EP0139724B1

EP0139724B1 - Annular packing unit and insert

Info

Publication number: EP0139724B1
Application number: EP19840901685
Authority: EP
Inventors: Joseph H. Hynes; James A. Burton
Original assignee: Hydril LLC
Current assignee: Hydril LLC
Priority date: 1983-04-18
Filing date: 1984-04-06
Publication date: 1987-07-22
Also published as: CA1209468A; JPS60501068A; WO1984004130A1; DE3464944D1; BR8406796A; EP0139724A1

Abstract

A packer unit and packer insert (50, 51) adapted for use in an annular blowout preventer. The packer insert includes a generally longitudinal web (31, 33) with its leading edge facing the axial bore of the packing unit sloping from top to bottom in a general radially outward direction.

Description

This invention relates generally to annular blowout preventers and more particularly to a packing unit and insert for such packing unit.
For many years the design of blowout preventer packing units has followed the principles described in U.S. Patent No. 2,609,836. Such packing units incorporate metal inserts equally spaced about the packer longitudinal axis and embedded in an elastomeric material. Upon inward constriction or closure of the unit about a well drill pipe, the elastomeric material is anchored by the insert webs as it produces vertical folds stretching radially inwardly to seal the pipe. When the packer unit closes on itself as in the case when no pipe is present in the longitudinal bore of the unit, elastomeric material of the folds advancing toward the axis must at certain times stretch or extend as much as 350 to 400%. Repeated closures produce excessive wear and fatigue of the elastomeric or rubber material, reducing the useful life of the packer due to such extreme stretching.
U.S. Patent Nos. 3,958,808 and 3,917,293 disclose a packing unit and inserts for such a packing unit which significantly increases the packing unit cycle lifetime. The increase in cycle lifetime results from locating the insert webs in the elastomeric material with spacing from the central longitudinal axis. and from each other in a differential manner in order to provide differential anchoring about the axis of circularly spaced portions of the elastomeric material subject to inward displacement. Rubber flow paths are opened between the inserts.
In one form of the invention disclosed in the above referenced patents, the anchoring of the rubber by certain webs is closer to the central axis than anchoring of the material by other webs. In other words, webs effectively closer to and further from the axis may alternate about the axis. In other forms of the invention, the webs are generally equally spaced from the axis but certain pairs of the webs have closer circular spacing about that axis than other pairs of webs. Significant increases in packer cycle life are achieved by the invention disclosed in the above referenced patents. A continuing need exists, however, for increases in packer cycle life over and above those achieved by the above referenced inventions.
British Specification GB-A-2100775 discloses several forms of packing unit inserts also aimed at increasing cycle life of the unit. In one form, the upper portion of the inner edge of the web is inwardly directed to resist upward displacement of packer material responding to inward displacement of the packer by the piston. In another form of the unit, the inner edge of the web is straight and an inwardly extending projection is provided on the upper plate of the insert to resist upward bulging of packer material.
Thus, the object of the present invention is to provide a packer and an insert designed for the packer which produces increased packer unit cycle life.
Accordingly, the present invention provides an insert adapted for use in an annular blowout preventer packing unit and having top and bottom plates interconnected solely by a generally longitudinal web, and wherein at least a part of the inward edge of the web extends downwardly and outwardly from the axis of the bore, the improvement comprising the formation of the inward edge of the web such that it is sloped downwardly and outwardly in a curved manner from the bore axis generally from a relatively smaller radius near the top plate to a relatively greater radius near the bottom plate.
The present invention also provides a packer unit adapted for use in an annular blowout preventer having an axial bore, the packer unit adapted for compressive inward radial displacement toward the axis of the bore, the packer unit comprising metallic inserts generally spaced circularly about the axis, the inserts having webs which extend generally longitudinally and top and bottom plates integral with said webs, said webs providing the sole connection between the plates, at least a part of the inner edge of the web extending downwardly and outwardly from the axis of the bore, and an annulus of elastomeric material extending about the axis and embedding the webs so that the webs anchor the material during inward compressive displacement of the packer unit, characterized in that the inner edges of the webs slope downwardly and outwardly in a curved manner from the bore axis generally from a relatively smaller radius near the top plate to a relatively greater radius near the bottom plate.
The insert of the present invention with its inward edge sloping downwardly and inwardly generally from the top plate to the bottom plate produces a reversing of the pressure profile on the pipe moving the peak pressure to the lower end of the packing unit thereby producing less extrusion about the top plate of the packing unit, with resulting increase in cycle life of the packer unit. Further, the elastomeric material in which the insert is embedded is placed in compression at the top portion of the web thereby reducing tearing and extrusion above the top plate of the packing unit.
In the drawings:

Figure 1 illustrates in a top cross-section view an annular prior art packer constructed generally according to one embodiment of a long life packing unit illustrated in U.S. Patent Nos. 3,958,808 and 3,917,293 and having prior art inserts similar to that shown in Figure 4;
Figure 2 illustrates the novel shape of the webs of the inserts according to the invention which may be substituted for the prior art inserts of the packing unit of Figure 1;
Figure 3 illustrates the novel insert and the integral web of the invention and illustrates the resulting pressure profile of a packing unit of an annular blowout preventer closed about a pipe employing the improved insert according to the invention; and
Figure 4 illustrates the web shape of a prior art insert and a corresponding pressure profile resulting from its use in a packing unit of an annular blowout preventer.

