EP0842869A1 - Tank with separable roof by a weakened connection - Google Patents

Abstract

The tank consists of a base, a side (3) e.g. cylindrical in shape with a right-angled reinforcing rim (9), a radial ring (10) and a cover (1) which is connected to the rim. The rim and cover are connected by two thin conical shells (12, 14), each attached by its outer edge to the radial ring and by its inner edge to the cover or tank side, using low-strength welds (S1, S2) about 3 mm thick. The cover can also rest on a frame structure (7) supported by the horizontal rib of the rim.

Description

Field of the invention

The invention relates to tanks and large fixed vertical containers containing products which, when stored, build up pressure or re-explode and create accidental overpressure. We think in particular tanks containing hydrocarbons or products chemical, and silos.

Definitions

Coat of a tank : vertical peripheral circular shell constituting the vertical walls of a tank.

Roof : sheet metal closing a tank in its upper part connected to the shore and resting on a support frame.

Shore : at the upper end of the dress, radial reinforcement of the edge of the dress to mechanically reinforce it and participate in fixing the roof of the tank.

Frangibility of a tank : state of least resistance at the peripheral junction between the coat and the roof of a tank.

Tank : any construction of medium and large dimensions, closed, arranged to hold certain things in reserve, such as liquids, gases, cereals, sludge, etc.

Prior art and problem posed

Internal explosions of tanks of hydrocarbons or chemicals sometimes caused a rupture of the funds of the bins of such tanks, to the right of the assembly between the bottom and the dress. This type of event generally results in projection in the air of the assembly constituted by the roof and the dress of said tank and sets off a wave massive amount of product in the tank and can be inflamed, which often breaks out of the bowls tank retention.

To avoid such accidents, i.e. dress tears or cutouts from the assembly tank dress / bottom, building rules in force in France (CODRES) define provisions to promote the opening of the roof to the level of its assembly on the dress. It is at this level that we use the term "frangibility" for the condition less resistance at the junction device between the coat and the tank roof.

It is currently accepted that only fixed roof type tanks built in the compliance with the rules established by the regulations CODRES and whose diameter is greater than 20 m can be called frangible.

The object of the invention is therefore to propose a type of tank whose junction between the roof and the dress has a frangibility character that meets to the regulations in force, whatever its diameter.

On the other hand, and with reference to the figure 1, we know from the US patent document US-A-4,989,752, a frangible joint for a roof of storage tank. Roof 1 is placed on a annular plate 5, itself resting horizontally on the horizontal branch of the angle 2, fixed to the upper end of the dress 3.

The roof 1 is fixed by means of a first weld 4 between the latter and the end outside of the annular plate 5. The latter is fixed by its inner edge to the angle 2 by a second weld 6. This entire assembly is shown on the right part of figure 1.

The process of separating the roof 1 by compared to dress 3 is shown on the left in Figure 1. We have indeed shown the plate annular 5 with its outer edge peeled up with respect to the horizontal part of the angle 2. Similarly, the roof 1 has been shown raised by a sudden rise in pressure inside the tank. Given the inclined position of the annular plate 5 relative to angle 2, finds that the first 4 and second 6 welds undergo deformations due to movements relative parts which are joined by these welds.

A position of the roof 1, in phantom, therefore symbolizes a total detachment of this roof and its detachment with respect to dress 3 of the tank.

This system provides a threshold of frangibility often still too high. In addition, the this roof remains directly linked to the shore, by through an annular plate, an angle iron and two welds, causing harmful compressions in the shore, which considerably lowers the performance and sensitivity of this system.

Furthermore, this arrangement promotes corrosion between ring 5 and edge angle 2 as well as at the second weld 6.

The object of the invention is therefore to remedy to these disadvantages by proposing a different concept separation of the roof from the dress.

Summary of the invention

• un fond;
• une robe renforcée dans sa partie supérieure par une rive en cornière ;
• un anneau radial fixé horizontalement sur la cornière ; et
• un toit fixé à la robe par l'intermédiaire de la cornière et de l'anneau radial et séparable par rapport à cet ensemble.

