A curved flapper configuration in surface-controlled subsurface safety valves provides either a larger bore for well production or a smaller valve outside diameter. However, this configuration often relies heavily on resilient or elastomeric seals to achieve acceptable sealing performance. This paper describes a new contoured, non-resilient flapper (CNRF) closure mechanism that achieves a true metal-to-metal seal without an elastomeric or resilient seal and passes API 14A Class I and II testing. The CNRF technology can be incorporated into both the conventional "flat plate" flapper structure as well as the new contoured flapper design. The paper will discuss the design of the flapper closure mechanism and compare the design to conventional flapper structures. The paper will also discuss the extensive functional testing performed to a 7 inch CNRF tubing retrievable safety valve to verify the concept.
Metal-to-metal sealing technology has been incorporated into every area of tubing retrievable subsurface safety valves (SSSV), including the flapper mechanisms. However, until now, these flapper mechanisms have required some type of resilient or elastomeric seal to enable them to pass the low pressure test during an A.P.I. Class I and II - type verification test.' The new Class I and II CNRF design answers the industry's need for a true metal-to-metal flapper seal by eliminating the dependency of the flapper on the resilient seal for a Class I and II rating. The new CNRF design uses a spherical-to-spherical contact in its novel sealing arrangement. Spherical, rotating-ball sealing technology has been utilized in ball-type SSSV closure mechanisms for over 40 years. A resilient closure seal on the ball or seat has not been required for a Class I and II rating by some manufacturers on their designs. Elements of this proven technology have been incorporated into the flapper closure mechanism, resulting in a vast improvement in sealing capabilities. The spherical-tospherical sealing surface also allows the flapper'sgeometry and physical dimensions to be contoured. This allows the annular space in which the flapper resides to be greatly reduced in the open position. The following comparison of the flat flapper design to the new CNRF design will illustrate how reducing the spacerequirements for the open flapper can be beneficial to the SSSV designer.
A conventional flat flapper has a two-dimensional sealing surface. The actual contact area between the flapper and its mating seat is characterized by a flat, narrow, circular ring. A resilient or elastomeric seal is then added to increase the sealing ability of the mechanism in a sand slurry environment. The resilient seal is designed to initiate the sealing process, with the metal-to-metal flapper seal occurring last to provide the primary closure (Figure 1). In the spherical-to-conical seat structure the flapper's spherical sealing surface engages its mating seat to form a conical seal, thus providing alignment and continuous contact which is described as a circular line.
