Ball Valve with SS316 + Ni55 Metal Seat — ANSI 150 Flange for High Temperature, Slurry, and Fluids with Suspended Solids

The ball valve with SS316 + Ni55 metal seat is the solution for services where conventional PTFE seats cannot operate: high temperature above 200 °C, fluids with abrasive suspended solids that would wear out PTFE in weeks, industrial slurries with particles that would lodge between the seat and the ball preventing tight shut-off, and process fluids that can carbonize or solidify in the elastomeric seat, blocking the valve in the open or closed position. The metal-to-metal seal between the Ni55-coated SS316 ball and the SS316 + Ni55 seat withstands all these conditions that PTFE cannot handle — with operating temperatures up to 350 °C and abrasive wear resistance far superior to fluoropolymer.

Why metal seat and not PTFE — the four services where PTFE is not viable

1. High temperature above 200 °C

PTFE maintains its sealing properties up to approximately 180–200 °C in continuous service. Above that range, PTFE begins to creep under the seat load — it progressively loses its shape and its contact force with the ball, resulting in leaks in the closed position that worsen over time. The SS316 + Ni55 metal seat operates without degradation from -20 °C to 350 °C — covering high-pressure steam services, high-temperature thermal oils, combustion gases, and process fluids at temperatures that PTFE cannot handle.

2. Fluids with abrasive suspended solids

In fluids with solid particles — sands, mineral fines, catalysts, process slurries, ore pulps — the particles act as an abrasive on the PTFE seat surface with each opening and closing cycle. PTFE, being a relatively soft material (Shore D hardness ~55), wears out quickly in this service. The Ni55 coating (nickel with an approximate Rockwell C hardness of 55 — equivalent to ~55 HRC) has a much higher surface hardness than PTFE and resists particle abrasion for thousands of cycles without significant material loss.

3. Slurries and fluids with high solids content

In industrial slurries (dredging slurries, wastewater treatment slurries, ore pulps, drilling slurries), suspended solids lodge between the seat and the ball when the valve closes — creating a layer of solid material that prevents direct contact between the sealing surfaces. PTFE, being compressible, can temporarily mask these particles, but over time it permanently deforms around the incrustations and loses its seal. The metal-to-metal seal has less tendency to trap particles, and the higher hardness of the surfaces allows particles to be expelled or crushed upon closing without damaging the seat.

4. Fluids that would carbonize or solidify the PTFE seat

Some process fluids — asphalt, pitch, high-melting-point paraffins, molten polymers, thermoplastic resins — can solidify or carbonize in the PTFE seat when the valve remains closed for extended periods. The solidified material adheres to the PTFE and can block the valve's opening or tear off fragments of the seat when forcing the opening. The metal seat does not have this problem — the surface hardness of Ni55 does not allow the adhesion of solid deposits in the same way as porous PTFE on a microscopic scale.

The Ni55 coating — why this material for the seat

Ni55 is a hard nickel coating applied by electrochemical or thermal process on the SS316 substrate. Its main properties for valve applications:

• Surface hardness: Approximately 55 HRC (Rockwell C) — comparable to hardened tool steel. Much higher than base SS316 (~22 HRC) and PTFE (~Shore D 55, equivalent to ~5 HRC). This hardness provides abrasive wear resistance.
• Corrosion resistance: Nickel has excellent corrosion resistance in the most common industrial fluids — better than SS316 in some acids and alkalis. The SS316 substrate additionally provides the base resistance of stainless steel.
• Surface finish: Ni55 can be polished to Ra ≤ 0.4 µm — the mirror finish necessary for a tight metal-to-metal seal. The quality of the surface finish of the seat and ball directly determines the tightness of the metal seal.
• Temperature: Ni55 maintains its hardness and adhesion properties up to 350 °C — sufficient for high-pressure steam services, thermal oils, and high-temperature process gases.
• Coating thickness: The thickness of the Ni55 over the SS316 substrate is sufficient so that normal abrasive wear in service does not expose the base SS316 during the valve's design service life.

Metal-to-metal seal vs. PTFE seal — comparative tightness

An important difference that the specifier should be aware of: the metal-to-metal seal does not provide the same hermetic tightness as the PTFE seal under low differential pressure conditions.

• PTFE Seal: PTFE is compressible and conforms to the micro-irregularities of the ball — the PTFE-metal seal is tight even with very low differential pressures because the polymer flows to fill any microscopic surface imperfections.
• Metal-to-metal seal: The contact between two hardened metal surfaces depends on the precision of machining and the surface finish of both parts. With an Ra ≤ 0.4 µm finish and very precise tolerance adjustment, the metal-to-metal seal is very good — but it generally allows for detectable micro-leakage in low-pressure tests that PTFE would not. In industrial practice, the metal-to-metal seal in well-made ball valves provides sufficient tightness for all services where it is specified (steam, slurries, high temperature) — but it should not be specified if total hermetic tightness is required in gas tests at low differential pressure.

