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Electropolishing vs. Passivation of Stainless Steel

The aesthetics or physical properties of metal may often see improvement by the application of various finishing techniques. For example, in custom metal basket applications, applying an appropriate finish will impact the functionality of the basket as much as the base material does. 

Two of the most popular finishing methods used for stainless steel include electropolishing and passivation. At Highland Equipment, our customers often ask: Is electropolishing the same as passivation? While both finishing methods improve the material’s durability and resistances, there are distinct differences to consider when choosing between electropolishing vs. passivation.  

Electropolishing

Electropolishing is a common finishing technique for the food and beverage, medical and dental, pharmaceutical, electrical, and semiconductor industries. The electropolishing process leaves a smooth, near-flawless finish. Manufacturers often use this method to impart non-stick qualities onto goods and components, making them easy to clean and ensuring process materials don’t stick to them during production.

The process uses a temperature-controlled chemical bath and an electric current to dissolve the metal’s outer surface layer. Electropolishing removes microscopic surface imperfections and eliminates discoloration from spot welds. It is a fast, cost-effective solution, even for parts with complex geometries.

Electropolishing is compatible with most stainless steels and a variety of other metals. Metal alloys that are good candidates for electropolishing include:

• Stainless steel: 200-300 series, 400 series, precipitating hardening grade, and unusual
• Nitinol
• Titanium
• Aluminum
• Brass
• Carbon steel
• Copper
• Nickel
• Specialty alloys

Passivation

Passivation is similar to electropolishing in that it uses a chemical bath to remove contaminants acquired during the manufacturing process. However, passivation uses an acidic solution that does not require an electrical current. Passivation won’t change the material’s aesthetic appearance, but it will improve the oxide layer that protects stainless steel. 

Passivation requires a thorough understanding of the type of alloy and how the chemical bath solution will interact with it. An inexperienced finisher using the wrong passivation solution could strip much more from the surface than intended and damage the workpiece beyond repair. 

The passivation process provides an excellent way to remove free iron and other contaminants from the surface of many stainless steel grades. Some stainless steel materials aren’t appropriate for this finishing method, however. When the steel has low chromium and nickel levels, or if the parts have been welded or brazed, passivation is typically not the appropriate finishing method.

Choosing the Right Finishing Process

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When selecting stainless steel electropolishing vs. passivation, consider the following application-specific factors:

Electropolishing:

• Offers an ideal solution for removing microscopic contaminants or imperfections
• Strips the entire outer layer of metal
• Will remove heat tinting and oxide scales
• Suitable for parts with complex geometries

Passivation:

• Does not require electrical current
• Removes free iron and other surface contaminants
• Won’t remove heat tinging or oxide scales but strengthens the oxide layer
• Gentler than electropolishing

The choice comes down to the application for the stainless steel. For a flawless finish or to finish components with complex shapes and angles, electropolishing offers an ideal solution. Passivation is a less complicated and gentler technique used to remove surface contaminants and enhance corrosion resistance without peeling off the material’s outermost layer.

Working with Highland for Sanitary Stainless Steel Process Equipment

At Highland Equipment, we offer passivation as one of our many value-added services. Our staff can help you to determine if passivation is the right finishing method for your project. For more information about our passivation capabilities, please contact us today. 

Factory Acceptance Testing vs. Site Acceptance Testing

Both Factory Acceptance Testing (FAT) and Site Acceptance Testing (SAT) involve extensive testing of systems or system components to determine or verify compliance with the preapproved specifications. While there are similarities between the two, they are distinct processes. The following blog post outlines the key differences between FAT and SAT.

What Is a Factory Acceptance Test?

Factory Acceptance Testing occurs at the vendor’s test facility before the completed equipment proceeds to the customer site. These tests verify whether the equipment meets all functionality and performance requirements as detailed by the User Requirements Specification (URS) document written by the manufacturer and executed by the customer or customer’s representative. They also provide vendors with an opportunity to identify issues and customers with an opportunity to make modification suggestions prior to shipment, both of which reduce the amount of time and money spent on resolutions and ensure the equipment is ready for use upon arrival. 

While FAT operations range from short and simple to comprehensive and complex, they are generally more rigorous than Site Acceptance Tests since vendors want to ensure the equipment fully complies with the terms of the contract. The tests conducted vary depending on equipment, customer, and vendor requirements. However, they generally cover the following: 

• Inspection: Does the equipment conform to the final design and drawing specifications?

• Contract Audit: Are all contractual obligations fulfilled?

• Water Testing: Does the equipment operate as intended?

Some of the typical issues uncovered by factory acceptance testing include:

• Quality or craftsmanship problems
• Improper labeling and guarding
• Insufficient throughput 
• Lack of sanitary design 

What Is a Site Acceptance Test?

Site Acceptance Testing occurs at the customer’s test facility after the completed equipment is delivered to the customer site. These tests verify whether the equipment meets and/or exceeds the functionality and performance requirements written up by the customer themselves. They occur after all commissioning tasks for the equipment are completed but before installation. 

SAT operations typically involve running the equipment for one to two weeks to see if it performs as expected and if any major problems occur. If the equipment does not perform as expected or a problem arises, the vendor and customer must discuss how to resolve the situation. If the equipment does perform as expected and no problems follow, the customer can have peace of mind that the system does its job effectively and safely. 

Highland Equipment: Ensuring Equipment Quality With Comprehensive Testing/Inspection Procedures

At Highland Equipment, we do our part to assure our customers that our equipment does what it needs to do. Our team employs a variety of non-destructive testing (NDT) methods to carefully inspect our systems and verify they comply with the highest standards. To learn more about our testing and inspection capabilities, contact us today.