WO1997045660A2

WO1997045660A2 - Gasket with inner diameter curb

Info

Publication number: WO1997045660A2
Application number: PCT/IB1997/000821
Authority: WO
Inventors: Steven M. Suggs; Reid M. Meyer
Original assignee: Acadia Elastomers Corporation
Priority date: 1996-05-29
Filing date: 1997-05-27
Publication date: 1997-12-04
Also published as: WO1997045660A3

Abstract

A gasket (10) for sealing flanges (80), formed of a plurality of expanded intercalated graphite worms (75) compressed together and defining an annular opening (12) therethrough, with the opposing sides (14) of the gasket (10) defining respective sealing surfaces having a first elevation (20) and a first density, with a flange-like curb (26) on a perimeter edge (28) of the annular opening (12) and extending outwardly on opposing sides of the sheet to extents (30) having a second elevation greater than the first elevation, a second density less than the first density, and a first porosity. The curb (26), being compressed between parallel flange surfaces (80), thereby defines a closed face on the inner diameter of the gasket having a third density greater than the second density and a second porosity less than the first porosity, for resisting leakage through the gasket (10) while sealing a flange. A method of sealing a flange joint is disclosed.

Description

GASKET WITH INNER DIAMETER CURB

TECHNICAL FIELD

The present invention relates to gaskets. More particularly, the present invention relates to gaskets having increased resistance to fluid leakage through the gasket .

BACKGROUND OF THE INVENTION

Modern industrial plants, especially those for processing chemicals, petrochemicals, and the like, have large numbers of interconnected pipes. These pipes communicate fluidal liquids and gases for processing in the plants. The fluids carried in the processing plant pipes are typically at high temperatures and/or high pressures. Adjacent longitudinally aligned sections of pipe are connected together at junctions with bolts that extend through aligned bores m the facing flanges at the ends of the respective pipes. A resilient material, or gasket, is typically disposed between the parallel mating faces of the flanges of the pipes to be joined together. The gasket seals the interconnection between the adjacent pipes to restrict fluid leakage from between the flanges forming the connection between the pipes.

Generally the flanges interconnect together by a plurality of bolts that pass through bores in the flanges. The bolts are secured by nuts, in order to tightly join the pipes together. The number and spacing of bolts and the geometric arrangement of the bolts around the flanges depends primarily on the diameter of the pipes and the pressure of the fluid flowing through the pipes and the flange connection.

As described above, gasket materials are used to seal the connection between the two flanges. Gaskets effect seals by deforming and filling the surface irregularities in the faces of the flanges. The gasket is compressed between the parallel faces of the flanges. The internal pressure of the fluid flowing through the flange joint attempts to blow out the gasket from between the flange faces. Hydrostatic end force, which originates with the pressure of the confined fluid, also attempts to separate the flange faces. The torqued bolts and nuts securing the flanges together resist these forces to hold the flanges together with the gasket compressed between the faces of the flanges for sealing the connection from leaks.

There are a number of known types of gaskets for sealing the flange connection. These gasket types include o-nngs, plate-like gaskets or spiral wound, and gaskets cut from sheets. The pre-cut gaskets are particularly useful for forming gaskets of irregular sizes and during emergency situations requiring a temporary gasket. Maintenance personnel use sheet gasket material to cut a gasket to fit a particular application. For many years, the primary type of sheet packing was asbestos fiber sheet having elastomeric or rubber binder. Due to environmental concerns, asbestos has generally been removed from the market and the packing industry has sought suitable substitute materials which take into account the pressure, temperature, and chemical requirements of gasket applications.

One known sheet packing is graphite paper or sheet graphite. Graphite sheet is formed from intercalated flake graphite which is expanded into worms, or vermiform, and then calendared into thin, usually high density sheets of graphite. Intercalated flake graphite is formed by treating natural or synthetic graphite flake with an intercalating agent such as fuming nitric acid, fuming sulfuric acid, or mixtures of concentrated nitric acid and sulfuric acid. The intercalated flake graphite is then expanded at high temperatures to form a low-density, worm¬ like form of particulate graphite having typically an eighty-fold increase in size over the flake raw material. The production of intercalated flake graphite is an intermediate step in the production of expanded intercalated graphite as described in U.S. Patent No. 3,404,061. Expanded intercalated graphite particles have thin structural walls and are light-weight, puffy, airy, and elongated worms or vermiform.