The main object of the invention is therefore a roof tank separable by weakened connection and comprising:

• a fund;
• a dress reinforced in its upper part by an angle edge;
• a radial ring fixed horizontally on the angle iron; and
• a roof fixed to the dress by means of the angle iron and the radial ring and separable with respect to this assembly.

According to the invention, two shells are used frustoconical thin, connected by welding, on the one hand, each to the ring by their outer edge by first low resistance welds mechanical and, on the other hand, respectively to the dress and to the roof by their respective internal edge.

In the case where the shore is an angle turned towards the inside of the tank by its rib horizontal, the roof has a framework which rests on the horizontal rib of the shore, the hull lower frustoconical being welded on this bank.

In a first embodiment, the ring lateral is horizontal, the two frustoconical shells being each welded to an edge.

In a second embodiment, the ring radial is composed of two parts welded together, to each of them being welded a shell tapered.

In this second embodiment, a first variant is that these two parts are pressed against each other, being horizontal.

In a second variant, these two parts are welded to each other by their edge internal, and are detached from each other by their outer edge.

In a third realization of tank, the two frustoconical shells are placed in the extension of the roof, overlapping, connected between them by the radial ring at this overlap. In this case, it is advantageous that the lower frustoconical shell is welded to the shore.

Preferably, the welds of junction of the radial ring and the frustoconical shells are made in the form of a throat bead calibrated to approximately 3 mm.

List of Figures

• figure 1, en coupe, un réservoir de l'art antérieur ;
• figure 2, en coupe, la jonction du toit à la robe d'un réservoir selon l'invention, dans sa première réalisation ;
• figure 3, en coupe, la jonction du toit à la robe d'un réservoir dans la première version d'une deuxième réalisation ;
• figure 4, en coupe, la jonction du toit à la robe d'un réservoir dans la deuxième version de la deuxième réalisation selon l'invention ;
• figure 5, en coupe, une adaptation de l'invention sur un réservoir existant ; et
• figure 6, en coupe, la jonction du toit à la robe d'un réservoir selon une troisième réalisation.

The invention and its various technical characteristics will be better understood on reading the following description, accompanied by several figures representing respectively:

• Figure 1, in section, a tank of the prior art;
• Figure 2, in section, the junction of the roof to the dress of a tank according to the invention, in its first embodiment;
• Figure 3, in section, the junction of the roof to the dress of a tank in the first version of a second embodiment;
• Figure 4, in section, the junction of the roof to the dress of a tank in the second version of the second embodiment according to the invention;
• Figure 5, in section, an adaptation of the invention on an existing tank; and
• Figure 6, in section, the junction of the roof to the dress of a tank according to a third embodiment.

Detailed description of several embodiments of the invention

In Figure 2, we find dress 3 of tank, as well as its roof 1. This rests on the dress 3 from which it is independent, through the frame 7 and in particular by means of feet peripherals supported on the horizontal branch from the edge into an angle 9. The latter is placed in this realization inside the dress 3, always by welding. Because of this, the weight of the roof and any precipitation it receives is therefore directly taken up by the angle 9 and the dress 3 of the tank.

In this first realization, the ring radial 10 is horizontal and is separated from the dress 3 and from shore 9 by a first frustoconical hull 12. The latter is inclined, its lower end 12I being welded to bank 9, its end upper 12S being fixed by a first weld S1 on the internal edge 10I of the radial ring 10. By its outer edge 10E this radial ring 10 is connected by a second weld S2 at the outer edge 14E of the second frustoconical shell 14. We notice that the inclination from the vertical of this second frustoconical shell 14 is very accentuated, that is to say that this second frustoconical shell 14 is almost flat. The internal edge 14I of this second frustoconical shell is fixed to the roof 1 of the tank.

