GB2214601A - Closure for pipe or vessel - Google Patents

Abstract

The closure comprises a set of segments 8 interposed between a neck or pipe 1 and a door 3 in such a manner that increase in pressure within a vessel or pipe only serves to place the segments 8 under greater compression. The segments 8 may form a ring L actuated by a collar 12, girth springs or garters 14, 15 may be provided to restrain the segments 8. A safety plug 33 is provided to block undesired release movement of the collar 12. <IMAGE>

Description

CLOSURE FOR PIPE OR VESSEL The present invention relates to closures for pipes or vessels and more particularly to closures which can be released quickly to gain access to the pipe or vessel for inspection or similar purposes.

There are a number of known such closures in practical use and a typical closure is described in British Patent No. 1508998 in which a plurality of blocks are slidably mounted adjacent the periphery of the door and are movable in a combined radial and circumferential movement to a protruding position to effect closure of the door. A further closure system is described in published European Patent Application No. 129,349 which employs an arcuate locking member disposed around the periphery of the door for locking the door.

It is an object of the present invention to provide a closure for a pipe or vessel of a design which is both novel and advantageous when compared with previous known designs.

The present invention provides a closure for a pipe or vessel including a door adapted to fit over a neck pipe extending from or being part of a pipe or vessel and including a plurality of segment members adapted to be interposable between the door and neck pipe when the door is in a closed position to retain the door in the closed position on pressurisation of the pipe or vessel, the segment members being movable to allow opening of the door on the de-pressurisation of the pipe or vessel.

In a preferred embodiment the segment members are generally 14- L-shaped and are movable by means of a retaining ring.

Preferably the retaining ring is prevented from movement by a latch means the latch means being operable to allow escape of gas or liquid from within the pipe or pressure vessel if the latch .s operated whilst the pipe or essel is still nrssris.

Preferably each segment member is provided with a portion having generally parallel surfaces one of which abuts the door and one of which abuts the outer surface of the neck pipe in the closed position of the door.

Preferably all segments are identical and preferably all segments are arcuate in shape the plurality of segments thereby forming a circular closure means.

Embodiments of the present will now be described, by way of example with reference to the accompanying drawings in which: Figure 1 shows a cross-section through a door and neck pipe illustrating the closure according to the present invention; Figure 2 shows a cross-section illustrating the segments in Figure 1; Figures 3A to F illustrate the segments and their movements to effect closure; Figure 4 shows the retaining ring and illustrates one possible method of moving the segments; and Figure 5 illustrates the forces involved in the closure system.

With reference now to Figures 1 to 3 the pipe or vessel P (shown only partially) is provided with a fixed element which is shown as a simple cylindrical body or "Neck-Pipe" 1. The "Door" is a cap-like structure consisting of a collar or rim 2 and a closing membrane of any suitable pressure-containing form 3, selected for efficiency and commercial availability. Typically a conventional "dished-end" is envisaged, for example ellipsoidal or torispherical, but the exact form does not influence the broad concept and it will be apparent to those skilled in the art that any approved form could be substituted, e.g. a cone, hemisphere, flat plate or integration with ~the rim itself.The rim of the door is of a size to surround and enclose the end of the neck pipe, with an annular ap of small radiai cinension 4 between the to. The sealing of this aperture to produce a fluid-tight assembly is performed at or near the inserted end 5 of the neck-pipe. The advantageous reason for this location will be described later. It will be well understood that numerous means exist in the art of pressure sealing for this purpose. The known difficulties of practical door design do however lead to a favoured sealing means, which takes profound advantage of specific features of the new design, and is described below. For present continuity, it may be accepted that fluid tightness can he established in the specified one.

The door must resist a force arising from ils effective internal area and directed along its longitudinal axis. This resisting means is also locatèd essentially within the inter-component annulus.

At the end of the neck-pipe 1 the external surface is formed as a male cone 6 increasing in diameter towards the free end. The slope of the conical surface relative to the longitudinal axis may vary but is typically in the range 1:3 to 1:5 (radial and longitudinal respectively).

