In severe service applications such as oil & gas, coal chemical, and slurry transport, valve sealing surfaces face a triple attack of high-velocity particle erosion, chemical corrosion, and high-temperature oxidation. Even expensive nickel-based alloys or titanium substrates will rapidly wear, pit, and leak. How can surface hardness and corrosion resistance be dramatically improved without altering substrate toughness? Yongjia TONGBALL Valve Co., Ltd. (TONGBALL) provides the answer: HVOF (High Velocity Oxygen Fuel) thermal spray coating technology.
What is HVOF?
HVOF is a high-velocity flame spray process. It combusts fuel (kerosene, propylene) with oxygen under high pressure, producing a supersonic (≥2000 m/s) hot gas jet that accelerates powder particles (tungsten carbide, chromium carbide, Stellite) to molten or semi-molten state, impacting the substrate to form a dense, high-bond-strength coating.
Compared to conventional spray processes (plasma, arc spray), HVOF offers:
✅ Very high particle velocity → extremely low porosity (<1%), density near wrought material
✅ Low heat input → minimal thermal effect on substrate
✅ Superior bond strength → ≥ 70 MPa (typical spray: 20-40 MPa)
✅ Excellent as-sprayed finish → Ra ≤ 5 μm, grindable to mirror Ra ≤ 0.1 μm
TONGBALL’s HVOF Coating Solutions
TONGBALL has full-size coating capability from DN10 to DN800 with an annual capacity exceeding 40 million units. The company has mastered HVOF process parameters for multiple high-performance coating materials, including:
l Tungsten Carbide + Co/Cr (e.g., WC-12Co, WC-10Co4Cr) : Hardness 1100-1300 HV, extreme wear & erosion resistance, suitable for sand-laden crude, slurry, coal slurry.
l Chromium Carbide + NiCr (e.g., Cr₃C₂-25NiCr) : Hardness 700-900 HV, high-temperature wear & oxidation resistance, suitable for hot flue gas, hot oil, coking service.
l Stellite alloys (Stellite 1/6/12) : Hardness 500-700 HV, high-temperature, cavitation, and corrosion resistance, suitable for steam, acid, high-temp valves.
l Nickel-based alloys (Ni60/55/45) : Hardness 500-650 HV, balanced performance, cost-effective, suitable for general wear & corrosion.
Taking WC-10Co4Cr tungsten carbide coating as an example:
l Bond strength ≥ 70 MPa (well above industry typical 40 MPa)
l Surface hardness 1100-1300 HV (~HRC 70-72, 2-3 times harder than hardened stainless steel)
l Coating thickness 0.2-0.5 mm (customizable)
l Wear life >10x that of uncoated stainless steel, 3-5x that of Stellite hardfacing
This means: in abrasive media, a hard-seated ball valve with HVOF WC coating can extend sealing surface life from traditional 1-2 years to 5-10 years, significantly reducing maintenance downtime and TCO.
HVOF vs. Other Surface Enhancement Processes: Why HVOF?
Compared to other surface enhancement processes:
l Plasma spray: Bond strength only 20-40 MPa, porosity 2-5%, low heat input but insufficient coating density.
l Hardfacing (welding) : Metallurgical bond, no porosity, but high heat input, requires post-weld heat treatment, and cannot apply brittle materials like tungsten carbide.
l Hard chrome plating: Low cost but environmental restrictions, purely physical adhesion, prone to spalling.
l Unique value of HVOF: Achieves high strength, low porosity coating without altering substrate toughness (avoiding HAZ embrittlement from welding), and enables use of very hard and brittle materials like tungsten carbide — impossible with hardfacing.
Data Verification: Reliability of TONGBALL HVOF Coatings
TONGBALL performs strict inspection on every HVOF coating batch:
✅ Bond strength per ASTM C633: ≥70 MPa
✅ Hardness multi-point Vickers test: variation ≤5%
✅ Porosity metallographic examination: ≤1%, no through-pores
✅ Surface roughness as-sprayed Ra ≤5 μm, ground Ra ≤0.1 μm
✅ Thermal shock test 500°C quench to room temperature: no spalling, no cracks
After 1.5 million cycle seal testing, HVOF-coated hard seats still achieve zero leakage with coating intact.
“HVOF coating is the ‘last mile’ of hard sealing technology.”
—— TONGBALL Technical Director
“Without high-performance coatings, even the best substrate will fail rapidly under particle erosion. Our HVOF process turns tungsten carbide — a material impossible to hardface — into the standard for valve sealing surfaces.”
Typical Applications
TONGBALL HVOF-coated ball valve components are widely used in:
l Oil & gas production: Sand-laden fracturing fluid, shale gas flowback (WC coating, erosion resistant)
l Coal chemical: Black water, grey water, high-hardness slurry (WC or Cr₃C₂ coating, corrosion+wear resistant)
l Long-distance pipelines: Natural gas with H₂S/CO₂ (Stellite coating, corrosion + SSC resistant)
l Power FGD: Limestone slurry, gypsum slurry (WC coating, acidic slurry erosion resistant)
Summary: HVOF Coating — The Core Engine of TONGBALL Long-Life Hard Sealing
l Materials: Tungsten carbide, chromium carbide, Stellite, nickel alloys
l Process: HVOF spray, bond strength ≥70 MPa, porosity <1%
l Effect: Sealing surface life increased 3-10x, TCO reduced >50%
l Capability: DN10-DN800, annual capacity 40 million units
With the integrated technology system of Materials + Precision Machining + HVOF Coating, Yongjia TONGBALL Valve continuously supplies long-life, maintenance-free ball valve core components to global customers. If you face challenges of severe erosion, high-temperature corrosion, or frequent cycling, TONGBALL’s HVOF-coated hard sealing solution is worthy of your trust.
