A method of inhibiting erosion of an interior surface of a process vessel by solid objects carried in a fluid passing over the interior surface includes providing at least one formation at or in close proximity to the interior surface to interfere with the flow of the fluid over the interior surface, and to interfere with the movement of the solid objects by the fluid. The invention extends to a process vessel (10) which includes a body (16) defining an interior vessel surface (20), a catalyst bed (12) in the body (16), retaining means (22) on the catalyst bed for retaining the catalyst bed in position, and at least one formation (26) at or in close proximity to the interior vessel surface above the retaining means for interfering with fluid flow above the retaining means.