FR2812117A1 - Thermal protection screen, for rotary shaft especially for primary pump in nuclear power plant, has sleeve fixed to shaft enclosing metal ring - Google Patents

Abstract

The screen comprises a stainless steel sleeve (11) fixed to a rotary shaft (1) and has an inner cavity (12) containing a multi-layer metal ring (21) that contacts the shaft. The sleeve is open at one end to receive the metal ring, comprising an inner layer of stainless steel and alternating layers of zirconium oxide and nickel-chrome alloy. The ring is closed at the other end by a shoulder on the shaft. The open end is closed by a ridge (21a) on the end of the ring or a collar on the sleeve.

Description

The present invention relates to a thermal protection screen for a

  rotating shaft, in particular for a primary pump shaft of a nuclear power plant. Many industrial installations have rotating shafts which are subject to temperature differentials between two zones

  generating on these trees variations in significant thermal stresses.

  This is particularly the case for primary plant pumps

  that carry hot water at high temperature.

  In their upper part, these primary pumps include a heat exchanger called a thermal barrier, which cools the water supplying a

  hydrodynamic bearing and rotating seals with the longitudi-

  nal. There is therefore a transition zone between hot and cold water located

at the bottom of the thermal barrier.

  The part of the tree located in this transition zone is by

  i5 consequently subjected to an important thermal gradient which favors instabili-

  thermal tees that can create cracks in the tree.

  To reduce this risk of cracking, a heat shield is

  arranged on the tree in the area where the thermal gradient is the greatest.

  So far, this heat shield is formed by a stainless steel ring surrounding the shaft in said area. This solution is not enough to completely guard against the risk of cracking, because after a few years

  during operation, cracks may appear in various places in the ar

bre below this ring.

  The object of the invention is to provide a thermal protection screen

  2 5 that which improves the effectiveness of the protection and thereby reduces the

  risk of cracking in the tree.

  The subject of the invention is therefore a thermal protection screen for a rotating shaft, in particular for a primary pump shaft of a nuclear power station, characterized in that it comprises, on the one hand, a sheath secured to the shaft and comprising an internal housing and, on the other hand, a metal ring

  multilayer in contact with the shaft and disposed in said internal housing.

  According to other features of the invention - the internal housing of the sheath is open at one end for

  mounting of the metal ring and is closed at the other end with a spar-

  Lement hooped on the shaft, - the open end of the inner housing of the sheath is closed by a projecting flange formed at one end of the metal ring, the end of the sheath being hooped on said flange, - the end open of the internal housing of the sheath is closed by a ring hooped on the shaft and on which the end of the sheath is hooped, - the screen comprises a transverse pin connecting the sheath with 0 lI'brebre,

  - the pin is mounted in a hole in the shaft and travels

  pours the shoulder of the sheath, the free end of said pin being welded to said sheath,

  - the pin is mounted in a hole in the shaft and travels

  i pours the ring and the sheath, the free end of said pin being welded to said sheath, - the sheath is made of stainless steel,

  - the multilayer metal ring is formed by a ring

  dull stainless steel on the outside of which a surface is applied

  perposition of several layers of zirconium oxide alternated with layers

  ches of nickel-chromium alloy, the last layer being a layer of nickel-chromium alloy, the layers of zirconium oxide and of nickel-chromium alloy are placed in a cylindrical counterbore formed on the external face of the internal ring, said cup being bordered at each of its ends by a projecting rim, - the edges of the counterbore are inclined at an angle between 30

and 60.

  The characteristics and advantages of the invention will become apparent from

  during the description which follows, given by way of example and made in reference to

  Refer to the accompanying drawings, in which: - FIG. 1 is a schematic half-view in axial section of a part of a primary pump fitted with a thermal protection screen according to the invention, - FIG. 2 is a schematic view in axial section and on a larger scale of a first embodiment of the thermal protection screen according to the invention, - FIG. 3 is a schematic view in axial section and more

  large scale of a second embodiment of the thermal protection screen

  according to the invention, - FIG. 4 is a schematic view in axial section of the multilayer metal ring of the thermal protection screen according to the invention,

  - Fig. 5 is a partial view on a larger scale of the base

multilayer coating.

  In Fig. 1, there is shown schematically a part of a:] 5 primary pump of a nuclear power station and which is intended to convey water

  hot at a temperature of the order of 300 C.

  Conventionally, this pump comprises a lower part

  upper A called hot in which circulates hot water at a temperature of about 300 C and an upper part B called cold in which circulates cold water at

about 40 C.

  Zones A and B are crossed by a tree 1 and the lower part

  it comprises, in a conventional manner, a wheel 2 and a pump casing 3.

  The upper part B comprises a casing 4, a hydrody-

  namique 5 and rotary seals 6.

