NO155779B - OIL OIL CONDITION WITH IMPROVED COLD PROPERTIES. - Google Patents

Abstract

Gas oils with improved cooling ratio are obtained if, in addition to the usual means for improving the flow ratio and / or the solidification point, an oil-soluble acid amide of a polyamine with a fatty acid having at least 8 C atoms, or a fatty acid analogue compound containing free carboxyl groups.

Description

Flange connection for connecting wall parts of a pressure vessel.

The present invention relates to flange connections for joining wall parts of one pressure vessel for internal excess pressure, in particular pressure vessels for nuclear reactors, of the kind which consist of two ring-shaped, by means of bolts held together, in one piece with each wall part made of flexurally rigid flanges, which are metallically abutting each other with si-

ne inner edges and before the prestressing of the bolts exhibit an axial distance from each other at their outer edges. When the pressure vessel is exposed to the high internal overpressure, the vessel walls expand more than the significantly thicker ring flanges, so that during operation there are axial bending stresses in the transition section between the flange and the wall part, and these

more in addition to the tensile stresses caused by the overpressure in the same transition section, so that stress concentrations occur, which must be taken into account when dimensioning and designing the flange connection.

The present invention is based on an appropriate design of the flange connection which, to the greatest extent possible, eliminates the aforementioned stress concentrations. A flange connection designed in accordance with the invention is mainly characterized in that the axial distance between the outer edges of the flanges is such that the bending stress that occurs in the transitional cross-section between each flange and the adjacent wall part when the bolts are tightened until the outer edges of the flanges are in contact with each other, as completely as possible compensates for the oppositely directed bending stress in the same cross-section, which is induced by the normal internal overpressure. As the bending stress in the transition section between the flange and the pressure vessel wall has been eliminated, the flange connection, especially where large pressure vessels for very high internal overpressures are concerned, can be made significantly easier and with less material consumption than has been possible up until now.

The invention shall be described in more detail below with reference to the attached drawings. Fig. 1, 2 and 3 illustrate different types of previously known flange connections. Fig. 4 shows a first embodiment of a flange connection made according to the invention. Fig. 5 and 6 each illustrate a further embodiment of the invention.

The one in fig. 1 previously known flange connection comprises an upper flange 1 and a lower flange 2, which are directed approximately at right angles from each part of a limiting wall 3, hereinafter for brevity called "mantel". The connection is thought to be part of a pressure vessel or a pressure line, so that the higher pressure" prevails to the left of the wall 3. Up to this, each of the flanges has a block-like projection 4, and between these there is a gasket 5. Tightening of the flange connection takes place using a number of bolts 6.

When tightening the bolts 6 while compressing the gasket 5, forces are clearly generated which seek to bring the outer edges of the two flanges closer to each other. Corresponding bending moment occurs at the casing walls 3, i.e. these tend to bend outwards from the connection's vertical axis of symmetry. In order to counteract this tendency, it is common to provide the transition between flange and casing with a conical collar 7. This, however, results in a relatively large increase in the manufacturing costs of the connection. In terms of calculation, it is sufficient to treat the internal stresses induced by the bending moments in the section planes A and B, under which, if collar 7 had not been there, the stresses in section A would be much greater than in section B.

in

The one in fig. 2 illustrated construction is in principle consistent with the flange connection according to fig. 1. The difference consists only in that the flanges are metallically abutting each other at the inner edge and that the sealing member 5 is not made up of a flat gasket, which is pressed together under the influence of the pretension in the bolts, but of a so-called O-ring, which for its function only requires eh negligible compression and contact between the flange halves.

Fig.3 shows a known flange connection for a pressure vessel for a nuclear reactor, in principle made in the same way as the flange connection according to fig. 2. Pressure vessels for nuclear reactors have very large dimensions, e.g. a diameter" of 5 metres, and is exposed during operation to high internal overpressures, e.g. to an internal overpressure of 80 atmospheres. To keep the axial bending stresses in the casing wall when tightening the bolts and the resulting rotation of the flanges within tolerable limits , the flanges 1 and 2 are made with considerable thickness and are designed to go into the casing wall with each of their conical collars.

