Metallic corrugated thermal insulation

Abstract

The invention relates to thermal insulation structures for equipment and piping in nuclear power stations. The present thermal insulation is comprised of thermal insulation blocks. Each block has a set of cylindrical flexible membranes disposed therein which are formed from stainless steel sheet having a thickness of 0.05-0.1 mm. The longitudinal and end walls of the blocks are configured in the form of closed rectangular adjacent corrugations arranged along the outer and inner perimeters of the walls of the blocks, creating closed outer thermally insulating air spaces which shield against the propagation of heat. The membranes are arranged on inner ledges of the corrugated walls of a block, with the convex side of the membranes oriented toward a top cover of the block. Each membrane consists of two halves which are connected in an overlapping manner parallel to the end walls and fastened together by sealing strips mounted in channel forming members by a sliding fit with minimal clearance. This makes it possible to achieve an optimal height of the thermal insulation block without detriment to the thermal physical characteristics thereof, as well as to provide reliable fastening of the membranes inside the block and a reduction in the weight of the insulation.

Description

[0001] METAL CORRUGATED THERMAL INSULATION

[0002] The invention relates to thermal insulation technology, and more specifically to designs for thermal insulation of pipelines and cylindrical vessels of nuclear thermal power plants (NPPs).

[0003] A block removable thermal insulation (hereinafter referred to as BRTI) is known, comprising BRTI thermal insulation blocks (hereinafter referred to as TB) placed close to each other on the outer surface of the thermally insulated equipment, joined together by longitudinal side walls and including boxes made of stainless steel and filled with thermal insulation material (see Russian patent RU2716771C2 - 2020, application RU No. 2017111880 dated 04 / 07 / 2017).

[0004] The disadvantage is that the patent design uses a heat-insulating material made of fiberglass. When the first circuit is decompressed, it is possible that fiberglass will enter the reactor core.

[0005] Known is a metal block thermal insulation (MBTI), containing thermal insulation blocks placed close to each other on the outer surface of the heat-insulated equipment, including boxes joined together by longitudinal side walls, made of stainless steel and filled with filtered atmospheric air (see Russian patent RU 2798333 dated 21.06.2023, application RU No. 2023102408 dated 03.02.2023). This patent with the description of MBTI is taken as a prototype.

[0006] The objectives of the proposed invention are: to create thermal insulation that is more compact than the BSTI installed at the Tianwan NPP (China), the Kudankulam NPP (India) and most NPPs in the Russian Federation; to eliminate fiberglass from the insulation and replace it with atmospheric air; to ensure the optimal height of the thermal insulation block while maintaining its thermal and physical characteristics; to securely fasten the membranes inside the block; to reduce the final weight of the thermal insulation.

[0007] The disadvantage of the prototype is that the problem of thermal bridges is not solved - the intersection of the walls of four adjacent thermal insulation blocks in contact with each other. Increased heat transfer occurs along thermal bridges, compared to heat transfer along the walls of the block.

[0008] During the operation of thermal insulation blocks under the influence of high temperatures, due to local deformations, the tight contact of flat walls can be disrupted (the so-called warping of walls), which leads to a deterioration in thermal-physical characteristics.

[0009] The essence of the proposed invention consists in increasing the number of contact overlaps of the walls of the heat-insulating block along the thermal path, which increases the tight contact of the walls, reduces the height of the side and end walls of the heat-insulating block, and eliminates thermal bridges of adjacent contacting blocks.

[0010] Metallic corrugated thermal insulation (hereinafter referred to as MCTI), containing thermal insulation blocks placed close to each other on the outer surface of the heat-insulated equipment, including boxes joined together by longitudinal and side walls, made of stainless steel and filled with filtered atmospheric air. The longitudinal and end walls of the thermal insulation blocks are made in the form of closed, rectangular, adjacent corrugations located along the outer and inner perimeters of the block walls, creating closed external thermal insulation air layers that screen the spread of heat.

[0011] The end and longitudinal walls, bottom and cover of the blocks are made of stainless sheet steel with a thickness of 0.1 - 0.3 mm, the sets of membranes are made of stainless metal sheets with a thickness of 0.05 - 0.1 mm and are located between the walls of the block.

