GB2221000A

GB2221000A - Improvements relating to metallic sealing rings and their manufacture

Info

Publication number: GB2221000A
Application number: GB8912539A
Authority: GB
Inventors: Terence Peter Nicholson
Original assignee: Specialist Sealing Ltd
Current assignee: Specialist Sealing Ltd
Priority date: 1988-06-01
Filing date: 1989-06-01
Publication date: 1990-01-24
Anticipated expiration: 2009-06-01
Also published as: GB2221000B; AU3693289A; CA1336198C; GB8912539D0; WO1989012189A1

Abstract

A metallic sealing ring particularly for sealing flange joints is of open or closed hollow sinuous radial cross-section with each of its axial end faces in-curved to define an axially outward facing deep peripheral groove (2). Alternatively at least one side wall can be curved to form a concave shallow arcuate profile groove (4), the axial end faces are oblique or the end portions at one end of the end faces are inwardly curved to make mutual contact. <IMAGE>

Description

IMPROVEMENTS RELATING TO METALLIC SEALING RINGS AND THEIR MANUFACTURE This invention relates to metallic sealing rings for sealing the joints between opposed parallel surfaces such as for instance, and in pdrticular, the end flanges by which pipe lengths are connected together by means such as studs, bolts and nuts, and to the manufacture of such rings The invention relates particularly, but not exclusively, to sealing rings capable of providing an improved alternative to the use of metallic sealing rings, i.e.

gaskets, which are of solid multi-sided radial cross-section as currently specified by the American Petroleu Institute (#PT) for sealing pipeline flange joints by location in opposed grooves in the flange faces. The standard groove cross section is a symmetrical trapezium.

In such applications leakage problems arise from time to time and particularly in the conveyance of gases at high pressure. In the main this is not primarily due to faulty design of the sealing rings but to the difficulty of ensuring that machining of the joint components is of a sufficiently high standard regardless of where they have been manufactured.

The leakage problem is particularly acute when the flanges are intended to be drawn into face to face abutment instead of slight spacing or stand-off, There are many situations where it is essential to hau face to face assemblies, In accordance with one aspect of the present invention there is proposed a metallic sealing ring which in radial cross-section is hollow and of sinuous profile having axial end faces sinuously curved so as each to define an axially outward facing deep peripheral grooue, the interior of the ring profile being in comnlunication with the exterior thereof, One or each radial face of the ring may be curved to define a laterally facing shallow arcuate profile groove. However1 this is not satisfactory in all working environments because there is a tendency when an abnormal or excessively high pressure is applied to the system, for instance in a blow-out or explosive situtin, for a radially outward groove not only to flatten out, but to become outwardly convex tight into a corner forned between adjacent parts of grooved pipe flanges between which the metallic sealing ring is received, this can cause movenent at the high pressure sealing areas of the seal which can initiate a leakage problem.

To provide a metallic sealing ring which can function efficiently even when subjected to excessively high pressures as aforesaid, one or each of its side walls is curved to define a radially outwardly directed shallow convex configuration in the region of the intended abutment or near abutment of the surfaces which are to be sealed.

The radial cross-section may be of closed hollow formation or alternatively a hollow formation which is open on one - and preferably its radially inward side. If the hollow formation is closed the ring will be formed with a normally radial vent hole, to transelit operating fluid pressure to the interior of the ring cross section so that in this configuration, as in the open configuration, the seal is self-energised by the fluid pressure acting on the interna ] surface of the cross section of the ring.

According to another aspect of the invention there is provided a metallic sealing ring which in radial cross-section is hollow, at least one of its radially inner and outer side walls being curved to define. a concave shallow arcuate groove, the interior of the ring being in communication with the exterior.

In accordance Iriith yet another aspect of the present invention there is proposed a metallic sealing ring which in radial cross-section is hollow and has oblique axial end faces and has a profile such that said axial end faces can be axially compressed towards one another in use, at least at their regions of greatest axial extent, the interior of the ring profile being in comuunication with the exterior thereof.

The dimensions of the ring are chosen such that in use the ring is jammed or wedged into the corners of seal grooves of tapered profile, in particular RPI standard grooves.

According to a preferred embodiment the metallic sealing ring in radial cross-section has, on each axial side of a median plane, a respective radially outer limb which extends, from its junction with the. other such limb, obliquely in the axially outward and radially inward directions at a relatively small angle to the axial direction, an end face portion extending, from the axially outer end of said outer limb obliquely at a greater angle to the axial direction than and in the sane sense as the axially outer limb, and an inner limb extending from the radially inner end of the end face portion towards the median plane and having a free end.

A compression spring nay be placed inside the sealing ring to increase the sealing load, e g. in the form of a ring or rings of sheet spring Instal.

The radial cross-section may be of closed hollow for#u#tion or preferably d hollow fotlnat.ion which is open on one - and preferably its radially inward - side. If the hollow formation is closed the ring will be formed with a nornially radial vent hole, to transntjt operating fluid pressure to the interior of the ring cross section so that in this configuration, as in the open configuration, the seal is self-energised by the fluid pressure acting on the internal surface of the cross section of the ring.

One or each radial face of the ring may be curved to define a laterally facing arcuate profile groove to permit said axial compression. However, this is not satisfactory in all working environments because of the above-mentioned tendency, when an abnormal or excessively high pressure is applied to the system, for instance in a blow-out or explosive situation, for a radially outward groove not only to flatten out, but to beconie outwardly convex tight into a corner fornied between adjacent parts of grooved pipe flanges between which the metallic sealing ring is received, this can cause movement at the high pressure sealing areas of the seal which can initiate a leakage problem. Therefore, to provide a metallic sealing ring which can function efficiently even when subjected to excessively high pressures as aforesaid, the outer side wall preferably has a radially outwardly directed shallow convex or angled configuration in the region of the intended abutment or near abutment of the surfaces which are to be sealed, and the inner side wall is open.