It should be noted that the latter preferably has a slope of about 1 / 5th. In addition, the shell 14 can extend a spherical roof to make it frangible (in this case the slope will be greater).

It can be seen that the roof 1 rests on the structured structure 7 fixed on the bank 9 welded to the upper end of the dress 3 of the tank.

In the event of a sudden increase in pressure inside a tank, the sheet metal roof 1 is lifted by pressure. She shoots the second tapered shell 14 which folds and curves as shown in phantom in Figure 2.

• une force composante verticale d'arrachement vers le haut ;
• une force composante horizontale qui comprime uniformément l'anneau.

The second shell 14 pulls uniformly on the second peripheral weld S2 from the outer edge of the radial ring 10, and exerts a tensile force in a direction tangent to this shell (cf. FIG. 2) which causes on the weld S2:

• a vertical component pulling force up;
• a horizontal component force which uniformly compresses the ring.

Ring 10, subject to these forces components on its outer edge, and, balanced by the reactions that act on its inner edge (S1 weld and shell 12) contracts under the action of compression and rotates around the center of its section under the action of the axisymmetric torsional moment generated by the vertical component forces tearing exerted on its inner edges and outside (torque).

• des contraintes de compression engendrées par la compression générale déjà citée ;
• des contraintes de compression engendrées par la rotation de l'anneau.

Thus, the outer edge of the ring 10 and therefore the weld S2 contain:

• compression constraints generated by the general compression already mentioned;
• compression stresses caused by the rotation of the ring.

• un effort d'arrachement direct augmenté d'un effet d'arrachement tournant qui sollicite vivement la racine intérieure de la soudure (effet cliquet), et
• une compression circonférentielle décrite ci-avant.

These two effects are added and the S2 weld is simultaneously subjected to:

• a direct tear-off force increased by a rotating tear-off effect which urges the inner root of the weld (ratchet effect), and
• circumferential compression described above.

The state of bi-axial stress in tension / compression in the root of the weld s2 promotes general plastic deformation leading to breaking.

Compared to tensile tests conventional standard, we determine the deformation widespread plastic in welding and so its rupture pressure.

• des contraintes de compression engendrées par la compression générale ;
• des contraintes de traction engendrées par la rotation de la section de l'anneau.

On the inner edge of the ring 10, the weld S1 contains:

• compression stresses generated by general compression;
• tensile stresses generated by the rotation of the section of the ring.

Unlike what's happening on the edge outside of the ring, the two effects are entrenched and the weld S1 is only subjected to a force severely reduced tear-off (angle of rotation in much lower weld).

So the break will happen in the weld of lower resistance S.

• une force verticale qui équilibre la force verticale d'arrachement agissant sur l'autre bore 10E,
• une force composante horizontale qui comprise aussi l'anneau 10. Cette dernière permet de doser l'effort de compression dans l'anneau en faisant varier l'angle de la génératrice de la première coque 12.

On the inner edge 10I of the ring 10, it breaks down into:

• a vertical force which balances the vertical tearing force acting on the other boron 10E,
• a horizontal component force which also includes the ring 10. The latter makes it possible to dose the compression force in the ring by varying the angle of the generator of the first shell 12.

• une force composante verticale qui tend à soulever la robe 3,
• une force composante horizontale qui, contrairement aux systèmes existants, tire la rive 9 vers l'extérieur et la met en tension, ce qui évite sa déformation.

On the other side, at the right of the connection on the shore, the force contained in the first frustoconical shell 12 is broken down into:

• a vertical component force which tends to lift the dress 3,
• a horizontal component force which, unlike existing systems, pulls the edge 9 outwards and puts it in tension, which avoids its deformation.

The welds S1 and S2 are preferably made in the form of calibrated throat cords. Preferably, calibrated grooves of 3 mm are produced. A grinding adjustment can also supplement such S1 and S2 welds. The metal deposited must be ductile and of the same nature as the steel constituting the tank. One thinks in particular of steel E24-2ou3 of the standard NF A 35-501.