[0012] The end and longitudinal walls are connected to each other using corner joining elements and contact welding.

[0013] The membrane row of the heat-insulating block is made using elastic membranes, the membranes are located on the internal shelves of the corrugated walls of the block and are made with a convexity directed towards the cover of the heat-insulating block. Each membrane consists of two halves of the membranes, connected to each other by an overlap allowance parallel to the end walls and fastened with sealing strips in the cases by a sliding fit with a minimum gap. Fastening and sealing of the membranes between the chambers of the air gaps, the end and longitudinal walls of the block body are made using one-sided spot contact welding on the shelves of the corner connecting elements and the internal shelves of the corrugated walls of the heat-insulating block.

[0014] Located along the outer perimeter of the block, the air layers are separated in the middle of each corrugated tray by sealing “U” shaped partitions, made flush with the protruding perforated walls of the block.

[0015] Thin-walled membranes form air gap chambers of the block with a thickness of less than 15 mm. The dimensions of the membranes increase from the bottom to the cover in proportion to the lengths of the arcs of each subsequent row by the value:

[0016] 2pDrU

[0017] AL = - , where:

[0018] 360

[0019] AL - increase in the length of the arc of the membrane surface of the next row;

[0020] A p is the gap from the surface of the previous row of membrane to the surface of the membrane of the next row, is within 5 - <15 mm;

[0021] Y is the angle between the generatrices of the flexible membranes and the longitudinal walls of the block.

[0022] A thermostatic gap, < 15 mm thick, as the primary insulating air layer of the annular section, is installed between the bottom and the heat-insulated body using sockets and cylindrical pins.

[0023] The side walls of the adjacent block covers are connected to each other by means of hook-ends fixed to the corners of the block cover walls and made in the form of a separate identical sector of the fourth part of the body of revolution: a ball or an ellipsoid in such a way that during the assembly connection of four adjacent sectors a body of revolution is formed, self-sealing in the removable funnel-grip, in the working position of the funnel-grip the elastic petals ensure tight compression of the hook-ends, and when the hook-ends pass the neck of the funnel-grip under the action of the applied force, the ability to elastically unclench with subsequent return to the initial position. A detachable elastic ring is additionally mounted on the funnel-grip, ensuring additional compression. The side walls of the bottoms of four adjacent blocks are connected to each other by means of guide cylindrical pins fixed to the block bottom and tightly entering four sockets of the centering metal socket.

[0024] Access to possible sensors located on the equipment under thermal insulation is achieved using cylindrical penetrations.

[0025] Thus, the patented MGTI has the following differences from the prototype:

[0026] 1. Elastic membranes with a thickness of 0.05-0.1 mm are located on the internal shelves of the corrugated walls of the block and secured with one-sided spot contact welding.

[0027] 2. The calculated thickness and height of the walls and covers of the MGTI blocks, similar to those of the BSTI, have reduced block thicknesses of 60 mm instead of 160 mm for the BSTI blocks.

[0028] 3. The problem of thermal bridges has been solved - the intersection of the walls of four adjacent thermal insulation blocks in contact with each other.

[0029] 4. Thermal insulation of MGTI, when replacing glass fiber with atmospheric air, is more than twice as light as the BSTI currently used at modern nuclear power plants in the Russian Federation, China and India by 39t (58%).

[0030] 5. Increasing the number of contacts between the walls of thermal insulation blocks improves the preservation of the thermal-physical characteristics of the blocks during operation.

[0031] 6. The presence of additional external air layers between the thermal insulation blocks creates closed external thermal insulation air layers that screen the normal spread of heat, increasing the efficiency of thermal insulation.

[0032] 7. The geometry and dimensions of the profiles of the corner connecting elements for MGTI of this radius of the insulated equipment have been unified. The maximum dimensions of the corner connecting element, equal to = 60 mm, allow its production by printing on a printer.

[0033] Table of comparative characteristics of the BSTI NPP "Kudankulam" and MGTI

[0034] There are three types of heat transfer: conduction, convection and radiation.

