What are the media and pickling steps for pickling stainless steel pipelines?
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This post was last edited by A Dai A Mu on 2012-1-9 at 22:40. There is a section of stainless steel pipeline that needs to be pickled; what acid should be used for this purpose? What are the specific construction steps required from the start of pickling to its completion?
Use the ready-made acidic solution available on the market, which is a mixture of sulfuric acid, hydrochloric acid, and nitric acid in specific proportions; when it is opened, acid mist is produced, and after some time its color turns red-brown – this color is due to nitrogen dioxide gas formed as a result of the decomposition of nitric acid； Specific method: Prepare a portable pickling device in advance, which includes a pressure gauge connected to the outlet of the pickling pump; the pump’s inlet is connected to a small storage tank. The stainless steel pipes are cleaned through the circulation of the pickling solution, and the pump’s outlet is connected via a rubber hose to the backwash point of a certain section of pipe, thereby enabling cleaning. Generally, the appearance of the pickling solution in the storage tank is used to determine whether the cleaning has been thorough. :lol
Generally, the parts are immersed in aqueous solutions such as sulfuric acid to remove films such as oxides from the metal surface. It is a pre-treatment or intermediate treatment for processes such as electroplating, enamel coating, and rolling. (1) The method of using acid solutions to remove oxide scales and rust from the surface of steel is called pickling. Oxides of iron such as scale and rust (Fe3O4, Fe2O3, FeO, etc.) undergo a chemical reaction with acid solutions, forming salts that dissolve in the acid and are thus removed. Acids used for pickling include sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, hydrofluoric acid, and mixed acids. The most commonly used ones are sulfuric acid and hydrochloric acid. The pickling processes mainly include immersion pickling, spray pickling, and rust removal using acid paste. The impregnation and pickling method is generally used, while the spraying method can be employed in large-scale production. Steel parts are generally pickled in a sulfuric acid solution of 10% to 20% (by volume) at a temperature of 40°C. When the iron content in the solution exceeds 80 g/L and the ferrous sulfate content exceeds 215 g/L, the pickling solution should be replaced. At room temperature, pickling steel with a 20%–80% (by volume) hydrochloric acid solution does not easily lead to corrosion or hydrogen embrittlement. Due to the strong corrosive effect of acids on metals, corrosion inhibitors need to be added. After cleaning, the metal surface turns silver-white; at the same time, the surface is passivated, thereby enhancing the corrosion resistance of the stainless steel. (II) To eliminate adsorption on the surface of the diatomite carrier and reduce peak tailing, the carrier must be treated with acid or alkali before use. Pickling involves immersing the carrier in 6 mol/L hydrochloric acid for 2 hours, or in concentrated hydrochloric acid at elevated temperature for 30 minutes; thereafter, it is filtered, washed with water until neutral, and dried. Pickling can remove impurities such as iron, aluminum, calcium, and magnesium from the surface, but it cannot remove silanol groups. The pickling carrier is suitable for analyzing acidic samples.
I had only heard of it before and seen the surface after pickling. Now that I’ve seen the specific steps, I’m much more familiar with it.
We usually use pickling paste for pickling; there are ready-made products available on the market, and their usage is similar to using dishwashing liquid to wash dishes
Pre-treatment for pickling and passivation: If there are surface contaminants on the stainless steel workpieces prior to pickling and passivation, they should be removed through mechanical cleaning, followed by oil and grease removal. Control of Cl- in pickling solutions and rinsing water: For water used in hydrostatic testing of petrochemical austenitic stainless steel pressure vessels, the Cl- concentration should be kept below 25 mg/L. If this requirement cannot be met, sodium nitrate can be added to the water to achieve the desired level. Excessive Cl- concentrations can destroy the passivation layer of stainless steel, leading to pitting, crevice corrosion, stress corrosion cracking, and other issues. Post-treatment of pickling and passivation: After pickling and rinsing with water, stainless steel parts can be immersed in an alkaline permanganate solution containing 10% (by mass) NaOH + 4% (by mass) KMnO4 at 71–82°C for 5–60 minutes to remove residues from the pickling process. Subsequently, they should be thoroughly rinsed with water and dried. If speckles or stains appear on the surface of stainless steel after pickling and passivation, they can be removed by scrubbing with fresh passivation solution or nitric acid of higher concentration. The stainless steel equipment or components that have been acid-washed and passivated should be properly protected; they can be covered or wrapped with polyethylene film to prevent contact between different metals and non-metals.
It depends on what kind of pipelines you are cleaning Is it an entire pipeline, or separate sections? Should the outside be cleaned or the inside? It’s fine to use the pickling paste on separate pipe sections, and it works for cleaning the outside as well; but it’s impossible to apply it to the inside of the pipes. If there are only a few pipe sections, it is also possible to purchase acid washing and passivation solution; as long as the proper method is followed. The one on the 5th floor is not suitable; hydrochloric acid can cause corrosive forces on stainless steel, so don’t use it. If it is a systematic pipeline that requires cyclic cleaning, it is recommended to hire a professional cleaning company; if the cleaning is not done properly, having someone else deal with it will cost more. This post was last edited by bingyu252 on 2009-4-10 15:05.]
Yeah, buy the cleaning solution based on the importance of the pipeline; don’t use it indiscriminately
Tell me what the material is, and I’ll provide you with a solution; different acids are used depending on the type of material, with mixed acids being the best option.