Another object of the present invention is to provide a seal which is better able to stand up to high pressure and corrosive gases, particularly those which exist in flange joints located at the bottom of the sea on oil drilling platforms. This kind of application is referred to in the art as a "sour-well" application because of the presence of hydrogen sulphide (H2S) which is very often present in an oil and gas mixture The hydrogen sulphide subjects the seal and flanges to a high degree of corrosion.

It is known in the art to coat the flanges and seals with nickel in order to remove the effects of corrosion thereby maintaining an effective seal between the metallic sealing ring and the flanges, Prior art seals are configured in such a way that sliding movement takes place at the contact point between the metallic sealing ring and the flange. Movement of this kind can lead to scuffing of the nickel coating This can result in a deterioration in the effectiveness of the seal, It is therefore another aim of the present invention to provide a metallic sealing ring which overcoines or at least alleviates these problems, and in particular a metallic sealing ring which can provide an effective seal which is not prone to scuffing.

According to this aspect of the present invention, there is provided a metallic sealing ring which in radial cross-section is hollow, the metallic sealing ring comprising a pair of linibs which are joined together at one end and are contiguous with respectively inwardly curved portions at their other end, wherein the inwardly curved portions each extend at least as far as a contact point for contacting a sealing surface, In a preferred embodinient the inwardly curved portions extend beyond the contact points so that their free ends are. directed towards the. interior of the sealing ring.

In this case, the metallic sealing ring may be configured such that the free ends contact one another when the seal is under compression thereby enhancing the effectiveness of the seal between the contact points and surface to be sealed, Q seal according to this aspect of the invention has the advantage that as the metallic sealing ring undergoes colllpression, the profile of the seal changes in such a snanner that sliding movement between the contact point of the inwardly curved portion and the surface to be sealed does not occur, Scuffing is therefore eliminated and so any nickel coating present on the metallic sealing ring and/or on the surface of the member to be sealed is maintained, the effectiveness of the seal thereby being snaintained, The non-sliding contact between the inwardly curved portions of the metallic sealing ring and the sealing surface is achieved by virtue of the fact that the inwardly curved portions undergo a rolling action under compression. That is to say the point of the inwardly curved portion contacting the sealing surface moves together with the sealing surface as the compression takes place. This action will be described in greater detail below with reference to the accompanying drawings.

X gap must exist between the limbs in seals embodying this aspect of the invention for the rolling action to occur otherwise the rolling action is restricted. The gap is present when the sealing ring is in its relaxed state and during most or all of the compressive stages of the sealing ring.

In an embodizllent where the limbs contact one another at the last stage of compression, the contacting of the limbs serves to push the soft plating or nickel coating of the inwardly curved portions against respective surfaces of the member to be sealed thereby ensuring the integrity of the seal at the contact points. This also serves to fill in any surface asperities or irregularities in the surfaces of the member to be sealed. This is achieved without restricting the rolling action provided that the limbs only contact one another during the last part of the conpression movement.

Seals embodying this aspect of the invention could he referred to as "rolling seals".

The fact that the seal performs the rolling action means that apart from avoiding the occurrence of scuffing, the seal also adjusts to accommodate dimensional variations in the grooves, which dimensional variations may result from manufacturing tolerances, In a preferred#embodiment of this aspect of the invention, at least part of each limb which is also configured for contacting a sealing surface of a respective groove is coated with low friction material.

This material nay be selected from silver, gold or PTFE or other low friction material of which there are many and well known in the art.

Embodiments are particularly suited for use in both R and RX rI.P.I. grooves. When a metallic sealing ring embodying this aspect of the present invention is used in association with such a groove, a non-scuffing seal is established between respective contact points of the inwardly curved portions and a side of respective opposing grooves. fi sliding seal is established between the portion of the limbs having the low friction material and the other side of the grooves. Use of the low friction material reduces the possibility of scuffing which may result from the sliding movement between the limbs and the outer sides of the groove.

In alternative embodinents the inwardly curved portions may extend beyond the contact point so that their free ends face one another. lternatively, between the contact point and the free end, the seal may be straight in profile. In either case, the part of the metallic sealing ring beyond the contact point will serve to strengthen the seal So that the seal can withstand higher compression forces.

The inwardly curved portions of the nietallic sealing ring flay be of constant radius, although this is not essential.

The limbs may be straight or curved in profile. The limbs are preferably joined together by means of a weld joint.

Embodiments of this aspect of the present invention are preferably self-energizing in nature. In the event that metallic sealing rings embodying the invention are configured so that the free ends of the inwardly cured portions contact one another under compression communication means is provided for connecting the interior of the sealing ring with the exterior. This perlnits equalization of pressure between the interior and exterior of the ring so that high pressure gas can serve to enhance the sealing contact between the metallic sealing ring and the grooves of the flanges.

The cortsnunication means may be in the form of openings provided in the inwardly curved portions or may be in the form of grooves extending along the curved portions at or near to the free ends.

For some applications it is desirable and advantageous to pre-compress the sealing ring before it is installed. This can substantially enhance the performance of the sealing ring. Typically, the sealing ring is pre-coi;pressed to approximately one half of the normal compression to be applied in use. The nolllinal full colnpression is typically about 15%.

Preferably, the sealing ring consists of two annular half-seals each forming one axial half of the radial cross section of the sealing ring, these half-seals being welded together along a circumferential weld line or lines, with each half-seal being pressed before welding, to a form corresponding to about one half of the nominal compression in use.

Some preferred embodiments of the invention are hereinafter described with reference to the accompanying drawings in which Figs. 1 to 49 without exception comprise radial cross-sections of the now proposed sealing rings for use with pipe flange joints.

Figs. 1 to 3 illustrate three different configurations of sealing rings to be used as an alternative to d ring section known as "RX't under the Qnlerican Petroleum Institute, (API), classification. Each ring is hollow but whereas the Fig, 1 ring is open on its radially inward side the rings of Figs. 2 and 3 are closed and formed with vent holes 10 on their radially inner sides. n11 the rings have circumferential median weld lines 12, at which two pre-formed half-seals are united in a plane perpendicular to the. seal ring axis.