• la première coque 12 ait la souplesse nécessaire permettant d'accentuer sa déformation bombée et par conséquent l'angle formé avec l'anneau radial 10,
• la deuxième coque 14 ait la souplesse nécessaire pour ne pas répercuter directement les efforts horizontaux de l'anneau 10 sur la rive 3 mais au contraire engager une tension vers l'extérieur de celle-ci.

The frustoconical shells 12 and 14 must be long enough so that:

• the first shell 12 has the necessary flexibility making it possible to accentuate its domed deformation and consequently the angle formed with the radial ring 10,
• the second shell 14 has the flexibility necessary not to pass directly on the horizontal forces of the ring 10 on the bank 3 but on the contrary to engage a tension towards the outside thereof.

We also note that the radial ring 10 may not be horizontal, but slightly inclined downwards by its outer side 10E. This amplifies the deformations in the welds, during an increase in pressure inside the tank.

Referring to Figure 3, a second realization of the invention plans to realize the ring radial 20 in two parts 21 and 22. In a first version, these two parts 21 and 22 are tapered, that is to say inclined. They are brought together by a S3 weld by their internal edges 21I and 22I.

The frustoconical shells 23 and 24 are each welded by their external end 23E and 24E to one of the two parts 21 and 22 of the radial ring 20 and this by other welds S4 and S5. We note that the weld S3 and welds S4 and S5 are of the same kind than those implemented in the first production. The lower frustoconical shell 23 and 24 is also welded by its internal end 24I to the dress 3 of the tank.

The upper frustoconical shell 24 is connected by its internal end 24I to the roof 1, by via a welded tapered ring 25 himself at the roof 1.

We understand that in this case also, a overpressure inside the tank leads to increasing the angle separating the two parts 21 and 22 of the radial ring 20, at the stretching of the weld S3 and the separation of these two parts 21 and 22 and release of the roof 1.

In Figure 4, a second version of this realization shows two parts 26 and 27 of the radial ring pressed against each other and fixed by an external weld S6. In this case, the increase pressure inside the tank leads to a inward opening of these two parts 26 and 27 of the radial seal.

The invention has just been described as being applied to new tanks with a roof resting on a frame fixed to the shore.

Referring to Figure 5, we propose to illustrate the adaptation of the invention to existing tanks. Indeed, it can be adapted to dress 30 of a tank whose upper end is terminated by bank 33 placed outside this one. The roof 32 is fixed directly to the second upper shell 14. The latter is connected to the radial ring 10 and at the first lower shell 12. The latter is itself directly linked to dress 30 of the existing tank.

So we see that the weld bead possibly connecting the shore to the upper hull 14 is deleted.

We can provide drainage holes for condensates 34 in the coat 30 of the existing tank.

In the variant proposed in FIG. 6, we find two frustoconical shells 42 and 44 of thin connected to a radial ring 40 by low resistance welds. These two hulls frustoconical 42 and 44 are arranged in the extension of the roof 1 and overlap in the manner of tiles. The slope of the frustoconical shells 42 and 44 is given by the slope of the roof 1 and the radial ring 40 makes the connection between them. The tapered shell lower 42 is welded to the edge 49.

The position of these elements suggested in broken lines represents the way in which a lifting of the roof 1 can take place. It is always the welds S ₇ AND S ₈ between the two frustoconical shells 42 and 44 and the radial ring 40 which drop.

In the first embodiment, the ring 10 works in compression and torsion. In this proposed variant, the ring 40 mounted on the roof 1 does not works only in torsion, which is more favorable and gives a lower burst pressure.

This variant allows the modification of existing tanks without modifications to the law of the bank 49, in particular concerning the dress / roof junction.

• escaliers ou échelles d'accès à la toiture ;
• garde corps périphérique de toiture ;
• piquages en toiture (niveaux, évents, etc.) ;
• piquages de haut de robe (tuyauteries de fluides divers et d'incendie, etc.).

