Abstract: An obvious deformation occurred at the hinged rotation movement of a ball valve and valve stem, resulting in a large area of flame spraying coating falling off on the surface. The reasons for the coating falling off were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis. The results show that the valve stem drived the ball valve to rotate by hinge, and the ball valve performed high-frequency and periodic motion during rotation. The alternating stress caused the creep deformation of the ball valve substrate, and the deformed substrate caused the brittle flame spraying coating to break and fall off in a large area.