FR2524967A1 - PERFECTLY DESIGNED DOUBLE WALL TUBES FOR STEAM GENERATORS - Google Patents

Abstract

ADVANCED DESIGN DOUBLE WALL TUBES FOR STEAM GENERATORS. A CORRUGATED SURFACE 5 IS PRODUCED ON THE OUTER FACE OF THE INNER TUBE 3. THE LONGITUDINAL STRETCHING OF THE TWO TUBES BRINGS THE INNER FACE OF THE OUTER TUBE IN CONTACT WITH THE OUTER FACE OF THE INNER TUBE; THE INTERFACE THUS LOCKED MECHANICALLY, THE TUBES SUBJECT TO TEMPERATURE DIFFERENCES CANNOT SLIDE WITH RESPECT TO ANOTHER, WHICH ELIMINATES ALL WEAR. APPLICATION IN PARTICULAR TO STEAM GENERATORS USED IN SUPERREGENERATOR REACTORS WITH LIQUID METAL COOLING.

Description

i

  The present invention relates to doubly

  Improved design wall for a steam generator used in a fast-cooling reactor

by liquid metal.

  One of the designs being developed for

  the steam generators used in fast reactors

  liquid-metal cooling units, uses double-walled tubes to form the interface for the exchange of

  heat between sodium and water The inner tube can contain

  water while the steam generator housing contains

  liquid sodium The heat exchange is made of liquid sodium

  to the water inside the tubes An internal space formed between the two tube walls contains a gas If the outer wall of the tube is pierced by sodium or if the water pierces the inner wall of the tube, leakage of one or the other of these elements can be detected before

  a reaction between sodium and water occurs.

  dull is filled with helium flowing at intermediate pressures

  between that of water or steam circulating in the in-

  the double-walled tube, and that of the sodium contained in the steam generator envelope at the interface of the two

  tubes, are formed four longitudinal grooves that are pro-

  along the entire length of the tubes and which communicate

  with an insulated gas tank This tank is formed

  yen assemblies of double wall pipes and plate

  This tank is connected, in turn, to

  detection of water leaks in order to monitor

  The region of the steam generator containing sodium is connected to detection instruments

  helium to monitor breakthroughs in the outer wall

the tube.

  This design of double-walled tubes is very cautious as regards the reactions between sodium and water, but it involves a possible danger of wear at the interface of the walls of the tubes. These walls are in contact in certain places. even if there is a theoretical interval

  In the steam generator, the tubes are often

  both longitudinal and radial temperature gradients One of the net results is a longitudinal slip at the interface of the tube walls These conditions lead to the possibility of periodic wear at the interface when the tube temperatures vary at start-up, during ups and downs and during other transient thermal states Due to the geometrical shape of the double-walled tube, the wear metal formed at the interface

  remain imprisoned in the meantime, which may increase

  the fact that this wear can occur, has been demonstrated by test results A possible solution to this phenomenon of sliding and wear between the tube forming the inner wall

  and the tube forming the external parci, consists of pre-contrain-

  the tubes during their manufacture The purpose of this

  prestressing is to prevent slippage

  terface We can also expect better performance

  of heat exchange, because of the current prestressing

  There is still some doubt about the effectiveness with

  prestressing can eliminate the phenomenon of

  at the interface It is not known to what extent the tubes

  prestressed will be relaxed during their lifetime u-

  tile. The main object of the present invention is therefore

  to provide a tube whose new design eliminates

  completely the phenomenon of wear at the interface without

  to heat exchange properties or the detection of

  The present invention also relates to a method of

manufacturing die of this tube.

  To achieve this object, the present invention resides

  into a steam generator for a fast breeder reactor

  liquid metal cooling, of the double-pipe type

  characterized in that the interface between the double tube walls is blocked by a mechanical means provided to prevent slippage of the tube forming the inner wall with respect to

  to the tube forming the outer wall.

  The present invention also resides in a method of mechanical blocking between the outer face of a tube forming

  the inner wall and placed in an outer tube, and the

  this interior of this outer tube, this method being characterized

  it includes the following stages: formation of

  non-smooth surface on the outer face of the inner tube; introducing this inner tube into the outer tube, the latter having a smooth inner face; and pairing the tubes forming the inner wall and the outer wall so as to cause deformation of the inner face of the outer tube by the outer face of the inner tube to

  to achieve a mechanical locking of the two tubes.

  The present invention will be well understood by reading

  of the following description made in relation to the

  drawings in which: FIG. 1 is a diagrammatic sectional view of a

  double-walled tube according to the prior art, intended for a

  steam generator; Figure 2 is a schematic sectional view, on a larger scale, of the area defined in Figure 1; and FIG. 3 is a schematic sectional view of the

  double-walled tube designed according to the present invention.

  Referring now to Figure 1 which illustrates

  the basic configuration of a double-walled tube for

steam generators.

