China titanium piping solution supplier: www.titaniuminfogroup.com

Selection of titanium pipe fittings

In this paper, the development of domestic standard titanium pipe fittings and the application of titanium pipe fittings are analyzed and reviewed, and the titanium elbow extrusion process is introduced to ensure uniform wall thickness.

Titanium pipeline conveying are flammable, explosive, toxic and corrosive media, there is a great deal of insecurity, so the requirements of titanium fittings are higher. At present in China, titanium pipeline has been widely used in chemical, petrochemical, pharmaceutical, marine engineering and other industries. Application in the serious corrosion of media more, such as ion membrane caustic soda, propylene oxide project, and formic acid, acetic acid, and methane chloride projects are used in titanium pipeline transport media, to solve the problem of pipeline corrosion [1].

1. Comparison of the production process of titanium pipe fittings

China began to use titanium in the civil industry in the 1970s in the chemical system, titanium pipeline life depends on the fittings, especially the standardization of titanium fittings is more important.

1.1 Commonly used titanium butt weld fittings type

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Figure.1 Titanium Elbow

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Figure.2 Titanium Tee
China’s titanium pipeline using the early domestic manufacturers do not produce standard titanium pipe fittings had to make people use multiple welded seam type commonly known as shrimp waist type) titanium elbow see Figure 4, it is a complicated processing. Usually used to cut the pipe into multiple sections of beveled, welded or plate gold into multiple sections of leaf-shaped unfolded material, and then rolled and welded, the amount of welded seam. Because the geometry of the weld is not continuous, will produce higher stress concentrations, therefore, the working pressure and working temperature of such fittings must be made strict provisions. The weld will greatly reduce the corrosion resistance, easy to leak, and the appearance is not good, the inner surface is folded and increases the pipe transmission resistance and the back of the weld is subject to serious scouring corrosion and reduce the life.

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Figure.3 Titanium Concentric Reducer

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Figure.4 “Shrimp waist” type titanium elbow

1.2 Welding tee

Tee as shown in Figure 5 to take a hole in the straight pipe, the branch direct pipe welded into, because the processing properties of titanium is not as good as other materials, the processing of the coherent line at the weld is also quite difficult [3]. More importantly, the right angle at the weld, one is a serious impact on the flow of media, increasing the transmission resistance of the pipeline, the second is the curve of the coherent line welding difficulties, the third is the right angle part of the scouring corrosion increases, so that the right angle part of the early loss.

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Figure.5 Welding Equal Tee

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Figure.6 Titanium elbow stamping forming
1. upper die 2. blank 3. lower die

1.3 Pressed sheet welded titanium elbow

In order to improve the defects of multi-weld titanium elbow, the pressed half piece welded titanium elbow is used. It is compared with the multi-seam “shrimp waist” type, welding seam correspondingly less, and the weld seam is not face to face by the scouring corrosion, but in the direction of the scouring, and therefore better corrosion resistance.

1.4 Casting type elbow

Attempts to get rid of the weld, the development of seamless titanium elbow, resulting in casting elbow, although the emergence of seamless elbow, but the wall thickness (at least 5 mm) and the pipe wall thickness (2 mm) can not match, and the surface finish is poor, and increase the transmission resistance. More importantly, there is a large number of internal defects such as porosity generated by the casting, seriously affecting corrosion resistance and life, not suitable for the use of butt-welded titanium pipeline, mostly used in small diameter seeded pipe fittings, the production of titanium pipe fittings of this process is costly, not recognized by users.

1.5 Stamping titanium elbow

Some people use stamping methods to punch titanium elbow, the appearance seems to be almost standard requirements, but from the substance, the processing is (see Figure 6) billet in the punch press stamping mold, the forming process will be the back of the elbow is pulled, forcing the back of the book, the abdominal wall is pressed and thickened resulting in uneven wall thickness or wrinkle. And the use of the elbow back to withstand scouring corrosion (see Figure 1), due to back wall thinning, so the back will produce early loss. Wall thickness is difficult to ensure that its pressure and life can not meet the standard wall thickness tolerance requirements, try not to use this process of production of titanium elbow.

