Valve operating device and method of overriding a malfunctioning valve operating device

1. A valve operating device for operating a subsea valve, the valve operating device comprising:

a housing;

thrust bearings supported by the housing, the thrust bearings comprising a connection part;

a chamber within the housing, the chamber comprising a first part of a linear guide;

a rotational shaft comprising a first end having an external interface and being located outside the chamber and the housing and a second end located inside the chamber, the rotational shaft comprising a first portion having a connection part connected to the connection part of the thrust bearings to form a connection therebetween which allows rotational movement of the rotational shaft while preventing axial movement of the rotational shaft relative to the housing, a second portion having a threaded portion and being arranged inside the chamber, and an intermediate portion located between the first portion and the second portion; and

a linear shaft arranged within the chamber, the linear shaft comprising a first portion and a second portion, the first portion having a threaded portion interacting with the threaded portion of the rotational shaft to form a threaded connection which translates rotational movement of the rotational shaft to linear movement of the linear shaft, and the second portion being connectable to a valve stem which operates the valve, wherein the linear shaft also comprises a second part of the linear guide, the first and second parts of the linear guide preventing rotation of the linear shaft relative to the housing;

wherein the rotational shaft comprises a pre-machined hole extending from the first end of the rotational shaft and along a center axis of the rotational shaft over a part of an axial length of the rotational shaft.

2. The valve operating device according to claim 1 , wherein the pre-machined hole extends to or past the connection part of the rotational shaft.

3. The valve operating device according to claim 1 , wherein the intermediate portion comprises a weakened part.

4. The valve operating device according to claim 3 , wherein the weakened part is positioned within the chamber.

5. The valve operating device according to claim 3 , wherein the weakened part is formed by a reduction in an outer diameter of the rotational shaft.

6. The valve operating device according to claim 5 , wherein the connection part of the rotational shaft comprises a recess with a reduced diameter, and wherein the weakened part is formed by the recess.

7. The valve operating device according to claim 4 , wherein the weakened part is arranged at the connection part of the rotational shaft or at a position further away from the external interface than the connection part of the rotational shaft.

8. A subsea valve tree comprising a subsea valve and a valve operating device according to any of claims 1-7 .

9. A method of overriding a malfunctioning valve operating device according to claim 1 , wherein the method comprises the steps of:

connecting a machining unit with a machining tool to the external interface of the rotational shaft;

machining a hole in a core of the rotational shaft guided by the pre-machined hole at least until a tip of the machining tool is at or close to the connection between the connection part of the thrust bearings and the connection part of the rotational shaft;

releasing the second portion of the rotational shaft from the first portion of the rotational shaft, and thus the housing, to thereby allow linear movement of the rotational shaft;

pushing onto a bottom of the machined hole in the core of the rotational shaft, and thus the valve stem connected to the valve, until the valve is operated to a desired position.

10. The method according to claim 9 , wherein the step of releasing the second portion of the rotational shaft from the first portion of the rotational shaft comprises:

providing a hydraulic override pushing tool with a stroke piston and bringing an end of the stroke piston in contact with the bottom of the machined hole; and

stroking the stroke piston onto the bottom of the machined hole until the rotational shaft breaks or separates.

11. The method according to claim 9 , wherein the step of releasing the second portion of the rotational shaft from the first portion of the rotational shaft comprises:

stroking the machining tool onto the bottom of the machined hole until the rotational shaft breaks or separates.

12. The method according to claim 9 , wherein the step of releasing the second portion of the rotational shaft from the first portion of the rotational shaft comprises:

machining out the core until the second portion is separated from the first portion.

13. The method according to claim 9 , wherein the method comprises, prior to the step of connecting the machining unit with the machining tool to the external interface of the rotational shaft:

removing an actuator and/or a motor connected to the external interface.

14. A valve operating device for operating a subsea valve, the valve operating device comprising:

a housing;

thrust bearings supported by the housing, the thrust bearings comprising a connection part;

a chamber within the housing, the chamber comprising a first part of a linear guide;

a rotational shaft comprising a first end having an external interface and being located outside the chamber and the housing and a second end located inside the chamber, the rotational shaft comprising a first portion having a connection part connected to the connection part of the thrust bearings to form a connection therebetween which allows rotational movement of the rotational shaft while preventing axial movement of the rotational shaft relative to the housing, a second portion having a threaded portion and being arranged inside the chamber, and an intermediate portion located between the first portion and the second portion; and

a linear shaft arranged within the chamber, the linear shaft comprising a first portion and a second portion, the first portion having a threaded portion interacting with the threaded portion of the rotational shaft to form a threaded connection which translates rotational movement of the rotational shaft to linear movement of the linear shaft, and the second portion being connectable to a valve stem which operates the valve, wherein the linear shaft also comprises a second part of the linear guide, the first and second parts of the linear guide preventing rotation of the linear shaft relative to the housing;

wherein the rotational shaft comprises a pre-machined hole extending from the first end of the rotational shaft and along a center axis of the rotational shaft over a part of an axial length of the rotational shaft; and

wherein the intermediate portion comprises a weakened part.