In recent years, the standardized production of titanium pipeline fittings has emerged in China, which is also a revolution in the application of titanium pipeline.In this paper, the development history of standard titanium pipe fittings in China, the working conditions of titanium pipe fittings and the titanium pipe fittings used in the past are analyzed and reviewed in detail.The birth and development of titanium pipe fitting standards at home and abroad as well as the production and standardization of titanium pipe fitting in China are introduced.
Comparison of production technology of titanium pipe fittings
China began in the 70 s in the civilian industry used in the chemical industry system of titanium, titanium as a corrosion resistant structure materials for use in the chemical plant, has established its status, and as the ideal material in chemical pipe for the transmission of corrosive media, the life of the pipeline depends on pipe fittings, titanium pipe fittings are also increasingly cause the attention of the engineering and technical personnel, especially the standardization of titanium pipes is more important.
1.1 working conditions of titanium pipe fittings first, let's analyze the working conditions of titanium pipe fittings:
Titanium pipeline is mainly conveying corrosive and dangerous medium, when the medium with corrosive medium through the titanium pipe fitting, the medium with a certain pressure, and the various parts of the pipe bearing pressure is not the same, to the most commonly used three kinds of pipe fitting (elbow, tee, reducing pipe) to analyze.
Elbow is one of the important fittings of various piping systems. It is not only used to change the direction of medium flow, but also to improve the flexibility of piping.When the medium through the elbow, with the pressure of the media directly into the back of the elbow, the media along the back flow to the outlet, so that the back of the elbow is under greater pressure and under severe erosion corrosion, indicating that the back load is greater than any part.
The working condition of the tee is similar to that of the elbow. When the medium passes through the tee, it is at the intersection of the branch road of the tee and the straight road, where the bearing pressure and erosion corrosion are greater than other parts.Branch of the main pipeline pressure relief shunt state.
The working condition of reducing pipe is that the medium usually flows from the big end to the small end when passing through reducing pipe. Due to the gradual reduction of cross-sectional area, the cone of reducing pipe is pressurized, and the inner surface of the cone not only bears large pressure but also suffers serious erosion and corrosion.
The above analysis shows that the titanium pipe fitting is an extremely important part of the titanium pipe, which directly affects the life of the titanium pipe.
1.2 Common titanium pipe fitting production process
1.2.1 multi-weld titanium elbow
At the beginning of the use of titanium pipes in China, there was no domestic manufacturer to produce standard titanium pipe fittings, so people had to adopt the multi-weld type (commonly known as "shrimp waist" type) titanium elbow, which has complicated processing technology.It is usually used to cut the pipe into multi - section oblique, welding or plate gold into a multi - section blade - shaped expansion material, and then roll welding, the amount of weld.Due to the discontinuous geometry of the welds, higher stress concentration will be generated, so the working pressure and working temperature of such fittings must be strictly regulated.The welding seam can greatly reduce the corrosion resistance, leak easily, and the appearance is poor, the inner surface is folded and increases the pipeline transmission resistance, and the back of the welding seam is seriously eroded and reduces the service life.
1.2.2 welding tee
Tee to take in the straight pipe hole, will branch direct pipe welding, because the processing performance of titanium is not as good as other materials, welding the intersecting line processing is also quite difficult.More importantly, the welding seam produces a right Angle, one is a serious impact on the flow of the medium, increase the transmission resistance of the pipeline, two is the intersecting line of the curve welding difficulties, three is the right Angle of the erosion corrosion increase, make the right Angle of the early loss.
1.2.3 plate welded titanium elbow
1. Upper die 2. Billet 3. Lower die
In order to improve the defect of the titanium bend of multiple welds, the titanium bend of half-plate welding is adopted.Compared with the multi-seam "shrimp waist" type, the welding seam is relatively less, and the welding seam is not face by erosion corrosion, but by erosion, so the corrosion resistance is better.
1.2.4 casting elbow
People try to get rid of welds, develop seamless titanium elbow, produced casting elbow, although appear with seamless elbow, but wall thickness (at least 5mm) and pipe wall thickness (2 ~ 4mm) can not match, and surface finish is poor, and increase transmission resistance.More importantly, there are a large number of internal defects caused by casting, such as porosity, which seriously affect the corrosion resistance and service life, so it is not suitable for the use of welded titanium pipes, most of which are used in the small diameter of the seed-type pipe fittings. The cost of titanium pipe fittings produced by this process is high and cannot be recognized by users.
1.2.5 punching titanium elbow
Some people use the stamping method to punch titanium elbow, the appearance seems to meet the standard requirements, but from the essence, the processing technology is the tube blank in the punch die stamping forming, forming the back of the elbow by tension, forcing the back to pull thin, abdominal wall compression and thickening resulting in uneven wall thickness or wrinkle.And in the process of using because of the back of the elbow to bear erosion corrosion, because the back wall thin, so the back will produce early damage.It is difficult to guarantee the wall thickness, its pressure and life are not up to the standard of the wall thickness tolerance requirements, try not to use this process produced titanium elbow.
1.2.6 pushing technology
How to improve the life of titanium pipeline?To improve the service life of titanium pipe fittings has become a major academic problem in the field of pipeline design technology.
Elbow extrusion technology is a new technology of steel elbow production introduced into China by Japan in the mid and late 1980s.Because the process can achieve continuous production, and the elbow wall thickness is uniform, it quickly replaced the traditional process.And successively developed titanium seamless tee, seamless reducer titanium seamless pipe fittings products, such as seamless pipe diameter Φ 219, and reached the ASTM B363-95 standard requirement.
Processing of titanium elbow push system based on titanium seamless pipe as blank, the push system of extrusion machine adopts the pipe diameter is less than the finished product diameter of billet extrusion, the forming die fixed motionless on a host computer, an activity thrust push pipe from the right direction to the left, when billet forming dies, are under the protection of heating and forming process of tube billet by expansion, in the process of forming force analysis show that the stress from different parts of the size is different, but are two to compression, tension, the axial compression, compression of the radial and circumferential tension.During the whole deformation process, diameter gradually increased, bending, length shortened and thickness basically remained unchanged.The experimental results of network method show that the deformation of the elbow mainly occurs in the lower part.The blank was painted with a uniform grid. During the forming, it was observed that the grid did not change much during the forming of the back of the elbow. The more serious the abdominal deformation was, the grid was lengthened in the circumference and compressed in the axial direction, while the total area of the grid remained unchanged, indicating that there was no significant change in the direction of thickness.