This is particularly interesting in the context of "frangibilisation" of existing tanks, because this procedure does not result in modifications to nearby ancillary equipment, in particular:

• roof access stairs or ladders;
• peripheral roof guard;
• roof connections (levels, vents, etc.);
• top of the dress fittings (piping of various fluids and fire, etc.).

Advantages of the invention

The concept according to the invention allows, during lifting of the roof 1, not to affect the shore 9 and dress 3 harmful influences, but at contrary to the forces which tend to preserve their integrity by peripheral tensioning.

Tapered shells 12 and 14 relatively long and the radial ring 10 contribute to this result. Indeed, during an accident, that is to say an ejection from the roof 1, the bank 9 is not deteriorated since it is not attached to the roof 1.

Least weld failure resistance of the invention comes at a very low pressure.

• supprime le risque de rupture de la liaison entre le fond et la robe 3 du réservoir par soulèvement dû à la surpression ;
• supprime le risque de déchirure sur la robe 9 dû à des déformations sur celle-ci, et
• réduit la distance d'éjection du toit 1 et les dangers inhérents à un tel événement.

Due to the preservation of the integrity of the bank 9 and of the dress 3, as well as the very low rupture pressure, the invention:

• eliminates the risk of rupture of the connection between the bottom and the dress 3 of the tank by lifting due to overpressure;
• eliminates the risk of tearing on the dress 9 due to deformations on the latter, and
• reduces the ejection distance from the roof 1 and the dangers inherent in such an event.

Given that this phenomenon of frangibility is better controlled, it is no longer necessary to anchor each tank by foundations in reinforced concrete or basic slabs.

In the tank according to the invention, it is possible to clarify and quantify the concept of frangibility since it is separate from constraints of the roof 1 on the dress 3 of the tank.

To avoid corrosion phenomena in the angle formed by the upper frustoconical shell 14 and the radial ring 10 (lesser weld resistance), just give the latter a slight slope (∼5%) allowing evacuation of condensates towards the inside of the tank.

The invention can be easily implemented place on an existing tank.

Claims (9)

Roof tank separable by a weakened connection, comprising: a fund ; a dress (3) reinforced in its upper part by an edge (9) in angle; a radial ring (10, 20, 40); a separable roof (1) fixed relative to the bank (9), characterized in that it comprises two frustoconical shells (12, 14, 23, 24, 42, 44) of small thickness, each connected by welding to the radial ring (10, 20, 40) by their external edge (12E, 14E, 23E, 24E) by welds (S1, S2, S4, S5, S7, S8) with low mechanical resistance and respectively to the whole of the dress (3) and the edge (9), and to the roof (1) by their internal edge (12I, 14I, 23I, 24I). Tank according to claim 1, the roof (1) resting on a structured structure (7) which rests on the horizontal rib of the bank (9), characterized in that the lower frustoconical shell (12, 42) is welded to the edge (9). Tank according to claim 2, characterized in that the side ring (10) is horizontal. Tank according to claim 1, characterized in that the radial ring (20) is composed of two parts (21, 22, 26, 27) welded together and to each of them being welded a shell frustoconical (23, 24). Tank according to claim 4, characterized in that the two parts (26, 27) of the radial ring are placed one against the other and are horizontal, fixed to each other by a external weld (S6). Tank according to claim 4, characterized in that the two parts (21, 22) of the radial ring (20) are detached and welded one relative to each other by their internal edge (21I, 22I). Tank according to claim 2, characterized in that the two frustoconical shells (42, 44) are placed in the extension of the roof (1), overlapping, interconnected by the radial ring (40) at the level of this overlap. Tank according to claim 7, characterized in that the lower frustoconical shell (42) is welded to the edge (49). Tank according to claim 1, characterized in that the welds (S1, S2, S4, S5, S7, S8) connecting the frustoconical shells (12, 14, 23, 24, 42, 44) to the radial ring (10, 20, 40) are cords throat about 3 mm.

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