What are “Metal Seats”?
Metal seated valves represent the fastest growing (by %) segment of the valve industry. These seats can be found in ball valves, butterfly valves, plug valves and others.
- Base Metal Contact (Gate and Globe Valves – Not Sliding Wear)
- Coated or Modified Metal (Most Common)
- Stellite Weld Overlay (Usually Stellite VI – Cobalt Based)
- “Surface Modification” of Sealing Surfaces: Ex. Nitriding, Boronizing, etc.
- Plating: Ex. Chromium Plating or ENP (Electroless Nickel Plating)
- HVOF Coating: Tungsten and Chromium Carbide are the most common
- Fused or Vacuum Deposition of “Coating” typically Tungsten Carbide
- There is no “One size fits all” for “Metal-to-metal” sealing. Coatings are very application dependent.
Metal Seated Valve Coating
1. HP-HVOF Process
- Chrome Carbide, Tungsten Carbide, Chrome Oxide and other specially formulated coatings.
- WC-Co / WC-Ni / WC-Co-Cr / WC-CrC-Ni
- Coating mechanically bonds to the Substrate Material.
- Mechanical bond – >12,000 psi bond strength for Carbides, 5,000 – 7,000 psi for Chrome Oxide Ceramic.
- Robotically positioned spray gun creates high kinetic energy allowing the coatings to be applied in a compressive state.
- Porosity – Poor Sealing on Gas
- Carbon Content makes these coatings vulnerable to Oxidation.
2. Spray & Fused Process
- Substrate material becomes annealed due to fusing temperatures; subsequent heat treatment required.
- Semi-molten coating “sags” or “sloughs” – gravity effect
- Coated Surface is “finish” machined using either CBN (cubic boron nitride) or PCD (polycrystalline diamond) tooling.
- Very Low Porosity – Best for small molecule gas and particles smaller than 1 micron.
Once again, Ladish will continue To Mark Progress.