& mechanical polishing

Electropolishing & mechanical polishing services

Astro Pak provides mechanical polishing, electropolishing, and electrolytic cleaning of stainless steel tanks, vessels and equipment for pre-operational preparation and for remediation after installation and use. Our surface finishing processes adhere to ASME BPE and ASTM B912 standards, providing optimal Ra (Roughness Average) finishes to your equipment and vessels. We use custom-designed tooling to ensure optimal contact with intricate stainless-steel surfaces, along with proprietary chemistry, for superior results. Our surface reconditioning solutions are geared towards enhancing the cleanability and durability of your equipment. 


Astro Pak Technician Mechanical Polishing
Before Mechanical Polishing
Before MP
Before Electropolishing
After MP

Mechanical polishing removes corrosion, pitting, scratches or etchings which compromise the passive layer of stainless steel, creating a low-chromium area that is more susceptible to corrosion. Mechanical polishing also smooths welds where ferrules and valves have been replaced or added. Mechanical polishing alone is often sufficient for dry product vessels. For other applications, it is most often the first step prior to electropolishing and passivation.


Astro Pak Technician Electropolishing
Before Electropolishing
Before EP
After Electropolishing
After EP

Electropolishing removes impurities, and other embedded contaminants, also known as the Bielby layer, which forms during mechanical polishing.  The result is a smooth, mirror-like finish where residue and even single-cell bacteria, will have no place to lodge. Often, electropolishing is the final process in preparing a vessel for service. However, combining electropolishing with passivation achieves a smooth chromium rich surface with improved cleanability and superior corrosion resistance.


Astro Pak Technician Electropolishing
Before Electrolytic Cleaning
Before ELC
After Electrolytic Cleaning
After ELC

Electrolytic cleaning is a short-form version of Electropolishing using similar tooling and chemistries. Rouge and other metallic surface contaminants can be rapidly removed from austenitic stainless (300 series) with an ELC process. Weld color or heat tint can also be removed using electrolytic cleaning, as this process is limited to the outermost surface of the metal.


Newly fabricated vessels and equipment may have a shiny appearance, but metal debris and iron oxides left behind from machining and welding can cause premature corrosion. Our surface finish and passivation solutions remove these contaminants and impart an optimized passive layer on the surface of stainless steel, thereby enhancing corrosion resistance and extending equipment maintenance intervals.


Over time existing systems may develop process application residues, rouge/rust, pitting, bioburden, scratches, and other internal or external surface conditions that can compromise product quality and equipment integrity. Our on-site mechanical polishing and electropolishing services will restore the surface finish of operational tanks and equipment with minimal downtime, and eliminate the need for system revalidation.


Austenitic Stainless SteelYes
Ferritic Stainless SteelSmall quantities, call for more info
Duplex Stainless SteelSmall quantities, call for more info
Precipitation Hardened Stainless SteelSmall quantities, call for more info
Nickel-based Alloys (Hastelloy, Inconel)Call for more info

exterior Surface Remediation

We also help our customers with exterior surface repair including removal of rust and/or staining on platforms, handrails, etc… While product purity and quality is the main focus of FDA inspections, don’t let staining on your facility exteriors have inspectors second guessing what’s going inside your system. While we’re cleaning your product contact surfaces, make sure you ask about our exterior surface repair services. Depending on your scope of work, we can tailor a plan that addresses your specific needs via mechanical, chemical, electrolytic, and/or hand detail methods. 


Frequently Asked Questions

Electropolishing smoothes the surface by removing material to form a more glassy or shiny surface.  Passivation improves the surface chemistry to reduce corrosion potential by removing iron from the top few molecular levels with no effect to surface finish.
Electropolishing is good for creating a surface that is cleaner, smoother, and more representative of the base metal than any other method currently in use. This lends itself to bio-pharmaceutical applications where vessels and equipment must be easily verified as being clean. Electropolishing also reduces surface area (vacuum applications), passivates the surface to a degree, and removes any imbedded impurities that may be present following mechanical polishing.
Electropolishing removes material while electroplating deposits material. The two processes are very similar in that both use electrolytes to carry an electrical current, but with different polarity.
An electropolished surface is only as durable as the base metal itself. Rough handling and chloride damage are the two principle types of damage we repair most often.
Most metals can be electropolished, but some of the necessary chemicals are very hazardous. With our current chemistries, we do not electropolish titanium or aluminum.
ASTM B-912 is the most common spec requested, but current BPE SF4 specs are a close second. There are many different semiconductor industry specs as well.
Electropolishing removes the peaks and cleans the valleys.  It only removes surface material and does not fill in gaps.
Mechanical polishing uses abrasives to cut the surface, while electropolishing uses chemicals and electricity to dissolve the surface.
Electropolishing removes the peaks and cleans the valleys. It only removes surface material and does not fill in. Typically, to achieve BPE specs, two to four ten-thousandths of an inch of surface material is removed.
Electropolishing can reduce existing surface roughness (Ra) by up to 50%, but Ra is only part of the story. EP’ed surfaces are flatter and smoother on a microscopic level, an order of magnitude finer than Ra alone can explain.
Astro Pak’s field methods allow us to progressively polish very large vessels. Complexity is usually more of a challenge than size.
That depends on the definition of ‘better’. Electropolishing provides a smoother surface, but does not provide the enhanced chrome / iron ratio that proper passivation does.
Not with our current chemistries. Most metals can be electropolished, but some of the necessary chemicals are very hazardous.