Seal assembly for a pressure plate in a blowout preventer

A seal assembly for sealing a pressure plate against an opening in a blowout preventer body has a seal groove formed in the pressure plate and a seal in the seal groove. The seal groove has a first groove portion adjacent to a sealing face of the blowout preventer, and a second groove portion extending past the sealing face into the opening of the blowout preventer body. The seal has a first seal portion in the first groove portion and a second seal portion in the second groove portion.

FIELD

This relates to a seal for a pressure plate in a blowout preventer.

BACKGROUND

Referring toFIGS. 1 and 2, a blowout preventer10has a body12, rams14that carry ram blocks16, and an internal cavity18that is closed by a pressure plate20. The pressure plate20is removable to allow access to the interior cavity18to service the blowout preventer10, replace the ram blocks16, etc. The depicted blowout preventer10is a “double gate”, although other designs, such as a single, triple, etc. gate design could also be used.

Referring toFIG. 3, the pressure plate20carries block guides22and is installed against a sealing area24on body12that surrounds the interior cavity18shown inFIG. 1. Referring toFIG. 4 through 6, the typical method to seal the pressure plate20is to provide an “o”-ring face seal26about each of the openings of the cavity18. The “o”-rings26are contained in specifically sized grooves28that are machined into the pressure plate20. The groove28is sized such that the seal26protrudes out of the face of the groove28, as shown inFIG. 4. When the pressure plate20is installed, the “o”-rings26are compressed against the face of the body12and squeezed into the groove28, as shown inFIG. 5. Referring toFIG. 4 through 6, the “o”-ring takes the general shape of the groove28, but does not fill the entire volume and leaves spaces30, particularly in the corners of the rectangular groove28, as can be seen inFIG. 5. This compression of the “o”-ring seal26into the groove28initiates the seal to contain well bore fluids. When the internal pressure increases, the well fluids act against the “o”-rings26to maintain the seal. The well fluid pressure acts directly on the “o”-ring26to further compress it into the remaining spaces of the rectangular groove, as shown inFIG. 6. This seal system allows pressurized well fluid to act directly against the “o”-ring26and fill the groove28. This action causes “wetting” of the groove28and face of the body12up to the “point of seal” against the “o”-ring26.

SUMMARY

There is provided a seal assembly for sealing a pressure plate against an opening in a blowout preventer body, comprising a seal groove formed in the pressure plate and a seal. The seal groove has a first groove portion adjacent to a sealing face of the blowout preventer, and a second groove portion extending past the sealing face into the opening of the blowout preventer body. The seal has a first seal portion in the first groove portion and a second seal portion in the second groove portion.

According to another aspect, the first seal portion may be integrally formed with the second seal portion, or may be separate and distinct from the second seal portion.

According to another aspect, the seal groove may be defined by a plate secured within a recess in the pressure plate. The second seal portion may comprises a slotted seal positioned on an outer circumferential edge of the plate.

According to another aspect, the second seal portion may be extruded into the opening of the blowout preventer body when the pressure plate is installed on the blowout preventer body.

DETAILED DESCRIPTION

As discussed above, the prior art seal system causes “wetting” of the groove28and face of the body12up to the “point of seal” against the “o”-ring26. This action can often result in corrosion and pitting of the wetted steel surfaces because of the nature of the well bore fluids, particularly if salts are present. When the damage is severe, both the pressure plate20and face of the body12must be repaired to ensure they will seal properly, generally using an expensive weld and machining procedure. The process often “warps” the pressure plate20because the welding is confined to the groove side. When put back into use and bolted, further damage can occur from the nuts torqued against the warped outside surface. Repeated repairs also cause material degradation due to the repeated thermal cycles of welding and stress relieving.

Referring toFIG. 7 through 9, the depicted pressure plate20is designed to cover two cavity openings as can be seen inFIG. 1, which are different in both shape and size for this particular blowout preventer. The number, size and shape may be made to match any opening to be sealed. The seal assembly32carried by the pressure plate20is designed to protect both the body face and the pressure plate from corrosive well fluids and reduce repair frequency. This is accomplished by denying well fluids access to the normally wetted surfaces in other designs described above.