A11 three rings are of sinuous radial profile and are characterised by having opposite-fdcing corrugated formations which constitute axially outwardly facing deep peripheral grooves 2 in the axial end faces of the rings.

fidditionally, one or each side wall of the ring profile may have a laterally facing shallow arcuate concave profile forming a groove 4. In the case of the ring illustrated in Fig. 1 which has an open profile, the groove 4 is in the radially outer side. The ring illustrated in Fig. 2 which has a closed profile has grooves 4 in both the radially inner and radially outer sides.

The ring illustrated in Fig. 3, which has a closed profile, does not have grooves 4 but instead has rectilinear axially extending radially' inner and outer walls 6 between the respective sinuous end regions.

The grooves 4 provide enhanced resilience and flexibility under compression.

The forn of seal in Fig. 1, completely open on the inner face with its annular groove around the outside diameter, is extremely flexible compared with the form in Fig. 2 which is totally enclosed with the inner and outer annular grooves and the vent hole/holes which makes it substantially stronger, i.e. requiring much higher clamping loads, The seal of Fig. 3 would be even stronger, because of the lack of the annular grooves 4.

This is to cope with higher pressures.

In the illustrated rings, the side walls and end regions are interconnected by obliquely extending rectilinear regions 8. Alternatively, these regions may be of curved cross-section, as shown in broken lines in the drawings, it has been established by test that the curved faces are operationally superior.

Figs. 4 and S show two further ring configurations having the same characteristics as have been nientioned above but which are intended as improved alternatives to what are known as type "R" ring seals or gaskets according to the API classification and therefore have a lower ratio of axial to radial dimensions.

Similarly, Figs. 6 and 7 show two further possible ring configurations having the same characteristics as v been mentioned above but which are intended as improved alternatives to what are known as type "BX" ring seals or gaskets according to the API classification and therefore have a stil ] lower ratio of axial to radial dimensions.

In each of Figs. 4 to 7 inclusive also, there are indicated by dashed lines alternative radius portions between the deep axial groove formations 2 and the shallow lateral grooves 4.

In Figs. 8, 9 and 10 stages in the formation of a sealed joint between two grooved pipe flanges 20 using a sealing ring with the Fig 1 radial configuration are illustrated, in fragmentary cross-section.

It is to be understood that each of the flanges 20 is an annular external flange provided on the end of a pipe.

In the. axially outwardly facing surface of the flange is a coaxial annular groove 22 of trapezoidal cross-section as specified by the API, so that when two such flanges are assembled face to face, the respective grooves in their surfaces together for'a an annular cavity of hexagonal cross-section accommodating the sealing ring.

Fig. 8 shows the positions of the flanges and sealing ring assembled together with the sealing ring seated in the respective grooves, before the flanges have been drawn together, and with the sealing ring in its natural uncompressed condition.

In use, the flanges are brought together, for example by means of bolts or clamps, into a stand-off configuration or, as illustrated in the drawings, into face to face contact.

This compresses the interposed sealing ring. Typically, for components having the nominal dimensions, the degree of conpression is about 15%, The grooves 22 are machined into the flange faces.

Inevitably, Inanufacturing tolerances lead to variations in the groove dimensions. These variations affect the interaction between the side walls of the grooves, and the sealing rings trapped between them, thereby creating a major difficulty in establishing a true face to face set-up with conventional NPI rings of solid cross section.

Fig. 9 illustrates the position taken up by the sealing ring when the flanges have been brought into face to face contact, in a situation in which one or other of the grooves has been machined to the upper tolerance limit, that is to say, to the maximum internal dimensions and therefore minimum compression of the sealing ring.As shown in Fig. 9, in these conditions the compression of the sealing ring is expressed primarily by lateral contraction of the groove formations 2, Fig. 10 illustrates the position taken up by the sealing ring under full compression, when one or other of the grooves has been machined to the lower limit of tolerance, that is to say, to the minimum internal groove dimensions.In this situation, the coilpression of the sealing ring is expressed primarily by deflection of its inner limbs 14, axially towards one another, It will be seen that in this configuration as well as in that illustrated in Fig. 9, there is ample sealing contact between the sealing ring and the groove walls.

The present seals have been designed to have sufficient strength to cope with the high torque loadings and pressures associated with 01R equipment, yet at the same time having sufficient flexibility to adjust in dimension to satisfy the variation in groove dimensions due to manufacturing tolerances to which these grooves are Machined.

When the seal is fitted into the grooves and the flanges clamped together, the diameter Do of the outer corrugation crest 20 is forcibly reduced in dimension and the diameter DI of the inner corrugation crest 21 is forcibly increased in dimension, This results in an extremely high loading force between the inner and outer diameters of the seal and the sloping faces of the grooves This is the reason for the grooves 2 which permit the diameters D0 and D1 to adjust independently to suit either of the sloping faces of the groove.

The depth of the annular groove 2 in each of the two annular faces is selected to suit the degree of variation between the two diameters and the variation in the dimensions of the groove in which the seal is to be compressed. This is in conjunction with the thickness of snetal from which the seal is manufactured. Briefly, if the groove is too deep it is possible for the metal on the inside of the seal to fracture, whereas if the groove was only a gentle undulation, it would act as a rigid strut which would reduce its flexibility to almost nil.

Figs. 11, 12 and 13 illustrate. successive stages in the formation of a spaced or stand-off joint between pipe #flanges, again utilising a sealing ring with a configuration as indicated in Fig. 1. By comparison with the joint illustrated in Figs. 8, 9 and 10 the grooves 26 in the flanges are shallower, and colnpression of the sealing ring and final spacing between the flanges is determined by an interposed pressure control ring 24.

Fig. 11 illustrates the position of the components before compression while Figs. 12 and 13 illustrate the configuration of the sealing ring under top tolerance and bottom tolerance conditions effectively.