Figure 1 illustrates in a cross-section view a packing unit disclosed in U.S. Patent Nos. 3,958,808 and 3,917,293. The ihvention to be described in detail below is related to the ones disclosed in such U.S. patents which are owned by the same assignee which owns the subject invention.
Figure 1 illustrates a prior art annular blowout preventer 10 and packing unit 18 having two differently shaped inserts 50 and 51 alternately spaced about the periphery of the packing unit. The inserts 50 and 51 are embedded in elastomeric material 34. Figure 2 illustrates an improved packing unit similar in construction to that illustrated in Figure 1, but in which inserts 50' and 51' according to the invention are substituted for the prior art inserts 50 and 51 of Figure 1.
Figure 2 shows the novel inserts 50' and 51' in an improved packing unit 18' in an annular blowout preventer which includes as is standard in the art of annular blowout preventers a metallic housing 11 which may be bolted to wellhead casing and other well equipment. The housing 11 contains a piston 15 movable upward in chamber 16 in response to fluid pressure exerted upwardly against the piston for radially constricting the annular improved packer unit 18' via pressure exertion from piston cam surface 22 against packer exterior surface 23. Surfaces 22 and 23 are frusto-conical and flared upwardly. The improved packer 18' when sufficiently radially inwardly displaced seals off about a well pipe 19 shown extending axially vertically through the preventer 10 in Figure 2 and in the absence of a pipe, the improved packer unit 18' will completely close off the vertical passage 20 through the preventer when the unit is sufficiently constricted by piston 15. Upon downward movement of the piston, the improved packer 18' expands radially outward to the open position. The improved packer unit 18' is normally confined in conventional fashion vertically under a housing cap, the lower interior surface 27 of which is illustrated in Figure 2.
In accordance with the disclosure of the above- mentioned U.S. patents, the prior art packer unit comprises metal inserts 51 and 50 generally circularly spaced about the longitudinal central axis of the unit 40. The prior art inserts 50 and 51 including webs 31 and 33 extend generally longitudinally. An annulus of elastomeric material 34 extending about the packer axis embeds the webs so that they anchor the material toward inward compressive displacement for constriction of the packer. The spacing of the webs from the axis and from each other creates differential anchoring about the axis of circularly spaced portions of the elastomeric material subject to inward displacement about the axis. As indicated in the above- mentioned U.S. patents such differential anchoring facilitates differential inward flow or extrusion of circularly spaced portions of the elastomeric material to the end that maximum stretching of the material is minimized and maximum stresses are correspondingly minimized.
Turning now to Figure 4, a prior art insert 51 (or alternatively 50) is illustrated as the packer unit in which it is a part is being closed about pipe 19. The web 33 of insert 51 is integral with a top plate 61 and a bottom plate 62. The shape of the top plate 61 and bottom plate 62 may be as those illustrated in Figure 1 and Figure 4 but are not important to this invention which is related to the inward edge shape of the web 33.
The prior art web 33 is characterized by an inward edge which slopes downwardly from a greater radius 63 to a smaller radius 68. In other words, the inward edge slopes downwardly from out to in. The prior art insert 51 illustrated in Figure 4 is illustrated in the condition of upward well pressure tending to force the elastomeric material 34 upward thereby extruding it past the upper plate 61. The pressure profile of the prior art packing unit embedding a prior art insert 51 as shown to the right of Figure 4 illustrates that the downwardly inwardly sloping inward edge of web 33 places the maximum point of pressure of the elastomeric material 34 against pipe 19 relatively high along the pipe. The arrows 64 showing the elastomeric material 34 along the upper part of the inner edge of the prior art insert 51 indicate that the elastomeric material is in tension tending to force the elastomeric material away from the embedded insert 51 and web 33, as the packer unit is closing about pipe 19. Such tension is believed to contribute to the tearing about the upper ridge 66 of upper plate 61 during repetitive opening and closing of the packer, thereby contributing to a tearing off of the upper part of the elastomeric material 34 as shown by dotted lines 67.
According to Figure 3, an insert 51' or alternatively an insert 50' which may replace inserts 51 or 50 of the packer unit illustrated in Figure 1 is illustrated having a top plate 61' and a bottom plate 62' but with novel integral web 33' constructed according to the invention. According to the invention, the inward edge of web 33' slopes downwardly from a smaller upward radius 64' to a larger downward radius 68'. In other words, the slope of the inward edge of the web of the insert slopes downwardly from a smaller radius to a larger radius. Another way to characterize the novel slope of the inner edge of web 33' is that it is sloped creating a positive angle (+8) with respect to the longitudinal axis of the packing unit in which it is embedded. The shape of the inner edge of web 33' is distinguished from the inner edge of web 33 of prior art insert 51 which slopes at a negative angle (-8) with respect to the longitudinal axis of the packing unit in which it is embedded.
As illustrated in Figure 3, the effect of the slope of the inward edge of web 33' causes relatively more of the elastomeric material 34 to be trapped in the lower part of the inner edge of web 33'. Such slope on the inner edge of the web 33' causes a lowering of the maximum point of the pressure profile against the pipe 19 about which the packer unit is closing as seen on the right hand side of Figure 3. It is believed that the downwardly outwardly sloping inner edge of the web 33' causes the elastomeric material to be placed in compression against the inner edge of the web 33' as illustrated at arrows 65. Even though the entire packing element is placed in tension because of the upward force of the well pressure below the packing unit tending to cause separation of the elastomeric material 34 from pipe 19 during pack-off about pipe 19, the elastomeric material bonded to the inner edge of web 33' is placed in compression. Less tearing at the upper edge 66' at the top plate 61' results from the compressive effect of the elastomeric material 34 at the top inner edge of the web 33'.
Figure 2 shows a preferred embodiment of the improved packer unit 18' similar to that in Figure 1 but where insert 50' having integral web 31' and insert 51' having integral web 33' are provided rather than the prior art packer unit of Figure 1 which has inserts 50 with their webs 31 and inserts 51 with their webs 33. Figure 2 showing the improved packer unit and inserts of the invention is a cross-section along lines 2-2 of Figure 1 with the improved inserts 50' and 51' replacing the prior art inserts 50 and 51, respectively. Figure 2 illustrates the downward sloping inner edge from the smaller topmost inner radius to a larger lowermost inner radius of the inner edge of the webs of 31' or 33' to inserts 50' or 51'.
Thus, the improved packer unit of elastomeric material with the novel inserts according to the invention is characterized by relatively more elastomeric material lower in the packer unit with more metal higher in the packer unit. The preferred range of internal angles of the lead edge of the webs of the inserts according to the invention is from a positive six (6) to twelve (12) degrees, depending on the geometry of the packer, causing the elastomeric material to move up into the upward part of the web (as illustrated in Figure 3), rather than pulling away (as illustrated in the prior art insert of Figure 4).
It should be emphasized that although the inserts are illustrated as being of the differential insert type as illustrated in Figures 1 and 2, the inserts may all be of identical shape equally spaced about the radius of the packer unit like those, for example, of U.S. Patent No. 2,609,836.
Thus, according to the invention, an insert and packer embedding one or more of such inserts is provided in which the inner edge of the web slopes downwardly from a relatively smaller inner radius adjacent the top plate to a relatively greater radius near the bottom plate. The shape of the inward edge of the web causes the rubber to be placed in relative compression at the upper inner edge of the web and thereby reduces tearing at its upper plate and places the pressure profile relatively lower along the pipe or other object in the bore of the packer unit during pack-off. Such lower pressure profile causes less tendency for tearing at the upper plate of the elastomeric material and contributes to a longer cycle I ife.