1.6 Pushing process

Elbow push extrusion process is a new technology for the production of steel elbows introduced into China by Japan in the mid to late eighties. Because the process can achieve continuous production, and the production of elbow wall thickness uniform, so it quickly replaced the traditional process [4]. Northwest Nonferrous Metals Research Institute was the first to successfully develop this new technology in the early 1990s with the development of pushed seamless titanium elbows. Seamless titanium tee, seamless reducer and other seamless titanium pipe fittings have been developed successively [5], and the maximum diameter of seamless pipe fittings can reach 219 and meet the requirements of ASTMB363-95 standard [6].
Push titanium elbow processing is seamless titanium tube as a billet, in the special push extrusion machine using a billet diameter less than the finished pipe diameter push extrusion molding, as shown in Figure 7 forming die fixed in the main machine does not move, there is a certain activity thrust to push the billet from the right to the left, the billet in the forming die, heated and protected, the forming process of the billet is expanded, the forming process force analysis shows that the different parts of the The force analysis of the forming process shows that the size of different parts of the force is different, but all are two-way pressure, a tensile, that is, axial pressure, radial pressure, circumferential tension. The deformation of the whole forming mainly occurs in the lower part (see Figure 8). Uniform grid drawn on the bad material, forming can be observed in the back of the elbow when forming little change in the square grid, to the abdomen the more serious deformation, the grid in the circumferential direction is elongated, axially compressed, while the total area of the grid remains unchanged, indicating that there is no significant change in the direction of thickness.

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Figure.7 Titanium elbow forming force diagram

2. China’s titanium pipe fitting standards and specifications

Titanium fittings standards first appeared in the U.S. Aerospace standards, the chemical industry’s titanium fittings in the international can find the only standard is ASTM B363 [5]. It is also a document often followed in the international trade of titanium fittings, ASTM B363 was established in 1961, the first revision in 1978, after several revisions (such as 83, 87) the most recent version is 1995, so that the standard is more complete.

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Figure.8
In 1994, China introduced the enterprise standard Q/XB 1507-94 “Titanium Butt-welded Seamless Pipe Fittings” by the Northwest Institute of Nonferrous Metals. Warmly welcomed by the design sector, the introduction of the standard represents the start of standardization of titanium fittings in China.
In order to make the standard can better guide China’s standardized production of titanium fittings, design selection, procurement distribution, installation and construction, the National Petroleum and Chemical Industry Bureau issued on July 13, 1999, the industry standard for titanium butt-welded seamless fittings, this standard was drafted by the Northwest Institute of Nonferrous Metals, standard number HG/T 3651-1999, has been implemented since June 1, 2000 the standard provides The dimensional tolerances of the fittings are equivalent to the American National Standard ANSIB16.9-1986 forged steel butt-weld fittings and our national standard GB12459-90 steel butt-weld seamless fittings, and the requirements of the fittings and the material properties of the finished fittings and the surface quality of the fittings are equivalent to the American Society for Testing and Materials standard ASTMB363-95 seamless and seamed titanium alloy butt-weld fittings.

3. Conclusion

  • (1) In order to ensure the life of the pipeline, titanium fittings should be preferred to seamless fittings, elbows should try to choose the production of pushing process, which can ensure uniform wall thickness, smooth and unobstructed surface.
  • (2) Should eliminate the choice of shrimp waist type elbow and tee in the pipeline directly welded straight pipe, this method of connecting the titanium pipeline will seriously affect the life of titanium pipeline.
  • (3) Titanium fittings have our industry standard HG/T 3651-1999, design, procurement, construction should be carried out in accordance with the standard.

Author: Dai Hongwei, Luo Jinhua, Zhou Zhaoqun

Source: China Titanium Pipe Fittings Manufacturer: www.titaniuminfogroup.com

Reference:

  • 1. Shi Yufeng, “Titanium Technology and Applications” published by Shaanxi Science and Technology Press 1989.12
  • 2. Xu Sihao, “Chemical Equipment and Piping” 2001.4
  • 3. Huang Jian, “welding” 1996.12
  • 4. Zhi Zuo, “Mechanical Engineer” 1996.1
  • 5. Dai Weihong, Duan Wensen, “China Chemical” published by China Patent Press 1998.11. American Society for Testing and Materials Standard ASTM B363-95
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