Preferably, but not essentially, the control ring 24 is of an internal diameter such as to provide a close fit adjacent the outermost diameter of the flange grooves 26 and sealing ring, It wtill be seen that the radially inner face of the control ring 24 is at all times in contact with the radially outermost portions of the seal ring. This overcolnes any possibility of the sealing being forced outward and being nipped between the flanges which could cause it to fracture.

The described seal rings have been found to work extremely well and to provide more reliable sealing and greater accommodation of groove machining tolerances, than the solid-section sealing rings which have hitherto been used as standard components under #PI requirements. However, in sone circumstances the recess 4 in the radially outer wall may be blown outwards, under conditions of very high internal pressure, and this can inlpair the sealing action, as already explained this is due to movenent of the seal during this reaction.

To avoid the problem of the groove 4 being flattened or forced outwards into the angle fornled by the radially outer walls of the grooves in d joint made with face to face contact, the groove 4 may be omitted, the outer face of the sealing ring being, instead, radius or angled in cross-section.

Accordingly, Fig. 14 to 17 illustrate two different configurations of sealing rings to be used as an alternative to a ring section known as 'zRX" under the American Petroleum Institute, API, classification; i.e.

that is 'R' section and BX section rings; and Figs. 18 to 20 illustrate stages in the formation of a sealed joint between two grooved pipe flanges using d sealing ring as illustrated in Fig, 14.

Each of the rings shown in Figs 14 to 17 in radial cross-section is hollow but whereas the rings of Fig 14 and Fig. 16 are open on their radially inward side, the rings of Figs. 1S and 17 are closed and are formed with vent holes 10. All the rings are formed with weld lines 12.

All four rings are of sinuous radial profile and are characterised by opposite-facing formations 2 which constitute axially outwardly directed deep peripheral grooves in the axial end faces of the rings Additionally each ring is characterised in that its radially outward wall is curved to define a radially outwardly directed shallow convex configuration 26 in the region of the intended abutment or near abutment of the surfaces which are to be sealed, Also the closed profile hollow rings shown in Figs, 15 and 17 are formed on their radially inward side with a shallow concave portion or groove 4.

In Figs, 18, 19 and 20 stages in the formation of a sealed joint between two grooved pipe flanges 20 using a sealing ring with the Fig. 14 radial configuration are illustrated, These rings can be used in a stand-off point, but it is essential to incorporate a compression control ring to prevent the seal being destroyed by over compression.

Fig. 18 illustrates the position of the components before the flanges have been drawn together into contact and before the sealing ring is compressed.

Fig. 19 illustrates the position taken up by the sealing ring when the flanges have been brought to face to face contact in a situation where one or other of the flange grooves 22 has been machined to the limit of upper tolerance, whereas Fig. 20 illustrates the final position of the sealing ring under conlprsssion when one or other of the grooves has been machined to d bottosi limit of tolerance, It will be seen from these drawings that under normal operating conditions, the sealing action of the sealing rings illustrated in Figs. 14 to 20 is similar to that of the rings illustrated in Figs. 1 to 13.However, under excessive internal pressure, because the outermost surface of the sealing ring is already convex, the pressure can cause only minimal movement of the sealing ring, insufficient to disturb the sealing contact between the sealing ring and the groove walls.

g Ininor disadvantage is that the absence of the groove or recess in the radially outer wall of the sealing ring reduces the cosnpliance of the sealing ring to some extent, so that it is somewhat less able to accommodate large groove machining tolerances than the rings illustrated in Figs, 1 to 13, but provided that the grooves are within tolerance there is no problem.

The sealing rings illustrated in Figs. 14 to 20 have smoothly curved convex external surfaces, filternatively, the external surface may form an angle at the weld line 12 as shown in Fig, 21, which illustrates a ring otherwise similar to that illustrated in Fig.

14, Figs. 22 to 24 illustrate the behaviour of this ring when clamped in grooves of top and bottom tolerances, analogous to Figs. 8 to 10 and Figs. 18 to 20. Fig. 21 shows dimensions in inches of a seal ring equivalent to an RX46 seal, by way of example only.

Other seal sizes would have generally proportionate dimensions.

Figs. 25 to 28 are corresponding drawings, illustrating a sealing ring intended for use at higher pressures, in the range 5 to 10 thousand PSI. This ring has a configuration generally resembling that of Fig. 15, but with an angle at the external weld line 12, and a relatively deep groove or recess 4 in its radially inner surface.

A sealing ring of this configuration has enhanced ability to accommodate tolerances in the machined groove dimensions, enhanced inherent restoring force, and enchanced radial and axial hoop stresses in operation.

It provides increased contact and therefore sealing pressure at the contact positions between its inner limb 16 and the groove walls. The inner groove 4 acts as a compression restricting Titans, to increase the contact load between the seal and the groove.

Figs. 25 to 28 also illustrate vent holes 10 placed in the side regions of the inner groove or recess 4, instead of at the centre of this recess as illustrated in Fig. 15. By placing the vent holes as shown in Fig, 25, the effect of these on the strength and stiffness of the sealing ring is minimized.

The seals of Figs 14 to 28, because of the absence of groove 4 on the exterior surface, are even stronger than that of Fig 2, requiring higher clamping loads, and being able to cope with higher fluid pressures and rougher nlachined faces.

Figs, 29 to 33 illustrate further configurations of hollow metal sealing rings, intended primarily but not exclusively to be used in place of the solid-section sealing rings currently specified by the API.

In Fig. 29 there is illustrated an alternative type BX ring wherein, instead of the deep grooves 2, the pressure receiving axial facing parts 18 of the ring are slightly outwardly convex.

This sealing ring is of closed cross-section, having grooves or recesses 4 in both its radially inner and radially outer faces, to provide the necessary self-energising spring action and ability to accoumiodate groove machining tolerances. Fig. 30 shows this sealing ring under compression.