[0035] In the prototype, the leading dimension of the thermal insulation thickness is the thermal conductivity of the side and end walls of the block, which determines the height of these walls and, as a consequence, the thickness of the thermal insulation as a whole, selected in accordance with the requirements of the regulatory documentation.

[0036] The maximum thickness of BSTI blocks is 160 mm with a wall thickness of 0.5 mm. The maximum thickness of MGTI blocks is 60 mm with a wall thickness of 0.2 mm. It has been experimentally proven that thinner layers, in which the air can be considered almost motionless, have a lower thermal conductivity coefficient than thicker layers with convection currents arising in them. The thermal conductivity coefficient of an air layer up to 15 mm thick is 0.035. An air layer up to 15 mm thick can be considered an insulator with a motionless air layer. Source: Technical Encyclopedia. Volume 4 - 1928.

[0037] Installing one screen between two parallel walls reduces radiant heat exchange by approximately two times. A design of six screens, including the bottom and cover, plus six thin air layers with fixed air layers, bordered by steel screens, reduces radiant heat exchange by approximately 64 times.

[0038] A cascade of metal membranes shields the outer surface of the MGTI from radiant heat exchange, and the practically motionless air is a good insulator from thermal conductivity from the membranes of hotter air layers.

[0039] Fig. 1 shows a MGTI heat-insulating block with a closed housing;

[0040] Fig. 2 shows a fragment of the cross-section of the MGTI block; Fig. 3 shows the joining of heat-insulating blocks 1 and 2;

[0041] Fig. 4 shows the sealing of the membranes along the perimeter with the walls of the block;

[0042] Fig. 5 shows a corner connecting element for side and longitudinal walls;

[0043] Fig. 6 shows the joining of side and longitudinal walls with a corner joining element;

[0044] Fig. 7 shows the fastening of the sealing support;

[0045] Fig. 8 shows the hook tip;

[0046] Fig. 9 shows a funnel-capture;

[0047] Fig. 10 shows the fastening of the covers and bottoms of the MGTI blocks;

[0048] Fig. 11 shows a schematic of the fastening of adjacent MGTI blocks with locks;

[0049] Fig. 12 shows the fastening of the bottoms of the MGTI blocks.

[0050] Fig. 1 shows a heat-insulating block of the MGTI, consisting of a cover pos. 1, two side walls pos. 2, located at an angle Q to each other, two end walls pos. 3, made in the form of flat annular sectors, a cylindrical bottom pos. 4, resting through pins pos. 15 and a socket pos. 16 on a heat-insulated surface pos. 5. At the corners of the end and side walls of the cover, hook tips pos. 18 are installed for connecting the TBs to each other using a funnel-grip pos. 19. The thermostatic gap pos. 9, <15 mm thick, as the primary insulating air gap of the annular section, is installed in the niche for the socket pos. 25, between the bottom pos. 4 and the heat-insulated body pos. 5 using sockets pos. 16 and guide cylindrical pins pos. 15. The purpose of the partition pos. 32 is shown in Fig. 2.

[0051] Fig. 2 shows a fragment of the cross-section of a part of the MGTI block. The production of curvilinear corrugations 3-10 mm high from a flat steel sheet is carried out by extrusion on a hydraulic press. The dimensions of the internal corrugation are selected depending on the thickness of the air gap, observing the condition: the maximum size of the corrugation along the wavelength must be less than 15 mm. The cover pos. 1, with longitudinal channels pos. 8 and stiffeners pos. 23, is secured by a welded joint with the end and longitudinal walls. Membranes pos. 6 form chamber air gaps pos. 17 with a layer thickness of A p (< 15 mm), in which the air is motionless and there are no convective currents. The membranes pos. 6 are sealed and fixed using 3-5 points per side by one-sided spot contact welding pos. 7 with copper electrodes on the shelves of the corner connecting elements pos. 30 and on the shelves of the block walls pos. 2 and pos. 3.The dielectric substrate, similar to a mechanical paw, for contact welding is placed inside the corrugation, outside the wall. The angle Y, which determines the dimensions of the membranes, is the angle between the outer generatrices of the flexible membranes with the longitudinal walls.