For some gasket applications, the calendared graphite sheet overlays a metal blank having an annular opening which aligns with the pipes to be sealed. The graphite sheet is coated with an adhesive for adhering the sheet to the metal blank. The sheet is cut to form the opening through the gasket. For other applications, the calendared graphite sheet is cut to the particular size and shape of the flanges to be sealed. As discussed above, the flanges are bolted together and compress the gasket between the faces of the aligned flanges for sealing the joint.

Sealability is an important physical characteristic indicative of whether a gasket material will function properly. The American Society of Testing and Materials provides a test designated F37 for evaluating the fluid sealing properties of gasket materials. When ASTM F37 is used as an acceptance test, generally sealability is evaluated with test conditions agreed upon by the manufacturer of the gasket material and the customer planning to use the gasket material in a sealing application. These test conditions include the fluid to be sealed, the internal pressure of the fluid, and the flange load. Gaskets are conventionally tested for comparison purposes with nitrogen gas at an internal pressure of 30 pounds per square inch and a flange load of 3,000 pounds per square inch, pursuant to ASTM F37. Measurement of the leakage rates at these conditions allows comparing one gasket material with another.

The report on ASTM designation F37 explains that the question is not whether a particular gasket material allows leakage, but rather how much leakage occurs with a given set of conditions of time, temperature, and pressure. The leakage measured comes either through the gasket, between the gasket and the flange faces, or both. The ASTM report states that experience shows that in most cases, the leakage measured is a result of leakage through the gasket.

While gaskets formed from calendared graphite sheet material generally perform satisfactorily for sealing in high temperature and high pressure environments, the graphite sheet material has drawbacks which limit its use in large industrial facilities. One problem with flexible graphite sheet is leakage through the gasket itself. Cutting the graphite sheet to form the annular opening of the gasket defines an exposed open-edge face on the inner diameter of the gasket . This edge is exposed to the fluid carried in the pipes. High pressures may force the fluid through the exposed face on the inner diameter of the gasket, and can result in leakage or blow-out of the gasket. The graphite sheet gaskets which have a sandwiched metal blank are not usable in corrosive applications, due to the exposed metal edge on the inner diameter. To overcome this problem, gaskets have been developed with the sheet overlaying the inner diameter. This however leaves a seam line with is susceptible to infiltration by the fluid and possible leakage through the gasket. Further, the use of adhesives in the gasket material can lead to problems with torqued bolts, particularly in high temperature applications. The high temperatures burn out the adhesive, and this can create loss of volume in the gasket. Bolts must be retorqued to take up the reduced volume of the gasket and to prevent leakage.

Accordingly, there is a need in the art for an improved gasket having increased resistance for leakage through the gasket for sealing flanges in high temperature and high pressure applications with reduced adhesive and increased tensile strength.

SUMMARY OF THE INVENTION

The present invention provides an improved gasket for sealing flanges while resisting fluid leakage through the gasket. The gasket is formed of a plurality of expanded intercalated graphite worms compressed together and defining an annular opening therethrough. The opposing sides of the gasket define respective sealing surfaces having a first elevation and a first density, for abutting against a flange surface to be sealed. A flange-like curb is defined on a perimeter edge of the annular opening. The curb extends outwardly on opposing sides of the sheet to extents having a second elevation greater than the first elevation. The curb has a second density less than the first density and a first porosity. The curb being compressed between parallel flange surfaces, defines a closed face on the inner diameter of the gasket having a third density greater than the second density and a second porosity less than the first porosity, for resisting leakage through the gasket while sealing a flange. In an alternate embodiment, the gasket includes a metal blank sandwiched within the gasket.

The present invention further provides a method of sealing a flange with a gasket formed of a plurality of expanded intercalated graphite worms compressed together and defining an annular opening therethrough. A sealing surface of the gasket is placed against a surface of a flange to be sealed. The sealing surface has a first elevation and a first density. The gasket includes a flange-like curb on a perimeter edge of the annular opening. The curb extends outwardly on opposing sides of the gasket to extents having a second elevation greater than the first elevation. The curb has a second density less than the first density, and a first porosity. A second flange to be sealed is aligned with the first flange, whereby a second sealing surface of the gasket is contacted by a face of the second flange. The flanges are bolted together which compresses the gasket. In the initial stages of compression, the soft density curb conforms to the surface irregularities of the flanges. As compression continues, the density of the curb increases, which reduces porosity and increases tensile strength. The curb, being compressed between the parallel flange surfaces, defines a closed face on the inner diameter of the gasket having a third density greater than the second density and a second porosity less than the first porosity, for resisting leakage through the gasket while sealing the joint between the flanges. Objects, features, and advantages of the present invention will become apparent from a reading of the following specification, in conjunction with the drawings and the appended claims .

