Manufacturing and testing method of high-pressure steam superheater

Abstract

The invention relates to the technical field of petrochemical equipment, in particular to a manufacturing and testing method of a high-pressure steam superheater, which comprises a prefabrication step, a water pressure testing step, an adjusting step and a welding step, in the prefabrication step, a high-pressure steam superheater body is manufactured, and a first gasket and a second gasket are arranged between a first flange and a second flange; and the sealing ring is arranged between the two gaskets, the sealing ring is tightly pressed through the outer side locking assembly to achieve temporary sealing, and the outer sides of the first gasket and the second gasket are in a non-sealing state. And then a water pressure testing step is implemented, and if the testing requirement is met, the outer sides of the first gasket and the second gasket are welded and sealed. If the test requirement is not met, the water leakage position is processed, for example, a sealing ring is replaced, and a welding seam between a gasket and a flange is subjected to repair welding or cutting and re-welding until the water pressure test requirement is met. Compared with the prior art, weld joints do not need to be cut repeatedly in the testing stage, manufacturing difficulty is lowered, and structural integrity is kept.

Description

Technical Field

[0001] This invention relates to the field of petrochemical equipment technology, specifically to a manufacturing and testing method for a high-pressure steam superheater. Background Technology

[0002] Chinese patent document CN107883789A discloses a heat exchange method for a U-tube heat exchanger. This method utilizes the U-tube heat exchanger proposed in this invention. The tube-side medium enters the U-tube. The shell-side medium enters the central tube, then flows into the inner heat exchange channel towards the tail end of the U-tube, undergoing pure counter-current heat exchange with the tube-side medium flowing towards the tube sheet in the return section of the U-tube. Subsequently, the shell-side medium enters the outer heat exchange channel and flows towards the tube sheet, undergoing pure counter-current heat exchange with the tube-side medium flowing towards the tail end of the U-tube in the inlet section. The heat-exchanged shell-side medium flows through the flow channel and finally exits from the shell-side medium outlet pipe. The heat-exchanged tube-side medium enters the tube-side medium accumulation chamber and finally exits from the tube-side medium outlet pipe.

[0003] This type of heat exchanger structure is already very mature. Earlier published documents, such as US Patent No. 5915465A, disclose a heat exchanger, and its related patents: CA2220607A1, CA2220607C, DE59705073D1, DK0864830T3, EP0864830A1, EP0864830B1, JP4032366B2, and JPH10300370A, all disclose this type of flow pattern in the tube side and shell side. In all of them, a manifold is set in the tube box. The tube side medium enters the heat exchange tube from the tube box, flows through the entire heat exchange tube, and then flows into the manifold and out. The shell side medium enters from the end away from the tube box, flows through the central tube and flows into the shell side near the tube sheet to exchange heat with the heat exchange tube.

[0004] Regarding the connection between the tube sheet and the shell, as can be seen from the existing technology, the earliest technology was to directly weld the two together. This method is not conducive to the removal of the heat exchange tubes during maintenance, as it requires destroying the weld structure between the tube sheet and the shell. Repeated cutting of the weld seam can easily damage the tube sheet / shell.

[0005] Later, a flange assembly was adopted to lock the shell and tube sheet together. Since the heat exchange tubes are welded to the tube sheet, when it is necessary to remove the heat exchange tubes, the locking assembly can be removed, and the tube sheet and heat exchange tubes can be pulled out of the shell.

[0006] For flange sealing, there are various existing technologies. One approach uses gaskets, as described in Chinese patent document CN101813434A. In this method, gaskets, particularly lip gaskets (plate-type weld lip structure, weld lip structure with stress relief grooves), are placed on the sealing surfaces of the flange assembly. The inner sides of the two gaskets are welded to the sealing surfaces of the two flanges, and the outer sides of the two gaskets are welded to each other. Based on this gasket design, the outer sides of the two gaskets must be circumferentially welded together. This achieves a welded seal between the gasket and the flange, and between the two gaskets. Combined with the tightening components around the outer periphery of the two flanges, a sufficiently strong seal is achieved. Other existing technologies disclosing similar gaskets include patent documents CN112923147A, CN203477673U, and CN212747476U.

