GB2247928A - Bolt tensioning devices - Google Patents

Abstract

An asymmetric bolt tensioning device (4) includes an asymmetric non-circular piston and cylinder arrangement provided with a non-circular seal 15 whose dimensions are selected such that the product of the total area of that part of the seal to one side of any diameter through the bolt 1 centre and the distance from that centre to the point within that part of the seal 15 at which the effective pressure developed therein acts, is at least approximately equal to the corresponding product for that part of the seal to the other side of said diameter. Sets of four bolt tensioning devices (4) are provided in blocks (5) each with a handle (6) and a fluid connector (7). Pistons 13 19 push up on a bolt puller 19 screwed on the end of the bolt 1 in a flanged joint used, for example, in chemical engineering plants and underwater oil pipelines. <IMAGE>

Description

Bolt Tensionin Devices This invention relates to a device for use in tensioning a bolt or like screw-threaded component to enable a nut or complementary screw-threaded member to be fully tightened on to the bolt or other component. Such a device will hereinafter be termed a "bolt tensioning device".

There are many situations in which the orthodox method of tightening a nut on to a bolt, i.e. by means of a spanner, proves to be unsatisfactory or very difficult, e.g. where the nuts and bolts are of large size as used in chemical engineering plants and in underwater oil pipe-lines. In such situations, a tool is used to tension the bolt so that the nut can be turned with relative ease. One known form of tool comprises an annular hydraulic ram through which the bolt can extend, a generally tubular spacer member for accommodating a nut, engaged with the bolt, and adapted to be located between one side of said ram and a surface against which the nut is to be tightened, and a puller member in the form of an auxiliary nut which is screwed on to the bolt until it abuts the other side of the ram.The effect of actuating the ram is to tension the bolt and the spacer member is arranged so as to allow access to the nut proper to enable it to be turned.

This known form of a ram is subject to the drawback that the ram has a very limited stroke and consequently when the nut proper has to be threaded a substantial distance along the bolt with the aid of the tool, it is necessarv to carrv out the operation in a series of steps involving readjusting the tool each time the ram reaches the limit of its stroke. This drawback arises primarly because of the construction of the ram in that extension of the piston is effected through the agency of a generally toroidal rubber seal into the interior of which the hydraulic oil is supplied.The ram stroke is related to the radial width of the toroid and to obtain a large ram stroke, e.g. 20 mm or more, it would be necessary to have an impracticably large piston chamber to accommodate the seal, i.e. the ram body would have to be made larger with consequent increase in its weight.

Patent GB-A-1,590,131 discloses a bolt tensioning device comprising a body, a piston mounted in the body, the piston and the body being of generally annular configuration to allow the device to be assembled in encircling fashion to a bolt or like component it is desired red to tension, and an annular chamber between the bod and the piston for the admission of fluid under pressure to effect relative axial displacement of the body and the piston whereby the axial dimension is increased, the piston comprising an inner part having a pressure area which is subject to the pressure in said chamber and an outer part to which the fluid pressure is transmitted via said inner part and an interposed mass of solid, yielding and substantially incompressible material whose effective pressure area is less than that of said inner piston part.

The arrangement is such that, in use, the pressure developed within said mass is at all times greater than the fluid pressure in the chamber, so that said mass expands radially to sealingly engage the walls of the chamber.

It will be noted that with this arrangement, the stroke of the piston is not limited b the configuration of the seal and thus a relatively long stroke, e.g. in excess of 20 mm, is possible.

In practice the incompressible material will usually be of natural or synthetic rubber.

In a preferred arrangement, the mass of said material is prestressed and thereby radially expanded independently of the hydraulic pressure. Otherwise there is a possibility that, during initial admission of oil into the chamber, some oil will leak past the seal.

In one embodiment of this earlier invention, the mass of material is constituted by a ring located between inner and outer parts of the piston, the ring being formed with one or more apertures so that the effective area is less than that of the inner end of the piston and the inner part being connected to the outer part by adjustment elements which can be operated to draw the piston parts together so as to apply an axial compression to the ring which results in its radial expansion, the adjustment elements being so arranged that they do not transmit force from the inner piston part to the outer piston part.

In another embodiment, one of the piston parts is formed with one or more recesses in which projecting portions of the other piston part are received but without making force-transmitting engagement therewith (at least as far as axial forces are concerned), said projections passing through apertures or the like in said mass of material.

For example, the inner piston part may be formed with a generally central, continuous rib received in a groove in the other part, the groove being sufficiently deep to preclude the possibility of the rib bottoming therein and said mass of material maybe constituted by two separate rings located one on each side of the rib.