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a preferred embodiment of a gasket of the present invention.

Fig. 2 is a cross-sectional view of an apparatus for forming the gasket of the present invention. Fig. 3 is a cross-sectional view of the apparatus illustrated in Fig. 2 for forming an alternate embodiment of the gasket of the present invention.

Fig. 4 is a perspective view of a flange connection between two pipes to be sealed by the gasket illustrated m Fig. 1.

Fig. 5 is a cross-sectional view of the gasket illustrated m Fig. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawings, in which like numerals indicate like parts throughout the several views, Fig. 1 shows a perspective view of a preferred embodiment of a gasket 10 according to the present invention. The gasket 10 is formed by compressing together a plurality of expanded intercalated graphite worms, as discussed below. Expanded intercalated graphite worms are discrete sealing material particles, which are particularly useful in the gasket of the present invention. The gasket 10 defines an annular opening 12 for alignment with pipes to be sealed by the gasket when joined together at flanges, as discussed below. The opposing sides 14 of the gasket 10 define respective sealing surfaces having a first elevation and the sealing surfaces of the gasket have a first density. In the illustrated embodiment, the sealing surfaces 14 define lands 16 and ridges 18. The extents 20 of the ridges 18 define the first elevation. In an alternate embodiment, the sealing surfaces 14 define planar lands having the first elevation.

The gasket 10 includes a flange-like curb 26 on a perimeter edge 28 of the annular opening 12. The curb 26 extends outwardly from the opposing sides 14 of the gasket 10 to an extent 30 having a second elevation greater than the first elevation. The curb 26 has a second density less than the first density and has a first porosity. Upon being compressed during installation of the gasket 10, the curb 26 defines a closed face on the inner diameter 28 of the gasket having a third density greater than the second density and a second porosity less than the first porosity, for resisting leakage through the gasket while sealing a flange, as discussed below.

The gasket 10 of the illustrated embodiment includes a flange-like curb 34 on a perimeter edge 36 of gasket.

The curb 34 extends outwardly from the opposing sides 14 of the gasket 10 to an extent 38 preferably of the second elevation and of the second density.

In an alternate embodiment, the gasket 10 includes a metal blank which is sandwiched by the compressed expanded intercalated graphite worms that form the sealing surfaces 14 of the gasket. The inner diameter edge 28 of the annular opening is sealed by an integral skin of the graphite worms and thereby no metal is exposed on the inner diameter. This embodiment is useful in applications having a corrosive environment . With reference to Fig. 2, the gasket 10 is formed in a die 50. The die 50 includes an annular lower die 52 and an annular upper die 54 with surfaces 56 and 58, respectively. The surface 56 of the die 52 defines an annular first recess 60 and an annular second recess 62. The surface 58 of the die 54 likewise defines an annular third recess 64 and an annular fourth recess 66. The first recess 60 and the third recess 64 are coaxially aligned and the second recess 62 and the fourth recess 66 are coaxially aligned when the dies 52 and 54 are brought together during operation of the die 50. The recesses 60, 62, 64, and 66 define the curbs 26 and 34 of the gasket 10, as discussed below. The portions of the die surfaces 56 and 58 between the recesses 60, 62, 64, and 66 define a surface pattern for the sealing surface of the gasket, such as the pattern illustrated m Fig. 1. The die 52 is preferably fixed in a support 68 while the die 54 is preferably attached with bolts 70 to a plate 72 attached to a distal end of a hydraulic piston 74. A pm 76 extends upwardly to define the annular opening 12 of the gasket 10. The cavity of the die 50 is filled with expanded intercalated graphite worms 75 that cover the surface 56 of the lower die 52. The upper die 54 is then forcibly pressed against the worms in the die 50 to form the gasket 10. The surfaces 56 and 58 come closer together and more densely pack the worms together. The depth of the aligned recesses 60 and 64 and recesses 62 and 66 provide more volume for receiving the compressed worms. Accordingly, the density of the compressed worms in the recesses is less than the density of the compressed worms between the surfaces 56 and 58 between the recesses 60, 64 and 62, 66. The worms in the recesses 60, 62, 64, and 66 define the curbs 26 and 34 of the gasket 10 The portions 14 of the gasket 10 between the curbs 26 and 34 preferably have a density of about 90 pounds per square inch. The curbs 26 and 34 preferably have densities of about 45 pounds per square inch. With reference to Fig. 3, the die 50 can be used for making an alternate embodiment of the gasket 10. In forming this embodiment of the gasket 10, a lower portion 80 of the cavity of the die is filled with expanded intercalated graphite worms 75 that cover the surface 56 of the lower die 52. A cylindrical sleeve (not illustrated) is received over the upper portion of the pin 76. A metal plate 82 having an annular opening is received on the sleeve-covered pin 76. The sleeve defines a jig that spaces the metal plate 82 from the pin 76. The sleeve is removed and this defines a gap betwen the inner diameter of the metal plate 82 and the pin 76. An upper portion 84 of the die 50 is filled with expanded intercalated graphite worms to cover the surface of the plate 82. The upper die 54 is then forcibly pressed against the worms and the metal plate 82 in the die 50 to encapsulate the metal plate with the compressed intercalated graphite worms, to form this alternate embodiment of the gasket 10. The surfaces 56 and 58 are forced together and more densely pack the worms together. The worms in the recesses 60, 62, 64, 66 define the curbs 26 and 34 of the gasket 10. The worms in the gap betweent the inner diameter of the metal plate 82 and the pin 76 compress together to cover the inner diameter of the metal plate. The metal plate 82 provides rigidity for handling of the gasket 10. The gasket 10 having the metal plate 82 sealed therein can be used in metal-corrosive environments.

