Electropolishing is an electrochemical process that removes a thin layer of material from the surface of stainless steel, resulting in a smooth, polished finish.
Within ultra-sterile research and production facilities, and in cleanroom grade B specifically, where compliance with ISO 14644 is critical, nothing but an obsessive approach to hygiene and contamination control will do.
Gaining insight from its cleanroom customers, Teknomek asked what their main considerations were when it comes to specifying new cleanroom furniture. The following two responses sum up the mood of the industry.
“The biggest consideration before purchasing would be how easy it is to clean and how resistant furniture is to cleaning products.”
“The key ones are movability, cleanability and resistance to cleaning chemicals, as we use a lot of strong chemicals.”
- Mechanically polished -
Because harsh sterilisation methods have become typical in pharmaceutical and microbiological manufacturing environments, cleanroom and laboratory furniture must be up to the job and be able to withstand the toughest of cleaning SOPs.
And that is why 304 or 316 grade stainless steel are the standard materials for the manufacture of furniture designed for hygienic environments.
As well as its hardiness, the composition of stainless steel has intrinsic hygienic qualities. 304 and 316 grades are austenitic stainless steels, which means no pores or cracks within which microorganisms could gain a foothold, or perhaps a flagellum hold.
It is also essentially inert to most acids and alkali, which eliminates any risk of pitting or crevice corrosion.
Stainless steel is also very easy to keep clean; it is often likened to glass or china.
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Tests conducted with commercial detergents have shown that around 97 percent of contaminants are eliminated from austenitic stainless steel surfaces.
But it is important to recognise that high concentrations of chemicals such as chlorine and hydrogen peroxide can significantly reduce the lifespan of furniture built from 304-grade stainless steel, corroding and pitting the surface over time and increasing the risk of contamination.
That’s where 316-grade stainless steel comes in. 316-grade stainless steel contains molybdenum, a naturally occurring element which has one of the highest melting points of all elements, alongside chromium and nickel.
It is more resistant to corrosion, mitigating the risk of rouging or tiger stripes while reducing contamination risk and supporting improved clean-down productivity.
The International Molybdenum Association, which represents the majority of the molybdenum industry worldwide, explains: “Type 316grade stainless steel includes approximately 2% molybdenum, a silvery metallic element most often used in steel alloying.
304 or 316 grade stainless steel are the standard materials for the manufacture of furniture
The addition of molybdenum provides Type 316grade stainless steel with superior corrosion resistance to Type 304.
If you’ve ever seen orange or brown dots that seem to eat away at the surface of stainless steel, this is likely what’s known as pitting corrosion.
This kind of corrosion can happen in response to chloride (salt) exposure.
The aggressive chloride-containing cleaning chemicals specified by ISO standards can cause etching or pitting corrosion in stainless steels with lower corrosion resistance.
Each pit is the site of a localised corrosion reaction, which penetrates the stainless steel’s protective passive layer and eats into the base metal.
In the case of 316-grade stainless steel, passivation is particularly important to ensure the product’s longevity
This process also generates corrosion products that are released into the air, which can contaminate the cleanroom atmosphere.”
Let’s talk more about the passive layer, mentioned above.
In cleanroom and aseptic environments, passivation of 316-grade stainless steel plays a crucial role in maintaining the integrity and cleanliness of surfaces.
Although stainless steel is named stainless, it is really stain-resistant. This property comes from its ability to spontaneously form a chromium oxide-rich passive layer on the surface, which helps resist corrosion.
Passivation is the process of using a chemical treatment to remove any impurities, contaminants or free iron from the surface to enhance this layer and improve its corrosion resistance.
Electropolishing can be employed for 304-grade stainless steel too
In the case of 316-grade stainless steel, passivation is particularly important to ensure the product’s longevity.
By removing impurities through passivation, the steel surface becomes more resistant to corrosion, thereby prolonging its lifespan and maintaining the desired level of cleanliness required in these controlled environments.
Electropolishing is often employed as a complementary process to passivation in the preparation of 316-grade stainless steel furniture for cleanroom environments.