Fig. 31 illustrates an alternative RX ring, with a cross-section like an hour-glass, providing an arcuate recess 36 in its radially inner and outer surfaces to provide self-energisation and ability to accoiiiinodate groove machining tolerances, and convex arcuate axial end surfaces 34 for engaging the groove walls, Fig. 32 shows this ring in position in a pair of opposed flange grooves, before being subjected to compression, and Fig 33 after coillpression.

In practice this seal worked well, but when subjected to a sudden burst of high pressure it may fail.

Fig. 34 shows a further alternative RX sealing ring, of closed kidney-shaped cross-section, providing a convex radially outer surface 31 and a concave radially inner surface 32, and convex end surfaces 38. Fig, 35 shows the same ring in place between a pair of flange grooves before compression, and Fig. 36 after compression.

This seal tends to suffer (but not as badly) from silnildr problems to that of the hour-glass one in Fig 31.

The rings illustrated in Figs, 29 to 36 have in common, a closed cross-section with a groove or recess in at least one of the radially inner and outer surfaces, in particular the radially inner surface, to provide self.-energisation under compression, and ability to accommodate groove tolerances.

Figs, 37 and 38 illustrate a configuration of sealing ring to be used as an alternative to a ring section known as "RX" under the American Petroleum Institute, (API), classification, The ring is hollow and open on its radially inward side, and has a circumferential median weld line 12, at which two pre-formed sheet metal half-seals are united in a median plane SO perpendicular to the seal ring axis.

Each half-seal, in profile, consists of three portions.

An outer limb 52 extends froi the weld line obliquely in the radially inward and axially outward directions, at a relatively shallow angle to the axial direction, slightly less than the slope of the side surface 54 of a seal groove 22 of trapezoidal cross section machined in a flange 20 of a piping component to be jointed and sealed. From the outer end of the limb 52, an end face portion 56 extends in the radially inward and axially outward directions, at a much large angle to the axial direction than the limb 52. This forms an axial end face which in use is opposite the bottom surface 58 of the groove. From the radially inner and axially outer end of the end face portion 56, inner limb 60 extends obliquely radially and axially inwards and terminates in a free end spaced from the median plane. This inner limb has a slope corresponding to that of the inner surface 62 of the groove.

Figure 37 shows the sealing ring in its initial uncompressed condition, and accordingly a gap is shown between the respective flanges 20. In this condition, the axial distance between the radially inner corners 64 formed between the inner limbs and the end face portions, is great than the axial distance between the radially outer corners 68 formed between the radially outer ends of the end face portions, and the outer limbs -52. The axial distance between the respective outer angles 68 is substantially equal to or slightly greater than the distance between the respective bases 58 of the grooves in the clamped condition of the flanges, shown in Figure 38.The axial distance between the radially inner corners 64 is approximately 10% greater than the distance between the groove bases 58 in the clamped condition, so that when the flanges are clamped together the sealing ring is subjected to approximately 10% compression. The length of the end face portion 56 between the corners 64 and 68 is somewhat greater than the radial extent of the groove base 58 Figure 37 shows the sealing ring seated in the grooves of opposed flanges but with no colnpression applied to the sealing ring. After the flanges are fully clamped together, the sealing ring is under compression and distorted as shown in Figure 38.Specifically, the radius corners of the sewing ring are rammed home into the corresponding corners of the grooves, Because the length of each end face portion is greater than that of the groove base, the corners of the sealing ring are firmly wedged into the corners of the groove, the outer limbs of the sealing ring are pressed outwards onto the outer side surfaces of the grooves, and the inner limbs of the sealing ring are rotated away from the inner groove surfaces. In this compressed condition the seal is completely leak-tight, with high sealing loads.

If it is necessary to increase the sealing load, a spring or springs 70 of pressed sheet spring nietal can be fitted inside the sealing ring as shown, by way of example only, in Figures 39 and 40. The spring or springs will of course act, at least primarily, axially between the corners 64. Figures 39 and 40 respectively show two different arrangements of axial compression springs#, in the uncolnpressed condition corresponding to Figure 37.

In the illustrated ring, the side walls and end regions are interconnected by obliquely extending rectilinear regions 52. Alternatively, these regions may be of curved convex cross-section.

It is to be understood that each of the flanges 20 is an annular external flange provided on the end of a pipe In the axially outwardly facing surface of the flange is a coaxial annular groove 22 of trapezoidal cross-section as specified by the API, so that when two such flanges are assembled face to face, the respective grooves in their surfaces together form an annular cavity of hexagonal cross-section accommodating the sealing ring.

In use, the flanges are brought together, for example by means of bolts or clamps, into a stand-off configuration or, as illustrated in Figure 38, into face to face contact. In a stand-off application d spacer ring is placed between the flanges outside the grooves.

In the compressed condition, the angle adopted by the inner lines 60 will vary, depending on the dimensional tolerances of the machined grooves and of the sealing ring. The sealing ring is designed to provide complete sealing in grooves of inaxinum tolerance.Because the seal ring is open on its radially inner side, it can provide ample compliance for groove tolerances, The present seals have been designed to have sufficient strength to cope with the high torque loadings and pressures associated with OIR equipment, yet at the sane time having sufficient flexibility to adjust in dimensions to satisfy the variation in groove dimensions due to manufacturing tolerances to which these grooves are machined.

The described seal rings have been found to work extremely well and to prouide snore reliable sealing and greater accomniodation of groove machining tolerances, than the solid-section sealing rings which have hitherto been used as standard components under API requirements.

Under excessive internal pressure, because the outermost surface of the sealing ring is already angled or convex, the pressure can cause only minimal movement of the sealing ring, insufficient to disturb the sealing contact between the sealing ring and the groove walls It inust be noted that these seals dre self-energising, This means that once the seals are clamped up and the systeil is pressurised, the fluid under pressure acts on the internal faces of the seals and forces the sealing faces of the seal even more firmly to the sloping faces of the groove, ensuring that the seal functions even more securely, The illustrated seals are made by initially pressing two snirror-ilnage half-seals from sheet metal, corresponding respectively to the upper and lower halves of the illustrated sealing rings. These pressed half-seals are then welded together along the circumferential weld line or lines 12, after being machined if necessary. After welding, the sealing ring is, if necessary, polished and plated.

