Stainless Steel vs Brass Rotary Joints: Material Selection Guide

The Material Decision

The housing material of a rotary joint affects its corrosion resistance, strength, thermal conductivity, weight, and cost. The two most common materials are brass and stainless steel — each with distinct advantages and trade-offs.

This guide compares both across the factors that matter most in real-world applications.

Factor 1: Corrosion Resistance

Brass

• Good resistance to water, coolant, and most neutral media
• Poor resistance to ammonia, acids, and sulfur-containing media
• Susceptible to dezincification in certain water conditions (high chloride, low pH)
• Surface patina develops over time (green/brown) — cosmetic, not functional

Stainless Steel

• Excellent resistance to most media including water, steam, oil, and many chemicals
• Superior resistance to chloride environments (316L grade)
• Resistant to dezincification, stress corrosion cracking
• Maintains appearance over time

Winner for corrosion resistance: Stainless steel — especially 316L for aggressive environments.

Factor 2: Thermal Conductivity

Brass

• Thermal conductivity: ~120 W/m·K
• Excellent heat dissipation from seal faces
• Helps prevent thermal buildup at the seal interface
• Better for high-speed applications where heat generation is a concern

Stainless Steel

• Thermal conductivity: ~16 W/m·K (304) / ~14 W/m·K (316L)
• Lower heat dissipation — seal faces may run hotter
• May require additional cooling measures at high speeds

Winner for thermal conductivity: Brass — by a significant margin. This is why the RT-DE CNC series uses forged brass housing.

Factor 3: Mechanical Strength

Brass

• Tensile strength: 350–500 MPa (depending on alloy)
• Adequate for most rotary joint applications
• Forged brass (used in RT-DE) is stronger than cast brass
• Good fatigue resistance

Stainless Steel

• Tensile strength: 500–700 MPa (304) / 485–620 MPa (316L)
• Higher strength for high-pressure applications
• Better resistance to impact and shock loads
• Required for pressures above 10 MPa in many designs

Winner for strength: Stainless steel — necessary for high-pressure hydraulic applications.

Factor 4: Weight

Brass

• Density: 8.5 g/cm³
• Heavier than stainless steel
• May affect mounting and support requirements for large joints

Stainless Steel

• Density: 7.9 g/cm³ (304) / 8.0 g/cm³ (316L)
• Slightly lighter than brass
• Minimal difference for most rotary joint sizes

Winner for weight: Stainless steel — marginally lighter.

Factor 5: Machinability

Brass

• Excellent machinability — easy to turn, mill, and drill
• Faster production = lower manufacturing cost
• Better surface finish achievable
• Easier to modify or customize

Stainless Steel

• Good machinability — but requires sharper tools and slower speeds
• Higher manufacturing cost
• Work hardening can be an issue
• More difficult to achieve fine surface finishes

Winner for machinability: Brass — significantly easier and cheaper to machine.

Factor 6: Cost

Brass

• Material cost: Moderate (copper-zinc alloy)
• Manufacturing cost: Lower (easier to machine)
• Total cost: Lower for most standard applications

Stainless Steel

• Material cost: Higher (especially 316L)
• Manufacturing cost: Higher (harder to machine)
• Total cost: Higher, but justified for corrosive or high-pressure applications

Winner for cost: Brass — typically 20–40% less expensive than stainless steel equivalents.

Factor 7: Food and Pharmaceutical Applications

Brass

• Not suitable for food or pharmaceutical contact
• Copper ions can leach into media
• Does not meet FDA or food-grade requirements

Stainless Steel

• Required for food and pharmaceutical applications
• 316L grade meets FDA and EU food contact regulations
• Easy to clean and sanitize
• Non-reactive with food products

Winner for food/pharma: Stainless steel — the only acceptable choice.

Factor 8: High-Temperature Performance

Brass

• Maximum continuous temperature: ~200°C
• Softens at higher temperatures
• Thermal expansion is higher than stainless steel
• Good for moderate-temperature applications

Stainless Steel

• Maximum continuous temperature: ~400°C (304) / ~450°C (316L)
• Maintains strength at higher temperatures
• Lower thermal expansion
• Required for high-temperature steam and thermal oil applications

Winner for temperature: Stainless steel — necessary above 200°C.

Decision Matrix

Factor	Brass	Stainless Steel	Winner
Corrosion resistance	Good	Excellent	Stainless
Thermal conductivity	Excellent	Poor	Brass
Mechanical strength	Good	Excellent	Stainless
Weight	Heavier	Lighter	Stainless
Machinability	Excellent	Good	Brass
Cost	Lower	Higher	Brass
Food/pharma	Not suitable	Required	Stainless
High temperature	Up to 200°C	Up to 450°C	Stainless

Application-Based Recommendations

Choose Brass When:

• Media is water, coolant, or neutral oil
• Operating temperature is below 200°C
• Pressure is below 10 MPa
• No corrosive media present
• Cost is a primary concern
• High-speed application (better heat dissipation)

Typical applications: CNC machining, general industrial, machine tool cooling

Choose Stainless Steel When:

• Media is corrosive (saltwater, chemicals, acids)
• Operating temperature exceeds 200°C
• Pressure exceeds 10 MPa
• Food or pharmaceutical application
• Hygienic environment required
• Marine or offshore application

Typical applications: Chemical processing, food processing, marine, pharmaceutical, high-pressure hydraulics

Ruitus Material Options

Ruitus offers both brass and stainless steel rotary joints:

• RT-DE CNC series: Forged brass housing — optimized for high-speed CNC applications with excellent heat dissipation
• JL-DD/JL-DC series: Precision-cast stainless steel — for corrosive environments, food processing, and high-temperature applications
• RTH series: Brass or stainless steel options — for general industrial applications
• RT-GY series: Steel construction — for high-pressure hydraulic applications

Need Help Choosing?

The right material depends on your specific application conditions. Share your media type, temperature, pressure, and environment with our engineering team, and we’ll recommend the optimal material selection.

Contact us for a material recommendation tailored to your application.