Abstract: A subsea wellhead assembly has the capabilities of communicating from a tree assembly mounted on an inner wellhead housing to a casing annulus. A passage in the wellhead assembly extends within the bore of the wellhead housing from the casing annulus to the tree assembly. A portion of the passage is located within a casing hanger. The passage is opened and closed by a valve. The valve does not open the passage until the tree assembly is connected to the wellhead housing and a tubing hanger orientation sleeve lands in the wellhead assembly. The tubing hanger orientation sleeve actuates the valve when it lands to open the passage. When the passage is opened, the casing annulus is in fluid communication with the interior surface of the wellhead housing, which is in communication with the tree assembly.

Abstract: In a subsea wellhead assembly, a connector attaches a production riser or subsea tree to a wellhead housing. The connector includes a piston that cams a plurality of dogs into and out of engagement with the wellhead housing while sliding axially upward and downward relative to the wellhead housing. The piston is typically actuated by injecting hydraulic fluid into either an upper chamber or lower chamber to move the piston axially up or down. While in the axially downward, or locked position, the piston houses an override chamber. Hydraulic fluid is injected into the override chamber to move the piston axially upward and unlock the connector when the seals of the lower chamber fail.