Referring toFIG. 7 through 9, each opening to be sealed is matched by an appropriately shaped, recessed profile34in the pressure plate20, which forms the groove35. Referring toFIG. 10, the outside edge36of the recess34, which forms the outside containment for the “o”-ring27, is preferably angled slightly to help hold the face seal “o”-ring27in place for assembly. In the depicted embodiment, the inside edge38of the groove35to contain the “o”-ring27consists of two parts. Referring toFIG. 14 through 16, the first part is an appropriately shaped plate40. For superior corrosion protection, stainless steel or chemically resistant composite are preferred choices of materials for this part. The plate40is contoured appropriately to match the opening to be sealed. Around the perimeter of the bottom side42of the plate is a notch44machined to receive a slotted “o”-ring46. “O”-ring27and slotted “o”-ring46may be considered a two-part seal between pressure plate20and blowout preventer body12in a groove defined by recessed profile34and plate40. A slotted “o”-ring design has been chosen for material availability and economic reasons. Other means may be employed, such as specifically shaped extruded profiles, cut to length and “joined” together, or integral moulded parts. These will be discussed in more detail below. The slotted “o”-ring46is sized to be “snug” around the profiled plate40without inducing too much stretching stress to cause failure. The slotted “o”-ring46may optionally be secured in place with a specific adhesive about the notch area.

Referring toFIG. 11, the combination of the plate40and the slotted “o”-ring46is sized to meet the opening with some of the slotted “o”-ring46protruding into the opening of the cavity18it is sealing. Referring toFIG. 9, the plate40and slotted “o”-ring46assembly may be secured to the pressure plate20with a stud and block guide22. These are common parts used in a blowout preventer of this type and are convenient to use to secure the plate40and slotted “o”-ring46assembly into the recess34if it is sealed appropriately as shown inFIG. 13. Once the plate40and slotted “o”-ring46assembly secured to the pressure plate12, the face seal “o”-ring27may be inserted into the resulting groove35, as shown inFIG. 10. Referring toFIGS. 10 and 11, when the pressure plate12is installed on the body12, the face seal “o”-ring27and slotted “o”-ring46are “squeezed” between the recess34and the seal surface of the body12.FIG. 11displays an approximate representation of the installed pressure plate12. It is important to note that the face seal “o”-ring27has sufficient space for compression during installation to prevent damage. This is evident by the “voids”48, or unfilled spaces in the groove area35that rubber from the face seal “o”-ring27has not filled. If an “o”-ring is not left sufficient space for compression, it can “bulge” out into the space between the mating steel surfaces and be damaged. This type of assembly problem is avoided by designing and positioning the slotted “o”-ring seal46such that excess slotted “o”-ring material “flows” out into the cavity18, as shown inFIG. 11. Referring toFIG. 12, when the well bore pressure increases, it acts upon the excess slotted “o”-ring material in the cavity18and forces it against the face seal “o”-ring27as the “voids” are filled within the seal system. In this manner, the face seal “o”-ring27conforms to its' confined space to maintain a seal by pressure applied to it from the slotted “o”-ring46, rather than pressure applied directly from corrosive well bore fluids. The plate40that houses the slotted “o”-ring46, sealed in place by the block guide22, protects the remainder of the recess in the pressure plate20. By denying the well bore fluids access to the face seal “o”-ring surfaces of the body12and the entire pressure plate20, corrosion of these critical seal areas is prevented. Repairs are greatly reduced and reliability substantially increased. As depicted, the groove35has two portions—one that is adjacent to the sealing surface24and another that extends into the inner cavity18. These portions may be distinct, or may be more generally defined, where the portion is defined by the function of the portion of the seal that is contained in that area. It will also be understood that the portion that extends into the inner cavity18is preferably also partially in contact with the sealing surface24of the body12.

Referring toFIGS. 17 and 18, it will be understood that other designs may also be used. In these examples, a seal groove50in pressure plate20that extends into the opening18to be sealed, as with the example discussed previously. Seal groove50has a first portion50athat is adjacent to the sealing area24, and a second portion50bthat extends out from under the sealing area24into the opening18. It will be noted that, in these examples, a plate40is not used to form the seal groove. A two-part seal52, which may or may not be integrally formed, is positioned within the seal groove50, such that it is compressed within the seal groove50when the pressure plate20is attached, and the pressure from the wellbore fluids is applied to the exposed portion of the seal52. A first portion52ais positioned in the first portion50aof the seal groove50to seal against the body12, while the second portion52bis positioned in the second portion50bof the seal groove, where it will extrude into the opening18when the pressure plate20is installed, and be exposed to the pressure of the wellbore fluids. While the portion of the pressure plate20that is within the inner cavity18is shown to be raised relative to the rest, it may also be sufficient to form a seal-retaining surface into the pressure plate20without a raised portion. The inner surface of groove50ais preferably curved to help retain seal52. InFIG. 17, the seal52is a single component, such as may be formed from an extruded piece of elastic material that is cut to the desired length and vulcanized InFIG. 18, an “o”-ring54is used with a gasket56. In these embodiments, the exposed surfaces, such as the central portion of the pressure plate20, are preferably coated in a rust-inhibiting surface, such as by electroplating.

The following claims are to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the described embodiments can be configured without departing from the scope of the claims. The illustrated embodiments have been set forth only as examples and should not be taken as limiting the invention. It is to be understood that, within the scope of the following claims, the invention may be practiced other than as specifically illustrated and described.