[0007] However, a hydrostatic test is required between manufacturing and use to check whether the two gaskets and the gaskets and flanges meet the sealing requirements. If the requirements are not met after the hydrostatic test, the weld seams on the outside of the two gaskets must be cut and re-welded. If the test fails multiple times, multiple cuts are required, causing great inconvenience. Summary of the Invention

[0008] In view of the above-mentioned technical problems existing in the prior art, the present invention provides a manufacturing and testing method for a high-pressure steam superheater.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A manufacturing and testing method for a high-pressure steam superheater is provided, comprising the following steps: Prefabrication steps: manufacture the high-pressure steam superheater body, which includes an upper tube box, tube sheet, shell-side shell and lower tube box arranged from top to bottom, with the shell-side shell and upper tube box separated by the tube sheet; The upper tube box is equipped with a manifold inside. The space between the inner side of the upper tube box and the outer side of the manifold serves as the tube flow chamber. The upper tube box is equipped with a tube inlet pipe that connects to the tube flow chamber. The manifold is connected to a tube outlet pipe that extends out of the upper tube box. The shell-side cylinder is equipped with multiple U-shaped heat exchange tubes. One end of the heat exchange tube is connected to the tube side flowing into the chamber, and the other end of the heat exchange tube is connected to the manifold. The shell-side cylinder is equipped with a central tube, the upper end of which extends to near the tube sheet. The lower tube box is equipped with a shell-side inlet tube and a shell-side outlet tube, and the shell-side inlet tube is connected to the lower end of the central tube. The tube sheet and the shell-side body are connected via a flange assembly structure, which includes a first flange, a second flange, a first gasket, and a second gasket, all of which are annular metal parts. The upper end of the first flange is fixed to the tube sheet, and the lower end of the second flange is fixed to the shell-side body. The annular first gasket and the second gasket are stacked on the mating surfaces of the first flange and the second flange, and the inner side of the first gasket is circumferentially sealed and welded to the end face of the first flange, and the inner side of the second gasket is circumferentially sealed and welded to the end face of the second flange. The outer sides of the first gasket and the second gasket remain unwelded. An annular sealing ring is provided between the first gasket and the second gasket; the first flange and the second flange are provided with a plurality of locking components arranged circumferentially to lock the two together, so as to squeeze the sealing ring to deform and seal the mating surfaces of the first gasket and the second gasket. Water pressure test procedure: Input liquid into the shell side cylinder to make the internal water pressure reach the preset range value, and monitor whether the flange assembly structure leaks water and the location of the leak; Adjustment steps: If leakage occurs in the flange assembly during the water pressure test, loosen the locking components, address the leakage location, and repeat the water pressure test. If no leakage is observed in the flange assembly during the water pressure test, the test passes and can then proceed: Welding steps: Disassemble part of the locking components to make room for welding, while keeping part of the locking components locked to prevent the sealing ring from loosening and plastic deformation; then weld the outer side of the first gasket and the outer side of the second gasket in a circumferential seal, and finally reassemble the disassembled locking components.

[0010] As a further alternative, during the welding step, the disassembled locking components and the locking components that remain locked are alternately distributed.

[0011] As a further optional solution, in the prefabrication step, a positioning groove is machined on the mating surface of the first gasket and the second gasket, the sealing ring is embedded in the positioning groove, and under the action of the locking assembly, the sealing ring is squeezed and deformed, so that the first gasket and the second gasket fit together.

[0012] As a further optional solution, in the prefabrication step, the first flange and the second flange extend outwardly integrally with annular flanges, and the flanges are circumferentially spaced with a plurality of locking holes, each of which is fitted with the locking assembly.

[0013] As a further optional solution, the locking assembly includes a stud and a nut, with the stud passing through the locking holes of the first flange and the second flange, and the nut threadedly fitted over the stud and abutting against the corresponding flange end face.

[0014] As a further alternative, the flanges of the first flange and the flanges of the second flange face outwards in a flared shape.