[0052] In order to localize air gaps and increase the longitudinal strength of the block, the air gaps located along the outer perimeter are separated and fastened by welding in the middle of each corrugated tray with steel sealing "U" shaped partitions pos. 32, 0.1 - 0.2 mm thick, made flush with the protruding perforated walls of the block, type "C" section "E - E". When assembling MGTI blocks, partitions pos. 32 mutually overlap with their contacting areas and divide the air gaps into equal sections. Fig. 3 shows the joining of heat-insulating blocks: 1 and 2. The air layers pos. 27 located along the outer perimeter of the block between the heat-insulating blocks significantly increase the efficiency of the MGTI thermal insulation. An increase in the number of contact walls of the heat-insulating blocks with each other increases the preservation of the thermal-physical characteristics of the block during the operation of the insulation in high-temperature mode.

[0053] Fig. 4, view A shows the fastening of the membrane, fixed by one-sided spot contact welding pos. 7 on the shelves of the corner connecting elements pos. 30 and on the shelves of the block walls pos. 2 and pos. 3. The shelves are shown by a dotted line. The mounting allowance pos. 31 of the two halves of the membranes pos. 6 is fastened with a sealing strip pos. 24, placed in the connected cases for fastening the sealing strip pos. 26. For a more detailed description, see Fig. 7.

[0054] Fig. 5 shows the corner connecting element pos. 30 for connecting the side and longitudinal walls by welding. The shelves pos. 28 and pos. 29 are intended for connecting by contact welding with the cover pos. 1 and the bottom pos. 4 of the heat-insulating block, respectively. The small dimensions of the corner connecting element (maximum dimensions = 60 mm) allow its production by printing. Section B-B shows the unified geometry of the corner element profiles for MGTI of this radius.

[0055] Fig. 6 shows the joining of end pos.3 and longitudinal pos.2 walls with the corner joining element pos.30. Contact welding along the entire height of the walls can be performed both from the outside and from the inside. When joining and welding the walls with the corner element, the following conditions must be met: flush and straightness of the joined surfaces.

[0056] Fig. 7 shows a sealing strip pos. 24 with a thickness of 0.2 mm, which, after installation, fastens by bending two tubes pos. 26, secured by contact welding pos. 7 on the upper membrane and the lower membrane with an installation allowance pos. 31 equal to 10 - 20 mm. The tube, pos. 26, is made of stainless steel with a thickness of 0.2 mm.

[0057] The assembly of the heat-insulating block begins with the assembly and welding of the side pos.2 and end pos.3 walls with the corner joining elements pos.30. Then the bottom pos.4 is welded to them by contact welding, and a hollow box is obtained. Two halves of the membranes pos.6 are installed inside the box, which are sealed and fixed using 3-5 points per side by one-sided spot contact welding pos.7 with copper electrodes on the shelves of the corner joining elements pos.30 and on the shelves of the block walls pos.2 and pos.3. The connector of the two membranes on the assembly allowance pos.31 is connected by sealing strips pos.24, through the tubes pos.26, which are previously attached to the membranes by spot contact welding during the control assembly. Then the two halves of the membranes of the next row are installed and fixed with the assembly allowance, welding is performed, and so on. The cover pos.1 is welded to the block walls pos.2, pos.3 and to the corner connecting elements pos.30.

[0058] Fig. 8 shows the hook tip pos. 18 with a rounding radius r. х . The hook tips are turned on a lathe and cut into 4 equal parts. They are installed and connected to the cover pos. 10 with argon-arc welding.

[0059] Fig. 9 shows a removable funnel-grip pos. 19, which is a counterpart of the hook tips pos. 18. Its elastic part is made with longitudinal petals pos. 20 in the form of a thin-walled body of revolution, with a neck - the narrowest place of compression of the longitudinal petals. To increase elasticity when connecting the covers of large-sized blocks, an open elastic ring pos. 12 is additionally mounted on the neck of the unified funnel-grip, secured to the funnel-grip with clamps pos. 13 using contact welding. The elastic part of the funnel-grip is secured to the cylindrical shell pos. 21 using contact welding. The elastic funnel-grip pos. 19 is made in such a way that, in its working position, the elastic petals pos. 20 are designed to compress the hook tips pos.18, and when the hook tips pass the neck of the funnel-grip - the narrowest place of compression of the longitudinal petals, under the action of the applied force, the petals are elastically unclenched and then return to their original position.