Claims

1. An insert (50, 51) for an annular packing unit (18) having an axial bore, said insert comprising a top plate (61), a bottom plate (62), and a web (31, 33) integral with and providing the sole connection between the top and bottom plates (61, 62), at least a part of the inner edge of the web (31, 33) extending downwardly and outwardly from the axis of the bore, characterized in that the inner edge of the web (31', 33') slopes downwardly and outwardly in a curved manner from the bore axis generally from a relatively smaller radius near the top plate (61') to a relatively greater radius near the bottom plate (62').

2. The insert of claim 1, characterized in that the inner edge of the web (31', 33') is generally sloped at a positive angle within a range of from six to twelve degrees with respect to the axis of the bore.

3. The packer unit (18) adapted for use in an annular blowout preventer (10) having an axial bore, the packer unit (18) adapted for compressive inward radial displacement toward the axis of the bore, the packer unit (18) comprising metallic inserts (50, 51) generally spaced circularly about the axis, the inserts (50, 51) having webs (31, 33) which extend generally longitudinally and top and bottom plates (61, 62) integral with said webs (31,33), said webs (31, 33) providing the sole connection between the plates (61, 62), at least a part of the inner edge of the web (31, 33) extending downwardly and outwardly from the axis of the bore, and an annulus of elastomeric material extending about the axis and embedding the webs (31, 33) so that the webs (31, 33) anchor the material during inward compressive displacement of the packer unit (18), characterized in that the inner edges of the webs (31', 33') slope downwardly and outwardly in a curved manner from the bore axis generally from a relatively smaller radius near the top plate (61') to a relatively greater radius near the bottom plate (62').

4. The packer unit of claim 3, characterized in that the inward edges of the webs (31', 33') are generally sloped at a positive angle from a range of six to twelve degrees with respect to the axis of the bore of the packer unit (18').