-In all instances the thickness of the metal of the sealing ring is adjusted to suit both the pressure to be applied and the size of the radial section.

The sealing rings can be manufactured in any metal but for almost all applications the rings are intended to be produced in stainless steel or the high nickel alloy Inconel (Trade Mark). A nicke ] or nicke3-rich coating nay be applied to avoid corrosion. Inconel 1171811 is particularly specified for sub-sea so-called "sour well" applications but requires an aging treatment to convert it to the specification approved by the North American Corrosion Engineers.

Other coatings such as silver, gold, copper, lead and PTFE can be used for other applications, Each of the five embodiments illustrated in Figs, 41 to 48 is intended for use. as an RX 46 ring seal according to the A.P.I. classification, In Fig 41, d metallic sealing ring comprises a pair of limbs 80, 82 which are joined at one end by a weld 12.

inwardly curved portions 84 and 86 are contiguous with the other end of each of the limbs 80 and 82. The sides of the limbs 80 and 82 are tangential with the curved sides of the respective inwardly curved portions 84 and 86, In this embodiment, the inwardly curved portions 84, 86 have a constant radius and, extend through approximately 2500 so that their free ends are directed inwardly with respect to the metallic sealing ring, A low friction coating 88 is provided on the limbs 80, 82, extending partly onto the inwardly curved portions 84, 86. The purpose of this coating 88 is to reduce scuffing which may occur between the limbs 80, 82 and the surface to be sealed during conpression.

The inwardly curved portions 84, 86 have centres of curvature R and R' (each of 6.67 mill) these being spaced by 15 lltln, The lateral spacing between the centres R, R' and the welded joint 12 is 9.68 mm. The ring itself is of Inconel 718, 1.02 nnn thick. Naturally, these dimensions can be varied according to requirements, Prior to applying a 0.25 @@ nickel coating for "sour well" applications, the rings are vacuum age hardened to increase the spring characteristics as well as to increase the corrosion resistance of the Inconel (Trade Mark) ring, The ring is then polished, vacuum heat treated for 4 hours at 70000 to anneal the nickel and then re-polished. The low friction coating can then be applied.

Fig. 42 illustrates the metallic sealing ring of Fig. 41 in position between opposing grooves 22, which are machined in opposing annular external flanges 20 provided on the ends of pipes 20.

Fig. 42 illustrates this sealing ring in its natural uncoinpressed condition. In use, the flanges 20 are brought together, for example by means of bolts or clamps, into a stand-off configuration or, as illustrated in Fig. 43, into face to face contact.

As the flanges 20 and are drawn together by the clamps or studs, the metallic sealing ring initially undergoes two changes in profile at the same time, This can be seen from Fig. 42 the limbs 80, 82 of the metallic sealing ring contact groove surfaces 54 at respective first contact points 90. As opposing faces of respective flanges 20 are drawn together, the limbs 80, 82 of the sealing ring are forced in the direction of arrows A and R at the first contact points 90 respectively. As the flanges and limbs 80, 82 move with respect to one another, the first contact points 90 slide on the tapered faces 54.The presence of the low friction coating serves to reduce or eliminate scuffing at this point due to the reduction in friction. Any scuffing which does occur does not unduly affect the quality of the overall seal provided by the metallic sealing ring because the integrity of the seal is iiiaintained by contact between the inwardly curved portions and respective tapered groove faces 92.

The configuration of the metallic sealing ring is such that as the flanges 20 are drawn together, the inwardly curved portion 84 rotates or rolls in a clockwise direction, and the inwardly curved portion 86 rolls in an anticlockwise direction on the groove surfaces. The radii of curvature R, R nlove towards one another as the seal undergoes compression. As a result of this rolling, there is no slip or scuffing between the respective inwardly curved portions 84, 86 and their respective tapered faces 92 at the contact points 94, Since the inwardly curved portions 84, 80 undergo this rolling action, no scuffing takes place at the contact point 94 between the nickel coated surface of the metallic sealing ring and the nickel coated surface of the flanges.This gives rise to a reliable seal at the contact points 94 since the maintenance of the nickel coating neans that the seal can withstand the corrosive elements in the case where the seal is used in sub sea sour well or similar applications.

The dimensions of the metallic sealing ring illustrated in Fig. 42 are such that when the seal is fully compressed within the grooves 22 as illustrated in Fig.

43, the inwardly curved portions 84, 86 contact one another in an interference situation at a point 96 near to their free ends. This establishes an additional seal loading line so that as the flange faces are drawn together until they meet, the free ends are urged in the direction of arrows C, C' and D, D' This action enhances the sealing line force present at the contact points 94. Depending on the precise dimensions of the metallic sealing ring and the flanges, the profile rjt the inwardly curved portions 84, 86 in the vicinity of the contact points 94 may flatten son,ewhat.

Nevertheless, the seal at the contact point 94 is maintained without slipping occurring, In order to ensure that the seal is self-energizing, vent holes 10 are provided in the inwardly curved portions 84, 86 for enabling pressure equalization to occur between the interior and inner exterior of the seal. As an alternative to providing the openings 28, radial grooves may be cut in the faces of the inwardly curved portions in the vicinity of the additional sealing line 96.

