HVOF Coatings for Severe Service Valves

Chrome carbide is one coating that can be done during manufacturing or repairs that extends service life of valves and other flow control components.

By Kelly Songer, Precision Spray & Coatings, Director of Valve Services

Valves are a vital component in oil and gas, water treatment, mining and chemical processing, regulating the flow of fluids with high precision and reliability.

Severe service valves are used in the most difficult environments within a process. These severe service environments include erosive, corrosive, high-pressure, high-temperature, and high-velocity media or slurry media.

Over time, valves experience wear leading to costly repairs or replacements. For valves facing severe service conditions, thermal spray coatings like high-velocity oxygen fuel (HVOF) applied coatings, specifically chrome carbide, offer a solution that significantly enhances the performance and longevity of critical components.

HVOF coatings: high performance for severe conditions

HVOF is a thermal spray process that involves spraying molten or heated material onto a surface at high velocity, creating a dense and durable coating. Developed in 1980, HVOF-applied chromium carbide has significantly advanced in the subsequent years, making it a good solution for valves and other components to extend the life of equipment by increasing wear and erosion resistance.

An orange robotic arm sprays a rack of ball valves with HVOF during a finishing process.

Ball valve component undergoing robotically applied HVOF spray process.
Source: Precision Spray & Coatings

The primary advantage of HVOF chrome carbide coatings is their mechanical bond, which offers superior adhesion compared to other spray processes. Unlike welded overlays, which create a metallurgical bond, HVOF coatings achieve a strong mechanical bond without altering the underlying material’s structure. This helps preserve the integrity of the valve while enhancing its performance.

Chrome carbide is particularly effective due to its exceptional hardness, wear resistance and ability to withstand high-temperature environments. Carbides are primarily used to create a hard surface to resist fretting, wear and erosion and to provide low coefficients of friction. Chrome carbides have an additional function of heat resistance and are generally prescribed for high-temperature applications.

A table with more than a dozen chrome carbide plated balls for ball valves

HVOF carbide coating balls for ball valves.
Source: Precision Spray & Coatings

These coatings are commonly applied to valves to enhance their wear resistance, hardness and durability. They provide excellent protection against harsh operating conditions. The dense, tough chrome carbide layer significantly improves the valve’s lifespan by reducing friction and preventing material degradation, making it an ideal choice for critical components exposed to extreme environments. This coating ensures the valves maintain optimal performance and reliability over time.
These characteristics make chrome carbide an ideal coating for valves, such as ball valves, that are subjected to erosive and corrosive conditions.

The need for valve repair and coating

Many operators choose to repair valves rather than replace them during shutdowns and planned maintenance. During the planned period, experienced vendors can be contracted to complete the repairs within a few weeks.

An employee uses a micrometer to inspect a lapped ball for a ball valve.

Inspection of chrome carbide-coated and lapped ball and seats.
Source: Precision Spray & Coatings

Valve repairs are a complex process involving the evaluation of components such as the stem, body and seats on all valves, and components such as the ball in ball valves. Soft goods like packing, gaskets and seals must be replaced, while metal parts can often be repaired through welding or coating to restore functionality. Repairing a valve instead of replacing it can save time and money for operators, especially because downtime is costly. The faster a turnaround happens, the faster the plant is returned to service. HVOF coatings can be an essential part of this repair process, restoring damaged surfaces and enhancing valve components’ resistance to wear and corrosion.

A cost-effective solution

When operators choose to finish valves with the addition of HVOF chrome carbide coatings, a valve’s lifespan is extended, minimizing the frequency of repairs and reducing long-term operational costs. The ability to modify and improve the valve during the repair process also provides an opportunity for performance optimization, making this solution even more attractive for industries that require high reliability. If you are an operator, working with a trusted valve repair service provider can save you not only money but time during crucial shutdowns, and can help prevent unscheduled maintenance and repairs in the future.

Kelly Songer is a third-generation industrial manufacturer with more than 20 years experience. In 2016, she was featured as a “Legacy Leader” by the National Association of Manufacturers and in 2017 she was honored with the Service Award from the Valve Manufacturers Association.

