Sheet steel processed by acid-pickling will oxidize (rust) rapidly when exposed to moist atmospheric conditions. To prevent this, a thin film of oil or similar waterproof coating is applied to avoid contact of pickled steel with moisture in the air. The oil film must be removed for any further fabrication, plating or painting processes. Feb 25, 2018 How to apply video of pickling and passivation chemical on stainless steel for clean and shining look. With safety measures.
![]() Why stainless steel pipe needed Acid Pickling and passivation?
Pickling and passivation are two forms of chemical metal finishing that provide protective properties to metal especially against rust. Actually,pickling and passivation refers metal submerged in a bathing liquid that removes imperfections and rust from the surface of stainless steel.
Where the steel has been heated by welding, or other heat treatments,to the point where a coloured oxide layer can be seen, there is a chromium depleted layer on the surface of the steel underneath the oxide layer. The lower chromium content gives lower corrosion resistance. To restore the best corrosion resistant performance, the damaged metal layer must be removed, exposing a fully alloyed stainless steel surface. Mechanical removal may leave abrasive or other particles embedded or may be impractical sometimes.Chemical treatments that are correctly performed can clean the surface and ensure the best possible corrosion performance.
Passivation and Pickling are often used together on equipment to remove all contaminates and oxidation, improving the corrosion resistance, extending the life and overall value of your components.
The difference between Pickling and Passivation>>
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1,Pickling removes both weld oxide and stainless steel But passivation does not remove weld oxides not attack stainless steel
2,Pickling are typically hydrofluoric, sulphuric (or in steel mills,hydrochloric) acid. It utilizes more aggressive acids than those used in passivation.Passivation are Nitric acid or electropolishing.
3,Pickling Removes surface breaking sulphides and carbon steel.Passivation Removes surface breaking sulphides and, less rapidly, carbon steel smears
4,Pickling Changes appearance as it lowers gloss by etching.Passivation Nitric and chelating treatments should not change appearance.
5,Pickling Usually mixed with nitric acid and with rinsing leaves a passive surface.Passivation will improve the passive film over a simply pickled one.
Standards of Pickling and Passivation>>
ASTM A380, Standard Practice for Cleaning, Descaling and Passivation of Stainless Steel Parts, Equipment and Systems.
ASTM A967 Standard Practice for Chemical Passivation Treatments for Stainless Steel Parts.
These very useful documents give detailed recommendations on many aspects of selection, application and evaluation of these treatments..
WORLDIRON STEEL supply welded A312 TP316L after pickling and passivation,and pickling ASTM A312 304 stainless steel pipe .If any interests ,Please let me know>>
Henkel process helps beer barrel manufacturer improve product quality
Henkel has helped Envases Técnicos Zaragoza S.L. (Entinox), a leading Spanish manufacturer of stainless steel beer barrels (“kegs”), set up an innovative pickling and passivating line using a nitric acid-free Bonderite process. Benefits include superior HSE performance and bath life over traditional mixed acid pickling systems as well as outstanding corrosion resistance.
The challenge in pickling solutions for stainless steel lies in removing all scale, iron contamination and welding oxides for achieving a fully passivated surface with an even, clean and aesthetic finish. In the food industry and for key products such as beer kegs, the surface must also be absolutely free from any traces of pickling agents after the process. In addition, manufacturers face increasingly strict health, safety and environmental (HSE) regulations with regards to the release of potentially harmful substances, such as NOx emissions in air and nitrate effluents in water.
“In our state-of-the-art keg plant at Zaragoza, we decided to implement Henkel’s Bonderite C-CP 1300 pickling and passivating process because of its excellent combination of high productivity and uncompromising sustainability,” states José Enrique Gerona, General Manager of Entinox. “Moreover, Henkel’s experts were instrumental in helping us set up and optimize the process.”
Bonderite C-CP 1300 is the latest generation of Henkel’s established nitric acid-free cleaning technologies that were originally developed several years ago. In contrast to common mixed acid pickling systems, which are still used in many stainless steel segments today, it contains no HNO3 (nitric acid), while delivering excellent pickling and passivating results. Furthermore, its absence of citric compounds also addresses the growing concern among beer brewers about residual flavors in the barrels.
“Our Bonderite C-CP 1300 process was developed with a clear target to eliminate the risks associated with HNO3 in traditional mixed acid pickling systems,” explains Ronald Elemans, Business Development Manager for Cleaners at Henkel. “Nitrogen oxide emissions from these systems can entail significant neutralization costs, and there is practically no feasible way of removing nitrate effluents in waste water. Both factors also limit the possibility of increasing the productivity of the pickling process without heavy investments for NOx and NO3 ion removal.”
Bonderite C-CP 1300 can be used in spraying or immersion lines and is suitable for almost any stainless steel grades based on austenite, ferrite, martensite or duplex, including high-chromium AISI/SAE 4XX qualities. The system includes a starter (ST) for bath make-up, two components (R & Z) to maintain the acidity of the bath as well as the oxidizing and passivating capacity of the pickling solution, and an optional accelerator (TO) for use in tough to pickle materials or in applications with limited contact times.
Entinox’s kegs are normally made from 1.4307 (AISI 304L) grade stainless steel sheet, which is one of the most widely used austenitic chromium-nickel steel alloys. After bending, forming and welding, each keg has a surface of 2 square meters. Prior to pickling, the barrels are cleaned and degreased using a Bonderite C-AK product in a spray washer. The Bonderite C-CP 1300 R and Z mix is then applied in another spraying step. The manufacturer’s new Zaragoza plant has a production capacity for up to 450,000 barrels per year and offers kegs in standard sizes of 20 to 50 liters as well as 7.75 and 15.5 U.S. gallons, including various customized options.
“The pickling quality and efficiency that we achieve with Henkel’s process is outstanding,” comments Angel Roche, Technical Manager for Entinox. “While the resulting corrosion resistance is on par with that provided by mixed nitric acid-based systems, Bonderite C-CP 1300 provides a significantly longer bath life. Moreover, as a more environmentally friendly nitric acid-free solution, it also eliminates the risk of nitric fumes within the production area. And the absence of hexavalent chromium means that all effluents can be treated in our existing waste water plant.”
Apart from kegs for transportation of beer to bars and restaurants, Bonderite C-CP 1300 has a wide potential for leveraging similar cost and environmental benefits in many other markets where stainless steel is processed. Examples span from heat exchangers and chemical process equipment to stainless steel devices and machines in the food and beverages industry as well as in the pharma and semiconductor segments. Technologies
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