Electropolishing vs. Passivation

Addressing Common Misconceptions

One of the most frequently asked questions online, “Which is better, passivation or electropolishing?” is driven by a misunderstanding of the two processes and the different roles they play. In fact, the two processes are frequently complementary and doing one without the other can result in an unreliable system requiring constant maintenance.

For some applications, treating stainless steel with both electropolishing and passivation may be necessary to maximize the metal’s resistance to corrosion and meet specific standards. Two major industry standards with stringent surface chemistry requirements that may necessitate both treatments are: SEMI (Semiconductor Equipment and Materials International) standard, which is widely used in the semiconductor and electronics manufacturing industries.

What is Electropolishing? Superior Finish and Performance

Electropolishing utilizes a combination of electricity and chemistry to smooth the metal’s surface by removing the metal from the peaks of any raised surfaces on a microscopic level.

The metal removal rate is controlled by the electrical settings of the electropolishing equipment, the process is repeatable for a given alloy, electrolyte concentration and conductivity, and current density combination.

A well-electropolished surface significantly reduces locations where contamination can become caught on the surface and become a point where corrosion will flourish.

What is Passivation? Enhancing Corrosion Resistance

Passivation, on the other hand, is a chemical treatment to enhance stainless steel’s natural passive layer which protects the underlying metal from corrosion.

The passivation chemistry removes free iron or other metallic impurities on the surface which would become a source of corrosion.

The result is a contaminant-free, chromium-rich oxide layer that is chemically inactive, or “passive.”

Identifying and Addressing Contamination or Corrosion

Early warning signs of contamination or corrosion are typically found during the regular quality control sampling and inspection of a system and, depending on the situation, can be addressed by remediation, cleaning and a passivation treatment.

However, in situations where the symptoms are missed, or not addressed, both metallic and biologic surface contamination can result in accelerated corrosion through the underlying metal. In the most serious cases, the part fails and will have to be replaced. It goes without saying that any product that has passed through this system risks being seriously compromised.

Even if the situation is caught before failure, the pitting that occurs due to corrosion will need to be repaired. This will involve mechanical polishing, followed by electropolishing and then passivation of the affected area to bring it up to the same level of protection and cleanliness as the rest of the system.

In most cases, electropolishing will need to be performed only once and then passivated as part of commissioning a system. The result is a smooth surface, meeting the surface roughness requirement of the system, presenting fewer opportunities for internal corrosion or contamination to spread through the system to other locations, or into the product itself.

By including passivation as part of a maintenance plan, plant owners can be proactive in preventing corrosion or other contamination buildup. This decreases the likelihood of
unscheduled remediation services and aids in the longevity of the system itself.

For more information, visit our website: www.mgnewell.com and www.newellautomation.com.