A preferred value is about 1:4.5 (about 12.so halfconical angle).

At the open end of the door rim 2 an internal conical element 7 is provided in the reverse formation and of similar slope, such that the smallest diameter or effective bore is at the free end. This bore is slightly larger than the outside diameter of the male cone on the neck-pipe, and the two may pass axially. When the door is disposed in the desired "closed" position (with the seal properly engaged the two conical faces are so located that they define a conical annular volume xvith long boundaries mutually parallel.For various technical reasons, this specification also allows the possibilitv that the two faces would be produced with some differences in taper so that the radiaily-measur#d #ap in the annulus would varqv along its length.

For purposes of illustration, it may now be assumed that this annular conical void is exactly filled by a correspondingly-shaped solid member. It will be apparent that withdrawal of the cap 2, 3 from the neck 1 would be absolutely prevented, the hypothetical solid circular key element resisting any such movement by shear strength along its long diagonal (viewed in section) and by bearing pressure as it is compressed between the two wedge-like structures. It will be clear that this represents an extremely strong, stable and stiff barrier to movement. It will also be obvious that if - as just described - the circular key were indeed solid, then the three-part assembly would be unattainable in real life.

In the present embodiment, the key ring is actually divided by longitudinal cuts into a series of individual arc-shaped segments 8 which, apart from the small circumferential gaps 9 produced by the 'cutting", , fill the void and react to the adjacent parts exactly as previously described. Because of the freedom permitted by the sectioning, an individual segment would now be free to move simultaneously axially and radially down to the smaller end of the conical annulus. Providing the total length of the inter-segmental gaps 9 is sufficient, all the key segments 8 can do this together, so that the divided key ring 8.8... appears to "contract until the major diameter, measured over the tops of the segments, is less than the bore of the rim, which is thereby free to move axially. In other words, the door is unlocked, and may thereafter be opened. There is a threedimensional complication of this sectional description which is harnessed as a safety feature described later.

To achieve the compound movement described for the segments, it. is only necessary to apply a simple coordinated pull to all of them. (or push to return) the enclosing faces providing the needful guidance constraints. This is achieved, in one embodiment, by providing a thin cylindrical connection 10 between the conical sections of the key segments 8 and a control ring or flange 11. This surrounds the neck-pipe l and is free to move substantially thereon, towards and away from the door rim 1. All the segments 8 are thus constrained to move in synchrony. This movement has both axial and radial components and the latter must be allowed for in the connection between key segments and control ring.

Hinged links or flat spring elements 12 may be substituted for the thin cylinder but in a preferred embodiment the control ring 11, the thin cylinder 10 and the key segments 8 are all subject to the same subdivision so that each solid component comprises a part of the ring, a part of the cylinder and a key segment.

Continuity of control is maintained by surrounding the outwardly-extending and now sub-divided ring by a nondivided collar 12, substantially a U-section embracing the ring. All sections of the latter are thus constrained to follow any axial movement of the collar i2 and the cooperating parts may advantageously shaped as shown 13 to provide close axial control whilst permitting the necessary angular freedom. Further to restrain the segments, they may be surrounded by girth springs or garters located at the major diameter 14, or at the thin section 15 or both.If the key ring assembly is circumscribed in this way, with the conical segments lying parallel with their "locked" position, although at a smaller overall diameter, it is advantageous to provided a lead-in or conical bell-mouth 16 at the outer end of the door rim 1 such that, when "locking", the outer tips of the segments enter this feature. They are thus constrained to tilt inwards and so be guided into the conical annulus along which then finally expand.

Minor variations are envisaged, in which the longitudinal movement of the key segments along the neck- pipe is facilitated by the provision of anti-friction elements such as rings or pads of suitable material interposed between the parts. The spacing of the segments around the circumference may be maintained by suitable compressible elements of "beads" between the segments and/or on one or the other of the garters. The control collar is a rigid item with straight-line movements and close proximity to the door rim when locked. It may readily be furnished with sealing means relative both to door rim 17 and neck-pipe 18 completely to exclude weather and other adverse ambient conditions, when locked, from the critical annulus. (This would not supplant the pressure seal).

