Application Of Tantalum Tubes In Ultra-High Tensile Steel Pickling

Recently, according to the test results and heat exchanger process parameters, the heat exchange area of the tantalum tube heat exchanger was designed to replace the original graphite heat exchanger. The results show that the flow characteristics and heat transfer performance of the tantalum alloy heat exchanger have been improved, and the scale inhibition performance is superior, which can extend the scaling cycle and improve the productivity of the pickling unit.

Conventional carbon steel pickling process generally uses hydrochloric acid, in order to ensure that the acid speed hydrochloric acid percentage concentration of 3% ~ 12%, the acid temperature needs to be maintained in the range of 70 ~ 90 ℃. In the current mainstream turbulent pickling process, the pickling unit is usually divided into 3 ~ 4 sections, each section is equipped with a separate pickling tank and pickling tank, and the concentration of hydrochloric acid and temperature can be adjusted in sections, generally using graphite heat exchangers to heat the hydrochloric acid and then sprayed onto the surface of the strip, the pickling solution reacts with the iron oxide on the surface of the strip and then flows back into the pickling tank for circulation. Graphite heat exchangers are mainly made of impermeable graphite impregnated with resin and have excellent corrosion resistance and heat transfer properties and have been widely used in the heat transfer process for cold rolling pickling corrosive media.

With the development and production of ultra-high-strength steels, turbulent pickling technology is used to produce ultra-high strength (780~1180 MPa) steel grades containing Si, Ti, Mn, Nb, Cr, and other elemental compositions The iron oxide on the surface of the strip steel also contains oxides composed of these elements. These oxides cannot be dissolved in the pickling solution during the pickling process, and as the pickling process proceeds, the solid insoluble content of the pickling solution will increase, causing blockage of the heat exchanger, and with the increasing production of ultra-high-strength steel, the blockage problem is becoming more and more prominent. Clogging occurs mainly in the graphite blocks of the heat exchanger.

Tantalum is one of the most corrosion-resistant metals, and the flow characteristics and heat transfer performance of a tantalum alloy heat exchanger are greatly improved compared to a traditional graphite heat exchanger, especially as the roughness of the inner surface of the tantalum tube is much lower than the roughness of the graphite block surface of the graphite heat exchanger, which is conducive to solving the heat exchanger blockage problem.

The DV(50) particle size of 5.25 um and the mass concentration of 0.2~0.7 g/L were analyzed for oxide particles insoluble in hydrochloric acid solution in the ultra-high-strength steel acid solution. When designing a tantalum tube heat exchanger, the flow rate in the tube should be increased to 2.5 m/s to extend the scaling cycle. The application of tantalum tube acid heaters on-site shows that their operating cycle is much greater than that of graphite heat exchangers, although their one-time investment is larger, there is a strong anti-scaling performance, to maintain a larger acid flow in the maintenance cycle, to ensure that the exit velocity of the acid tank nozzle, effectively improving the production efficiency of the pickling unit.