GB2266543A - "Blast wall structure" - Google Patents

Abstract

A blast wall structure includes a support frame e.g. (11) and at least one pressure-relief panel e.g. (10) releasably secured to the frame. The means for releasably securing the panel to the frame includes a bolt assembly (14, 15, 18) and a retaining washer (17) having one or more radial projections (19). When a significant overpressure arises within the blast wall structure, these projections distort or break to permit the bolt assembly to pass through an aperture (12) in the frame. The washer may have inwardly-directed projections (Fig. 3, not shown) and be located within a housing (Figs. 5, 6, not shown). <IMAGE>

Description

Blast wall structure The present invention concerns blast walls of the type comprising a support frame and one or more panels which are secured to the frame and are designed to blow out in response to pressure on the emote side of the wall and thus to release that pressure.

It is known that the adverse effects of an explosion within a confined space can be greatly reduced by the provision of such blast walls whereby overpressure within the space can be readily and quickly vented to the surrounding atmosphere. To achieve this result, it is desirable that the blast walls should yield to pressures not greatly exceeding those normally encountered within the space. However it is also important that the walls should withstand pressures from an external direction, in order to protect the interior space from unusual environmental conditions without yielding inwardly.For example, in offshore locations such as on exploration or production rigs, it may be necessary for the wall panels to be fire-rated and heat-insulating and therefore gas-tight, while at the same time being weather tight and able to withstand the extreme weather and wind conditions which are encountered in locations such as the North Sea.

The ideal blast wall is one which is able to withstand the maximum external pressure which can be anticipated, including outwardly-directed wind suction pressures, but will yield outwardly in response to an internal pressure which is relatively close to that maximum anticipated external pressure, say perhaps twice that pressure. By way of example, in extreme storm conditions in the North Sea, blast walls on oil rigs may be subjected to external wind suction levels exceeding 2.5 kN/m2. . In this setting, it would be attractive to have blast panels which will relieve internal pressures of, say, 5 kN/m2 . In general, available blast walls cannot satisfactorily meet this canbination of criteria.

It is an bbject of the present invention to provide an improved blast wall structure in which sane at least of the disadvantages of prior such blast walls are reduced or overcame, and which is particularly suitable for use in demanding locations such as those discussed above.

The blast wall according to the present invention comprises a support frame to which at least one pressurerelief panel is releasably secured, the means for releasably securing the panel comprising at least one aperture in said frame, a bolt assembly extending through the panel and through the aperture and having, at the end thereof extending through said aperture, a maxinnzn lateral dimension less than the minimum dimension of said aperture, and, secured about the bolt on that side of the frame which is remote fram the relief panel, a retaining washer having one or more projections extending generally radially with respect to said bolt and said aperture, said one or more projections being distortable or breakable so as to permit said bolt assembly to pass wholly through the aperture, thereby releasing said panel fram said frame.

Thus the pressure-relief panel is held to the support frame by one or more bolt assemblies, for example each comprising at least a bolt and a retaining nut, and the bolt assemblies are able to pass out through the apertures when overpressure on the panel causes the projection or projections on the washer to bend or break. Typically, a panel may be held in place by, say, four such assemblies; as an alternative, the panel may be hinged to the support frame and then held to the support frame in a position or positions away fran the hinge (s) by one or more bolt assemblies. In this latter way, the danger which can arise fran a panel being forcibly blown fram the frame is avoided. Preferably, the bolt assemblies are distributed symmetrically along the peripheral edge of the panel.

A typical bolt assembly camprises at least a bolt and a nut to retain it in place. At one end, for example that at which the nut is fitted, the assembly extends through the aperture in the support frame and is of such a maximum dimension that it could pass wholly through the aperture.

However it is prevented fran doing so by the radial projection or projections on the retaining washer. The projections are of such material and dimensions, including thickness, that they will yield in response to pressures exceeding the selected relief pressure and thereby allow the bolt assembly to pass through the aperture. The yielding of the projections may be by breaking but it is a much preferred feature of the invention that the projections should yield by bending, since this allows the yield pressure to be designed to approach more closely the normal operating pressure.

Preferably the retaining washer has at least two said radial projections, for example three or four projections, which very preferably are disposed symmetrically around the circumference of the retaining washer. The projections may extend radially outwardly, to engage the inner face of the support frame around the aperture, or may extend radially inwardly to engage the face of the retaining nut or bolt, In the former case, when the panel is released in response to a predetermined overpressure, the retaining washer passes through the aperture with the bolt assembly. In the latter case, the panel ns released as a result of the retaining nut or bolt passing through the retaining washer and then in turn through the aperture.

