Anodic Protective Seal in a Blowout Preventer

Abstract

An anodic sacrificial seal element is installed at vulnerable regions of a blowout preventer. A zinc cylinder, for example, is included at the well-bore pressure side of a bonnet which seals around a rod as it extends through a bonnet which joins an actuator to the body of the BOP. Similarly, a zinc O-ring may be used in a seal groove provided between the bonnet and the body of the BOP. In this way, the high electropotential of the material from which the additional seal element is made is oxidized first, before any attack on the BOP material, thereby increasing the time period between maintenance events on the BOP.

Description

DESCRIPTION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/61 8,489 filed Oct. 13, 2004.

FIELD OF THE INVENTION

The present invention relates generally to the field of metal systems subjected to harsh, corrosive environments, such as for example blowout preventers for tubing, and, more particularly, to a sacrificial anodic seal element for use in such an environment on such a metal system.

BACKGROUND OF THE INVENTION

The use of a blowout preventer in drilling, completion, workover, and production of oil and gas wells is well known. Such a blowout preventer generally includes a housing with a bore extending through the housing. Opposed chambers extend laterally on either side of the bore in the housing and communicate with the bore. Rams within the chambers are connected to rods that are supported for moving the rams inwardly into the bore to close off the bore. The rods also serve to retract outwardly from the bore to open the bore.

A volume is provided within a bonnet to provide a space to receive the ram when the rod is pulled back away from the bore. This volume is typically filled with a stagnant liquid having corrosive properties. Over time, the bonnet material which defines the volume begins to corrode and eventually the entire actuator assembly, including the ram, must be refurbished or replaced. This maintenance evolution costs money and causes down time for the well.

Relatively inaccessible blowout preventers, such as those mounted on the ocean bottom, one typical solution involves coating BOP surfaces which are subjected to the stagnant corrosive fluid with a layer of Inconel® and machining the Inconel® to design tolerances. However, this solution is expensive and is not tolerable for most BOPs and applications. Inconel® is a registered trademark of Inco Alloys International, Inc.

Thus, there remains a need for a structure which eliminates or at least slows the corrosion of material of the bonnet of a BOP and similar structures. The present invention is directed to filling this need in the art.

SUMMARY OF THE INVENTION

The present invention addresses these and other needs in the art by providing an anodic sacrificial seal element at vulnerable regions of a blowout preventer. A zinc cylinder, for example, is included at the well-bore pressure side of a bonnet which seals around the rod as it extends through the bonnet. Similarly, a zinc O-ring may be used in the seal groove provided between the bonnet and the body of the BOP. In this way, the high electropotential of the material from which the additional, sacrificial seal element is made is oxidized first, before any attack on the BOP material, thereby increasing the time necessary between maintenance events on the BOP.

These and other features and advantages of this invention will be readily apparent to those skilled in the art from a review of the following detailed description along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages and object of the present invention are attained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to embodiments thereof which are illustrated in the appended drawings.

FIG. 1 is an elevation section view of an actuator and coiled tubing ram constructed in accordance with the teachings of the present invention.

FIG. 2 is a detail view of an O-ring seal between the body of the BOP and the bonnet.

FIG. 3 is a detail view of an anodic seal element around the rod of the ram assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to all of the drawing figures, FIG. 1 illustrates the present invention in its intended environment. While the present invention is illustrated at particular point in a BOP, it will be immediately apparent to those of skill in the art that the invention may be applied in other regions of this and similar structures having pressure seals and stagnant, corrosion fluid captured within a vulnerable metal body.

An actuator assembly 10 includes a cylinder body 12 enclosing a cylinder chamber 14 having a piston 16 therein. A close port 18 directs hydraulic fluid pressure to one side of the piston 16 to close the ram, and an open port 20 directs hydraulic fluid pressure to the other side of the piston to open the ram. The piston 16 connects to a rod 22 which terminates at a ram head 24 which connects to a ram 26, for example, although any other appropriate type of ram head may be used.

The ram 26 moves within a body 28 of a blowout preventer which is aligned along a center axis 30. It is to be understood that a similar ram and associated actuator assembly (not shown in FIG. 1) are positioned opposite the ram 26 to enclose a tubular, such as a coiled tubing 32, passing through a bore 33 of the blowout preventer. Upon actuation, the ram 26 closes in around the coiled tubing 32.

The rod 22 penetrates to well-bore pressure through a bonnet 36. A seal member 38 seals between the rod 22 and the bonnet 36. Seals in this application are commonly known in the art. The present invention, however, provides an anodic sacrificial element 40 between the seal member 38 and the bore 33 of the BOP. The element 40 is preferably formed of zinc which has an electropotential of +0.758, far higher than that of iron, which has an electropotential of +0.441, although another appropriate material may be used so long as its electropotential is higher than that of the material from which the BOP is made.

The bonnet 36 defines a chamber 42 to receive the ram 26 when the ram is retracted. This chamber 42 serves as a reservoir of stagnant fluid, typically well-bore fluid, over extended period when the BOP is inactive. This stagnant fluid is an electrolyte creating a corrosive atmosphere for the materials of the BOP. The anodic element 40 thus corrodes in order to save the BOP materials.

An O-ring seal 44 is also commonly used between the bonnet 36 and the body 28 of the BOP. In the present invention, however, an anodic seal element 46 is provided between the seal 44 and the well-bore 33 to provide an anodic protective function like that of the element 40.

It should also be apparent to those skilled in the art that, while the foregoing has emphasized the present invention in the environment of a blowout preventer, the present invention should not be perceived as limited to only this application. The present invention may be adapted to use in any seal between two moving metal elements which must exist in a corrosive environment.

The principles, preferred embodiments, and mode of operation of the present invention have been described in the foregoing specification. This invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention.

Claims

1. A blowout preventer actuator assembly joined to a blowout preventer body, the assembly comprising:

a bonnet;

a cylinder body coupled to the bonnet and enclosing a cylinder chamber having a piston therein;

a rod connected to the piston at one end and to a ram head at the other end; and

a first anodic seal element between the bonnet and the rod.

2. The assembly of claim 1, wherein the first anodic seal element is made of zinc.

3. The assembly of claim 1, further comprising a first pressure seal element adjacent the first anodic seal element.

4. The assembly of claim 1, wherein the first anodic seal element defines a cylinder.

5. The assembly of claim 1, further comprising a second anodic seal element between the bonnet and the blowout preventer body.

6. The assembly of claim 5, wherein the second anodic seal element is made of zinc.

7. The assembly of claim 5, wherein the second anodic seal element is made of a material having an electropotential higher than the material from which either the bonnet or the rod are made.

8. The assembly of claim 5, further comprising a second pressure seal element adjacent the second anodic seal element.

9. The assembly of claim 8, wherein the second pressure seal element and the second anodic element are each formed in the shape of a ring.

10. A seal element between first and second metal components comprising an anodic member having an electropotential higher than either of the first and second metal components and positioned adjacent a pressure seal element.