VALVE MAGAZINE Winter 2025

PROTECTIVE COATINGS FOR VALVES

Repairing a ball valve: coating, grinding and lapping

Lapped chrome carbide-coated ball before reassembly.

Ball valves are a great candidate for HVOF coatings. The repair process for a ball valve begins with the disas sembly 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-applica tion, 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 grind- ing 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. There are two types of lapping: rough lapping and finish lapping. Rough lapping removes 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.

Inspection of chrome carbide-coated and lapped ball and seats.

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 equip ment by increasing wear and erosion resistance. 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

Chrome carbide is an ideal coating for valves.

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

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VALVE MAGAZINE

WINTER 2025