Instead of the retaining washer, within the region of its periphery, itself directly engaging the inner face of the supportframe oundthe aperture in that frame, a holder for the retaining washer may be interposed between the washer and the frame. The holder may then provide an internal shoulder to engage and retain the retaining washer. In this way, the dimensions of the aperture cooperating with the washer can be controlled more accurately, since it is easier to manufacture off-site to accurate dimensions a large number of such holders than it is to provide accurate apertures in the support frame.

Because the aperture will normally be much wider in a radial direction than the shaft of the bolt, locating of the bolt assembly in position in the aperture may be greatly assisted by the preferred provision of a second, conventional annular washer placed within the aperture.

The preferred material for the retaining washer is aluminium, which possesses the optimum characteristics of strength and ability to bend as required. The bolt assembly is preferably of stainless steel.

When the blast wall. according to the invention is to be installed in a corrosive environment, for example in an off-shore location, the bolt assembly and retaining washer are preferably- protected fran harmful exposure by being enclosed in protective covers, for example of marine-cuality aluminium The above-describe holder for the retaining washer may assist in performing this function.

The invention will now be further described and illustrated, by way of example only, with reference to the accompanying drawings, wherein: Fig. 1 illustrates in plan view a first embodiment of retaining washer; Fig. 2 is a sectional view showing a part of a blast wall structure incorporating the retaining washer of Fig. 1; Fig. 3 is a plan view of a second embodiment of retaining washer; Fig. 4 is a view, corresponding to Fig. 2, of a blast wall structure incorporating the retaining washer of Fig. 3; and Figs. 5 and 6 are further sectional views showing parts of alternative blast wall structures incorporating the retaining washers of Figs. 1 and 3 respectively.

Referring firstly to Figs. 1 and 2, a relief panel 10 is secured to a support frame 11 by four bolt assemblies disposed symmetrically in the regions of the four corners of the panel. The structure in the area of one of the bolt assemblies is shown in Fig. 2.

The frame 11 has a circular aperture 12 cut through its thickness and that aperture is occupied by an annular washer 13. The bolt assembly comprises a bolt 14, which extends in turn through a washer 15, an aperture 16 in the panel 10, the washer 13 and a retaining washer 17, and a nut 18 by which the bolt is secured.

The retaining washer 17 is illustrated in Fig. 1 and has four tabs 19 extending radially outwardly fram symmetrically-placed positions around its periphery.

The diameter of the annular part of the retaining washer 17 is less than that of the aperture 12 but the overall diameter of the washer 17, measured between the outer ends df the tabs 19, is greater than that of aperture 12. Thus the relief panel 10 is retained in place by the tabs 19 abutting the inner face of the support frame 11, in positions outside the periphery of the aperture 12.

When an overpressure above a predetermined value arises within the structure protected by the illustrated blast wall, the tabs 19 readily and quickly bend and thereby allow the retaining washer 17 and the nut 18 to pass through the aperture 12 and thus release the relief panel 10.

Referring now to Figs. 3 and 4, wherein components which are the same as those of Figs. 1 and 2 are identified by the same reference numerals, a bolt 20 and nut 18 cooperate with a retaining washer 21 to hold the relief panel in position.

The retaining washer is illustrated in Fig. 3 and has four tabs 22 extending in a radially inward direction. The overall diameter of the retaining washer 21 is greater than that of the aperture 12, while the least radial dimension of this washer is less than the diameter of the head of the bolt 20.

In the assembled condition, as illustrated in Fig. 4, the peripheral area of the washer 21 abuts the inside face of the support frame 11, while the inside face of the washer (relative to the structure protected by the blast wall) abuts the head of the bolt 20. Overpressure within the structure above a predetermined value causes the tabs to bend and thereby permits the bolt 20 to pass through the washer 21 and thus release the relief panel 10.

The structure shown in Fig. 5 is an alternative to that of Fig. 2 wherein the retaining washer 17 is housed within a holder 30. The holder 30 is cylindrical and has a shoulder 31 on its inner surface against which the washer 17 engages. In turn, the holder 30 abuts the face of a support frame member 32 around an aperture 33 in that member. A relief panel 34 is held in position against the support frame by a bolt 35, the shaft of which extends through the central hole in the washer 17, the aperture 33 and an aperture 36 in the relief panel. The bolt 35 is retained in position by a washer 37 and nut 38. A weatherseal cover 39 of a plastics material is fitted over the holder 30 to protect the bolt assembly, and in particular the retaining washer 17, from the corrosive effects of the ambient weather.

