Pickling vs Electropolishing. What’s the difference?

If you came here looking for a brine or vinegar solution in which foods are preserved, this is not that kind pickling! This article is going to talk about the differences between pickling stainless steel vs electropolishing as a metal surface treatment. Ultimately, both processes are intended to enhance the available chromium material on the surface and promote the formation of chrome oxide, but their intended uses and results differ considerably.

In general, the pickling of stainless steel is the removal of oxide layers resulting from welding and heat-treating.  In particular, stainless steel pickling is a metal surface treatment used to remove impurities, such as stains, inorganic, contaminants, rust or scale from stainless steel, where a solution containing strong acids is used to chemically etch the surface of the material and preferentially remove iron molecules. Metal pickling or chemical descaling can be used solely or in conjunction with follow-up processes including passivation or electropolishing.

Allegheny Surface Technology uses pickling solutions consisting of nitric and hydrofluoric acids to remove the scale and underlying chromium depleted layers. This restores the corrosion resistance of stainless steel, whereas mechanical removal of those imperfections may leave abrasive material or other particles embedded in the surface. This makes mechanical polishing impractical for some applications. Metal pickling is considered the preferred solution for the restoration of the corrosion resistance in stainless steel and furthermore, creates a desirably-uniform matte finish on the workpiece, and utilized in a number of areas including oil field equipment, wastewater treatment facilities, and any marine environment.

By comparison, electropolishing may be preferred to metal pickling for some applications. In the electropolishing process, metal removal is achieved by applying electric current to a part submerged in an electrolytic bath. Unlike the dull finish of pickling, electropolishing typically creates a bright, smooth, and more highly corrosion resistant, sanitary finish. Other advantages of electropolishing include:

1) Reducing the surface area on a microscopic level. This reduces product adhesion and contamination build-up, and cleaning can be performed more efficiently.

2) Electropolishing has been proven to reduce bacterial biofilm build-up and the appearance of rouging.

3) De-burring- The electropolishing process naturally has greater current densities at high points and less at low points. Due to the higher current densities at the high points, the burrs are removed at a much faster rate, leading to a smooth clean surface.

4) Aesthetics- Through proper electropolishing, the microscopic surface becomes smooth and clean, containing a nickel-chromium enriched surface that results in a lustrous finish. This facilitates a visual inspection since any remaining imperfections will be magnified.

Have more questions? Feel free to contact one of our pickling specialists by calling (866) 266-9293, or Request a Quote right here on our website.

Allegheny Surface Technology is your trusted provider of high-performance, ASTM and BPE compliant electropolishing, pickling, mechanical polishing, and passivation services. Specializing in both in-house and on-site stainless steel surface refinishing/refurbishment services, AST assures both the quality and reliability of our services through multi-step Quality Assurance and inspection protocols.