GB2177180A - Pressure vessels - Google Patents

Abstract

A vessel intended to be pressurised comprises a hollow substantially cylindrical member (1) and a closure member (2) which extends across the cylindrical member when in position to close an end thereof. Screw-down fastenings (9) for holding the closure member on the cylindrical member in its position to close the end of the cylindrical member are disposed in a first ring (9A) around the two members and in a second ring (9B) outboard of the first ring. A seal (3) for maintaining fluid-tight closure between the members (1,2) during radial movement of the cylindrical member comprises a carrier of ring configuration carrying seal means disposed to be in contact with inner surfaces of these members (1,2) when the closure member is in position to close the end of the cylindrical member, the carrier being able to expand or contract to permit the seal means to remain so in contact during radial movement of the cylindrical member. The seal (3) is also able to slide axially of the cylindrical member and therefore the gap between the closure member and the cylindrical member may be closed as the vessel is pressurised. <IMAGE>

Description

SPECIFICATION Pressure vessels This invention relates to pressure vessels such as vessels intended to be filled with water and pressurised so that items therein can be subjected to the water pressure within the vessel for test purposes.

A pressure vessel can be a cylindrical steel pressure vessel having a closure that is secured by studs and nuts. The studs are loaded to more than their full loading while the vessel is at zero pressure in order to keep opposing flange faces of the closure and the main body of the vessel together, and to prevent a rubber seal extruding, or to compress a gasket. When the vessel is pressurised the loading on the studs remains the same but the interface pressure is less. The seal (or gasket) is still able to function. With increase in vessel size, and increase in pressure, a point is reached when it is no longer possible to fit in sufficient studs in a single row to resist the axial load.However, if two rows of studs, that is an inner row and an outer row, are used and tightened in the same way as just discussed, the distribution of load on the two rows is changed when the vessel is pressurised because of bending of the flange of the closure member. The inner row might then be over stressed and the outer row under utilised. Attempts to correct this by differences in tightening could be made but torque loading would be likely to be insufficiently accurate and precise measurement of stud extension would be required on every stud. Also if an endeavour were to be made to maintain pressure on a face seal with two rows of studs, there would be a difficulty in avoiding a gap opening up at the inside due to the different moment arm at which each row of studs would operate. The flange on the closure member would tend to bend and a gap would open.

According to the present invention there is provided a vessel intended to be pressurised and comprising a hollow substantially cylindrical member and a closure member which extends across the cylindrical member when in position to close an end thereof; screw-down fastenings for holding the closure member on the cylindrical member in its position to close said end of the cylindrical member being disposed in a first ring around the two members and in a second ring outboard of the first ring; a seal for maintaining fluid-tight closure between these members during radial movement of the cylindrical member comprising a carrier of ring configuration carrying seal means disposed to be in contact with inner surfaces of these members when the closure member is in position to close said end of the cylindrical member, the carrier being able to expand or contract to permit the seal means to remain so in contact during said radial movement of the cylindrical member, and the seal being able to slide axially of the cylindrical member whereby a gap may be permitted to open between faces of the closure member and the cylindrical member as the vessel is pressurised, the seal sliding axially as such a gap opens to maintain sealing contact with the closure member and the cylindrical member.

The seal means in this vessel is a seal means as described in United Kingdom Patent Specification No. 1479513 to which reference is directed so detailed description.will not be given again herein. By making use of such a seal that can slide axially, a flange on the closure member can be allowed to bend by a small amount and, in addition, there is no need to keep the flange faces of the closure member and the cylindrical member in contact when the vessel is pressurised. Therefore the two rows of screw-down fastenings can be lightly tightened by torque loading initially, and full load allowed to come onto them when the vessel is put under pressure. If necessary a slight difference in torque loading of the two rows of fastenings may be made to allow for bending of the flange.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing in which: Figure 1 is a side view, half in section, on line I-I of Figure 2, Figure 2 is a plan view of a pressure vessel, and Figure 3 is a sectional side view showing a seal suitable for use in the vessel of figures 1 and 2.

The pressure vessel of the Figures is a steel vessel having a cylindrical chamber 1 that is closed by a closure member 2 which extends across the cylindrical chamber 1 when in position (as shown) to close one end of the chamber. A seal 3 for maintaining fluid-tight closure between the chamber 1 and the closure member 2 during radial movement of the chamber is a seal as described in United Kingdom Patent Specification No. 1479513.An example of such a seal is shown in Figure 3 herein comprises a carrier 4 of ring configuration car rying seal elements 5A, 5E and 5C respec tively disposed to be in contact with inner surfaces of the chamber 1 and the closure member 2 and a surface on a shoulder of a seal retaining ring 6 when the closure member 2 is in position to close the chamber and pressure is applied as indicated by arrow 7 to expand the carrier 4 radially (the non-pressur ised condition is shown in Figure 3). The car rier 4 is able to expand or contract to permit the seal element 5A to remain in contact with the chamber during radial movement of the chamber. The whole seal 3 can move axially to ensure that contact between the seal ele ment 5E and the closure member 2 is maintained.The retaining ring 6 is heid in place by nuts and studs 8.

Referring to Figures 1 and 2, the closure member is retained in position on the cylindrical chamber by nuts and studs 9 disposed in a first ring 9A around the chamber 1 and closure member 2, and in a second ring 9E outboard of the first ring. The studs pass through flanges IA and 2A of the cylindrical chamber 1 and the closure member 2 respectively and the nuts are screwed down onto the closure member flange 2A. As mentioned above, the nuts are lightly tightened by torque loading initially, full load being allowed to come onto the nuts and studs when the vessel is put under pressure. As the vessel is put under pressure a gap can be allowed to develop between the chamber 1 and the closure member 2 as the seal 3 will slide axially to maintain sealing contact with the chamber 1 and the closure member 2. If necessary a slight difference in torque loading of the two rings 9A, 9E can be made to allow for flange bending.

The vessel described is particularly wellsuited for use as a test chamber that can be filled with water and pressurised so that items suspended from the closure member can be subjected to the water pressure within the chamber for test purposes. Such use may well require frequent removal and replacement of the closure member so that it is of great advantage that the fastenings (the nuts and studs 9) securing the closure member in position can simply be made fast without recourse to complicated setting equipment for ensuring that the nuts are screwed down within precisely defined limits.

Claims (2)

1. A vessel intended to be pressurised and comprising a hollow substantially cylindrical member and a closure member which extends across the cylindrical member when in position to close an end thereof; screw-down fastenings for holding the closure member on the cylindrical member in its position to close said end of the cylindrical member being disposed in a first ring around the two members and in a second ring outboard of the first ring; and a seal for maintaining fluid-tight closure between these members during radial movement of the cylindrical member comprising a carrier of ring configuration carrying seal means disposed to be in contact with inner surfaces of these members when the closure member is in position to close said end of the cylindrical member, the carrier being able to expand or contract to permit the seal means to remain so in contact during said radial movement of the cylindrical member, and the seal being able to slide axially of the cylindrical member whereby a gap may be permitted to open between faces of the closure member and the cylindrical member as the vessel is pressurised, the seal sliding axially as such a gap opens to maintain sealing contact with the closure member and the cylindrical member.

2. A vessel having a closure member held in a closing position on a cylindrical member by screw-down fastenings, substantially as hereinbefore described with reference to the accompanying drawing.