Zirconium is a very lively chemical properties of the elements, in the high temperature is very easy to react with all kinds of gases in the atmosphere, corrosion resistance, in petroleum, Zirconium chemical, nuclear energy and other industries are used. In zirconium welding, Zirconium weld and heat affected areas are easily polluted by oxygen, hydrogen and nitrogen in the air, producing hard and brittle compounds, and producing brittle needle-like tissue, so that the hardness, strength, plasticity and corrosion resistance of welded joints are decreased. Therefore, the zirconium welding should be fully protected from the molten pool, weld seam and heat affected zone to completely isolate the air. The welding of zirconium materials is generally tungsten inert gas shielded welding, Zirconium other welding methods include: electron beam welding, plasma arc welding and resistance welding. Its welding performance and titanium metal welding are relatively close, because of the thermal expansion coefficient and elastic modulus of zirconium, welding deformation and weld residual stress is relatively small. In the case of no contamination, the weld seam is not easy to appear crystal crack and cold crack. Zirconium at high temperature is generally easy to react with the atmosphere, in 200 Shan began to absorb oxygen, 300 Shan absorption of hydrogen, 400 Shan absorption of nitrogen, Zirconium the higher the temperature of the intensity of the reaction more intense. Another major problem with zirconium welding is that the weld seam is too easy to soften and leads to a dislocation of the weld, the root weld is easy to burn, so when welding zirconium, it should be suitable to fix the welding pieces and to use double-sided welding as far as possible. Zirconium cannot be directly welded with other metals except titanium, niobium, silver and vanadium.
The Tungsten Argon arc welding of zirconium and zirconium alloy is used as the welding wire. Its appearance must be smooth, round, not allowed to exist burr, wrinkle, overlap, cracks, Zirconium pores and other defects, when necessary metallographic microscopic examination, do not allow the existence of segregation, slag and other defects. The following table is commonly used in zirconium and zirconium alloy welding wire recommended.
(1) The establishment of special prefabricated sites, while the welding site should be kept clean and dry.
(2) The ambient temperature should be greater than 5 Shan
(3) Welding site is strictly prohibited to have ferrous metal welding, cutting, grinding and other work.
(4) on-site welding should be windproof, rain prevention measures, Zirconium when the wind speed is greater than 0./, relative humidity is greater than 80%, prohibit the application of welding.
The material and specification should be checked before the zirconium material pipe is cut, and the transplant of material mark should be done. Should use non-corrosive marking pen, forbid to hit the seal. Zirconium material cutting should use mechanical methods, if the use of plasma or grinding wheel cutting, Zirconium cutting pipe rotation, so that it is always in the best position, the use of plasma cutting should take measures to protect the inside and outside the tube surface, in order to prevent the surface by spark burns, and mechanical methods to remove the pollution layer. Clean the dirt on the tool regularly before each use. Zirconium material pipe no matter with mechanical processing or sawing, should also use a file to repair the incision, and then use stainless steel brush or electric stainless steel wire wheel and other tools, further processing, so that the groove surface smooth, no burr, pits, Zirconium sand and other defects. In the process of pipe and fitting, no strong group is allowed, no hammering or scratching of material surface is strictly prohibited.
Because the liquid metal fluidity of the zirconium material is very good, the pipe Groove group should be in strict accordance with the technical instruction book in order to avoid burning when welding. The technical measures and welding materials of pipe fitting welding shall be consistent with the formal welding, Zirconium the height of the spot welding shall not exceed 2/3 of the thickness of the pipe wall, and the weld seam shall not have any defects such as cracks, pores or oxidation discoloration which are not allowed to exist, or should be polished.