High-pressure cap equalization valve

1. A cap for protecting a sealing surface of a hub of a subsea device with an interior environment, comprising:

a pressure-seal portion configured to form a pressure seal between an inner face of the cap and the hub;

an equalization valve, comprising:

a valve body comprising a pressure equalization conduit;

a sleeve disposed about the valve body and comprising a port allowing fluid communication across the sleeve, the sleeve being exposed to the environment outside the cap;

a valve spring configured to bias the sleeve to a closed position;

wherein the sleeve is configured to move to an open position in response to a force that depresses the sleeve and causes the valve spring to compress;

wherein the port is fluidly isolated from the pressure equalization conduit in the closed position and is in fluid communication with the pressure equalization conduit in the open position; and

a fluid conduit that couples the inner face of the cap and the pressure equalization conduit such that, in the open position, the interior environment of the subsea device is in fluid communication with the environment outside the cap through the equalization valve.

2. The cap of claim 1 wherein the equalization valve is positioned along the circumference of the cap.

3. The cap of claim 1 wherein the equalization valve is positioned on the outer face of the cap.

4. The cap of claim 1 wherein when the sleeve moves to the open position, pressure is equalized across the cap through a fluid path comprising the port, the pressure equalization conduit, and the fluid conduit.

5. The cap of claim 1 wherein the volume of fluid displaced in the exterior environment does not change when the sleeve moves from the closed position to the open position.

6. The cap of claim 1 wherein the valve spring comprises a spring constant less than 53 pounds/inch.

7. The cap of claim 1 further comprising a running tool configured to couple to the cap, wherein the running tool is configured to depress the sleeve of the equalization valve and remove the cap from the hub.

8. The cap of claim 7 wherein the running tool is configured to be operated by a remotely-operated vehicle.

9. A subsea hydrocarbon production system, comprising:

a Christmas tree to control the flow of hydrocarbons from a wellhead, comprising a hub;

a cap to protect a sealing surface of the hub, comprising:

a pressure-seal portion configured to form a pressure seal between an inner face of the cap and the hub;

an equalization valve, comprising:

a valve body comprising a pressure equalization conduit;

a sleeve disposed about the valve body and comprising a port allowing fluid communication across the sleeve, the sleeve being exposed to the environment outside the cap;

a valve spring configured to bias the sleeve to a closed position;

wherein the sleeve is configured to move to an open position in response to a force that depresses the sleeve and causes the valve spring to compress;

wherein the port is fluidly isolated from the pressure equalization conduit in the closed position and is in fluid communication with the pressure equalization conduit in the open position; and

a fluid conduit that couples the inner face of the cap and the pressure equalization conduit such that, in the open position, an interior environment of the Christmas tree is in fluid communication with the environment outside the cap through the equalization valve.

10. A method of protecting a sealing surface of a hub of a subsea device and isolating an interior environment of the subsea device from an exterior environment, comprising:

installing a cap on the hub, thereby creating a pressure seal between the cap and the hub, wherein the cap is exposed to the exterior environment;

lowering the subsea device into a fluid, the fluid comprising the exterior environment, wherein the densities of the exterior environment and interior environment are different such that a pressure differential is created across the cap when lowering the subsea device;

depressing a sleeve of an equalization valve to an open position creating a fluid path between the exterior environment and the interior environment, wherein the sleeve is biased to a closed position; and

removing the cap from the hub.

11. The method of claim 10 wherein depressing the sleeve to the open position causes pressure to be equalized across the cap through the fluid path.

12. The method of claim 10 wherein the sleeve is biased to the closed position by a valve spring.

13. The method of claim 12 wherein the valve spring comprises a spring constant less than 53 pounds/inch.

14. The method of claim 10 wherein a running tool depresses the sleeve of the equalization valve and removes the cap from the hub.

15. The method of claim 14 wherein a remotely-operated vehicle operates the running tool.

16. The method of claim 10 further comprising monitoring the pressure differential across the cap and, when the pressure differential is within an acceptable range, removing the cap from the hub.

17. The method of claim 16 wherein an ROV monitors the pressure differential across the cap.

18. The method of claim 10 further comprising unlocking the cap from the hub prior to removing the cap from the hub.

19. The method of claim 10 further comprising coupling another subsea device to the hub after removing the cap from the hub.