Equipment operating in these harsh conditions is subject to severe degradation. These wear mechanisms include abrasion and/or erosion from drilling muds, corrosion (pitting and crevice attack) and stress corrosion cracking due to hot acidic conditions. To counteract this, thermal spray coatings are becoming more widely used by the major manufacturers in their efforts to reduce downtime and improve the performance of their tools and equipment.
Some of the more common applications include:
- ball and gate valves
A High Velocity Oxygen-Fuel (HVOF) tungsten carbide (WC) thermal spray coating is applied to the metal-to-metal (MTM) sealing faces of the valve, which are then diamond ground and polished to a super-finish. This allows for a very intimate relationship between the sealing faces, whilst providing a very smooth corrosion and abrasion-resistant surface, designed to withstand the aggressive/high pressure fluids flowing within.
Highly alloyed metal matrix – tungsten carbide (WC) bearing materials are being developed in order to reduce the sticking effects common in valves that have been dormant for long periods. These new coating materials reduce the operating torque requirement, and as a result smaller actuators and supporting systems can be used, thus reducing overall cost of plant and equipment.
- mud rotors
Due to the combined effects of severe erosion and corrosion experienced by mud rotors, surface enhancement is required to provide protection against premature failure. Historically, this has been done via hard chromium plating; however, due to increased environmental concerns, and the improved performance of thermal spray coatings, HVOF tungsten carbide / chromium carbide (WC/Cr2C3-Ni) is now being specified by the major OEM’s.
- directional drilling (actuation components)
Thermal spray coatings are applied to a multitude of components within the actuation systems. Their use has been proven to significantly reduce maintenance costs as well as dramatically increase downhole time between planned refurbishment. HVOF tungsten carbide is used routinely to protect against impact damage, abrasion and chemical corrosion.
- well logging sensors
Thermal spray coatings are applied to many components that make up well logging sensors. HVOF tungsten carbide composite coating is used for wear protection on many of the parts that move against the tunnel wall and are being used more and more as the industry drives to reduce weight and equipment diameter. Thermally sprayed ceramic coatings are also applied to formation resistivity sensors to provide electrical insulation between sub-assemblies and/or the external environment.