SEALING ASSEMBLY BETWEEN PLANAR SEALING SURFACES

Abstract: A pressure tight seal is formed between the confronting planar sealing surfaces (5, 11) on the flanges of a nuclear reactor pressure vessel (3) and its head (9), by a toroidal, crushable tubular seal member (25) which is locked into a flat annular spacer member (27) by a resilient annular member (29), seated in a V-shaped recess (31) in the inner surface of the flat annular member (27). The flat annular member (27) is provided with axial bores (37) which register with the mounting bolts (15) to provide positive positioning of the tubular seal member (25) without the necessity of providing grooves in the confronting planar sealing surfaces (5, 11).

Description: This invention relates to devices for forming a pressure seal between two planar sealing surfaces and more particularly to such a device which includes a toroidal, crushable seal member and a spacer unit for positioning the seal member between the planar sealing surfaces and for controlling the deformation of the seal member as it is crushed between the sealing surfaces. There are many types of equipment which require the formation of a pressure tight seal between confronting planar sealing surfaces. Such equipment includes, for example, pump housings, high pressure fluid conduits, and pressure vessels. Often the confronting planar sealing surfaces are formed on annular flanges which are bolted together. It is common practice to use organic or inorganic gaskets or "O" rings to form such seals and to provide annular grooves in one or both of the confronting planar sealing surfaces to position the seal member. There is a tendency in many such installations for the flanges to bend about the pivot formed by the edge of the gasket or the "O" ring. One type of installation in which a pressure tight seal is required between confronting planar sealing surfaces is the pressure vessel of a nuclear reactor. The upright cylindrical pressure vessel terminates at its upper end in a radially outwardly extending flange to which is bolted a complimentary flange on the hemispherical vessel head. In order to provide a seal to withstand the high pressure developed in the pressure vessel with adequate safety margins, a crushable, tubular, metallic torus is typically inserted between the flanges. As the bolts are tightened to draw the flanges toward each other, the crushable tubular metallic torus is deformed to form the pressure tight seal. Annular grooves in the flanges position the torus and prevent it from slipping as the bolts are tightened. Holes in the inner surface of the tubular torus, admit reactor coolant into the tubular seal to pressurize it. Such grooves however are difficult to manufacture and to keep clean. On the other hand, without grooves, the torus is difficult to place in proper position since there is generally some clearance between the torus and an annular spacing member surrounding the torus. In the arrangement shown in U.S. Patent No. 4,155,571, a metallic torus is received within a retainer ring which limits radial expansion and sets the axial distance to which the torus can be compressed. However, retainer ring and torus must be handled separately which is cumbersome in the reactor environment. It is therefore the principal object of the present invention to provide a seal assembly for smooth flat surfaces which is easily positioned and handled even by remotely operated tools and which remains in proper position and provide for a good seal when the assembly is tightened. With this object in view the present invention resides in a sealing assembly for providing a seal between confronting planar sealing surfaces on two annular structural members which are drawn by securing means toward each other and in firm engagement with a toroidal, crushable seal member disposed therebetween, and a flat annular spacer unit surrounding said seal member, the thickness of said spacer unit being less than that of said toroidal, crushable seal member to set the distance that the planar surfaces are drawn toward each other and therefore provide uniform crushing of the toroidal, crushable seal member, characterized in that said spacer unit is a flat annular member with a radially extending annular recess in its inner surface and an annular resilient member received in said annular recess, said resilient member having an inner diameter which is slightly less than the outer diameter of the toroidal, crushable seal member and surrounding said seal member to position the same between said planar surfaces adjacent said recess while permitting the seal member to expand radially as it is crushed by the drawing of the planar surfaces on said structural members toward each other by the securing means. The invention will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of example only, in the accompanying drawings in which: Figure 1 is an exploded view in vertical section through a nuclear reactor pressure vessel incorporating the invention; Figure 2 is a plan view of a sealing assembly according to the invention; Figure 3 is an enlarged vertical sectional view through the seal assembly of Figure 2 taken along the line 3-3; and Figure 4 is a sectional view similar to that of Figure 3 showing the seal assembly as installed in the nuclear reactor pressure vessel of Figure 1. As illustrated in Figure 1, a nuclear reactor pressure vessel 1 in connection with which the invention will be described, includes an upright cylindrical body 3 having a radially, outwardly extending flange 5 at its upper end which defines an axial facing planar sealing surface 7. A removable, hemispherical head 9 terminates at its lower end in a mating, radially extending flange 11 which also defines an axially facing sealing surface 13. The head 9 is secured to the pressure vessel body 3 by a number of bolts 15 which extend through bores 17 and 19 in flanges 5 and 11 respectively. Under normal operating conditions, reactor coolant is introduced into the pressure vessel 1 at a pressure between 140 and 210 kg/cm². In accordance with the invention, a seal assembly 21 provides a pressure tight seal between the confronting sealing surfaces 7 and 13 on the flanges 5 and 11. As can best be seen from Figures 2 and 3, the seal assembly 21 includes a spacer unit 23 and a toroidal, crushable seal member 25. The spacer unit 23 includes a flat, ring shaped member 27 with a resilient inner portion which is formed by a circular coil spring 29 seated in a radially extending V-shaped recess 31 in the inner surface formed by the bore 33 of the ring shaped member. Alternatively, an elastomeric solid or hollow O-ring can be used in place of the circular coil spring 29. The toroidal, crushable seal member 25 is a circular metallic tube which is received in the bore 33 in the ring shaped member 27 and rests on a shoulder 35. The seal member 25 is locked in place within the ring-shaped member 27 by the circular coil spring 29 so that the seal assembly 21 can be maneuvered as a unit. This greatly facilitates alignment of the seal and is an important feature of the invention. The ring-shaped member 27 is provided with a number of axial bores 37 which register with the flange bores 17 and 19 to positively locate the seal assembly 21 between the sealing surfaces 7 and 13. The thickness t1 of the seal member 25 is greater than the thickness t2 of the ring-shaped member 27, so that as the bolts 15 are tightened to draw the sealing surfaces 7 and 13 toward each other the seal member 25 is contacted first and crushed between the sealing surfaces. As this occurs, the seal member 25 flattens out against the sealing surfaces 7 and 13 as shown in Figure 4 to form an in depth seal. The spacer unit 23 maintains the proper position of the seal member 25 while it is being crushed yet the resiliency of the circular coil spring 29 permits it to expand radially as it is deformed. Preferably, the ring-shaped member 27 is made of a rigid material such as steel so that its thickness, t2, provides a positive limit for the crushing of the seal member 25. The tubular seal member 25 is provided with radial bores 39 along its inner surface to admit pressurized reactor coolant into the interior of the seal member to improve its sealing capability. The alignment of the toroidal seal member 25 relative to the planar sealing surfaces 7 and 13 without the necessity of cutting grooves in, or providing other special arrangements of the planar sealing surfaces, is another important feature of the invention. By way of example, a typical seal unit made in accordance with the teachings of the invention for use in sealing the head on a nuclear reactor pressure vessel includes an annular 4.08 m O.D. seal member 25, made of 1.27 cm O.D. tubular stainless steel material with a 1.27 mm wall thickness and 1.5 to 1.8 mm aperatures 39 and coated with a 0.025 mm to 0.051 mm layer of silver to fill in machining imperfections. The spacer unit 23 includes a flat 11.94 mm thick ring member 27 having a 4.65 m O.D. and a 4.20 m I.D., and a solid annular 4.18 O.D. resilient member 29 made of 6.4 mm elastomeric material.