The bolt tensioning device may be embodied in a tool in which case it will have an auxiliary nut or puller member associated therewith which, in use, is screwed on to the component and co-operates with said piston to effect boltstretching. Alternatively the device may be embodied in a nut or the head of a bolt and, in this event, i. is used in conjunction with one or more spacers or shims which are inserted between the nut or bolt head and a fixture, e.g.

a flange, after stretching of the bolt or, alternatively, the nut body or bolt head may be provided with an radially adjustable abutment portion (such as a screw-threaded sleeve) which can be adjusted into abutment with the flange or other fixture after the bolt has been stretched to take up the resulting gap between the nut or bolt head and the flange.

When the device is subject to large hydraulic pressures, there is a tendency for the mass of material to extrude past the outer piston part. One way of reducing this tendency is to provide a rigid back-up ring located between said mass and the outer piston part, the back-up ring having its peripheral edges in close fitting relation with the chamber walls and being composed of a material having a low coefficient of friction e.g. P.T.F.E.

In trials conducted using the bolt tensioning device disclosed above however it was found that while satisfactory results are obtained over a wide range of fluid pressures, at high pressures there is a susceptibility to leakage of oil past the seal afforded by said mass. This is because the high pressure acting on the rubber or like mass tends to extrude it down the sides of the piston even when the back-up ring is present. This problem can be alleviated by using a chamber of greater width but this means that the overall radial dimensions of the device must be increased with consequent increase in weight and greater handling difficulty.

According to a preferred feature of the earlier invention, said mass of material is received within a recess or groove in the outer piston part.

Preferably the arrangement is such that the mass of material, as well as expanding radially, when pressurised, to sealingly engage the chamber walls, also stresses and elastically deflects the side walls of the recess or groove towards adjacent surfaces of said body to further enhance sealing. In the preferred embodiment, the side walls of the recess or groove are of tapering configuration and terminate in a substantially lineal edge (a "feather edge") facing said inner piston part. The base surface of the recess or groove may be substantially flat and the side surface thereof may be of frusto-conical configuration, the junctions between the base surface and the side surfaces being radiussed, the radius being relatively sharp to aid the aforesaid flexure of the side walls. Alternatively, the side surfaces of the recess or groove may be arcuate and merge smoothly with the base.In both cases, the seal is conveniently contoured to correspond with the internal configuration of the recess or groove.

In the preferred embodiment, the chamber is in the form of a deep annular cavity in said body and the outer piston part includes a leading annular section which extends into the open mouth of the cavity and is a close sliding fit therein and a trailing section of reduced width which is of sch extent that the root portions of the side walls of the recess or groove are of reduced dimension thus enhancing the capability of the side walls to deflect elastically. The reduced width trailing section also reduces the drag resistance to displacement of the piston and allows the piston to misalign with the body to some extent to compensate for any out-of-alignment that may be present.

Whilst the invention described above is extremely successful, there are circumstances where its use is difficult. In particular, serious problems arise where adjacent bolts of a set are to be tightened simultaneously and the space between them is not great enough to permit installation of conventional hydraulic bolt tensioning tools. One attempt to over-come this, by use of an asymmetric tool, is described in GB-A-1,592,092, but the hollow asymmetric seal arrangement set forth therein is not an easy one to make.

It is an object of this invention to at least simplify construction of an asymmetric bolt tensioning tool.

According to this invention, hydraulic bolt tensioning apparatus comprises a non-circular piston and cylinder device provided with a non-circular seal (as seen in plan), the dimensions of which are selected such that the product of the total area of that part of the seal at one side of any diameter through the bolt centre and the distance from that centre to the point within that part of the seal at which the effective force developed therein acts, is at least approximately equal to the corresponding product for that part of the seal to the other side of said diameter.

The distance from the centre to the point where the pressure effectively acts will be herein referred to as the centroid. By so dimensioning the seal that there is this relationship between seal area on either side of a diameter through the bolt centre and the centroid, out-of-balance forces are minimised and accordingly the risk of bending a bolt is also minimised.

The application of this concept to the earlier tensioning apparatus described in GB-A-l,590,131 is particularly a dven tage ous, since it renders that apparatus susceptible of use in a very much wider range of environments, whilst preserving all the technical advantages of the earlier apparatus.In order that this be better understood, one preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a plan view of a plurality of bolt tensioning tools in accordance with the invention disposed to tension simultaneously a plurality of bolts around a flange, Figure 2 is a composite cross-sectional side visw through two of the tools of Figure 1 taken along lines Z-Z thereof, Figure 3 is a plan view of a seal constructed in accordance with the invention, for use in the bolt tensioning apparatus of Figures 1 and 2.

In the interests of convenience, like parts in each Figure bear like reference numerals. Referring firstly to Figure 1, a plurality of stud bolts 1 are distributed around the circumference of a flanged joint (item 2 in Figure 2) and it is intended to stress all of these prior to tightening retaining nuts 3 (shown only in Figure 2). To this end, bolt tensioning tools 4 are installed around the flanged joint, each tool 4 being one of a set of four identical tools incorporated into a single arcuate block, 5. Each block is provided with a carrying handle 6, although only one of these is shown in the Figures. Each block has a fluid connector 7 through which hydraulic fluid can be admitted to all four of the associated tensioning tools at once.