In the mechanism so far described, a locking member - of very small weight and spatial requirements relative to the surrounding pressure parts, functions under the control of a small axial movement by a surrounding collar 12. It is clearly necessary that this motion be substantially uniform around the periphery so that all segments 8 reach the proper load-bearing position and smoothly disengage therefrom. Three points are necessary and sufficient to define a plane. Three-point control of the collar is therefore a preferred method, with connections preferably spaced at approximately 1200. The motion is short and does not involved large forces.

Designers skilled in the art will recognise many ways of achieving this uniformity. For example, three interconnected jacks uniformly spaced, could be envisaged. A preferred method suitable for direct manual use is described.

A lever linkage, as shown in Figure 4, is located substantially in the plane of the control collar 12, which is furnished with three connecting means, in this case simple radially projecting pins or pegs 19 at equal pitches. A rocking shaft 20 bearing two short levers 21 suitably spaced interacts with two of the pegs by engagement with the lever ends. A Longer lexer .or an extension past the engagement point of one of the short ones 22) is carried beyond the centerline towards the side remote from the rocking shaft, at which side is the remaining peg 19 on the collar.A secondary lever 23 connects between that peg and the extended arm 22 just described, the fulcrum 24 being chosen so that the enhanced motion of the extension is reduced in due proportion and the three pegs 19 move the same distance and in unison. The levers 21, 22 may be disposed in a variety of ways around the closure and either may be selected as the input handle 25 for the actual manual effort.

Familiar and well-understood sealing means may be used in conjunction with the new locking mechanism. For example, an O-Ring or similar can be conventionally housed in a groove on the male element or neck-pipe 1, cooperating with a bore in the rim 12. Equally conventionally, this can be reversed, with the seal housed in the outer bore. Other sections may be envisaged by seal specialists, within the restrictions that no clamping force is available and some axial compliance is necessary.

Precision cylinder seals are not well suited to repeated engagement and disengagement in possible difficult and dirty conditions. Because of its door-like function, a closure seal must be instantly responsive to very low pressures after closing, yet withstand immediate transition to potentially very high pressures from this situation without further attention. It should also be simple in form, self-retaining yet readily exchanged without tools and - if possible - in a format which can be manufactured in a variety of elastomeric materials to suit a wide range of duties.

A particular feature of the 'cap over neck' format adopted in the present specification is that it permits a naturally-energised Lrailing-lip seai to be located in the door. The seal 26 incorporates an inwardly projecting thin flange or lip 27 which is also directed away from the door opening. It will be apparent that as the door closes over the end of the neck-pipe, such a lip can make contact with a suitable cylindrical or slightly tapered surface 28 with little force and some tolerance of misalignment.Such features usually suggest a vulnerability to higher pressures, but in this specific configuration of the three parts, pressure exists on the free, non-contact, concave side of the lip which thus is pressed more tightly to its mating surface by servo action, and enables the seal to move into a higher pressure regime.

As the seal is housed in the female part it must be self-retaining (unlike a garter format) and to confer versatility it should be adaptable to different curvatures, suggesting a compact and fairly symmetrical cross-section.

The new seal section can be defined as derived from four circles conjoined in a "square" formation and "solidified", or as a nominal square with convex corners and concave faces. One of the corners is then considered to be elongated into a tapering lip 27 extending substantially along a diagonal. The working seal is an elastomer hoop of the stated cross-section with the lip 27 protruding inwards. The outer slightly bulbous features engage in and are held by a slightly dovetailed female groove 29, the shape also providing a fixed fluidtight seal. On contact with the neck-pipe, the lip makes light contact with the taper, and the inner bulbous corner abuts a shoulder-like feature on the neck. It is this which forms the abutment against the highest pressure forces, and contact can be maintained in these conditions even with some relative door movement because of the mid-line flexibility of the seal section.