[0015] As a further optional solution, in the prefabrication step, a transition cylinder is provided at the upper end of the shell-side cylinder, the upper end of the transition cylinder is circumferentially sealed and welded to the second flange, and the lower end of the transition cylinder is circumferentially sealed and welded to the shell-side cylinder.

[0016] As a further alternative, a raised ring extends downwards from the lower end face of the tube sheet, and the upper end of the first flange is circumferentially sealed and welded to the raised ring.

[0017] As a further alternative, the wall thickness of the first flange increases downwards, and / or the wall thickness of the transition cylinder and the second flange increases upwards.

[0018] As a further alternative, two or more of the sealing rings may be arranged with inner and outer separation.

[0019] The beneficial effects of this invention are: This invention discloses a manufacturing and testing method for a high-pressure steam superheater, comprising a prefabrication step, a hydrostatic testing step, an adjustment step, and a welding step. In the prefabrication step, the high-pressure steam superheater body is manufactured, primarily consisting of the flange assembly structure between the tube sheet and the shell-side cylinder. A first gasket and a second gasket are placed between a first flange and a second flange, and a sealing ring is placed between the two gaskets. A temporary seal is achieved by tightening the sealing ring using an external locking assembly, while the outer sides of the first and second gaskets remain unsealed. Then, the hydrostatic testing step is performed. If the test requirements are met, the welding step is initiated to weld and seal the outer sides of the first and second gaskets. If the test requirements are not met, the adjustment step is performed to address any leaks, such as replacing the sealing ring, repairing or re-welding the weld between the gasket and the flange, until the hydrostatic testing requirements are met.

[0020] Compared with existing technologies, the testing phase eliminates the need for repeated cutting of weld seams, reducing manufacturing difficulty and maintaining structural integrity.

[0021] In the prior art, whether there is leakage between two gaskets or between a gasket and a flange, the outer weld between the two gaskets must be cut first. However, in this application, even if there is leakage between the gasket and the flange and the weld needs to be cut and re-welded, the cutting process of the outer weld of the gasket is reduced compared to the prior art.

[0022] The sealing level of a compressed sealing ring is often lower than that of a welded one. This is similar to the principle of "using the lighter to indicate the heavier": if a sealing ring can meet the pressure requirements even without welding the outer side of the gasket, then welding it in combination will better meet the pressure requirements. This satisfies both short-term hydrostatic testing performance and long-term service performance.

[0023] A sealing ring is used in the middle as a transitional structure during the manufacturing, testing and use cycle. After testing, the sealing ring is retained in the middle to achieve a double sealing effect.

[0024] Conventional thinking dictates that testing a device should only be conducted after the target object has been fully manufactured. However, in this case, before the manufacturing process was complete and before the outer seals of the two gaskets were welded, a water pressure test was performed using easily removable, sub-sealing level sealing rings. The idea was that if the sealing rings could pass the test, then the combination of sealing rings and welded seals would be even more likely to pass, achieving a synergistic effect greater than the sum of its parts. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings. However, the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the high-pressure steam superheater body in the embodiment.

[0027] Figure 2 for Figure 1 A magnified view of point A in the middle.

[0028] Figure 3 for Figure 2 The enlarged view at point B shows the flange assembly structure during the hydrostatic test phase.

[0029] Figure 4 for Figure 3 A further schematic diagram showing the outer sides of the first and second gaskets after welding.

