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A lifting device configured to lift a bonnet of a blowout preventer. The lifting device includes two or more lifting pins, each lifting pin including, a body having an elongated shape and configured to enter through a hole in the bonnet; a shoulder connected to the body and having an external diamet

A lifting device configured to lift a bonnet of a blowout preventer. The lifting device includes two or more lifting pins, each lifting pin including, a body having an elongated shape and configured to enter through a hole in the bonnet; a shoulder connected to the body and having an external diameter larger than an external diameter of the body; and two or more threaded regions at different locations on the body and configured to receive threaded screws, each threaded region being formed in the body such that a coordinate of the threaded region in a given inertial system is substantially identical to a coordinate of a center of gravity of a corresponding bonnet in the same given inertial system when the lifting pin is inserted into a hole of the corresponding bonnet.

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1. A lifting device configured to lift a bonnet of a blowout preventer, the lifting device comprising: two or more lifting pins, each lifting pin including,a body having an elongated shape and configured to enter through a hole in the bonnet;a shoulder connected to the body and having an external di

1. A lifting device configured to lift a bonnet of a blowout preventer, the lifting device comprising: two or more lifting pins, each lifting pin including,a body having an elongated shape and configured to enter through a hole in the bonnet;a shoulder connected to the body and having an external diameter larger than an external diameter of the body; andtwo or more threaded regions at different locations on the body and configured to receive threaded screws, each threaded region being formed in the body such that a coordinate of the threaded region in a given inertial system is substantially identical to a coordinate of a center of gravity of a corresponding bonnet in the same given inertial system when the lifting pin is inserted into a hole of the corresponding bonnet. 2. The lifting device of claim 1, wherein each lifting pin is cylindrical. 3. The lifting device of claim 1, wherein each lifting pin includes an end threaded region extending along a longitudinal axis of the lifting pin and opposite to the shoulder. 4. The lifting device of claim 3, further comprising: a swivel hoist attached with a screw to the end threaded region and configured to be attached to a crane for moving the bonnet. 5. The lifting device of claim 1, further comprising: a safety pin attached to at least one of the two or more lifting pins, the safety pin extending partially inside the body of the at least one lifting pin in a radial direction. 6. The lifting device of claim 5, further comprising: a spring completely provided inside the body and configured to bias the safety pin; anda set screw configured to be screwed into the body to contact the spring and fix an end of the spring. 7. A method for lifting a bonnet of a blowout preventer with a lifting device, the method comprising: inserting two or more lifting pins to corresponding holes in the bonnet, each lifting pin including, a body having an elongated shape and a shoulder connected to the body and having an external diameter larger than an external diameter of the body;contacting the shoulder of the lifting pin with a shoulder of the corresponding hole in the bonnet;selecting a threaded region of two or more threaded regions formed at different locations in the body and configured to receive threaded screws, the selected threaded region being formed in the body such that a coordinate of the selected threaded region in a given inertial system is substantially identical to a coordinate of a center of gravity of the bonnet in the same given inertial system; andattaching a swivel hoist to the selected threaded region with a threaded screw. 8. The method of claim 7, further comprising: unlocking and opening the bonnet prior to inserting the lifting pins;closing the bonnet after the insertion of the lifting pins; andapplying a tension to the lifting pins with a crane. 9. The method of claim 8, further comprising: removing a pin holding a hinge of the bonnet attached to the blowout preventer; andremoving the bonnet from the blowout preventer. 10. The method of claim 9, further comprising: moving the bonnet while the bonnet does not experience sudden movements due to a misalignment of the coordinate of the center of gravity with the coordinate of the threaded region. 11. The method of claim 9, further comprising: inserting the two or more lifting pins into the bonnet until corresponding safety pins attached to two or more lifting pins exit the bonnet. 12. An adjustable lifting pin for lifting a bonnet of a blowout preventer, the lifting pin comprising: a body having an elongated shape and configured to enter through a hole in the bonnet, the body having an internal threaded region;a shoulder connected to the body and having an external diameter larger than an external diameter of the body;a pin having an external threaded region at a first end and configured to mate with the internal threaded region of the body, the pin also having a hole at a second end; anda swivel hoist attached to the second end of the pin and configured to be attached to a crane,wherein the pin is configured to be adjustable to enter or exit the body such that a coordinate of the hole in the pin in a given inertial system is substantially identical to a coordinate of a center of gravity of the bonnet in the same given inertial system when the lifting pin is inserted into the hole. 13. The adjustable lifting pin of claim 12, further comprising: a lock nut attached to the pin and configured to maintain in position the pin relative to the body during operation. 14. The adjustable lifting pin of claim 12, further comprising: plural marks formed on an exterior surface of the pin, each mark being indicative of a type of bonnet. 15. The adjustable lifting pin of claim 12, wherein the shoulder is cylindrical and has a smooth external surface. 16. The adjustable lifting pin of claim 12, wherein the hole has an internal threaded region extending along a longitudinal axis of the lifting pin and opposite to the shoulder. 17. A method for lifting a bonnet of a blowout preventer with an adjustable lifting pin, the method comprising: inserting the adjustable lifting pin into a hole in the bonnet, the adjustable lifting pin including a body having an elongated shape and an internal threaded region;contacting a shoulder connected to the body and having an external diameter larger than an external diameter of the body with a shoulder of the hole in the bonnet; andscrewing a pin into the body to adjust a length of the pin coming out of the body such that a coordinate of an internal threaded region of the pin in a given inertial system is substantially identical to a coordinate of a center of gravity of the bonnet in the same given inertial system, the pin having an external threaded region at a first end and configured to mate with the internal threaded region of the body, the pin also having the internal threaded region at the second end. 18. The method of claim 17, further comprising: unlocking and opening the bonnet prior to inserting the lifting pin;closing the bonnet after the insertion of the lifting pin; andapplying a tension to the lifting pin with a crane. 19. The method of claim 18, further comprising: removing a pin holding a hinge of the bonnet attached to the blowout preventer; andremoving the bonnet from the blowout preventer. 20. The method of claim 19, further comprising: moving the bonnet while the bonnet does not experience sudden movements due to a misalignment of the coordinate of the center of gravity with the coordinate of the internal threaded region.