Of particular importance in field conditions is the simple shape of the seal contact surfaces 30, 28, open to inspection and cleaning or refurbishing but not exposed to damage from inside the pressure environment.

A notable feature of this proposal is the resolution of forces arising from the mechanism and the seal arrangement. As will be seen in the diagram Figure , the whole interior of the neck-pipe is subjected to the internal hydrostatic pressure. Opposed to this is the inward component from the locking mechanism which (neglecting friction) is amplifa-ing the loneltudinal force by the effect of the wedge angle. (Say by a factor of about 4 As the longitudinaL tress in a cylindrical P.V. is of course half the corresponding hoop stress, the resulting inwards compressive stress from the locking action does not greatly exceed in magnitude the ordinary outwards tensile stress. This note is not an analysis of formal stresses, of course, but illustrates the balance achieved.The wedge-amplified outward force on the door rim 2 is clearly not so balanced, but it is distributed over a longer periphery and is so located that adequate reinforcement 31, if called for, can easily and economically be added. This point is reinforced by the extraordinary radial compactness achieved by this design.

Safety Codes require a so-called Safety Bleed Plug, which must be removed (thus demonstrating any internal pressure) before the door can be unlocked before opening.

This very basic and mandatory item is particularly easy to embody in the new design. The control ring 12 is a full circle, and its movement towards unlocking can be blocked :32 at any convenient point. by a suitably located plug and fitting 33. As a further reminder to the operator, the lever actions themselves may readily be associated with safety features in familiar ways.

In recent years more fundamental safety philosophies have evolved. One of these is Whole-door involvement as the pressure sensor for the very low pressure (but still hazardous) case.

The new proposal embodies this concept and carries it forward in an absolutely fundamental way. If the door is in its pressurised position, even if the actual pressure is zero, the segments 8 are trapped by virtue of their geometry. To release them, the door must be moved further inwards - in the closing direction. The asdepressurised door is safe, and the intense difficulties arising in other concepts, in defining the sirnificant levels of very low pressures, are avoided.

The ambushing of the segments arises in the following way. The ^unlocking action was described above as in section, with a parallel element sliding as if between parallel faces. Each segment of course extends circumferentially as a rigid body, and In the locked position the confirming conical surfaces all correspond.

This cannot be true at any other radius and for all cross-sections of the segment simultaneously. (As for example, segment ends 4). Putting it another way; in a perfectly fitted condition the key segments 8 would be captive just as in the hypothetical "solid" case.

Clearance for the segment ends 34 must therefore be increased by axial movement of the door, which "closing" travel is precluded by pressure.

Claims (6)

1. A closure for a pipe or vessel including a door adapted to fit over a neck pipe extending from or being part of a pipe or vessel and including a plurality of segment members adapted to be interposable between the door and neck pipe when the door is in a closed position to retain the door in the closed position on pressurisation of the pipe or vessel, the segment members being movable to allow opening of the door on the depressurisation of the pipe or vessel.

2. A closure for a pipe or vessel as claimed in claim 1 in which the segment members are generally L-shaped and are movable by means of a retaining ring.

3. A closure for a pipe or vessel as claimed in claim 2 in which the retaining ring is prevented from movement by a latch means the latch means being operable to allow escape of gas or liquid from within the pipe or pressure vessel if the latch is operated whilst the pipe or vessel is still pressurised.

4. A closure for a pipe or vessel as claimed in any one of claims 1 to 3 in which each segment member is provided with a portion having generally parallel surfaces one of which abuts the door and one of which abuts the outer surface of the neck pipe in the closed positon of the door.

5. A closure for a pipe or vessel as claimed in any one of claims 1 to 4 in which all segments are arcuate in shape the plurality of segments thereby forming a circular closure means.

6. A closure pipe or vessel substantially as described with reference to the accompanying drawings.