GB2294276A

GB2294276A - Explosion relief wall

Info

Publication number: GB2294276A
Application number: GB9520673A
Authority: GB
Inventors: Arthur Robin Mableson; Nicholas Tudor Tattersall
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1994-10-12
Filing date: 1995-10-10
Publication date: 1996-04-24
Also published as: GB9520673D0

Abstract

An explosion relief wall for a compartment surrounding a zone in which an explosion can take place comprises a structural member e.g. a metal grid (5, 9, 11) having venting means e.g. apertures providing fluid communication between the inner side and the outer side of the structural member. The explosion relief wall further comprises at least one vent panel (20) arranged at the outer side of the structural member and substantially covering said venting means. Each vent panel is connected to the structural member by releasable connecting means e.g. shear pins (51) which are released upon the occurrence of an explosion in said zone thereby allowing movement of the vent panel away from the structural member, which movement of the vent panel is limited by vent panel retaining means. <IMAGE>

Description

EXPLOSION RELIEF WALL The present invention relates to an explosion relief wall for a compartment in which an explosion can take place. In particular the invention relates to an explosion relief wall for use as a horizontal or inclined wall of such compartment. One example of such compartment forms a wellbay module of an offshore hydrocarbon production platform. Although stringent safety measures onboard offshore platforms substantially reduce the risk of an explosion, for example due to hydrocarbon gas leakage, additional safety measures may be required to reduce the risks of unacceptable consequences resulting from an accidental explosion.The overpressure generated during an explosion in a conventional wellbay module can be up to 800 kPa, depending on several parameters such as the gas/air mixture composition, geometry and obstructions within the module, location of the ignition source, and size and location of vent areas. Model calculations have established that a wellbay internal overpressure of between 400 - 600 kPa can be tolerated without causing structural damage to the platform. It is therefore desirable that the overpressure generated during an explosion in such compartment does not exceed a critical level at which damage to the surrounding structure is caused.

It is therefore an object of the invention to provide an explosion relief wall for a compartment surrounding a zone in which an explosion can take place, which wall allows the overpressure due to an explosion in the compartment to be reduced in a controlled manner.

In accordance with the invention there is provided an explosion relief wall for a compartment surrounding a zone in which an explosion can take place, the explosion relief wall comprising a structural member having venting means providing fluid communication between the inner side and the outer side of the structural member, the explosion relief wall further comprising at least one vent panel arranged at the outer side of the structural member and substantially covering said venting means, each vent panel being connected to the structural member by releasable connecting means which is released upon the occurrence of an explosion in said zone thereby allowing movement of the vent panel away from the structural member, which movement of the vent panel is limited by vent panel retaining means.The overpressure which is generated in the compartment during an explosion acts upon the inner surface of the vent panel via the venting means provided in the structural member, thereby causing immediate release of the connecting means and quick removal of the vent panel from the structural member.

Thereby the venting means are uncovered to allow pressurised gas to escape via the venting means. The vent panel retaining means limit the movement of the vent panel to a suitable distance away from the structural member so that damage to surrounding equipment due to uncontrolled movement of the vent panel is prevented.

Suitably the vent panel is further connected to the structural member by hinge means allowing the vent panel to hinge in outward direction relative to the structural member upon release of the releasable connecting means.

In a preferred embodiment of the explosion relief wall, the structural member forms a metal grid of two sets of parallel bars, the bars of one set extending substantially perpendicular to the bars of the other set.

The invention is further described in more detail and by way of example with reference to the accompanying drawings, in which Fig. 1 shows schematically a plan view of an embodiment of an explosion relief wall according to the invention, whereby the vent panels are not shown for reason of clarity; and Fig. 2 shows cross-section II - II of Fig. 1, whereby the vent panels are shown.

Referring to Figs. 1 and 2 there is shown an explosion relief wall 1 including a structural member 3 of rectangular shape and formed of a steel metal grid of two orthogonal sets of parallel flat bars. One of the sets has inner bars 5 and outer bars 7, and the other set has inner bars 9 and outer bars 11. The bars 5, 7, 9, 11 are welded to each other to form the structural member 3.