With reference to Fig. 4, the gasket 10 of the present invention is installed between a pair of flanges 80 to be rigidly connected together for joining aligned pipes 82. The gasket 10 is placed with one of the sealing surfaces 14 against a face surface 84 of one of the flanges 80. The second flange 80 is coaxially aligned with the first flange, whereby the second of the sealing surfaces 14 is contacted by the face surface 84 of the second flange 80. Bolts 86 are passed through openings 88 m the flanges 80 and threadmgly engage nuts 90. Tightening the nuts and bolts secures the flanges 80 together and compresses the gasket 10 between the face surfaces 84 of the flanges. In the initial stages of compression, the soft density curb 26 conforms to the surface irregularities of the face surfaces 84 of the flanges 80. As compression continues, the density of the curb 26 increases, which reduces its porosity and increases its tensile strength. The curb 26, being compressed, defines a closed face on the inner diameter 28 of the gasket 10 and changes density to the third density greater than the second density. Also, the compression reduces the porosity of the face portion of the curb 26 to the second porosity. The curb 26 thereby provides a closed face on the inner diameter of the gasket 10 for resisting leakage through the gasket while sealing the joint between the flanges 80. Fig. 5 is a cross-sectional view of the gasket 10 shown in Fig. 1 to illustrate features of the gasket 10 having the metal blank 82 and the integral skin formed of the intercalated graphite worms 75. The gasket 10 m the illustrated embodiment has sealing surfaces 14 defined by the lands 16 and ridges 18. The extents 20 of the ridges 18 define the first elevation. The flange-like curb 26 on the perimeter edge 28 of the annular opening 12 of the gasket 10 extends outwardly to an extent 30 having the second elevation which is greater than the first elevation. The flange-like curb 34 on the perimeter edge 36 of the gasket extends outwardly to an extent 38.

The gasket 10 of the present invention accordingly provides a sealing member that resists fluid leakage through the gasket. The curb 26 increases density during installation which decreases the porosity of the curb surface on the perimeter edge 28 of the gasket 10 The decreased porosity and increased density resists fluidal penetration into the gasket 10. The higher density of the curb surface also increases the recovery of the gasket. Accordingly, the gasket of the present invention provides protection from leakage through the gasket in high pressure applications while the gasket also has closely conformed to the surface irregularities of the flange. The curb 34 functions similarly to the curb 26.

The specification has thus described in various embodiments the gasket of the present invention including the manufacture and use thereof. It is to be understood, however, that numerous changes and variations may be made in the construction of the present invention. It should therefore be understood that modifications to the present invention may be made without departing from the scope thereof as set forth in the appended claims.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A gasket for sealing flanges, comprising: a plurality of expanded intercalated graphite worms compressed together to form a gasket and defining an annular opening therethrough, with the opposing sides of the gasket defining respective sealing surfaces having a first elevation and a first density; and a first flange-like curb formed of compressed expanded intercalated graphite worms on a perimeter edge of the annular opening, the curb extending outwardly on opposing sides of the gasket to extents having a second elevation greater than the first elevation, a second density less than the first density, and a first porosity, whereby the curb, being contacted and compressed between parallel flange surfaces, defines a closed face on the inner diameter of the gasket having a third density greater than the second density and a second porosity less than the first porosity, for resisting leakage through the gasket while sealing a flange.

