DE1285809B - Flange connection for wall parts of large diameter pressure vessels - Google Patents

Description

1 2

The invention relates to a flange connection through the screw bolts inclined in opposite directions for wall parts of pressure vessels large parting plane of the flanges in the intersection of these Diameter, in particular of Kernreaktorbehäl- parting plane with the neutral plane of the tern, consisting of two ring-shaped wall parts connected by flanges to go through Screw bolts connected, each with a wall 5 leave. Do this with this flange connection as well Partly one-piece, rigid flanges, which are already connected with the accumulation of material in the area of the high bending stresses associated with their flanges before the preload of the screw bolts the sealing elements having inner edges of the transition point from the flanges to the anmetallic lie against one another and on their outer wall parts bordering on the pressurization of the edges have an axial distance from each other, ίο pressure vessel disadvantageously noticeable. To the bending case known flange connections of this type is to reduce stresses, it is also necessary the axial distance between the outer edges of the flanges so the transition point from the flange to the wall part in the great that they taper conically even after tightening the screw cross-section. Besides, the do not touch the bolt. This can be done in a dependent flange design, in particular due to the zigzagging of the degree of the tightening of the bolts of the 15 mutually offset arrangement of the Contact pressure of the flanges in the area of their inner projections penetrated by the screw bolts relative to the edges choose freely, depending on tiv involved and thus costly. The spread dem also has the expected pressure inside the pressure of the flange towards the inside of the vessel vessel. The more the bolts are tightened, the more the internal diameter of the flange decreases greater bending stresses arise in the transition area 20 which is less than that of the pressure vessel. Since the area from the flanges to the adjacent water diameter is critical, this brings the emergency wall parts. In order to keep these tensions low, the entire pressure vessel is maneuverable So far, one has felt compelled to make the flanges behave.

nismäßig large and, in addition, the object of the invention is to provide a

Transition point from the flange to the wall part in the flange connection of the type mentioned above Tapering cross-section conically. With consideration to design that despite considerable material the Very large dimensions of the pressure vessels are saved due to the smaller flange design As a result, correspondingly large dimensions result in damaging stresses at high operating pressures of the flange connections. Not to mention the concentration at the transition point from the from the manufacturing difficulties, there are also 30 flanges to the adjacent wall parts

the material costs are very significant. In addition, there is avoidance. . -.

in the event of temperature changes, the temperature difference and thus the temperature tensions in the compound of the type defined at the outset, mentioned according to the invention Transition point for solved by such a distance of the compared to FIG Pressure vessel relatively large flanges become larger. 35 outer edges that by tightening the screws-Zur Reduce the dimensions of such a bolt until it touches the outer edges Flange connection, it is known, the flanges on the other or on a rigid intermediate layer in the over-smaller and train them with angled thread cross-section from each of the flanges to the Bore bores for the accommodation of alternately adjacent wall parts are counterbalanced by a bending preload inclined screw bolt 40 can be aimed by the normal operating pressure to provide. The heads of the screw bolts support the bending stress in the pressure vessel on pressure pieces, which on the one hand is opposite to this cross-section and this Outside of the associated flange and compensated as completely as possible. When bracing on the other hand, on the pressure pieces of the respectively adjacent screw bolt, the predetermined hard screw bolt. In this way, 45 bending tensioning of the container wall at the transition should be achieved that, when tensioning, the cross-section to the flange is generated as soon as the flanges Screw bolts in the transition area from the flange with their outer edges to the mutual contact do not see any uncon- ceived to the adjoining wall parts. Subsequently, another is displaced Tensions-occur. Not to mention the tension of the 'screw bolts as a function of from the fact that with such a flange connection 50 the later operating pressure in the pressure vessel pred by the accumulation of material in the area of the flanges, which the flange connection has to withstand has one when the pressure vessel is pressurized. Because of the bending stiffness of the flanges, everyone calls different elongation of the flanges in comparison further prestressing of the screw bolts none occurs to the adjacent wall parts, so that there is a significant change in shape in the flange and then high bending stresses at the transition point 55 with no change in the bending prestress at the transition cross-section from the flanges to the adjoining wall parts, make noticeable disadvantageous, is also the considerable with correct dimensioning of the distance between

Manufacturing costs disadvantageous, because these flanges are the outer edges of the flanges bond requires. Operating pressure caused bending stresses at

To almost completely compensate for the occurrence of bending stresses at the transition cross-section from the flanges to the flanges, and this creates a damaging tension Wall parts avoided when tightening the screw concentration in that cross-section. These To avoid bolts of the flange connection without any beneficial effect is without additional For this purpose, the costly pressure pieces can be achieved, since costs are even saved, to have to operate, it is also already known, 65 It has been shown that with the invention Flanges in the form of a widening for the flange connection of the material-vessel interior according to the invention as well as to the outside of the vessel requires in comparison to the previously usual flange and the central axes of the alternating connections can also be reduced by about half.

There are known flange connections for connecting pipes which have fixed flanges and bending stresses occur in the wall of the transition cross-section to the pipe connection. Also at In these known flange connections, the mutually facing flange surfaces close a radially an outwardly open angle with each other. This gaping of the flanges is used there to achieve a certain pressure distribution on the flexible flange seal inserted between the flanges, to achieve a perfect seal. In the flange connection according to the invention, however, is The prerequisite is that the flanges are in metallic contact in order to achieve a precisely defined bending prestress to achieve.

