China titanium piping solution supplier: www.titaniuminfogroup.com

Pickling process of industrial pure titanium pipe

In the production process of industrial pure titanium pipe, pickling is a very important process, which can not be ignored. In the process of thermal processing or heat treatment, titanium tubes will chemically react with oxygen and other gases in furnace gas without protective atmosphere to form oxide layer. The oxide layer formed on the surface of titanium pipe is very harmful not only to each process after pickling, but also to the quality of the final product.

20220107093700 18713 - Pickling process of industrial pure titanium pipe

In the production process of industrial pure titanium pipe, pickling is a very important process, which can not be ignored. In the process of thermal processing or heat treatment, titanium tubes will chemically react with oxygen and other gases in furnace gas without protective atmosphere to form oxide layer. The oxide layer formed on the surface of titanium pipe is very harmful not only to each process after pickling, but also to the quality of the final product.
If titanium pipe is rolled with oxide layer, the pipe will have defects. At the same time, due to the existence of oxide layer, the oxide layer will be pressed into the pipe surface, resulting in unsatisfactory surface. It directly affects the quality of titanium pipe products, material consumption, productivity and economic benefits. As we all know, pickling is a process in which metals are treated in acid, alkali, salt and their solutions to remove the surface oxide layer.
There are many methods to remove the oxide layer. The traditional method is to use inorganic strong acids, such as sulfuric acid (H2SO4), hydrochloric acid (HCI), nitric acid (HNO3) and hydrofluoric acid (HF). This kind of method uses the chemical reaction between the oxide layer and acid to remove the oxide layer. For different materials, one of them can be adopted according to their performance characteristics.
The oxide layer of industrial pure titanium tube is mainly titanium dioxide (TiO2), followed by many low-cost titanium oxides, such as TiO, Ti2O3 and TiO2. In addition, there are high valence oxides of titanium, such as TiO2. The research shows that at room temperature, when the titanium pipe is pickled in < 5% dilute sulfuric acid pickling solution, a protective oxide layer is formed on the surface of the titanium pipe to protect the titanium from further erosion by dilute sulfuric acid, but there is an obvious reaction between pickling and titanium in > 5% sulfuric acid.
At room temperature, about 40% sulfuric acid has the fastest corrosion rate on titanium. Hydrochloric acid with concentration less than 5% does not react with titanium at room temperature. When the temperature increases, even dilute hydrochloric acid will corrode titanium, but more than 10% hydrochloric acid will corrode titanium obviously at 70 ℃ and 1% hydrochloric acid at 100 ℃. However, when there is an oxide layer or metal ions (such as copper) in hydrochloric acid solution, the corrosion effect of hydrochloric acid on titanium can be reduced. Hydrofluoric acid (HF) is the strongest solvent for titanium. Even hydrofluoric acid with a concentration of 1% can react violently with titanium: 2Ti + 6HF = 2tif3 + 3h2. When there are metal ions such as iron and copper in hydrofluoric acid solution, the dissolution of titanium can be accelerated. Titanium tubes with rough surface are most likely to react with cold and hot dilute nitric acid (HNO3): 3Ti + 4hno3 + 4H2O = 3h4tio4 + 4no3ti + 4hno3 + H2O = 3h2tio3 + 4NO.
In view of the corrosion characteristics of various acids on titanium pipes, in order to effectively remove the oxide layer on the surface of titanium pipes, relevant data introduce that nitric acid and hydrofluoric acid are used for pickling titanium pipes. The formula and process are as follows: the solution concentration ratio is: (35% ~ 40%) HNO3 + (5% ~ 7%) HF + residual H2O solution temperature is: 30 ℃ ~ 50 ℃. The test shows that the above formula and process have some shortcomings: first, the reaction of titanium pipes entering acid solution is too intense, Make the acid temperature rise rapidly, and even make the acid boil. This situation is very easy to cause oxidation and combustion of titanium tube matrix, resulting in increased loss of titanium tube matrix; Second, the acid spilled during such a violent reaction is quite harmful to the operators; Third, the operating environment of employees is poor and the pollution is too great.
In view of the above reasons, the pickling formula and process of titanium pipe are adjusted as follows:

  • Main components of solution: nitric acid (HNO3) + hydrofluoric acid (HF)
  • The solution concentration ratio is: (25% ~ 28%) HNO3 + (3% ~ 5%) HF + residual H2O
  • Solution temperature: ≤ 30 ℃
  • Pickling time: 10 ~ 20 minutes

The practice shows that the adjusted pickling condition is good, the reaction of titanium pipe entering acid solution is stable, and the pickling loss rate of titanium pipe matrix can be reduced by 30% ~ 50%.
It should be noted that the titanium pipe after pickling must be washed and dried. After the titanium pipe is pickled in acid solution, although the purpose of removing the oxide layer is achieved, there is more or less a part of residual acid on the surface of the titanium pipe eroded by acid. If this part of residual acid is not removed, part of hydrogen will diffuse into the titanium pipe matrix due to the chemical action of residual acid, so as to reduce the plasticity of the titanium pipe. At the same time, the residual acid on the surface of titanium tube will cause premature wear of roll and waste of titanium tube.

Therefore, residual acid is not allowed on the surface of titanium pipe after pickling. The purpose of drying is to drive out the hydrogen atoms in the metal lattice in time, so as to avoid hydrogen embrittlement during rolling and improve the lubrication performance.

SourceChina Titanium Pipe Manufacturer: www.titaniuminfogroup.com

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