Construction Materials

• Body: Two pieces in CF8M stainless steel (ASTM A351) — cast equivalent of SS316
• Ball: Solid SS316 with Ni55 coating on the entire sealing surface — floating ball
• Seat: SS316 with Ni55 coating — metal-to-metal seal with the coated ball
• Stem: SS316 stainless steel with expanded graphite packing — graphite is the standard packing material for high-temperature services where PTFE is not sufficient
• Connection: ANSI 150 raised face (RF) flanges, ASME B16.5 drilling
• Actuator mount: Integrated ISO 5211

Technical Specifications

• Type: Quarter-turn floating ball
• Body design: Two-piece body
Body material: CF8M (ASTM A351) — cast SS316 equivalent
• Ball: SS316 + Ni55 coating
• Seat: SS316 + Ni55 coating — metal-to-metal seal
• Stem: SS316 with expanded graphite packing
• Connection: ANSI 150 RF flanges — face-to-face ASME B16.10
• Flange drilling: ASME B16.5
• Available diameters: 1½" (DN40), 2" (DN50), 2½" (DN65), 3" (DN80)
• Nominal pressure: ANSI 150 — up to 290 psi (20 bar) at 38 °C
• Operating temperature: -20 °C to +350 °C — far exceeding PTFE's limit
• Seal type: Metal-to-metal (hard seat)
• Actuator mount: ISO 5211
• Recommended flange gasket: SS316 + graphite spiral wound for high temperature

Comparison — ball with PTFE seat vs. ball with Ni55 metal seat

Automation — high-temperature considerations

In high-temperature services (above 200 °C), actuator selection and mounting require additional considerations compared to standard services:

• Stem extension (yoke extension): When the fluid temperature exceeds 80–100 °C, the temperature at the top of the stem — where the actuator is mounted — can be high enough to damage the actuator's seals and electronics. A stem extension distances the actuator from the hot body and allows sufficient thermal dissipation to protect the actuator.
• Pneumatic actuator for high temperature: An aluminum or stainless steel pneumatic actuator with the correct stem extension is the most common configuration for automating high-temperature valves — it has no electronic components in the actuator body that could be damaged by temperature.
• Electric actuator for high temperature: Conventional electric actuators have a maximum ambient temperature of 60–80 °C. For services where the valve body temperature exceeds 150 °C, specify a high-temperature electric actuator or a pneumatic actuator with an extension.

• See ball valve assemblies with pneumatic actuator →
• See ball valve assemblies with electric actuator →

Main industries and applications

• Wastewater treatment — primary and secondary sludge: Isolation and control of sludge in municipal and industrial wastewater treatment plants. Primary sludge (density ~1.02–1.05 g/cm³, solids 2–8%) and secondary sludge (solids 0.5–2%) contain particles that would rapidly degrade PTFE — the valve with a Ni55 metal seat is the standard specification for this service.
• Mining — ore pulps and process slurries: Isolation in ore pulp lines in flotation, leaching, and concentration plants. Mineral pulps (20–50% by weight solids, abrasive particles of quartz, pyrites, and other hard minerals) are the most abrasive service for valves — the Ni55 of the seat and ball provides the necessary wear resistance for an acceptable service life.
• High-temperature steam (150–350 °C): Isolation of high-pressure steam lines in industrial process plants, cogeneration, and thermal power plants where the temperature exceeds the PTFE limit. The valve with a Ni55 seat and graphite packing covers the full range of process steam up to 350 °C.
• Refining — heavy oils and asphalt: Control of high-viscosity, high-temperature fluids in vacuum distillation units, coking, and asphalt production. Heavy oil and asphalt at temperatures of 200–350 °C would solidify in the PTFE seat upon cooling — the metal seat does not have this problem.
• Paper industry — pulp and process slurries: Isolation in cellulose pulp lines (2–12% solids), kaolin slurries, and lime slurries in kraft paper plants. Cellulose pulp has fibers that lodge between the PTFE seat and the ball — the metal seat provides greater resistance to fiber trapping.
• High-temperature thermal oils: Industrial heating systems with thermal oil (Therminol, Dowtherm, Mobiltherm) at temperatures of 200–350 °C in presses, calenders, reactors, and temperature-controlled process systems. Thermal oil at these temperatures exceeds the PTFE limit — the Ni55 seat with graphite packing is the correct specification.
• Combustion gases and high-temperature fluids: Isolation in high-temperature process gas lines, air preheaters, and heat recovery units where the fluid temperature consistently exceeds 200 °C.

For the complete range of flanged SS316 ball valves, see the ANSI flanged ball valves category →

Data Sheet