How to Choose the Right Disc Material for Butterfly Valves

Publish Time: 06/06 2026 Author: Site Editor Visit: 4

Why Disc Material Matters

The disc is the component that rotates to open, close, or modulate flow. It is constantly exposed to the process media. Unlike the valve body (which is often protected by a liner), the disc is usually bare metal or coated metal.

An improper disc material will result in:

Corrosion pitting leading to leakage across the seat.
Erosion from abrasive slurries causing loss of disc edge integrity.
Galvanic reaction between the disc and stem or body.
Contamination of sensitive media (food, pharmaceutical, pure water).

Common Butterfly Valve Disc Materials and Their Applications

1. Ductile Iron (DI) with Coating (Epoxy or Nylon)

Best for: Water, wastewater, air, mild chemicals, HVAC.

Ductile iron is economical and strong. However, bare ductile iron rusts rapidly. Kinko uses fusion-bonded epoxy or nylon 11 coating to create a barrier against water and mild corrosives.

Advantages: Low cost, high strength, good abrasion resistance when coated.
Limitations: Coating damage exposes iron to rapid corrosion. Not suitable for acids, solvents, or high temperatures (>120°C).

2. Stainless Steel (CF8 / SS304)

Best for: Potable water, food processing, mild acids, oils, gases.

SS304 offers excellent resistance to atmospheric corrosion and many organic chemicals. It is the standard choice for general industrial and sanitary applications.

Advantages: Good corrosion resistance, food-grade compliant, cost-effective for moderate duty.
Limitations: Susceptible to chloride attack (pitting) in seawater or brine. Limited in strong reducing acids.

3. Stainless Steel (CF8M / SS316)

Best for: Chemical processing, seawater, pharmaceutical, pulp and paper, aggressive environments.

SS316 contains molybdenum, which dramatically improves resistance to chlorides and acidic environments. Kinko recommends CF8M for any application involving salt water, bleach, or sulfuric acid dilution.

Advantages: Excellent pitting resistance, high tensile strength, wide chemical compatibility.
Limitations: Higher cost than SS304 or coated iron.

4. Aluminum Bronze (Al-Bronze)

Best for: Seawater, brackish water, high-velocity flows, marine applications.

Aluminum bronze offers exceptional resistance to seawater corrosion and cavitation erosion. It is non-sparking and has high mechanical strength.

Advantages: Superior erosion resistance in high-velocity liquids, excellent seawater performance.
Limitations: Not compatible with ammonia or strong mineral acids.

5. Nickel-Plated or Chrome-Plated Discs

Best for: Sticky media, resins, viscous fluids, applications requiring low friction.

A hard chrome or nickel coating over ductile iron or brass reduces friction between the disc and seat, lowering operating torque. It also provides a smooth, non-stick surface.

Advantages: Very low coefficient of friction, easy to clean, good wear resistance.
Limitations: Coating can chip if abused; not for highly corrosive acids.

6. PTFE (Teflon) Lined or Coated Discs

Best for: Highly corrosive acids, solvents, chemical transfer, ultrapure water.

For extreme chemical resistance, a PTFE layer over a stainless steel core isolates the metal from the media. Kinko offers PTFE encapsulated discs for aggressive chemical automation.

Advantages: Inert to almost all chemicals (except molten alkali metals), non-stick, wide temperature range (-40°C to 180°C).
Limitations: Soft surface prone to scratching; expensive.

How to Select: A Step-by-Step Decision Matrix

To choose the correct disc material for your Kinko butterfly valve, ask these four questions:

Selection Factor	Question to Ask	Recommended Kinko Disc Material
Media Type	Is the fluid water, chemical, gas, or slurry?	Water → Coated Ductile Iron; Chemical → CF8M or PTFE; Slurry → SS316 or Al-Bronze
Temperature	Does it exceed 80°C (176°F)?	Yes → SS316 or PTFE (avoid coated iron above 120°C)
Chloride Content	Does the fluid contain salt or bleach?	Yes → CF8M (SS316) or Aluminum Bronze (never use SS304)
Hygiene Requirement	Is the media food, beverage, or pharmaceutical?	Yes → SS316 (CF8M) with Ra ≤ 0.8µm surface finish

Kinko Disc Material Specifications Table

Below are the standard disc material options available across our Kinko butterfly valve series (wafer, lug, and automated configurations).

