Mud Motor Rotors
HVAF Thermal Spray Equipment and Wear Resistant Coatings for Mud Motor Rotors
Wear resistance of the mud rotor surface is one of the key factors of an oil well directional drilling cost.
While there is a consensus that “old school” hard chromium coatings are insufficient for the drilling application, there are still a lot of attempts to enhance HVOF tungsten carbide coatings with “ceramic sealants.” The whole idea of sealing a ground coating having less than 1% porosity seems pointless to us.
We believe that the reason for HVOF WCCoCr coating failures hides not in the 5 microns of a surface being sealed but in the HVOF process flaws. And we know how to fix it.
Kermetico HVAF technology and equipment provide a way to protect mud motor rotors with gas-tight, 1,350-1600+ HV300 hard and ductile tungsten carbide coatings. Other mud motor components, such as flow restrictors and drive shafts, also benefit from these coatings. And Kermetico produce Convertible HVAF + HVOF equipment for companies that still need to spray conventional HVOF coatings for conservative clients.
The Kermetico HVAF System Spraying a WCCoCr Coating onto a Mud Motor Rotor
Numerous researchers have found that Kermetico HVAF WCCoCr coatings provide wear resistance several times longer than HVOF or electrolytic hard chrome.
The Wear of Mud Rotors
Downhole drilling motors, or positive displacement motors (PDM), consist of a helically shaped metallic rotor rotating within a molded stationary elastomer lined stator.
The heart of the mud motor is the rotor-stator pair. The circulation of the rotor transforms the pressure of hydraulic energy of drilling mud into the mechanical energy causing the motion of the drill.
Mud-rotors have been plagued with excess wear, corrosion, erosion and coating delamination resulting in small drilling times. Most mud rotors had historically been chrome plated or nickel plated, but frequent coating failures have forced the industry search for other solutions.
Drilling mud is contaminated with chlorides that permeate the micro-cracks and pores of traditional chrome plating and corrode the underlying steel.
The appropriate coating should increase drilling times, reduce wear, increase corrosion resistance and minimize repair times.
The coating must be capable of sustaining horizontal and vertical flexing and needs to be impact resistant.
For performance in the harsh conditions the coating should:
- Have very low residual stresses
- Be as ductile as possible
- Have very high cohesive and adhesive strength
Kermetico HVAF Coating Features
Kermetico High Velocity Air Fuel (HVAF) has been shown to be very competitive for mud rotors’ protection.
HVAF carbide coatings ARE superior to HVOF rivals regarding both wear protection and production cost. The high velocity of the in-flight particles (greater than 1,000 m/s) in our HVAF process enables the production of very dense coatings with high bond strength.
Moreover, the small combustion spraying temperature (1,960-2,010°C | 3,560-3650°F depending on fuel gas) and gentle particle heating lead to minimal feedstock phase transformation and almost nonexistent elemental depletion/decomposition of the in-flight particles.
Furthermore, the replacement of HVOF using pure oxygen with air in the HVAF process significantly reduces the oxide content in the coatings, which is desirable for high-performance coatings.
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