Fig. 44 illustrates a further embodiment of the present invention in which the dimensions of the metallic sealing ring are such that under full compression (as illustrated in Fig, 46) an additional seal loading line is not established between the inwardly curved portions 84, 86. The nature of the contact points in this metallic sealing ring are the same as those described with reference to Figs. 41 to 43.In this embodiment, it is not necessary to provide vent holes or grooves in the inwardly curved portions since self energization of the seal is maintained by virtue of the fact that the inwardly curved portions do not meet when the seal is fully compressed Figure 45 illustrates the seal in situation prior to comprission and Figure 46 illustrates the seal in its fully compressed situation, In this embodiment, the radii of curvature R, R' are spaced by 17,8 iiim, The lateral spacing between the points R and the weld joint 12 is 9.65 mm, and the radii of curvature R, Rt are each 6.02 línll, Figs. 47 and 48 illustrate two further embodiments of the present invention. In the embodiment illustrated in Fig. 47, the inwardly curved portions 84, 86 extend between respective limbs 80, 82 and as far as the contact points 94 for contacting a sealing surface of an RX A.P.I. groove, but the free ends of the inwardly curved portions 84 and 86 beyond the contact point are straight. As the metallic sealing ring of Fig. 47 undergoes compression, a non-slip sealing contact will be established at contact points 94 and the free ends will tend to be directed inwardly with respect to the metallic sealing ring as the inwardly curved portions 84 and 86 undergo the rolling action.

The embodiment illustrated in Fig. 48 differs from the embodiment of Fig. 47 in that the straight free ends of the inwardly curved portions 84, 86 are directed outwardly (towards the axis of the ring) when the metallic sealing ring is in its uncompressed state. The contact points 94 of this embodiment nevertheless maintain non-slip seals with flanges of the groove (not shown) as the metallic sealing ring undergoes compression.

Modifications may be niade to the embodiments described above without departing from the scope of the present invention. In particular, the nickel coating need not be applied to the sealing ring in the event that the seal is to be used in non-corrosive environments. Also, the specific dimensions of the seal can be adjusted depending upon the groove in which the seal is to he enployed.

It must be noted that these seals are self-energising.

This means that once the seals are clamped up and the system is pressurised, the fluid under pressure acts on the internal faces of the seals and forces the sealing faces of the seal even more firmly to the sloping faces of the groove, ensuring that the seal functions even more securely.

The illustrated seals are made by initially pressing two mirror-image half-seals from sheet metal, corresponding respectively to the upper and lower halves of the illustrated sealing rings. These pressed half-seals are then welded together along the circumferential weld line or lines 12, after being machined if necessary. After welding, the sealing ring is, if necessary, polished and plated.

In all instances the thickness of the metal of the sealing ring is adjusted to suit both the pressure to be applied and the. size of the radial section.

The sealing rings can be manufactured in any metal but for almost all applications the rings are intended to be produced in stainless steel or the high nickel alloy Incone ] (Trade Mark). A nickel or nickel-rich coating may be applied to avoid corrosion. Inconel "718" is particularly specified for so-called "sour well applications but requires an aging treatment to convert it to the specification approved by the North American Corrosion Engineers.

It has been found in practice that for "sour well" use coatings such as silver, lead and PTFE should be avoided wherever possible and that nickel is usually essential to avoid corrosion.

With nickel-coated rings, problems can arise if the grooves also have surfaces of nickel, or nickel-rich surfaces, for example of Inconel 718 to avoid corrosion in the grooves. Because of the relative sliding between the tapered sides of the groove and the surface of the seal ring, and the similarity of the materials of these surfaces, serious scuffing or galling between the groove surface and the sealing ring occurs, It has been found that this problem can be overcome, and other advantages can be obtained, if the sealing ring is shaped before use, to a shape corresponding to that which it would adopt if compressed to a degree less thdn the noijinal degree of compression in use. Preferably the ring is or its components are pre-compressed, preferably to about one half of the nominal compression, which is typically about 15%.

Preferably, the sealing ring consists of two half-rings welded together along a circumferential weld line, for example as shown at 12 in Figure 1, and each of the half-seals is axially compressed after initial pressing to shape and before welding, by about one half of the norriinal compression in use.

It has been found that pre-compression of the sealing rings can not only reduce or eliminate problems of scuffing or galling between nickel or nickel-rich surfaces, but can also increase the strength and performance of the seal irrespective of the nature of the seal and groove surfaces.

A preferred method of nlanufacture is as follows.

Two mirror-iinage half seal rings of stainless steel or Inconel are pressed to the appropriate corrugated cross section, corresponding for example to the upper and lower halves of the sealing ring shown in Figure 21.

Additional compression is then applied so that the final form of the pressed half seal corresponds to the form of the basic sealing ring as it would be when subjected to one half of the nominal compression in use Thus for example, each half seal may be pressed to a profile intermediate between that illustrated in Figure 8 and that illustrated in Figure 10, with the height of the inner corrugation peaks less than that of the outer corrugation peaks, This compression can be applied for example by placing the initially pressed half-seal between two forming dies of the required profile, corresponding in particular to the grooves in which the finished seal is to be used, and colnpressing it to an appropriate extent.

The pressed half-deformed half-seals are then machined in the weld area, and are welded together along a circumferential weld line or lines for example as shown at 12 in Figure 21, to form the complete sealing ring.

The welded sealing ring is fully age-hardened and then polished.

The hardened and polished sealing ring is then nickel-plated, and polished.

The nickel plating is then annealed, for example by vacuum heat treatment for about 4 hours at about 700 C, The resulting sealing ring, when used then undergoes 50% of noininal compresslon, that is to say about 7-8% further compression.

It has been found that this pre-compress#on, or prelinrinary modification of the sealing ring profile, substantially eliminates scuffing and galling between the sealing ring and the grooves.

There may remain a small risk of scuffing on the radially outer surface of the sealing ring during compression, and to eliminate this, the sealing ring may have a very light coating of a suitable low-friction material at least at its outside surface or on the regions thereof liable to scuffing. Alternatively, other forms of lubrication may be provided in this region of the sealing ring.

The described method of manufacture. leads to a number of significant advantages.

The contact travel of the sealing ring and the groove is effectively halved, and this reduction in travel of the groove faces over the surface of the sealing ring reduces or eliminates scuffing, galling, and failing to seal. This advantage is particularly significant when the groove and sealing ring surfaces both comprise nickel or a high-nickel composition.