The structural member 3 is positioned on a support structure 13 (Fig. 2) including a number of T-bars 15 which are attached to each other in any suitable manner and which define the overall shape and size of a compartment made up of a suitable number of explosion relief walls 1. The structural member 3 is fixed to the support structure 13 by means of a number of angled bolts 17 and nuts 18 clamping the member 13 to the flat surfaces of the T-bars 15, the bolts 17 being flat along their end parts 19 to adapt to the flat surfaces of the T-bars 15. Furthermore, the angled bolts are accessible and removable from the side of the explosion relief wall 1 opposite the support structure 13.Thus, each bolt 17 can be inserted into the structural member 3 from the side opposite the support structure 13 and be rotated to the position shown in Fig. 2 whereafter the nut 18 is fixed to the bolt 17 thereby clamping the structural member 3 to the support structure 13. In Fig. 2 is furthermore shown another explosion relief wall 1' similar to explosion relief wall 1 and located adjacent thereto, the two explosion relief walls 1, 1' being symmetrical relative to each other about plane of symmetry 24. Like reference numerals for like parts of walls 1 and 1' have been indicated in Fig. 2, however the reference numerals of wall 1' are provided with a (').

For reasons of clarity, explosion relief wall 1' and support structure 13 are not shown in Fig. 1, except that in Fig. 1 the inner contour 26 of the support structure 13 is indicated as a dotted line.

Two vent panels 20, 21 are provided at the side of the structural member 3 opposite the support structure 13, which vent panels are not shown in Fig. 1 for reason of clarity. Each vent panel 20, 21 covers one half of the structural member 3, the vent panels 20, 21 being symmetrical relative to plane of symmetry 22. The vent panels 20, 21 consist of two layers 23, 25 of composite material including a polyester matrix material and reinforcing aramid fibres and glass fibres. A PVC foam core 27 is located between the two layers 23, 25. The vent panels 20, 21 are hinged with respect to the structural member 3 by means of hinges 29 having hinge axes 31. Each hinge 29 is located in a recess 33 formed in structural member 3 and fixed to the structural member 3 by bolts 35 which are shown schematically only. Each hinge 29 is connected to the vent panels 20, 21 by a metal connecting frame 37 bolted to the vent panels 20, 21 by (schematically shown) bolts 39. Plywood inserts 41 are located between the layers 23, 25 at the locations of the hinges 29 to strengthen the connections of the hinges 29 to the panels 20, 21. Furthermore, plywood inserts 43 are located between the layers 23, 25 at locations where the layers 23, 25 are bolted together, such as at bolt 45. Each vent panel 20, 21 is furthermore connected to the structural member 3 by means of a shear pin arrangement 47 and a bracket 49 fixed to the bar 9 closest to the plane of symmetry 22.The shear pin arrangement 47 is of conventional type and consists of a bolt 51 fixedly attached to vent panel 20, 21 by a nut 53, the bolt 51 being held attached to the bracket 49 by a shear pin 55 extending through a transverse opening in the bolt 51. The shear pin 55 is designed to shear at the occurrence of a selected overpressure at the inner side of the vent panel 20, 21, so that the bolt is released from the bracket 49 upon the occurrence of said overpressure.

Sealing strips 57 are provided between each vent panel 20, 21 and the edges of the bars 7, 9 located at the outer circumference of each vent panel 20, 21, the strips 57 being fixed to said edges of the bars 7, 9.

Each vent panel 20, 21 is furthermore provided with two flexible retaining straps 59, each strap 59 at one end thereof being connected to the vent panel 20, 21 by a bolt-nut connection 45, and at the other end thereof being connected to the structural member 3 by suitable connecting means (not shown). The flexible straps 59 are of sufficient length to allow the vent panels 20, 21 to hinge about the hinges 29 up to a selected angle at which the flexible straps become tight and thereby prevent further hinging of the vent panels 20, 21.

A drain channel 61 extends between the two bars 9 adjacent plane of symmetry 22, the drain channel 61 being located a selected distance below the vent panels 20, 21. Furthermore, a drain channel 63 extends between the two bars 11, 11' adjacent plane of symmetry 24, which drain channel 63 is fixed to the upper surface of T-bar 15 and is sealed from the support structure 13 by suitable elastomeric seals 65. The drain channels 61, 63 serve to discharge liquid flowing from the vent panels 20, 21 into the drain channels 61, 63.

