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Characteristics of Seamless Titanium Alloy Pipe and Welded Titanium Alloy Pipe


Titanium pipes are mainly divided into seamless titanium pipes and welded titanium pipes. In recent years, with the improvement of the rolling mill and automation level, the specifications of seamless titanium pipes have been further expanded, and the dimensional accuracy and product quality have been further improved, thus producing more characteristic products to meet the needs of different industries. Meanwhile, the concentration of the titanium industry is not high at present. Production enterprises should gradually carry out equipment transformation and upgrading based on existing equipment, actively seek cooperation, cooperate with large metallurgical equipment manufacturers to expand the product specification range using large-scale equipment, develop new products, and improve product quality.


In terms of titanium welded pipes, with the establishment of titanium strip production lines and the improvement of strip production technology, the quality of strip products has steadily improved, resulting in a reduction in the production cost of titanium welded pipes and stable prices. As the welding quality of titanium pipes improves, the market share of titanium welded pipes will be further expanded, gradually replacing the use of seamless titanium pipes.


1.Common Welding Methods for Titanium Alloys


1.1 Metal Inert Gas (MIG) Welding


Metal Inert Gas (MIG) welding uses argon as a shielding gas and a consumable wire electrode for melting. Its characteristics include high deposition rate, minimal welding deformation, suitable for welding medium-thickness titanium materials, and using direct current reverse connection. Although MIG welding has the advantages of high productivity and minimal welding deformation, during the welding process, the molten droplets transition in fine granular form, making the filler metal susceptible to impurity contamination, resulting in relatively severe spattering issues, which affect weld bead formation and gas shielding effectiveness, making weld bead formation inferior to Tungsten Inert Gas (TIG) welding.


1.2 Laser Welding


Laser welding utilizes the high energy density, good coherence of electromagnetic energy, strong monochromaticity, and good directionality of lasers for welding. Laser welding focuses a powerful light source on a very small area, melting the metal in that area to achieve material connection. To avoid the influence of impurities such as oxygen, hydrogen, and nitrogen, argon gas is used for protection during laser welding. Laser welding of titanium alloys results in a small heat-affected zone, minimal workpiece deformation, and accurate welding. During welding, it can be done through a glass window without direct contact with the welding area, unaffected by magnetic fields, requires no welding filler material, has a short welding time, and many scholars at home and abroad have studied laser welding of titanium alloys such as TC4, proving that laser welding is an effective method for welding titanium alloys.


1.3 Resistance Welding


Titanium has a high electrical resistivity and low thermal conductivity, making it relatively easy to perform resistance welding. Resistance welding utilizes the heat generated by electric current passing through the resistance between welding contact surfaces while applying pressure to the welding joint. When resistance welding titanium plates, inert gas protection is not required because the welding surfaces are already in close contact under pressure, less susceptible to atmospheric contamination. Flash welding can be used to weld tubular titanium materials. However, the tensile strength and fatigue strength of resistance welded joints are significantly lower than those obtained by methods such as TIG welding and electron beam welding. Additionally, the high cost of resistance welding equipment also limits its application.


2. Production Process and Product Characteristics Analysis of Seamless Titanium Pipes


Currently, the titanium seamless pipes produced on the market generally adopt the cold rolling and vacuum annealing process. Titanium ingots are forged into bar blanks, which are then processed into pipe blanks. The pipe blanks undergo multiple rolling and annealing processes to finally form seamless titanium pipes. In the production of pipe blanks, there are mainly two production processes. One method is hole drilling and extrusion for producing pipe blanks. This method consumes a large amount of titanium metal, and the pipe wall thickness is uniform. Selecting the appropriate glass lubricant is crucial during extrusion, and a large tonnage extruder is required, resulting in significant equipment investment. Another method is inclined piercing, commonly used in steel pipe production. This method consumes less titanium metal, but the pipe wall thickness tolerance is slightly larger. Sometimes, there may be a phenomenon of failure to penetrate during piercing, where the tip gets stuck in the blank material. This is a technical problem worth researching in current production technologies.