In fig. 4 shows on the same scale a flange connection made according to the invention for the same pressure vessel. The height of the flanges 1 and 2 is, as will be seen, reduced quite significantly, but it is however only insignificantly smaller than the radial width, so that the rectangular cross-section of the flange can be considered as bending stiff. Between the opposite outer edges of flanges 1 and 2, a spacer 9 of metal is inserted. The open gap between the spacer and the opposite flange at the outer edge is denoted by,A.h. When the bolts 6 are tightened, the two flanges 1 and 2 rotate until the gap h between the flanges at the outer edge is closed. The rotation of the flanges induces a change in shape in adjacent parts of the casing wall, which causes bending prestresses in the transition section A between the respective flanges and the corresponding casing wall. A stress curve is drawn on the figure, which schematically shows the magnitude and designations for the axial bending stresses that occur in section A, when the flanges 1 and 2 are turned against each other also at the outer edges when the bolts are tightened. On the outside of the neutral line, determined by the intersections between the stress curve and section A, there is a tensile stress + ^~bs1# while on the inside there is an equally large compressive stress -(Tbs^ By continuing to tighten the bolts to produce a prestress in these, which is sufficiently large to be able to maintain the mechanical contact between the flanges at the inner edge, when the pressure vessel is later exposed to the normal internal overpressure, does not result in any significant bending of the flanges between the contact surfaces, and thus also no significant further deformation of the jacket wall. The axial bending prestressings in the upper

• I '

the cross section A thus becomes almost completely independent of the final pretension of the bolts, and depends only on the gap .A. h between the outer edges of the flanges.

When, after final tightening of the bolts, the pressure vessel is subjected to the operational internal excess pressure, the container wall stretches more than the significantly thicker flange, and because of this, it occurs in resp. transition section A axial bending stresses, consisting of tensile stresses on the inside of the pressure vessel and compressive stresses on its outside. The axial bending stresses in the transition section A caused by the internal excess pressure are thus directed opposite to the bending prestresses that occur when the bolts are tightened. According to the invention, the distance £± h between the outer edges of the flanges is chosen so large that the bending prestresses that occur when the bolts are tightened are approximately as large as the oppositely directed bending stresses, which are caused by the internal overpressure, whereby these latter are compensated. In this way, an undesirable stress concentration in the transition zones A is avoided.

As is immediately apparent from a comparison between fig. 4 and fig. 3, the invention results in a significant reduction of material consumption to approx. half, and a significant simplification of the construction, as the conical transitions are eliminated. In addition, substantially reduced stresses are achieved in the transitions between flange and vessel.

In the embodiment according to fig. 5 there is no separate intermediate layer ring, and instead the flanges 1 and 2 at the outer edges of

the sides facing each other designed with blocks 8 of such a height that the distance between them before the bolts are tightened becomes equal to

the desired distance/\h.

In the embodiment according to fig. 6, the facing surfaces of the flange rings 1 and 2 are made slightly divergent in the direction radially outwards, so that the flange rings lie directly against each other at the inner edges, but are at the distance Z±h from each other at the outer edges. When the bolts are tightened, the rings are turned into contact with each other along the entire opposing surfaces, whereby the desired compensating bending prestresses occur in the transition sections between the flange and pressure vessel wall.

In addition to the axial bending stresses ( F^ s and <T^p, an axial tensile stress arises as a result of the pressure difference in the transition sections

tf* , which is evenly distributed over the thickness of the mantle wall. If all these stresses are combined, the following design rules are obtained, under which only axial stresses are noted.

Véd screw tightening shall apply

/ ( Tha/^ s. permissible calculated value for the material at the current temperature.

During operation shall apply:

permissible calculated value at operating temperature.

In the practical application of the invention can, afterwards

(7~xtpt is determined, the value ofZ^h is calculated in diagrams.

Claims (1)

Flange connection for joining wall parts of a pressure vessel for internal excess pressure, in particular pressure vessels for nuclear reactors, consisting of two annular, bolted together, made in one piece with each wall part, rigid flanges, which metallically abut each other with their inner edges and before the prestressing of the bolts exhibits an axial distance from each other at their outer edges, characterized in that the axial distance (Z.\h) between the outer edges is such that the bending stress that occurs in the transition cross-section (A) between each flange (1,2) and the adjacent wall part (3) by attracting ning of the bolts (10) until the outer edges of the flanges rest against each other, compensating as completely as possible^"the oppositely directed bending stress in the same cross-section, which is caused by the normal internal overpressure.