During compression of the sealing ring there is a sliding action between the groove wall and the radially outer surfaces of the sealing ring, particularly in the regions identified by reference numeral 8 in the drawings, while, at least in the case of sealing rings having profiles similar to that shown in Figure 1, a rolling action occurs between the inner limbs and the groove walls during compression Due to the aging during manufacture, the sealing ring is made stronger.Consequently, during compression the forces on the sealing ring are roughly hdlf-wdy between axial and radial, whereas in a sealing ring made by welding without age hardening, and without pre-compression or pre-deformation of the half-seal profiles, the forces on the sealing ring are essentially axial Also due to the aging, hoop stresses during compression are increased, increasing the contact load between the inner limbs of the sealing ring and the groove walls, ensuring that the nickel coating is forced under preasure to fill any surface asperities of the mating faces. The contact pressure is substantially greater than in the case of a sealing ring made without aging, so that the sealing performance becomes Ignore reliable.

The enhanced rolling action at the inner limbs of the sealing ring, and reduced sliding in these regions, remove the possibility of scuffing in these regions.

Figure 49 shows, by way of example only, a sealing ring having a profile generally resembling that shown in Figure 21, but manufactured as just described and therefore having a modified profile in that the axial distance between the corrugation peaks adjacent the inner limbs is less than the axial distance between the corrugation peaks adjacent the outer limbs of the sealing ring. By way of example only this drawing shows typical dimensions in inches, clearly illustrating the extent to which the inner limbs have been axially moved towards one another, and rotated towards one another, compared with the sealing ring profile illustrated in Figure 21.

Claims

CLAIMS:

1. A metallic sealing ring which in radial cross-section is hollow and of sinuous profile with its axial end faces curved sinuously so as each to define an axially outward facing deep peripheral groove, the interior of the ring profile being in communication with the exterior thereof.

2. A metallic sealing ring as claimed in claim 1 wherein one or each of its side walls is curved to define a concave shallow arcuate profile groove, 3 A metallic sealing ring as claimed in claim 1 which is of closed radial section with each of its side walls curved to define a concave shallow arcuate groove.

4. A metallic sealing ring as claimed in claim 1 which is of closed radial cross-section, with its radially inner side wall curved to define a concave arcuate groove and its radially outer side wall generally convex.

5. X metallic sealing ring as claimed in claim 1 which in radial cross-section is closed only on its radially outward side which is curved to form a concave outwardly facing shallow arcudte groove.

6. A metallic sealing ring as claimed in claim 1 which in radial cross-se.ction is closed only on its radially outward side which is generally convex.

7. n metallic sealing ring as claimed in any of claims 1 to 6, in which the sinuous profile defines, at each axial end face, a respective. corrugation peak radially within and without the said groove, the radially inner corrugation peak having a smaller axial height than the radially outer corrugation peak.

8. A metallic sealing ring which in radial cross-section is hollow, at least one of its radially inner and outer side walls being curved to define a concave shallow arcuate groove, the interior of the ring being in communication with the exterior.

9. A sealing ring as claimed in claim 7 in which the ring cross-section is essentially closed, and the sealing ring is provided with at least one vent hole.

10. A metallic sealing ring which in radial cross-section is hollow and has oblique axial end faces and has a profile such that said axial end faces can he axially compressed towards one another in use, at least at their regions of greatest axial extent, the interior of the ring profile being in communication with the exterior thereof.

11. A sealing ring as claimed in claim 10 which in radial cross-section has, on each axial side of a median plane, d respective radially outer limb which extends, from its junction with the other such limb, obliquely in the axially outward and radially inward directions at a relatively small angle to the axial direction, an end face portion extending, from the axially outer end of said outer limb obliquely at a greater angle to the axial direction than and in the same sense as the axially outer limb, and an inner lines extending from the radially inner end of the end face portion towards the median plane and having a free end, 12. A sealing ring as claimed in claim 10 or 11 having within its cross-section an axially acting compression spring.

13. A metallic sealing ring which in radial cross-section is hollow, the metallic sealing ring comprising a pair of limbs which are joined together at one end and are contiguous with respectively inwardly curved portions at their other end, wherein the inwardly curved portions each extend at least as far as a contact point for contacting a sealing surface, 14, A sealing ring as claimed in claim 13 in which the said inwardly curved portions extend beyond the contact points so that their free ends are directed towards the interior of the sealing ring.

15. A sealing ring as claimed in claim 14 having a configuration such that the free ends contact one another when the seal is under compression thereby enhancing the effectiveness of the seal between the contact points and surface to be sealed.

16. g sealing ring as claimed in any preceding claim, having been pre-compressed by an amount less than its nominal degree of compression.

17. A sealing ring as claimed in any of the preceding claims having a nickel or nickel-rich surface.

18. A sealing ring as claimed in any preceding claim consisting of, in radial cross section, two annular half-seals abutting and welded together in a plane perpendicular to the axis of the sealing ring.

19. A sealing ring as claimed in claim 17 having a circumferential weld line on its radially outer side and a low-friction coating on this weld line.

20. A method of making a sealing ring as claimed in any preceding claim, comprising for'inning two annular half-seals each forming a respective axial half of the seal ring cross section, axially compressing each half-seal to a degree less than the nominal compression in use, and then welding the half-seals together along a circumferential weld line or lines.

21. The method claimed in claim 19 further comprises age-hardening the sealing ring after the welding.

22. The method claimed in claim 19 or 20 further comprising nickel-plating the welded sealing ring and annealing the nickel plating.

23. A method of making a sealing ring, substantially as hereinbefore described.

24. A sealing ring made by the method claimed in any of clans 19 to 23.

25. A metallic sealing ring having a radial cross-section substantially as hereinbefore described with reference to, and as shown in, any of Figs. 1 to 49 of the accompanying drawings.

26. A sealed flange joint incorporating a metallic sealing ring as claimed in any of claims 1 to 18, 24 or 25.