2. The gasket for sealing flanges as recited in claim 1, further comprising a metal blank having an annular opening sandwiched by the gasket formed of the plurality of expanded intercalated graphite worms, whereby the inner diameter edge of the annular opening is sealed by an integral skin of graphite worms compressed together into an integral skin.

3. The gasket for sealing flanges as recited in claim 1, further comprising a second flange-like curb formed of compressed expanded intercalated graphite worms on an exterior edge of the gasket, the second curb extending outwardly on opposing sides of the gasket to extents having a third elevation greater than the first elevation, a third density less than the first density, and a second porosity.

4. A method of sealing a flange, comprising the steps of :

(a) placing a sealing surface of a gasket against a face of a flange to be sealed, the gasket formed of a plurality of expanded intercalated graphite worms compressed together and defining an annular opening therethrough, the sealing surface having a first elevation and a first density, and a first flange-like curb formed of compressed expanded intercalated graphite worms on a perimeter edge of the annular opening, the curb extending outwardly on opposing sides of the gasket to extents having a second elevation greater than the first elevation, a second density less than the first density, and a first porosity;

(b) aligning a second flange to be sealed with the first flange, whereby a second sealing surface of the gasket is contacted by a face of the second flange; and

(c) compressing the gasket between the first and the second flanges by bolting the flanges together, whereby the curb, being contacted and compressed between the parallel flange surfaces, defines a closed face on the inner diameter of the gasket having a third density greater than the second density and a second porosity less than the first porosity, for resisting leakage through the gasket while sealing the joint between the flanges.

5. A gasket for sealing flanges, comprising: a plurality of discrete sealing material particles joined together to form a skin of a gasket and defining an opening therethrough, with the opposing sides of the gasket defining respective sealing surfaces each having a first elevation relative a transverse axis of the gasket and a first density; and a raised portion integral within the skin and formed of portions of the discrete sealing material particles joined together, the raised portion extending outwardly on opposing sides of the gasket to extents having a second elevation greater than the first elevation and having a second density less than the first density, whereby the raised portion of the gasket, being initially contacted and compressed between a pair of substantially parallel flange surfaces to be sealed, defines a first sealing surface which effects a seal at a lower load, for sealing the flange surfaces.

6. The gasket as recited in claim 5, wherein the raised portion includes a greater number of discrete sealing material particles per unit area than in the sealing surfaces, whereby the raised portion, being compressed between the flange surfaces, reaches a final density greater than that reached by the sealing surfaces, for resisting leakage through the gasket while sealing the flange surfaces.

7. The gasket for sealing flanges as recited in claim 5, wherein the discrete sealing material particles comprise expanded intercalated graphite worms.

8. The gasket for sealing flanges as recited in claim 5, further comprising a metal blank having an opening, the blank being sandwiched by the gasket formed of the discrete sealing material particles.

9. The gasket for sealm^~< flanges as recited in claim 8, wherein the raised porticn covers a perimeter edge of the opening for sealingly covering same with the skin.

10. The gasket for sealing flanges as recited in claim 5, further comprising a second raised portion formed of the discrete sealing material particles on an exterior edge of the gasket, the second raised portion extending outwardly on opposing sides of the gasket to extents having a third elevation relative to the transverse axis, which third elevation is greater than the first elevation and a third density less than the first density.

11. A method of sealing a flange, comprising the steps of:

(a) placing a gasket against a face of a flange to be sealed, the gasket formed of a plurality of discrete sealing material particles joined together and defining an opening therethrough corresponding in cross-section to the openings in the flanges to be sealed by the gasket, the gasket defining a sealing surface having a first elevation relative to a transverse axis through the gasket and a first density, and a raised portion integral within the skin and formed of portions of the discrete sealing material particles joined together, the raised portion extending outwardly on opposing sides of the gasket to extents having a second elevation relative to the transverse axis greater than the first elevation and having a second density less than the first density, the raised portion defining initial sealing surfaces on opposing sides of the gasket;

(b) aligning a second flange to be sealed with the first flange, whereby the initial sealing surfaces and the sealing surfaces of the gasket are brought into contact with a face of the second flange; and (c) compressing the gasket between the first and the second flanges by bolting the flanges together, whereby the raised portion, being contacted initially and compressed between the parallel flange surfaces, effects a seal therebetween at a low load.

12. The method as recited in claim 11, further comprising the step of providing the raised portion with a greater number of discrete sealing material particles per unit area, whereby the raised portion reaches a third density greater than the second density, for resisting leakage through the gasket when the flanges are bolted together.