Disc Material	Material Code	Pressure Range	Temperature Range	Key Media Compatibility	Relative Cost
Epoxy Coated Ductile Iron	DI + E	Up to 16 bar	-10°C to 120°C	Water, air, light oils, wastewater	$
Nylon Coated Ductile Iron	DI + N	Up to 16 bar	-20°C to 100°C	Potable water, mild chemicals	$
Stainless Steel 304 (CF8)	SS304	Up to 25 bar	-20°C to 180°C	Food, beer, vegetable oils, mild acids	$$
Stainless Steel 316 (CF8M)	SS316	Up to 25 bar	-40°C to 200°C	Seawater, bleach, acids, pharmaceuticals	$$$
Aluminum Bronze	Al-Bronze	Up to 25 bar	-40°C to 250°C	Seawater, brackish water, high-velocity flow	$$$
PTFE Lined / Encapsulated	PTFE / PFA	Up to 16 bar	-40°C to 180°C	Strong acids, solvents, ultrapure chemicals	$$$$

Note: Pressure and temperature ranges are interdependent. Higher temperatures may require derating. Consult Kinko engineering for exact curves.

Common Mistakes to Avoid

❌ Using SS304 in Seawater

SS304 will pit rapidly in chloride-rich environments. Always specify SS316 or Aluminum Bronze for marine applications.

❌ Coated Ductile Iron for Abrasive Slurries

The epoxy or nylon coating will erode quickly, exposing the iron base. Use solid SS316 or Al-Bronze for slurries.

❌ PTFE Discs for High-Pressure Gas

PTFE is soft. Under high differential pressure, the disc edge may deform. For gas >10 bar, use SS316 with a resilient seat.

❌ Mixing Disc and Body Materials Carelessly

Dissimilar metals in the presence of an electrolyte (wet media) create a galvanic cell. Kinko recommends matching disc and body metallurgy or isolating with a liner.

Kinko Recommendation by Industry

Industry	Typical Media	Recommended Disc Material	Kinko Series
Water Treatment	Raw water, chlorinated water	SS316 (CF8M)	Kinko LT-200
HVAC	Chilled water, hot water	Epoxy Coated DI	Kinko LT-100
Food & Beverage	CIP solutions, juices, dairy	SS316 (CF8M) polished	Kinko Sanitary Series
Chemical Processing	Acids, caustics, solvents	PTFE Encapsulated	Kinko Chem-Series
Marine	Seawater, brine	Aluminum Bronze	Kinko Marine-LT
Pulp & Paper	Black liquor, bleaching chemicals	SS316 or Duplex	Kinko Heavy-Duty

Conclusion

Choosing the right disc material for your butterfly valve is not an afterthought—it is a core engineering decision that directly impacts plant uptime, maintenance costs, and product purity.

Kinko offers a comprehensive range of disc materials from economical coated ductile iron to high-end PTFE encapsulated and aluminum bronze options. Every disc material is available in our low-torque, automation-ready platform with ISO 5211 direct mounting.

Need help selecting the optimal disc for your corrosive or sanitary process? Upload your media datasheet or contact our valve application engineers for a free material compatibility review.

Frequently Asked Questions (FAQ)

Q: Can I change the disc material on an existing Kinko butterfly valve without replacing the whole valve?
A: Yes, for most Kinko series (LT-100, LT-200), the disc is replaceable. However, the seat and stem bearings must also be compatible with the new disc material. Contact Kinko support for a retrofit kit.

Q: Which disc material offers the lowest torque for electric actuation?
A: Polished SS316 or nylon-coated ductile iron provides the lowest friction coefficient against EPDM or PTFE seats, reducing operating torque by up to 30% compared to uncoated SS304.

Q: Is SS316 always better than SS304?
A: Not always. SS304 is more ductile and sometimes preferred for cryogenic or high-impact applications. However, for corrosion resistance, SS316 is superior in 90% of industrial fluid applications.

Q: Does disc material affect fire safety rating?
A: Yes. For fire-safe designs, metal-seated discs (SS316 or Inconel) are required. Soft-coated discs (nylon, PTFE) are not fire-safe. Kinko offers fire-safe certified series upon request.

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ZHEJIANG KINKO FLUID EQUIPMENT CO.,LTD