qingnan
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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