Electropolishing can also be employed for 304-grade stainless steel too.
While passivation primarily aims to remove impurities and contaminants from the surface of stainless steel to enhance its corrosion resistance, electropolishing goes a step further by improving the surface finish and microstructure of the material.
while passivation addresses the chemical composition of the surface, electropolishing focuses on refining the surface topography
When used in conjunction with passivation, electropolishing enhances the overall corrosion resistance of the stainless steel furniture by creating a more passive surface layer.
By removing a thin layer of material during the electropolishing process, any remaining impurities or embedded contaminants are effectively eliminated, further reducing the risk of corrosion and ensuring the longevity of the furniture in cleanroom environments.
Therefore, while passivation addresses the chemical composition of the surface, electropolishing focuses on refining the surface topography, collectively contributing to the performance and cleanliness of 316 stainless steel furniture in cleanroom settings.
The benefits of electropolishing summed up:
Improved corrosion resistance
Electropolishing enhances the corrosion resistance of stainless steel by removing impurities and irregularities from the surface.
The addition of molybdenum provides Type 316grade stainless steel with superior corrosion resistance to Type 304
The process removes a thin layer of surface material, eliminating embedded contaminants, impurities, and any existing surface imperfections, which can act as initiation sites for localised corrosion, such as pitting and crevice corrosion, which can compromise the integrity of the furniture over time.
In cleanroom environments, where the presence of particles and bacteria must be minimised, a smoother surface is easier to clean and disinfect, reducing the risk of contamination and maintaining the desired cleanliness levels.
The electropolishing process induces the formation of a dense and tightly adherent passive oxide layer on the surface of the stainless steel.
This passive oxide layer enhances the material's resistance to corrosion by acting as a barrier between the metal surface and corrosive environments.
The formation of this protective oxide layer is more uniform and consistent after electropolishing, further improving the overall corrosion resistance of the 316 stainless steel furniture.
Electropolished surfaces are easier to clean due to their reduced porosity and improved smoothness
Therefore, through the combined effects of contaminant removal, surface smoothing, and passive layer formation, electropolishing significantly enhances the corrosion resistance of stainless steel furniture, making it highly suitable for use in cleanroom environments where durability and cleanliness are paramount.
Microbial resistance
The smooth and polished surface produced by electropolishing minimises the presence of microscopic surface irregularities where bacteria and other microorganisms can potentially lurk and multiply.
This makes electropolished stainless steel an ideal choice for cleanroom surfaces, reducing the risk of microbial contamination and facilitating easier cleaning and sterilisation processes.
Easy cleaning and maintenance
Effective cleaning and maintenance protocols are essential for all businesses where cleanrooms form part of the working environment.
Electropolished surfaces are easier to clean due to their reduced porosity and improved smoothness.
Electropolishing also improves the aesthetic appeal of stainless steel surfaces
Because the absence of crevices and surface imperfections makes the cleaning process more effective and efficient.
It’s important to note here that the design and positioning of hygienic furniture within a cleanroom also plays a critical role in contamination management.
Avoid furniture with flat surfaces where possible to minimise liquid pooling and consider where HVAC vents are located in relation to furniture to avoid dead air spaces.
Enhanced aesthetic appeal
Beyond its functional benefits, electropolishing also improves the aesthetic appeal of stainless steel surfaces.
Cleanroom environments require a visually clean and professional appearance, and electropolishing contributes to achieving this standard while maintaining the necessary functional properties.
316-grade stainless steel remains the go-to material for furniture and equipment made for ultra-hygienic environments
But just because a workspace looks clean, it doesn’t mean it IS clean.
View your cleanroom as an auditor would and ensure that there are no hard-to-reach corners or harbourage points where microbes can accumulate and cause problems.
In conclusion, 316-grade stainless steel remains the go-to material for furniture and equipment made for ultra-hygienic environments. By specifying an electropolished finish, you are protecting your investment for the long haul.
N.B. This article is featured in the April 2024 issue of Cleanroom Technology. The latest digital edition is available here.