[0060] Fig. 10 shows the fastening of the covers and bottoms of the MGTI blocks. The standard assembly of the hook tips pos. 18 with a rounding radius ri of adjacent heat-insulating blocks with a removable elastic funnel-grip pos. 19 is shown.

[0061] The funnels-captures are made with bottoms pos. 22. The bottoms of four adjacent blocks are connected to each other using guide cylindrical pins pos. 15, which fit tightly into four sockets of the centering socket pos. 16.

[0062] Fig. 11 shows a schematic fastening of MGTI blocks with locks in the angular joints of the block boundaries, pos. 14. The angular fastening of blocks allows avoiding the adjustment and welding = 6000 of locks with block covers during installation of locks at the NPP.

[0063] Fig. 12 shows the connection with the bottoms of the blocks pos. 4 of the guide cylindrical pins pos. 15 with the centering rosette pos. 16, resting on the heat-insulated body pos. 5. The tight connection of the bottoms of the blocks with the help of rosettes and pins is very important because any thin-walled cylindrical heat-exchange body has a natural permissible ellipticity. When assembling the blocks in a ring around the heat-insulated body, an uncontrolled ellipticity also occurs on the inner surface of the blocks. With an unfavorable, especially perpendicular misalignment, of the above-mentioned surface deviations, gaps and unacceptable loosening of the bottoms of the blocks occur, which lead to a deterioration in the thermal insulation properties of the insulation.

[0064] Estimated calculation of the thickness of the cover and walls of the block

[0065] When using lid reinforcement with ribs and channels 10 mm high and 0.3 mm thick, the following MGTI blocks are obtained:

[0066] The thickness of the stainless thin-walled steel shell of the BSTI is equal to Si= k x D VP / [6]; The thickness of the stainless thin-walled steel shell of the MGTI is equal to S2= kg d / [6];

[0067] 51 kiD VP / [6] kiD

[0068] 52k2d P / [6] k2d , canceling the radicals, we find that

[0069] Si k2d 1.0 x 0.56 x 200

[0070] S2= - = - = 0.26 mm, where: kiD 0.43 x 1000 d is the step of the cell of the MGTI cover stiffening ribs, equal to 200 mm; D is the size of the BSTI block cover, equal to 1000 mm;

[0071] Si and S2 are the thicknesses of the stainless thin-walled steel covers of the BSTI and MGTI; ki and k2 are the coefficients that take into account the method of fastening the edge of the facing steel shells. Source: "Standards for calculating the strength of equipment and pipelines of nuclear power plants". PNAE G-7-002-86. Moscow, 1989.

[0072] Considering the thickness of the BSTI cover equal to Si= 1.0 mm, ki=0.56, D=1000 mm, k2=0.43, 1=200 mm, we obtain a preliminary equal-strength thickness of the stainless thin-walled cover equal to S2=0.26 mm. The safety margin of the MGTI block cover for external uniform loads is 1.15 times greater than that of the BSTI block cover.

[0073] By calculation, the thickness of the walls of the MGTI blocks is taken to be 0.2 mm. The maximum static load on the walls of the MGTI is 0.01192 kg / cm 2 . The additional inertial load when assessing seismic impact using the standard ratio of 10 points is 0.8. The total load using the static seismic assessment method is 0.021456 kg / cm 2 Thus, the safety margin exceeds the permissible limit by several orders of magnitude.

[0074] Approximate calculation of the weight of MGTI

[0075] In total, the BSTI block covers with a thickness of 1 mm contribute 29.5 tons to the total weight of the BSTI insulation, equal to 67.0 tons. In total, the MGTI block covers with a thickness of 0.2 mm contribute 10.2 tons to the total weight of the MGTI insulation, equal to 28.0 tons. The total reduction in the weight of the MGTI is also achieved due to the smaller thickness and height of the side walls, the weight of the fastening locks and the exclusion of 25 tons of fiberglass with clips from the MGTI composition.