Although the processing technology of titanium alloy seamless pipes is relatively mature, due to limitations in existing equipment, titanium pipe materials are mainly low-strength and low-alloyed pure titanium, titanium-molybdenum-nickel, and other medium to low-strength titanium pipe materials, with cold rolling as the main processing technology. The production of medium to high-strength titanium alloy pipe materials, such as Ti-6Al-4V pipe materials, requires the use of hot rolling technology, adding induction heating devices to the pipe rolling mill for further heating of the titanium pipe before rolling.


3. Production Process and Product Characteristics Analysis of Welded Titanium Pipes


Titanium welded pipes, as a relatively unique titanium pipe product, are produced by supporting the pipe shape with cold-rolled titanium coils and then welding them using tungsten inert gas shielded welding. Due to the excellent corrosion resistance of titanium materials, titanium welded pipes gradually replaced stainless steel and copper alloy pipes as the preferred materials for condensers and heat exchangers after their introduction to the market. They are widely used in coastal power plants, seawater desalination, offshore oilfields, and other applications requiring seawater as a cooling medium.



Compared to seamless titanium pipes, welded titanium pipes can be used to manufacture pipe fittings with thinner walls, with a minimum wall thickness of 0.3 to 0.5mm, while the minimum wall thickness of seamless titanium pipes is around 0.9mm. Additionally, welded titanium pipes have high raw material utilization rates, high production efficiency, and good economic benefits. Moreover, due to the characteristics of long length and stable performance, there is a great demand for thick-walled titanium welded pipes in industries such as petrochemicals. Although some progress has been made in the development of thick-walled titanium welded pipes domestically, the industrialized production technology of thick-walled titanium welded pipes is still immature, which will be the next development direction of titanium welded pipes.


With the stable supply of titanium strips and further cost reductions, the competition in the titanium welded pipe market has become more intense. Prompted by the rapid changes in the supply situation of titanium strip raw materials and the expected stimulation of China's nuclear power construction plan, mainland China has witnessed a strong investment boom in titanium welded pipe production lines since 2008. According to incomplete statistics, more than 50 production lines have been built with a production capacity exceeding 12,000 tons. Customs data shows that China imported 3,032 tons of titanium welded pipes in 2010, but with the outbreak of the financial crisis and the Fukushima nuclear power plant accident, the welded pipe market suddenly entered a downturn. In 2011, China only imported 2,300 tons of welded pipes. Currently, the quality of domestically produced titanium welded pipes still needs to be improved, and the market prospects are promising. It can be foreseen that the cost advantage of titanium welded pipes will promote their partial substitution for seamless titanium pipes in the future.


4. Welding Process and Inspection of Titanium Pipes During Construction


During the construction process, implementing the welding process of titanium pipes should focus on two key aspects: the skill level of the welder and non-destructive testing of the weld seam, which must be strictly carried out in accordance with relevant national regulations.


When carrying out the welding process of titanium pipes, it is essential to first prepare for construction, including cleaning the welding components and selecting the base material. Based on the specific construction conditions, appropriate welding techniques should be chosen, and necessary construction materials and equipment should be prepared to ensure that the construction materials pass quality inspection and that the construction equipment operates normally.


After completing the welding work, the titanium pipe should be inspected according to the requirements of the titanium pipe welding inspection specifications. Post-weld inspection should also include a visual examination of the weld seam to observe any phenomena such as undercut, porosity, etc. It is important to assess whether defects such as cracks and inclusions exist to ensure the quality of the welded titanium pipe seam.


Furthermore, the weld seam of the titanium pipe should maintain smoothness within 1.5 millimeters. When inspecting the coloration of the titanium pipe, the outer surface and both sides of the base material are typically examined for the presence of porosity, cracks, etc.


Additionally, post-weld radiographic inspection of the titanium pipe should be conducted according to the appropriate radiographic inspection methods, and the results should be graded according to standards. Subsequently, pressure and leak tests should be performed to ensure the success rate of titanium pipe welding.


In conclusion, strengthening research on the welding process of titanium pipes during the construction process, as well as non-destructive testing of the weld seam, will play a positive role in quality control of welded titanium pipes and their promotion.


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