Surface Finish Explained: 32Ra vs 20Ra vs Electropolish

Surface finish in sanitary stainless-steel equipment refers to the microscopic smoothness of the metal surface. It is typically measured in surface finish microinches using Ra (roughness average).

• 32 Ra is the standard finish for most food, beverage, and dairy processing equipment.
• 20 Ra provides a smoother surface that improves cleanability and reduces product adhesion.
• Electropolished surfaces (typically ~15 Ra or smoother) offer the highest level of cleanliness, corrosion resistance, and microbial control for pharmaceutical and biotech applications.

Choosing the correct finish helps ensure effective CIP cleaning, product purity, and compliance with sanitary standards.

What Is RA Surface Finish in Sanitary Equipment?

Surface finish describes the microscopic peaks and valleys present on stainless steel surfaces after machining or polishing. These microscopic features affect how easily equipment can be cleaned and how resistant the surface is to contamination.

In sanitary processing environments, surface finish directly impacts:

• Cleanability
• Bacterial adhesion
• Product residue buildup
• Corrosion resistance
• Regulatory compliance

Because of this, industries such as food processing, dairy production, pharmaceutical manufacturing, and biotechnology specify surface finish requirements for process equipment.

Understanding Ra (Roughness Average)

Surface finish Ra is the most common measurement used to describe surface finish in sanitary equipment.

It represents the average surface roughness Ra value of a surface profile, measured in microinches (µin).

Lower Ra values indicate smoother surfaces.

Example scale:

A smoother surface reduces areas where product, microorganisms, or cleaning chemicals can accumulate.

32 Ra Surface Finish

What Is 32 Ra?

A 32 Ra finish is the most common mechanical polish used in sanitary processing equipment.

It is typically achieved through mechanical polishing or fine grinding, leaving a smooth but still slightly textured surface.

Where 32 Ra Is Used

This finish is widely used in:

• Food processing plants
• Beverage manufacturing
• Dairy facilities
• General hygienic process systems

Most sanitary fittings, valves, tubing, and pumps used in food-grade applications meet this finish requirement.

Advantages of 32 Ra

• Cost-effective manufacturing
• Suitable for most CIP cleaning processes
• Widely accepted by hygienic standards
• Compatible with standard sanitary equipment

For many food and beverage processes, 32 Ra provides the right balance of performance and cost.

20 Ra Surface Finish

What Is 20 Ra?

A 20 Ra surface finish provides a smoother mechanical polish than the standard 32 Ra finish.

The polishing process removes more microscopic peaks, resulting in a more uniform and cleanable surface.

When 20 Ra Is Preferred

20 Ra finishes are often selected for processes that require:

• Improved cleanability
• Reduced product adhesion
• Lower contamination risk

Industries commonly using this finish include:

• Nutraceutical production
• Specialty food processing
• High-value beverage production
• Some pharmaceutical support systems

Benefits of 20 Ra

• Improved sanitation performance
• Reduced product buildup
• Better compatibility with CIP systems
• Lower microbial adhesion risk

While slightly more expensive than 32 Ra, the improved cleanability often justifies the investment.

Electropolished Stainless Steel

What Is Electropolishing Stainless Steel?

Electropolishing is an electrochemical finishing process that removes microscopic surface material from stainless steel.

Instead of mechanically grinding the metal, an electrical current is applied in a chemical bath, dissolving high points in the metal surface.

This process produces:

• Extremely smooth surfaces
• Enhanced corrosion resistance
• Improved passivation of stainless steel

Typical Electropolished Surface Finish

Electropolished sanitary equipment typically achieves 15 Ra or smoother.

However, the biggest advantage is not just lower roughness — it is the microscopic smoothing and chromium enrichment of the stainless surface.

Applications for Electropolished Surfaces

Electropolished finishes are widely used in:

• Pharmaceutical manufacturing
• Biotechnology production
• Sterile processing environments
• High-purity chemical systems

These industries require extremely smooth surfaces to prevent microbial growth and contamination.

Mechanical Polish vs Electropolish

Electropolishing provides a microscopically smoother surface and significantly improves corrosion resistance.

Why Surface Finish Matters for Cleanability

Surface roughness influences how easily equipment can be cleaned.

Rough surfaces can trap:

• product residue
• microorganisms
• cleaning chemicals

Smoother surfaces help:

• improve CIP performance
• reduce contamination risk
• shorten cleaning cycles

This is why sanitary equipment specifications often include strict surface finish requirements.

Surface Finish and Regulatory Standards

Many sanitary standards reference surface finish limits to ensure hygienic performance.

Examples include:

• 3-A Sanitary Standards for dairy and food equipment
• ASME-BPE standards for pharmaceutical and biotech systems
• FDA material requirements for food-contact surfaces

Typical guidance:

• Food processing equipment: ≤ 32 Ra
• High purity pharmaceutical systems: ≤ 20 Ra or electropolished

Meeting these requirements supports regulatory compliance and process validation.

Equipment Commonly Specified with Surface Finish Requirements

Surface finish specifications commonly apply to:

• sanitary fittings
• valves and actuators
• process tubing
• pump components
• diaphragm valves
• tank internals

Properly finished surfaces help ensure consistent hygiene and reliable process performance.

Best Practices for Selecting Surface Finish

When specifying sanitary equipment, consider:

1. Industry Requirements

Pharmaceutical processes typically require smoother finishes than food processing.

2. Cleaning Method

CIP and SIP systems benefit from smoother surfaces.

3. Product Characteristics

Sticky, viscous, or protein-rich products may require improved surface finishes.

4. Regulatory Compliance

Certain industries require specific finishes to meet sanitary standards.

Selecting the appropriate finish ensures optimal performance without unnecessary cost.

FAQ: Surface Finish in Sanitary Processing

What does 32 Ra mean?

32 Ra refers to the average surface roughness of stainless steel measured in microinches. It is the standard finish for most sanitary food and beverage processing equipment.

Is 20 Ra better than 32 Ra?

Yes. A 20 Ra finish is smoother than 32 Ra, which improves cleanability and reduces areas where product or bacteria may accumulate.

Why is electropolishing used in pharmaceutical equipment?

Electropolishing produces extremely smooth surfaces and improves corrosion resistance, which helps maintain sterile conditions in pharmaceutical and biotech manufacturing.

Does a smoother surface improve CIP cleaning?

Yes. Smoother surfaces reduce microscopic crevices where product or microorganisms can collect, making cleaning processes more effective.

Summary

Surface finish is a critical factor in sanitary processing equipment because it affects cleanability, corrosion resistance, and regulatory compliance.

• 32 Ra is the standard finish used in most food and beverage systems.
• 20 Ra provides enhanced smoothness and improved sanitation performance.
• Electropolished finishes deliver the highest level of cleanliness and corrosion resistance for pharmaceutical and high-purity applications.

Choosing the correct finish helps ensure efficient cleaning, product quality, and long-term equipment performance.

This article is part of the Steel & O'Brien Product Knowledge Hub, created to help engineers, operators, and procurement teams select sanitary processing equipment with confidence.