[0076] To estimate the weight of the MGTI, the TB variant with four membranes 0.1 mm thick, five air gap chambers, with a distance between membranes p = 11 mm, with a wall thickness of 0.2 mm and block covers 0.3 mm thick, and a bottom thickness of 0.1 mm was considered. The weight of the MGTI is: 10.2 t (the sum of the weights of all covers with reinforcements of 5 ribs and 5 channels 0.3 mm thick) + 1.7 t (the sum of the weights of all walls) + 11.8 t (the sum of the weights of all membranes) + 1.04 t (the total weight of all strips) + 2.4 t (the weight of all bottoms) + 0.86 t (the sum of the weights of locks and sockets) = 28.0 t.

[0077] The weight of the BSTI is: 30.0t (the sum of the weights of all the covers) + 7.88t (the sum of the weights of all the walls) + 25.0t (the weight of all the BSTI fiberglass) + 1.72t (the sum of the weights of all the locks) + 2.4t (the weight of the bottoms) = 67.0t.

[0078] The weight savings of the MGTI thermal insulation for one NPP power unit, according to the estimated estimate, compared to the weight of the operating BSTI NPP Kudankulam - India (67.0 t), is 39.0 t (58.0%).

[0079] The expected economic effect, without taking into account the revision of the drawing and technical documentation, from the implementation of MGTI per one NPP power unit is approximately 45 million rubles.

[0080] 1. Lid

[0081] 2. Side wall of the block

[0082] 3. End wall of the block

[0083] 4. Bottom

[0084] 5. Thermally insulated body

[0085] 6. Membrane

[0086] 7. Contact welding

[0087] 8. Cover support channel

[0088] 9. Thermostatic gap

[0089] 10. Argon arc welding

[0090] 11. Elastic part of the funnel

[0091] 12. Elastic ring

[0092] 13. Clamp

[0093] 14. Block boundary

[0094] 15. Guide cylindrical pin

[0095] 16. Centering socket

[0096] 17. Inner chamber of the air gap

[0097] 18. Hook tip

[0098] 19. Funnel-capture

[0099] 20. Petal

[0100] 21. Shell

[0101] 22. Bottom

[0102] 23. Lid stiffener

[0103] 24. Sealing strip

[0104] 25. Niche for socket

[0105] 26. Case for fastening the sealing strip

[0106] 27. Outer air gap chamber

[0107] 28. Welding shelf with block cover

[0108] 29. Shelf for welding with the bottom of the block

[0109] 30. Corner connecting element

[0110] 31. Allowance

[0111] 32. "U" shaped partition

Claims

Invention formula Metal corrugated thermal insulation (MCTI) comprising thermal insulation blocks placed close to each other on the outer surface of the heat-insulated equipment, including boxes joined together by longitudinal and side walls, made of stainless steel and filled with filtered atmospheric air, characterized in that the longitudinal and end walls of the thermal insulation blocks are made in the form of closed, rectangular, adjacent corrugations located along the outer and inner perimeters of the block walls, creating closed external thermal insulation air layers that screen the spread of heat; the end and longitudinal walls, bottom and cover of the blocks are made of stainless sheet steel with a thickness of 0.1 - 0.3 mm, sets of membranes are made of sheets of stainless metal with a thickness of 0.05 - 0.1 mm and are located between the block walls; the end and longitudinal walls are connected to each other using corner connecting elements and contact welding;the membrane row of the heat-insulating block is made using elastic membranes, the membranes are located on the inner shelves of the corrugated walls of the block and are made with a convexity directed towards the cover of the heat-insulating block. Each membrane consists of two halves of the membranes, connected to each other by an overlap allowance parallel to the end walls and fastened with sealing strips in the cases by a sliding fit with a minimum gap; the fastening and sealing of the membranes between the chambers of the air gaps, the end and longitudinal walls of the block body, are made using one-sided spot contact welding on the shelves of the corner joining elements and the inner shelves of the corrugated walls of the heat-insulating block; located along the outer perimeter of the block, the air gaps are separated in the middle of each corrugated tray by sealing "U" shaped partitions, made flush with the protruding perforated walls of the block.

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