Welding and corrosion repair measures for titanium metal

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bg1.png Titanium has an appearance very similar to that of steel; its density is 4.51 grams per cubic centimeter, which is less than 60% of that of steel, making it the metal element with the lowest density among the refractory metals. 　　Titanium is very stable in air at room temperature. When heated to 400–550°C, a strong oxide film is formed on the surface, serving as a protection against further oxidation. Titanium has a strong capacity to absorb oxygen, nitrogen, and hydrogen; these gases are harmful impurities for metallic titanium, and even trace amounts (0.01%–0.005%) can significantly affect its mechanical properties. 　　Titanium is highly resistant to corrosion in wet chlorine, which is why its use is increasing in the chlor-alkali industry. However, if damaged titanium equipment is not repaired properly, it will inevitably lead to rapid damage during further use; therefore, sufficient attention should be paid to the welding repair of titanium. 　　Titanium is highly reactive; at temperatures above 600°C, it reacts with O2, H2, and N2 to form TiO2, TiO, TiH2, and TiN2. If the sheet metal is not cleaned thoroughly, titanium will react chemically with oils, cotton fibers, and similar substances on the sheet metal during high-temperature welding, resulting in the formation of TiC. The above compounds are hard and brittle, causing titanium to lose its plasticity at room temperature and compromising its mechanical properties. 　　Oils and cotton yarns are hydrocarbons; the high temperatures associated with welding cause these hydrocarbons to decompose, producing H2. When this hydrogen penetrates into titanium materials, it can lead to hydrogen embrittlement. Hydrogen is also one of the causes of weld porosity. It is very harmful for metals such as titanium to contaminate the surface of titanium or to be incorporated into titanium materials during manufacturing. Therefore, it is necessary to isolate the atmospheric pollutants, while simultaneously thoroughly cleaning the titanium material to remove surface oils, rust, and oxides. 　　Titanium has a thermal conductivity 5 times lower than that of iron, and 23 times lower than that of copper, with a melting point of 1660°C. Therefore, HanTieShi needs to strengthen the cooling system to prevent the expansion of the heat-affected zone and avoid grain growth ； Prevent a decrease in the plasticity and strength of the weld. 　　The cleaning quality has a decisive impact on the welding quality; the oxide layer formed when titanium reacts with oxygen in the air can hinder smooth welding. Using a copper wire brush and gauze will only damage the oxide layer without removing it completely; only acid washing can eliminate it entirely. Each acid wash reduces the thickness of titanium by about 0.08 mm. 　　Recommended pickling solution formula (by weight ratio): http://www.oilequipcn.net/data/attachment/forum/201502/05/133722uaj1c0vzz4zxmh0c.jpg The titanium material should be immersed in the acid solution for 2–5 minutes, until it gains a metallic luster. After removal, it should be rinsed thoroughly with clean water and dried. The acid pickling temperature should be below 60°C. To prevent H2 generated during acid pickling from reaching the surface of the newly formed titanium, the concentration ratio of HF to HNO3 in the mixture is set at (1:5) to (1:7); HNO3 is used to immediately passivate the surface of the newly formed titanium.