Effect of HVOF spray coating on the tribological surface of onshore gate valves

Abstract

Gate valve is one of the most common design concepts in onshore Oil & Gas installations. This equipment is composed of a wedge-shaped obturator that performs linear sliding movements during activation. Fluid sealing is achieved through metallic contact between the surfaces of the gate and seat components. Metal surfaces are commonly hardened by heat treatment or coated with Stellite 6 alloy by plasma-transferred arc welding (PTAW). The application of high-velocity oxygen fuel (HVOF) coatings on these surfaces for wedge-gate valves has not yet been foreseen. In addition, comparative studies on the tribological performance of technical surfaces used in onshore wedge-gate valves are also scarce. Therefore, this study presents the results of tests performed on specimens using a ball-on-flat tribometer with linear reciprocating sliding, simulating a gate valve tribosystem in operation: flat (gate) and ball (seat). Martensitic stainless steel 13Cr was used with the contact interfaces under the following conditions: (A) heat treated, (B) Stellite 6 coating by PTAW, (C) Stellite 6 coating by HVOF, and (D) tungsten carbide coating by HVOF. The flat/ball tribological pairs investigated were A/B (TRIM 8), B/B (TRIM 5), C/B, and D/B. The coefficient of friction (COF), surface wear, and wear mechanisms were comparatively evaluated. The results showed that the newly proposed surfaces (C and D) are promising alternatives to reduce material consumption and improve the performance of valves in operation according to the application requirements.