  The casing 4 is fixed to the volute 3 by means of connecting elements

  7 removable, such as studs.

  Between the lower part A and the upper part B, the pump comprises a heat exchanger 8 called a thermal barrier, which cools

  the water feeding the hydrodynamic bearing 5 and the rotary seals 6.

  Between the lower part A called hot and the upper part B called cold, there is a transition zone C between hot water and cold water at the bottom of the heat exchanger 8 and in which the shaft zone is subject to

  a significant thermal gradient of the order of 260 C.

  In this transition zone C, - the shaft 1 is equipped with a screen

  of thermal protection designated as a whole by the reference 10.

  As shown in Figs. 2 and 3, the protective screen 10

  thermal comprises, on the one hand, a sheath 11 integral with the shaft 1 and comprises

  both an internal housing 12 and, on the other hand, a multilayer metal ring 21

  in contact with the shaft 20 and disposed in said internal housing 12 of the furnace-

1 1.

  The sheath 11 is in abutment against a shoulder provided

on the tree 1.

  According to a first embodiment shown in FIG. 2, the

  internal housing 12 of the sleeve 11 is open at one end 1 la for mounting

  tage of the metal ring 21, as will be seen later, and is closed at the other end 11b by a shoulder 13 formed integrally with said sheath

  1. The shoulder 13 of the sleeve 11 is fixed to the shaft 1 by shrinking.

  Furthermore, the open end 1a of the housing 12 of the sleeve 1 is closed by a protruding rim 21 formed at one end of the metal ring 21 The end of the sleeve 11 in contact with the protruding rim 21a

  2 0 of the metal ring 21 is hooped on this projecting rim 21 a.

  In addition, the metal ring 21 projects from the open end 11a of the sleeve 11 so as to form a bearing surface for the wheel 2 of the

  pump, as shown in Fig. 2.

  A transverse pin 25 completes the connection of the sleeve 11 with

  I'arbre 1. This pin 25 is mounted in an orifice 9 formed in the shaft 1 and trav-

  pours the shoulder 13 of the sleeve 11. The free end of the pin 25 is welded to

the sleeve 11.

  According to a second embodiment shown in FIG. 3, the

  internal housing 12 of the sleeve 1 1 is open at its end 1 1 b for the

  of the metal ring 21 and is closed at its other end 11a by a

shoulder 14.

  The shoulder 15 forms a bearing surface for the metal ring-

  lique 21 and is hooped on the shaft 1.

  The open end llb of the internal housing 12 of the sheath 11 is, in this embodiment, closed by a ring 14 hooped on the shaft 1 and on which the end of the sheath 11 is hooped. The connection between the sheath 11 and tree 1 is completed

  by a pin 25 mounted in an orifice 9 formed in the shaft 1. This pin 25 travels

  pours the ring 14 and the sheath 11 and the free end of this pin 25 is welded

on the scabbard 11.

  i0 As shown in Fig. 3, the sleeve 11 and the ring 14 are

  resting on the shoulder 1 formed on the shaft 1.

  Preferably, the sheath 11 is made of stainless steel.

  Referring now to Figs. 4 and 5, we will describe the ba-

multilayer metallic coating 21.

  This multilayer metal ring 21 is formed by an internal ring 23 made of stainless steel comprising, on the one hand, an internal bore 23 whose diameter corresponds substantially to the diameter of the zone C of the shaft 1 and, on the other hand, on its external face, a counterbore 24 cylindrical and concentric with said

bore 23.

  The inner edges of each protruding rim, respectively

  21 a and 21 b of the counterbore 24 are inclined at an angle between 30 and 60.

  The multilayer metal ring 21 also comprises on the external face of the internal ring 22, that is to say in the circular counterbore 24, a superposition of several layers of zirconium oxide 30 alternating with the

  nickel-chromium alloy layers 31.

  Preferably, the first layer applied to the outer face of the inner ring 22 is formed by a layer 30 of zirconium oxide and the last layer is formed by a layer of nickel-chromium alloy 31

  whose thickness is greater than the thickness of the other layers of nickel alloy

kel-chrome 31.

  For example, the assembly consists of six layers of zirconium oxide each having a thickness of 0.5 mm and by six layers

  of nickel-chromium alloy each having a thickness of 0.25mm, except

  tion of the last one which has a thickness of 0.5mm to allow machining of this assembly and thus obtain an outside diameter corresponding to the mounting criteria. The different layers 30 and 31 are produced by coating

by projection.

  Furthermore, the inclined profile of the edges of the circular counterbore 24 makes it possible to obtain in this zone the perfect overlap of the different layers

and 31.

  : 0 In the case of the first embodiment shown in FIG. 2, the thermal protection screen 10 is mounted on the shaft 1 using the

next way.