Figure 2 shows the internal construction of two adjacent tools (from one block of four) in more detail. The Figure is a composite one, since the lines Z-Z include a right angle step. Thus the left hand half of Figure 2 shows the tool as seen in section at right angles to the tool as seen in the right hand half of the Figure. As previously mentioned, like parts bear like reference numerals and, referring to both halves of Figure 2, the common body portion 5 contains a recess 8 surrounding the retaining nut 3, over which a sleeve 9 is placed. The latter has an inner hexagonal profile whilst its exterior is cylindrical, with a plurality of tommy bar holes 10. The latter can be accessed for the purpose of rotating the nut 3 through cut-outs 11 in the body 5 (see Figure 1). The body contains an annular, but non-circular recess 12 which in plan view corresponds to Figure 3.The recess contains a correspondingly shaped piston 13 whose lower most region terminates in feather edge sections 14. These define an annular (but non-circular) recess containing a sealing ring 15, the plane view of which is shown in Figure 3.

The ring is held into the recess by a back-up plate 16 by a plurality of set screws 17 which extend through apertures 18 in the sealing ring 15. It is to be noted that these set screws are engaged in screw threaded bores in the plate 16, but are otherwise free to move in their axial direction relative to the piston 13. Their action is discussed in detail in GB-A-1,590,131 and need not be further discussed here.

The piston 13 acts at its upper face on the underside of a puller 19. This is an annular nut, internally screw threaded to match the stud bolt 1, down which it is screwed until it seats against the upper face of the fully-retracted piston 13. Tommy bar holes 20 are provided to facilitate tightening/untightening of the puller 19. For the sake of completeness, although not strictly relevant here, each stud bolt 1 has at its free end a nut profile 21 which can be used for various purposes such as to prevent unwanted bolt rotation, to remove and/or insert the bolt.

Because the view in Figure 2 is a composite one, the width of the section of sealing ring 15, reflects the fact that radially inwardly/outwardly of the pitch circle of bolts 1 (Figure 1) the seal is relatively wide, whilst in the direction of the pitch circle, it is relatively narrow, to reflect the overall asymmetry of the bolt tensioning tool, as best seen in Figure 1, although the close proximity of individual bolts is clearly shown in Figure 2, where adjacent recesses 8 are so close together as to be almost contiguous, only a thin web 22 separating them. It will be appreciated that the web 22 is necessary, to even out the forces acting on the flange below, as well as to minimize distortion of the block 5.

Referring now to Figure 3, the plan view of the seal includes holes for the set screws 7. However, as can be seen, the width of the ring at 30 is rather greater than at 31, which lies radially outwardly of the ring of tools (Figure 1). The intermediate regions 32, 33 are narrower, to reflect the asymmetry just mentioned. In accordance with this invention, the asymmetry does not result in asymmetric, or bending forces on the bolt 1. The reason is that regardless of which diameter through the bolt centre is used to divide the ring into two halves, the area on each side of that diameter multiplied by the centroid distance is substantially constant. In other words, the area of each part of the sealing ring is adjusted in relation to its effective distance from the centre so as to maintain a balance between the pressures exerted on opposite sides of the bolt centre.

It should be appreciated that the invention is not limited to completely symmetrical sealing rings. It can be applied equally successfully to irregular sections, provided care is taken to ensure that diametrically opposed areas and the respective centroid distances are in balance, as explained above. In the case of the arrangement illustrated, even closely spaced bolts can be simultaneously tensioned, without resorting to expedients such as tensioning only alternate bolts in the set, followed by transferring the tools to the unt ensi on ed bolts, to finish the job.

Claims (6)

1. Hydraulic bolt tensioning apparatus comprising a non circular piston and cylinder device provided with a non-circular seal (as seen in plan), the dimensions of which are selected such that the product of the total area of that part of the seal to one side of any diameter through the bolt centre and the distance from that centre to the point within that part of the seal at which the effective pressure developed therein acts, is at least approximately equal to the corresponding product for that part of the seal to the other side of said diameter.

2. Hydraulic bolt tensioning apparatus according to claim 1 wherein a plurality of piston and cylinder devices are mounted in a common support block.

3. Apparatus according to claim 2 wherein said devices are disposed to lie on an arc of a circle whose diameter corresponds to the pitch circle diameter of a set of bolts at least some of which are to be simultaneously tensioned.

4. Apparatus according to any preceding claim 3 wherein the piston and cylinder device together with the seal are asymmetric relative to at least one diameter through the centre of the bolt to be tensioned.

5. Apparatus according to claim 5 wherein there is asymmetry relative to a plurality of said diameters.

6. Apparatus for tensioning a bolt substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.