An exemplary embodiment is explained below with reference to the drawing. It shows

F i g. 1 a conventional flange connection and

F i g. 2 shows a flange connection according to the invention prior to bracing.

F i g. 1 shows one of the known flange connections mentioned above with regard to their shortcomings for wall parts of large-diameter pressure vessels, for example nuclear reactor vessels. This flange connection comprises an upper flange and a lower flange 2 adjacent to one wall part 3 each. The flanges 1, 2, which are integral with the respective associated wall part 3, lie with them their inner edges 4,5 metallic to one another, while their outer edges 6, 7 an axial distance have from each other. For this purpose, at least one (1) of the two flanges 1, 2 has an inner edge-side axial projection 8 is provided, in which one or more seals 9 are embedded. Of the A number of bolts 10 are used to brace the flanges 1, 2 against one another.

The forces generated when the bolts 10 are tightened endeavor to twist the flanges 1, 2 with their outer edges 6, 7 towards one another. Correspondingly, bending prestresses arise in the transition cross-section A from each of the flanges 1, 2 to the adjoining wall part 3. In order to keep this small, the flanges 1, 2 are very thick in the conventional flange connection. In addition, there the transition areas from the flanges 1, 2 to the adjacent wall parts 3 are conically shaped, so that a further transition B is created.

A calculation of the stresses that occur shows that with the conventional flange connections according to FIG. 1 the stresses in the cross-sections A, if no conical taper is provided, are greater than when a conical transition zone is created with the cross-sections / 4 and B.

Quite apart from the high material costs, the manufacturing costs are also such Flange connection very significant. This is due to the extraordinarily large dimensions of the pressure vessels traced back. Nuclear reactor vessels have, for example, a diameter of 3 to 10 m. The bolts 10, which can reach a length of several meters, are correspondingly large also the thick flanges penetrated by them.

In the flange connection according to the invention according to FIG. 2 are the much smaller flange dimensions as well as the omission of the upper conical transition zone can be seen.

In the connection according to FIG. 2 , a rigid intermediate layer 11, for example a metal ring, is arranged in the area of the outer edges 6, 7, the thickness of which determines the distance Ah of the outer edge 6, 7 of the flanges 1, 2 in the non-tensioned state.

A certain distance A h between the outer edges can also be achieved by diverging design of the two mutually facing surfaces of the flanges 1, 2 radially outward, so that the flanges only touch the inner edges when they are not clamped.

The meaning of the distance A h is explained below. As shown in FIG. 2, the dash-dot line, which represents the connection cross-section A between wall part 3 and flange 1, shows a stress curve which schematically illustrates the magnitude and course of the bending stress that occurs in the connection cross-section when the bolts 10 are attracted and the vessel is then pressurized. When the bolts 10 of the flange connection are tightened, the flanges 1, 2 initially rotate until their outer edges 6, 7 are in mutual contact via the metal ring 11. In this way, the connection cross-section receives a certain bending prestress. When the desired prestress is reached, a tensile stress + <? & »,, occurs on the outside of the wall outside the neutral line, which is indicated by the intersection of the prestress curve with line A , while on the inside of the wall a compressive stress - a _bSl of same size occurs. The bolts 10 are then tightened further up to a value which is determined by the pressure to be absorbed by the vessel. Since the flanges are rigid, this final tightening of the screw bolts has no effect on the initial bending prestress in the transition cross-section.

As soon as the vessel is placed under internal overpressure, the wall parts 3 tend to expand more than the flanges 1, 2. Axial bending stresses ± a _bp occur on the inside and outside of the wall, which are directed in such a way that they generate tensile forces on the inside and compressive forces on the outside. Accordingly, the state of tension is opposite to the above-mentioned state of tension and is therefore compensated for by the distance Ah if the distance Ah is suitably large. The internal overpressure also generates an axial tensile stress a _xp , which is evenly distributed over the thickness of the wall parts 3. If all of these stresses are superimposed, the following design rules can be used, in which only the axial stresses that are essential for strength in this case are taken into account.

When the bolts are tightened, the following condition must be met for the bending stress in the transition cross-section A:

a _bs <jj is the allowable stress value for the material at the temperature in question.

During work, the resulting axial stress on the inner and outer edges of the wall will be:

^Xtot ~ ^{bs b} *, ^xp .... _

* the permissible voltage value

^The working temperature.

When the invention is used in practice, A h is taken from diagrams over _axiot as a function of Ah. Such diagrams need to be for each individual

Case and taking into account the mechanical strength data of the material in question or measurement. However, to get an idea of the magnitude of the profit too give, which can be achieved with regard to the purely mechanical strength, should be mentioned, for example, that the conventional one shown in FIG Flange connection occurring during operation maximum material stresses in the transition cross-section are about twice as large as in a flange connection designed according to the invention.

Claims (1)

Claim: Flange connection for wall parts of large diameter pressure vessels, especially of Nuclear reactor vessels, consisting of two ring-shaped, connected by screw bolts, with one wall part each, one-piece, rigid flanges which lie against one another with their inner edges having the sealing elements and which are axially spaced from one another at their outer edges, characterized by such a distance (Δ h) between the outer edges (6, 7) even before the pretensioning of the screw bolts ) that by tightening the screw bolts (10) until the outer edges rest against one another or against a rigid intermediate layer (11) in the transition cross-section (A) from each of the flanges (1, 2) to the adjacent wall part (3), a bending prestress can be achieved, which is opposite to the bending stress caused by the normal operating pressure in the pressure vessel in this cross-section (A) and compensates for it as completely as possible. 1 sheet of drawings