  First, the sleeve 11 is fitted onto the shaft 1 and the shoulder

  1a of this shaft 1 provides the axial abutment of said sheath 11. Then, the shoulder

  Lement 13 of the sleeve 11 is hooped on the shaft 1 in its axial position.

  The multilayer metal ring 21 is fitted onto the shaft 1 and placed in the housing 12 of the sleeve 11 so that there remains a

  clearance between the rim 21b and the shoulder 13 and that the rim 21a projects beyond the former

  end of the sheath 11, as shown in FIG. 2.

  The end of the sheath 11 in contact with the rim 21a of the multilayer metal ring 21 is hooped on this rim 21a and the pin 25 is

  installed and is welded to the sleeve 11.

  The outer diameter of the sleeve 11 is machined to bring it to the

  desired dimension and the wheel 2 is mounted on the shaft 1.

  In the case of the second embodiment shown in FIG.

  3, mounting of the thermal protection screen 10 is carried out as follows:

  boasts. First of all, the ring 14 is fitted on the shaft I in such a way that it abuts on the shoulder 1a of this shaft 1. This ring 14 is

  3 o hooped on the shaft 1 in its axial position.

  The multilayer metal ring 21 is then introduced on the shaft 1 and is placed in abutment on the ring 14. The sheath 11 is put in place

  and covers both the ring 14 and the multi-metal ring

ticouche 21.

  The shoulder 14 of the sheath 11 abuts on the rim 21a of the multilayer metal ring 21 and this shoulder 14 is hooped on the shaft 1. In addition, the end of the sheath 11 in contact with the ring 14

  is also hooped on this ring.

  The pin 25 is then put in place and its free end is supported

dée on the scabbard 11.

  The outer diameter of the sleeve 11 is machined to the desired dimension

  and the wheel 2 is placed in position on the shaft 1.

  The alternation of the zirconium oxide and nickel-chromium alloy layers of the metal ring 21 makes it possible to keep a certain ductility

to the entire ring.

  The thermal protection screen according to the invention has the advantage

  compared to the solution used until now, to obtain a more effective thermal protection of the tree thanks to the higher thermal resistance

  of the multilayer metal ring, while retaining an identically

  than. Under these conditions, the thermal gradients in the shaft are attenuated and occur more gradually so that the risks of cracking of the shaft, in particular in the case of a primary pump shaft, are

thereby diminished.

Claims (11)

  1. Thermal protection screen for a rotating shaft (1), no-   especially for a primary pump shaft of a nuclear power plant, characterized in   what it comprises, on the one hand, a sheath (11) integral with the shaft (1) and comprises   both an internal housing (12) and, on the other hand, a multilayer metal ring   (21) in contact with the shaft (1) and disposed in said internal housing (12).   2. Screen according to claim 1, characterized in that the housing-   internal ment (12) of the sleeve (11) is open at one end for mounting the metal ring (21) and is closed at the other end by a shoulder (13; 14) hooped on the shaft (1).   3. Screen according to claim 2, characterized in that the extremi-   open tee of the internal housing (12) of the sleeve (11) is closed by a projecting rim (21a) formed at one end of the metal ring (21), the end   (11 a) of the sleeve (11) being hooped on said flange (21 a).   4. Screen according to claim 2, characterized in that the extremi-   open tee of the internal housing of the sleeve (11) is closed by a ring (14)   hooped on the shaft (1) and on which the end (11b) of the sheath (11) is hooped.   5. Screen according to claim 2, characterized in that it com-   carries a transverse pin (25) connecting the sleeve (11) with the shaft (1).   6. Screen according to claims 2 and 5, characterized in that the   pin (25) is mounted in an orifice (2) formed in the shaft (1) and crosses the shoulder   lement (13) of the sleeve (11), the free end of said pin (25) being welded to said sheath (11).   7. Screen according to claims 4 and 5, characterized in that the   pin (25) is mounted in an orifice (2) formed in the shaft (1) and passes through the an-   ring (14) and the sleeve (11), the free end of said pin (25) being welded to said sheath (11).   8. Screen according to any one of the preceding claims,   characterized in that the sheath (11) is made of stainless steel.   30 9. Screen according to claim 1, characterized in that the multilayer metal ring (21) is formed by an internal ring (22) of stainless steel on the external face of which is applied a superposition of several layers (30) of oxide of zirconium alternated with layers (31) of nickel-chromium alloy, the last layer being a layer (31) of nickel-chromium alloy. 10. Screen according to claim 9, characterized in that the layers (30 31) of zirconium oxide and of nickel-chromium alloy are placed in a cylindrical counterbore (24) formed on the external face of the ring internal (22), said counterbore (24) being bordered at each of its ends by a protruding rim (21a, 21b).   11. Screen according to claim 9, characterized in that the   lo the edges of the counterbore (24) are inclined at an angle between 30 and 60.