In mid-June, Wuhan Bojin New Material Technology Co., Ltd. successfully welded 10 mm diameter titanium welded pipe in a single trial run on a high frequency induction welding experimental line with independent intellectual property rights using 0.5 mm thick titanium strip coil. The welding speed is over 80 m/min, which is 10 times higher than that of argon arc welding. The welding seam is smooth, high precision, no pore, stable quality, and the yield is over 96%. After the product is off-line, the strength of the welding seam is basically equal to that of the base metal. Before that, Wuhan Bojin New Material Company has completed the trial production of thin-walled and ultra-thin-walled copper alloy and stainless steel welded pipes, with a minimum wall thickness of 0.13 mm and a maximum welding speed of more than 150 m/min. Authoritative test reports show that the product width, height, thickness, shear accuracy, flatness, verticality and other accuracy indicators are in line with EU standards. The relative standard deviation of the measured burst pressure of any sample of welded pipe is not more than 10%. After welding these metal strips into pipes, various performance tests prove that the high frequency induction welding technology studied by the company can be applied to the production of thin-walled titanium, copper, stainless steel and other metal thin-walled welded pipes, and the welding speed is fast, the efficiency is high, the quality is good, which is conducive to the production of high-quality and low-cost thin-walled metal welded pipes.

Titanium pipes have excellent seawater corrosion resistance and are widely used in the manufacture of condensers and heat exchangers for seawater cooling medium in coastal power plants, nuclear power plants, seawater desalination, petrochemical industry, etc. Compared with titanium seamless tubes, titanium welded tubes are selected by more enterprises because of their thinner wall, uniform thickness, less fouling, high heat transfer coefficient and high production efficiency.

At present, compared with Japan, France, Korea, the United States and other advanced countries, there is a big gap in the titanium welded pipe industry in China. In addition to the backward localization and high cost of raw materials for titanium strip coil in the past few years, the more important reason is that the process level, production efficiency, product quality and product specifications of titanium welded pipe production are still lack of international competitiveness.

The existing domestic production lines of titanium welded pipes all adopt argon arc welding technology, and most of them are imported pipelines, so the technology digestion is not complete. There are some limitations in argon arc welding, such as slow heating speed, wide heat affected zone, inadequate extrusion force after welding, low density of weld structure and slow welding speed. When it is used to weld titanium welded pipe, either the welded zone is not easy to form a molten pool, or it is easy to form a variety of low melting point eutectic and hydrogen pore, or it is difficult to complete the welding, or the welding quality is difficult to guarantee, and it is easy to produce hot cracks, deformation and corrosion resistance decline. This is mainly due to the low density of titanium, low thermal conductivity, easy to produce coarse grains in the weld zone, the formation of superheated structure and the decrease of plasticity. The brittle titanium martensite is easy to be produced when the welding cooling is faster, which also makes the plasticity of the welded joint decrease. Titanium has small elastic modulus, large welding deformation, large resilience of cold deformation and difficult forming. In the process of melting, titanium will react with gaseous elements hydrogen, oxygen, nitrogen and carbon to form compounds, which seriously affects the mechanical properties and corrosion resistance of welded joints.

High frequency induction welding is based on the basic principle of electromagnetic phenomena, which makes the welded base metal produce induction current. Then the skin effect and proximity effect of high frequency current are used to make the induction current highly concentrated at the edge of the welded base metal, and the resistance heat of the material is used to heat the base metal to the welding temperature in a very short time. Then the pressure welding is carried out under the extrusion force of the extrusion roll.

High-frequency induction welding belongs to a solid-state welding method. It uses induction ring outside the welded pipe, without touching the plate, only produces a very small molten pool, so that the edge to be welded can reach a hot melting state, and the upsetting force can be applied rapidly to realize solid-state connection between metals under the strong extrusion force. As long as the current density at the edge of the billet is suitable and the heating speed is too fast, the heat affected zone of the weld is too small, the metal bonds with compact grains can be formed and the performance of the weld can be enhanced. Secondly, the melting point of metal oxides and impurities is generally higher than that of metal itself, and the viscosity of liquid metal oxides or impurities is generally higher than that of liquid metal. In the process of welding extrusion, these metal oxides and impurities will be extruded to form a good weld structure.

Titanium and titanium alloys, like copper and copper alloys, belong to non-magnetic materials. The welding speed of high frequency induction welding is much higher than that of magnetic materials. Otherwise, there will be difficulties in welding and poor weld formation. Because of the strong extrusion during welding, the weld grain is refined and uniform, and becomes a fine forging structure. The faster the welding speed, the smaller the weld grain size and the larger the enlargement rate after welding. High frequency induction welding technology has significant advantages in the field of thin-walled and ultra-thin-walled non-ferrous metal pipe manufacturing, which is obviously better than other welding processes. Especially suitable for welding eutectic and porous titanium and titanium alloys, copper and copper alloys, as well as super stainless steel and other special materials which are prone to phase transformation.

The industrial high frequency induction welding pipeline independently developed by Wuhan Bojin New Material Science and Technology Company has completed the independent design of various non-standard components and commissioned customization. It is expected that the integrated commissioning will begin in September this year and will be put into production formally in October. At present, there are more than 10 intentional customers. The products in demand include thin-walled and ultra-thin-walled titanium welded pipes, copper alloy welded pipes, stainless steel welded pipes, internal threaded welded pipes, etc.