Frequently Asked Questions About Electropolishing

Is On-Site Vessel Reconditioning Beneficial?

Did you know you can perform vessel reconditioning on-site? There are several reasons to evaluate this process.

  • On-site reconditioning reduces downtime when you compare it to the replacement of a vessel.
  • It doesn’t require re-validation of the vessel since you only need to treat the surface of the existing vessel.
  • You can monitor the progress of the process giving you a better idea as to how long the process is going to take.
  • You can repair small scratches, shallow pitting, and other microscopic surface imperfections faster

The importance of doing that is to improve the cleanability and reduce the corrosion potential of that surface. In general, the goal is to get the vessel back to its original state, both from a surface condition and a corrosion resistant condition.

What’s the Difference Between Electropolishing and Buffing?

Buffing is a process that is sometimes used after mechanical polishing to make the surface appear electropolished and extremely shiny.

However, the American Society of Mechanical Engineers – Bioprocessing Equipment (ASME-BPE) has banned buffing surfaces with polishing compounds because it entraps metal particles and other debris into the surface finish. Not only does that lead to surface damage, but it also decreases the corrosion resistance of the metal. Although the surface appears shiny, it’s actually dirty underneath.

Why Passivate After Electropolishing?

Electropolishing is a passivation process. However, like most passivation techniques, electropolishing is only as good for passivation as using phosphoric acid which result in chrome to iron ratios in the range of 1.2 to possibly as high as 1.4. That is under the passivation requirement of nitric acid which is at 1.5.  It definitely falls short of passivating with citric acid which ranges from 1.8, even to as high as 2 points.

Although electropolishing provides a passive film, it is at the lowest level acceptable. To achieve a fully passivated highly corrosion-resistant surface, you must add a post electropolishing passivation step utilizing passivation specific chemistries.

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Mike Montgomery

Since 2012 Mike has served as the Technical Director of Electropolishing at Astro Pak Corporation. With over thirty years of mechanical, machining, and metal finishing experience, Mike brings practical knowledge, capability and excellence to vessel restoration projects across the country. Mike develops and implements training programs, including confined space entry, ensuring technical excellence and safety amongst all Astro Pak MP/EP Technicians.

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