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Surface pickling process of pure titanium GR1 and Gr2 seamless pipes

Why do industrial pure titanium GR1 and GR2 seamless tubes need pickling?

Pickling is a very important process in the production of industrial pure titanium GR1 and GR2 seamless tubes. This is because in the process of hot processing or heat treatment of titanium seamless tubes, without a protective atmosphere, it often generates an oxide layer by chemical interaction with oxygen and other gases in the furnace gas.

20220409220706 29045 - Surface pickling process of pure titanium GR1 and Gr2 seamless pipes

Pickling is the process of removing the surface oxide layer by treating the metal in acid, alkali, salt and their solutions to improve the quality of the product, which has a key role in the subsequent processing and material quality.
The reasoning is very simple, industrial pure titanium seamless tubes have two major hazards if they are not pickled.
1. If the titanium seamless tube is rolled with an oxide layer, impurities and deviations in the performance of the parent material will cause defects in the tube, and stable corrosion cannot be obtained.
2. Because of the presence of the oxide layer, so that the oxide layer pressed into the surface of the pipe, forming a defective surface. Above, it directly affects the quality, material yield, productivity and economic efficiency of titanium seamless tube.
There are various methods to remove the oxide layer by pickling, and the traditional process method is to use inorganic strong acids, such as sulfuric acid (H2SO4), hydrochloric acid (HCI), nitric acid (HNO3) and hydrofluoric acid (HF). This type of method uses the chemical reaction between the oxide layer and the acid to remove the oxide layer. Depending on the processed material, one of them can be used according to its performance characteristics.
In the oxide layer of industrial pure titanium GR1 and GR2 seamless tubes, it is mainly titanium dioxide (TiO2), followed by various types of low-valent titanium oxides, such as TiO, Ti2O3, TiO5, and even high-valent titanium oxides, such as TiO3, etc.
(1) In nitric acid environment
Titanium seamless tube with rough surface is most likely to react with cold and hot dilute nitric acid (HNO3) as follows.

  • 3Ti+4HNO3+4H2O
  • =3H4TiO4+4NO3Ti+4HNO3+H2O
  • =3H2TiO3+4NO

(2) In hydrofluoric acid environment
Hydrofluoric acid (HF) is the strongest solvent for titanium. Its corrosion behavior is contrary to that of sulfuric acid, hydrochloric acid and nitric acid, and it has its own unique corrosion mechanism. Even the hydrofluoric acid with a concentration of 1% can react violently with titanium: 2Ti+6HF=2TiF3+3H2When metal ions such as iron and copper are present in the hydrofluoric acid solution, the dissolution of titanium can be accelerated.
(3) In hydrochloric acid environment
Concentration <5% hydrochloric acid at room temperature does not react with titanium, when the temperature rises, even dilute hydrochloric acid will corrode titanium, but >10% hydrochloric acid at 70 ℃ with and 1% hydrochloric acid at 100 ℃ on titanium corrosion occurs obviously. However, when there is an oxide layer or metal ions (such as copper, etc.) in the hydrochloric acid solution, it can reduce the corrosion effect of hydrochloric acid on titanium.
(4) Under sulfuric acid environment
Research proves that when titanium seamless tube is pickled in <5% dilute sulfuric acid pickling solution at room temperature, a protective oxide layer is generated on the surface of titanium seamless tube to protect titanium from continued erosion by dilute sulfuric acid, but pickling in >5% sulfuric acid has obvious reaction with titanium. At room temperature, about 40% sulfuric acid has the fastest corrosion rate for the corrosion of titanium.

Early pickling method for pure titanium seamless tubes

In view of the corrosion characteristics of various acids on titanium seamless tube, in order to effectively remove the oxidized layer on the surface of titanium seamless tube, relevant information introduces titanium seamless tube pickling by nitric acid plus hydrofluoric acid.
The formula and process are as follows: solution concentration ratio: (35%-40%) HNO3+(5%-7%) HF+remaining H2O. solution temperature: 30℃-50℃.
The test proves that there are certain shortcomings in the above formula and process: First, the reaction of titanium seamless tube into the acid solution is too violent, so that the acid temperature rises rapidly and can even reach the point of making the acid boil, which is very easy to cause oxidation and combustion of the titanium seamless tube matrix, thus causing increased loss of the titanium seamless tube matrix; second, the acid solution spilled during such a violent reaction is quite harmful to the operators; third, the workers The operating environment is poor and the pollution is too great.

The improved pickling process of pure titanium seamless pipe

In view of the above three reasons, the industry has optimized and adjusted the pickling formula and process for titanium seamless pipes as follows.
The main ingredients of the solution are as follows: nitric acid (HNO3) + hydrofluoric acid (HF) solution concentration ratio: (25%-28%) HNO3 + (3%-5%) HF + remaining H2O. solution temperature: ≤30℃; pickling time: 10-20 minutes.
Practice has proved that the adjusted pickling is better, the titanium seamless tube enters the acid solution with smoother reaction, and the pickling loss rate of titanium seamless tube matrix can be reduced by 30%-50%. The hazards and pollution are reduced.
Tips: It should be noted that the titanium seamless tube after pickling must be rinsed and dried.
After pickling in the acid solution, although the oxidation layer is removed, the surface of titanium seamless tube is corrosive and corrosive by the acid, and there is more or less part of residual acid, if this part of residual acid is not removed in time, it will make part of hydrogen gas diffuse into the titanium seamless tube matrix due to the continued erosion and chemical action of residual acid, so that the processing performance of titanium seamless tube is reduced. At the same time, the residual acid on the surface of the titanium seamless tube will endanger the equipment in the subsequent rolling, increase the wear of the equipment, and thus cannot guarantee the accuracy of the subsequent titanium seamless tube, thus increasing the scrap rate.
SourceChina Titanium Pipe Manufacturer:



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