During normal use of the explosion relief wall 1 the support structure 13 with one or more explosion relief panels 1 attached thereto encloses a zone in which an explosion can take place. Such zone can, for example, be formed of a well bay of an offshore hydrocarbon production platform. Although stringent safety measures are taken onboard such offshore platform to prevent the occurrence of an explosion, additional safety measures can be required to reduce the risks involved when an explosion occurs. The explosion relief walls 1 are arranged so that the vent panels 20, 21 are located at the outside thereof. In case of an explosion the overpressure generated in the zone enclosed by the explosion relief wall 1 acts on the side of the vent panels 20, 21 facing the structural member 3.The overpressure causes shearing of the shear pins 55 and moves the vent panels 20, 21 in outside direction so that the vent panels 20, 21 hinge about hinges 29 until the flexible straps 59 become tight thereby limiting the hinge angle of the vent panels 20, 21. Thus the explosion relief wall 1 allows fast release of pressurised gas formed during an explosion in the zone enclosed by the explosion relief wall 1. The flexible straps 59 prevent the vent panels 20, 21 from interfering with adjacent vent panels. The pressurised gas in said zone is thereby allowed to escape through the rectangular openings of the structural member 3.

Furthermore, the structural member 3 provides adequate protection against impact of objects, such as drill collars, which may accidentally drop on the explosion relief wall 1.

Instead of the vent panels being connected to the structural member by hinges, the panels can alternatively be connected to the structural member by a plurality of shear pin arrangements so that, upon the occurrence of an explosion, the shear pins are sheared thereby allowing the vent panels to freely move away from the structural member until the vent panels are retained by the vent panel retaining means.

The invention further relates to a compartment surrounding a zone in which an explosion can take place, the compartment comprising the explosion relief wall described hereinbefore.

Claims

1. An explosion relief wall for a compartment surrounding a zone in which an explosion can take place, the explosion relief wall comprising a structural member having venting means providing fluid communication between the inner side and the outer side of the structural member, the explosion relief wall further comprising at least one vent panel arranged at the outer side of the structural member and substantially covering said venting means, each vent panel being connected to the structural member by releasable connecting means which is released upon the occurrence of an explosion in said zone thereby allowing movement of the vent panel away from the structural member, which movement of the vent panel is limited by vent panel retaining means.

2. The explosion relief wall of claim 1, wherein the vent panel is further connected to the structural member by hinge means allowing the vent panel to hinge in outward direction relative to the structural member upon release of the releasable connecting means.

3. The explosion relief wall of claim 1 or 2, wherein said structural member forms a metal grid of two sets of parallel bars, the bars of one set extending substantially perpendicular to the bars of the other set.

4. The explosion relief wall of any of claims 1-3, wherein the vent panel comprises a layer of fibre reinforced composite material.

5. The explosion relief wall of claim 4, wherein said layer of fibre reinforced composite material comprises a matrix material in which a plurality of fibres selected from the group of aramid fibres and glass fibres are embedded.

6. The explosion relief wall of claim 5, wherein said matrix material comprises polyester.

7. The explosion relief wall of any of claims 4-6, wherein the vent panel comprises two layers of fibre reinforced composite material and a core layer located in-between said two layers of fibre reinforced composite material.

8. The explosion relief wall of claim 7, wherein the core layer comprises a plastics foam material.

9. The explosion relief wall of claim 8, wherein the core layer comprises polyvinyl chloride foam.

10. The explosion relief wall of any of claims 1-9, wherein the releasable connecting means includes a shear pin which mechanically fails upon the occurrence of said explosion.

11. The explosion relief wall of any of claims 1-10, wherein said vent panel retaining means comprises a flexible strap interconnecting the structural member and the vent panel.

12. The explosion relief wall of any of claims 1-11, wherein said venting means includes at least one opening provided in the structural member, each opening providing fluid communication between the inner side and the outer side of the structural member.

13. The explosion relief wall substantially as described hereinbefore with reference to the drawings.

14. A compartment surrounding a zone in which an explosion can take place, the compartment comprising an explosion relief wall according to any of claims 1-13.