Claims: A sealing assembly (21) for providing a seal between confronting planar sealing surfaces (7, 13) on two annular structural members (5, 11) which are drawn by securing means (15) toward each other and in firm engagement with a toroidal, crushable seal member (25) disposed therebetween, and a flat annular spacer unit (23) surrounding said seal member (25), the thickness (t2) of said spacer unit being less than that (t1) of said toroidal, crushable seal member (25) to set the distance that the planar surfaces (7, 13) are drawn toward each other and therefore provide uniform crushing of the toroidal, crushable seal member (25), characterized in that said spacer unit (23) is a flat annular member (27) with a radially extending annular recess (31) in its inner surface and an annular resilient member (29) received in said annular recess (31), said resilient member (29) having an inner diameter which is slightly less than the outer diameter of the toroidal, crushable seal member (25) and surrounding said seal member to position the same between said planar surfaces (7, 13) adjacent said recess (31) while permitting the seal member (25) to expand radially as it is crushed by the drawing of the planar surfaces (7, 13) on said structural members (5, 11) toward each other by the securing means (15). A sealing assembly (21) according to claim 1, characterized in that said radially extending annular recess (31) is substantially V-shaped and said annular resilient member (29) is a toroidal coil spring disposed in said annular recess (31). A sealing assembly (21) according to claim 1 or 2, characterized in that said toroidal, crushable seal member (25) is a metallic, tubular member. A sealing assembly (21) according to claim 3, wherein said structural members (5, 11) define a fluid pressure chamber, characterized in that said metallic, tubular seal member (25) has radial bores (39) on its inner surface which communicate with the pressure chamber and through which pressurized fluid passes to pressure the seal member (25).

Inventors: EZEKOYE, IKE L., RUSNICA, EDWARD JOSEPH, SEPP, HENRY A., JR.
Applicants: WESTINGHOUSE ELECTRIC CORPORATION
Application year: 1987
Main classification: F16J15
IPC codes: B65D53, F16J15, F16L23, G21C13