The assembly of Fig. 5 functions, fram the point of view of blast pressure relief, in the same way as that of Fig. 2.

That is, any significant overpressure within the structure being protected causes the tabs 19 on the retaining washer 17 to bend and thereby allow the washer 17 and bolt 35 to pass through the aperture 33 and so release the panel 34. Compared with the assembly of Fig. 2, that of Fig. 5 has the important advantage that the aperture to be engaged by the washer 17 is in the holder 30 rather than in the support frame member. This allows better control of the dimensional accuracy of that aperture, since the washer and holder can readily be manufactured off site in quantity.

Fig. 6 shows a partial view of a blast wall structure which is an alternative to that of Fig. 4, for use with the retaining washer 21 of Fig. 3. In this alternative structure, the washer 21 is located in a cylindrical holder 40 and abuts a shoulder 41 on the inside face of the holder. A collar bolt 42 extends through the washer 21, through an aperture 43 in a support frame member 44 and through an aperture 45 in a pressure relief panel 46 and is retained in position by a washer 47 and nut 48.

The assembly is protected against the weather by a plastics cover 49.

In the event of an overpressure beyond a predetermined value, distortion of the tabs 22 allows the bolt 42 to pass through the washer 21 and aperture 43 and release the relief panel 46.

The blast wall structure according to the present invention, in particular in its illustrated forms, is a very effective structure for relieving overpressures, in particular pressures relatively close to normal maximum ambient pressures. It further has the p ticul advantage canpared with other available structures that it may be designed to respond to bending forces, as opposed to shearing forces, in the metal component, in the present invention the retaining washer, which allows the pressure relief. This allows the structure to be designed to respond with greater accuracy to a given value of overpressure.

Claims (17)

1. A blast wall catpri;"sing a support frame to which at least one pressure-relef panel is releasably secured, the means for releasably securing the panel comprising at least one aperture in said frame, a bolt assembly extending through the panel and through the aperture and haying, at the end thereof extending through said aperture, a maximum lateral dimension less than the minimum dimension of said aperture, and, secured about the bolt on that side of the frame which is remote fran the relief panel, a retaining washer having one or more projections extending generally radially with respect to said bolt and said aperture, said one or more projections being distortable or breakable so as to permit said bolt assembly to pass wholly through the aperture, thereby releasing said panel fran said frame.

2. A blast wall as claimed in claim 1, wherein said panel is secured to said support frame by four said bolt assemblies and retaining washers.

3. A blast wall as claimed in claim 1, wherein said panel is hinged to said support frame and is secured to said frame in a position away fran the hinge by one or more said bolt assemblies and retaining washers.

4. A blast wall as claimed in any of the preceding claims, wherein the or each bolt assembly camprises at least a bolt and a nutt

5. A blast wall as claimed in any of the preceding claims, wherein said projections are designed to bend to permit the bolt assembly to pass through said aperture.

6. A blast wall as claimed in any of the preceding claims, wherein said retaining washer has three or four said projections.

7. A blast wall as claimed in claim 6, wherein said projections are disposed symmetrically around the circumference of the retaining washer.

8. A blast wall as claimed in any of the preceding claims, wherein said projections extend radially outwardly from said retaining washer.

9. A blast wall as claimed in any of claims I to 7, wherein said projections extend radially inwardly towards said bolt.

10. A blast wall as claimed in any of the preceding claims, wherein a holder for the retaining washer is interposed between said washer and said support frame.

11. A blast wall as claimed in claim 10, wherein said holder has an internal shoulder to engage said washer.

12. A blast wall as claimed in claim 10 or claim 11, wherein said holder ;i:s closed by a cover.

13. A blast wall as claimed in any of the preceding claims, wherein a second washer is located within said aperture.

14. 9 blast wall as claimed in any of the preceding claims, wherein said retaining washer is of aluminium.

15. A blast wwall as claimed in any of the preceding claims, wherein said bolt assembly is of stainless steel.

16. A blast wall substantially as hereinbafore described with reference to, and as illustrated in, Figs. 1 and 2 or Figs. 3 and 4 of the accompanying drawings.

17. A blast wall substantially as hereinbefore described with reference to, and as illustrated in, Fig. 5 or Fig. 6 of the accompanying drawings.