HVOF material options

Several types of materials can be HVOF coated, and the specific material chosen depends on the desired properties for the application. Here are some of the materials commonly used in HVOF coating:

Metallic Materials

Stainless steels: These offer excellent corrosion resistance, high strength and wear resistance.
- Examples: 316L, 904L, 410
Nickel Alloys: Often used for applications requiring high resistance to heat and oxidation. Examples: Inconel 625, Inconel 718, Monel
Cobalt Alloys: Known for high wear resistance, good corrosion resistance and high-temperature stability. Examples: Stellite 6, Stellite 21
Iron Alloys: These can be used to improve wear resistance in some cases. Examples: Hardened steel, cast iron
Titanium Alloys: Useful for applications needing a combination of strength, low weight, and corrosion resistance. Examples: Ti-6Al-4V, pure titanium (Grade 2, Grade 5)

Carbide Materials

Tungsten Carbide (WC) Coatings: These are widely used in applications where wear resistance is a priority, such as in mining, drilling and other harsh conditions.
Chromium Carbide (Cr₃C₂): Provides excellent wear resistance and is used in various applications, including oil & gas, petrochemical, mining and cement industries.

Composite Coatings

WC-Co (Tungsten Carbide-Cobalt): Composite coatings often combine hard ceramics like tungsten carbide with a metal matrix, such as cobalt, to improve wear resistance and toughness.
WC-Ni (Tungsten Carbide-Nickel): Another composite coating, this provides improved wear resistance while offering better toughness than pure tungsten carbide.

Other Alloy Materials

Copper Alloys: Coatings made from copper and its alloys can improve electrical conductivity and corrosion resistance. Examples: Bronze, brass.
Molybdenum: Molybdenum coatings are used for high-temperature applications requiring strength and wear resistance.

Common applications of HVOF coatings

Aerospace: Protection of turbine blades, compressor blades and other engine components.
Oil & Gas: Coatings for drill bits, pumps and valves exposed to extreme abrasion and corrosion.
Automotive: Coatings on engine components to improve wear resistance and protect against corrosion.
Mining and Cement: Coatings for tools and equipment exposed to high abrasion.

Considerations for HVOF Coating Materials

Adhesion Strength: The material must bond well with the substrate.
Wear Resistance: The material chosen should be able to withstand abrasive and erosive environments.
Thermal Properties: Some applications require materials with high resistance to heat and oxidation, such as in turbines.
Corrosion Resistance: In environments where exposure to chemicals or saltwater is a concern, corrosion-resistant materials like nickel alloys or stainless steels are often preferred.

Choosing the right material for an HVOF coating is crucial for ensuring the coating meets the performance and durability requirements of the specific application.

Repairing a ball valve: coating, grinding and lapping

Ball valves are a great candidate for HVOF coatings. The repair process for a ball valve begins with the disassembly and evaluation of its individual components. The valve is inspected for signs of wear, the damaged areas are identified, and if the valve is able to be repaired the coating is removed. Grit blasting is used to remove old coatings, paints and any scale buildup before the new coatings are applied to prepare for coating re-application, taking the components back to the base metal.

At this stage the roundness of the ball is verified and it is determined if it is still usable and repairable or must be replaced. Once all components are verified as complete and in spec, the surface is prepared, the HVOF coating process is performed, followed by grinding and lapping to achieve the required surface finish and dimensional tolerance. Grinding is a general abrasive process that refines the valve surface, while lapping is a precision abrasion process used to bring a surface to a desired finish or dimensional tolerance by removing an extremely small amount of material at a time, ensuring a smooth and even finish for a metal-to-metal seal.

A photo of a lapped ball for a ball valve on a table in the foreground of a valve repair shop.

Lapped chrome carbide-coated ball before reassembly.
Source: Precision Spray & Coatings

There are two types of lapping — rough lapping and finish lapping. Rough lapping is used to remove a lot of material quickly, while finish lapping removes an extremely small amount of material at a time to achieve a sealing surface. These processes are critical to ensuring that the ball valve, once repaired, functions as intended, providing a reliable and tight seal to prevent leaks.