  An inner tube 2 introduced into an outer tube 3 constitutes a "double-walled tube" with an interface.

  (the vapor) circulates inside the tube 1 while the

  liquid dium surrounds the tube Gas-filled grooves 4 communicate with a gas tank (not shown) The arrows shown in FIG. 1 illustrate the sliding movement as it can occur during variations.

  In the case of a straight pipe with a double wall

  form, the average area of shear during the expansion

  In the prestressed tube of current design, the interface 5 is subjected to a compression which prevents sliding and the resulting wear. The longitudinal resistance due to the temperature differences is the right cylindrical surface at the interface of the walls. Slip results from surface friction and shear strength of the asperities 6 formed on the surface of the tube as shown in Figure 2. The contact area probably represents approximately 5% of the total area in a truly prestressed tube and

  having a nominal range of 0.0025 to 0.0063 mm

  terface 5 Very small variation in dimensions and / or

  loss of compression at the interface 5 resulting from a relaxation

  stress or significant temperature gradients

  in use would allow a sliding of the tubes.

  Figure 3 illustrates the basic concept of the pre-

  invention, that is to say the mechanical blocking of

  these wall-mounted tubes at the interface 5 In this design,

  slip at interface 5 can not occur without the

  sanding a significant amount of base metal in the vicinity of the interface Just give this blocking device a configuration that will prevent any movement of

  shear in the longitudinal direction It is not necessary

  to prevent temperature gradients in the radial direction, provided that variations in the size of the gap are

  weak compared to the length of the penetration

  The required blocking can be done on a macroscopic or microscopic scale and

  simple configuration such as that of the corrugated interface it-

lustrous in Figure 3.

  It's easy to create an interface configuration

  as shown in Figure-3 Characteristics

  microstructural deposits of various double-walled pipes have

  experimentally shown that the desired configuration of

  terface could be obtained by a process called twinning.

  In this process, there is initially an outer tube whose inner face is relatively smooth and an inner tube

  whose outer face has the desired configuration.

  duit the two tubes into each other and stretch them all

  two in the longitudinal direction Stretching causes contraction

  the outer tube on the inner tube whose outer face

  preformed form permanently deforms the inner face

  of the outer tube It has been observed that, as a result of

  rage during the pairing operation which is part of common manufacturing processes, the outer face of the inner tube penetrates from 0.0016 to 0.0019 mm in the space formed by the longitudinal grooves which are preformed in the inner face of the tube This indicates that,

  even in the present process, the metal flutes during the twinning

  ge in sufficient quantity to make the blocking interface

  if the outer face of the inner tube is correctly

formed.

  To produce ridges and circumferential valleys

  on the outer face of the inner tube, the inner face

  While remaining smooth, cylindrical and of a correct diameter, it can be carried out planetary stamping or simply a rough grinding of the outer face of the inner inner tube

to proceed with the twinning.

  As part of a program to develop

  double-walled prestressed tubes, two samples of double-walled tubes with 20 mm interface contact, were subjected to loads of up to 4300 kg and were loaded cyclically at 4100 kg or more for minus 95 cycles at 400 ° C A sample was tested in the raw state of

  prestressing and another after a thermal treatment of

  laxation of the constraints The two samples presented

  moreover, a mechanical blocking at the microscopic scale.

  No samples were slipped and no wear was found Similar samples that did not have a contact interface slipped under loads of

  36.3 kg and a wear occurred at the interface.

  The addition of a mechanical block to the dou-

  wall allows the removal of prestressing.

  For the appreciation of some of the values of

  above, it must be taken into account that they come from converting imperial units to metric units. The present invention has been designed in the context of

  of a contract concluded with the Government of the United States

  only under No. DOE-AC 02-77 and 37201.

  The present invention is not limited to the examples

  which has just been described, it is necessary to

  which may be subject to variations and modifications which

to the man of the art.

Claims (4)

REVENDl CATI ONS   l Steam generator for liquid metal-cooled dual-tube reactor   wall, characterized in that the interface between the double   The tube is blocked by a mechanical means intended to prevent sliding of the tube forming the wall.   relative to the tube forming the outer wall.   2 Mechanical blocking process between the outer face   a tube forming the inner wall and placed in an outer tube, and the inner face of the outer tube, this method being characterized in that it comprises the stages of forming a non-smooth surface on the outer face of the outer tube;   inner tube; introduction of this inner tube into the   be exterior, the latter having a smooth inner face; and pairing the tubes forming the inner wall and the outer wall so as to cause deformation of the inner face of the outer tube by the outer face of the tube   inside to achieve a mechanical locking of the two tubes.   Process according to Claim 2, characterized   in that the non-smooth outer face of the inner tube pre-   feels a configuration produced by a rough grinding of this outer face.   4 Steam generator according to xevendication 1,   characterized in that a corrugated surface is formed by embossing   weaving on the inner tube for a contact of this tube inside with the outer tube.