[0030] Figure label: Upper tube box 1, tube side inflow chamber 11, tube side inlet tube 12, tube side outlet tube 13, manifold 14; Tube sheet 2, convex ring 21; Shell side cylinder 3, transition cylinder 31; Bottom tube box 4, shell side inlet tube 41, shell side outlet tube 42; Heat exchanger tube 5; Flange assembly 6, first flange 61, second flange 62, flange 63, lock hole 631, first gasket 64, second gasket 65, positioning groove 66, sealing ring 67, locking assembly 68, stud 681, nut 682; Central tube 7. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0032] This embodiment provides a manufacturing and testing method for a high-pressure steam superheater, such as... Figures 1 to 4As shown, the process includes prefabrication, hydrostatic testing, adjustment, and welding steps. The prefabrication step produces a product as shown... Figure 1 The high-pressure steam superheater body shown includes, from top to bottom, an upper tube box 1, a tube sheet 2, a shell-side cylinder 3, and a lower tube box 4. The upper tube box 1 is welded and fixed to the top of the tube sheet 2, and the shell-side cylinder 3 and the upper tube box 1 are separated by the tube sheet 2. A manifold 14 is provided inside the upper tube box 1, and the manifold 14 is fixed to the top of the tube sheet 2. The space between the inner side of the upper tube box 1 and the outer side of the manifold 14 serves as the tube-side inflow chamber 11. The upper tube box 1 has a tube-side inlet pipe 12 that connects to the tube-side inflow chamber 11, and the manifold 14 is connected to a tube-side outlet pipe 13 that extends out of the upper tube box 1. Multiple U-shaped heat exchange tubes 5 are provided inside the shell-side cylinder 3. Both ends of each heat exchange tube 5 are welded and fixed to the tube holes of the tube sheet 2. One end of the heat exchange tube 5 passes through the tube sheet 2 and connects to the tube-side inflow chamber 11, and the other end of the heat exchange tube 5 passes through the tube sheet 2 and connects to the manifold 14. During use, the tube-side medium flows sequentially through: tube-side inlet pipe 12, tube-side inflow chamber 11, heat exchange tube 5, manifold 14, and tube-side outlet pipe 13.

[0033] A central tube 7 is provided inside the shell-side shell 3, and the central tube 7 is arranged coaxially with the shell-side shell 3. The upper end of the central tube 7 extends to near the lower end face of the tube sheet 2. The upper end of the central tube 7 is provided with multiple circumferentially spaced openings. The lower tube box 4 is provided with a shell-side inlet pipe 41 and a shell-side outlet pipe 42. The shell-side inlet pipe 41 is connected to the lower end of the central tube 7. In use, the shell-side medium enters the central tube 7 through the shell-side inlet pipe 41, then flows upward, flows out through the opening at the upper end of the central tube 7 and enters the shell-side shell 3. While flowing downward, it exchanges heat with the tube wall of the heat exchange tube 5, and finally flows out through the shell-side outlet pipe 42.

[0034] Combination Figures 1 to 3 As shown, in this embodiment, the tube sheet 2 and the shell-side cylinder 3 are connected via a flange assembly structure 6. The flange assembly structure 6 includes a first flange 61, a second flange 62, a first gasket 64, and a second gasket 65, all of which are annular metal parts. The annular first gasket 64 and the second gasket 65 are stacked on the mating surfaces of the first flange 61 and the second flange 62. The inner side of the first gasket 64 is circumferentially sealed and welded to the end face of the first flange 61, and the inner side of the second gasket 65 is circumferentially sealed and welded to the end face of the second flange 62. An annular sealing ring 67 is provided between the first gasket 64 and the second gasket 65. The first flange 61 and the second flange 62 are provided with a locking assembly 68 to lock them together, thereby deforming the sealing ring 67 to seal the mating surfaces of the first gasket 64 and the second gasket 65.

[0035] In this embodiment, the upper end of the first flange 61 is fixed to the tube sheet 2. The shell-side cylinder 3 includes a short cylindrical transition cylinder 31. The upper end of the transition cylinder 31 is circumferentially sealed and welded to the second flange 62, and the lower end of the transition cylinder 31 is circumferentially sealed and welded to the shell-side cylinder 3. The purpose of setting the transition cylinder 31 is that when it is necessary to separate the second flange 62 from the shell-side cylinder 3, the weld between the transition cylinder 31 and the second flange 62 can be cut without damaging the shell-side cylinder 3. Even if the transition cylinder 31 is damaged after multiple cuts, only the short cylinder needs to be replaced.

[0036] In this embodiment, a raised ring 21 extends downward from the lower end face of the tube sheet 2, and the upper end of the first flange 61 is circumferentially sealed and welded to the raised ring 21.

[0037] Specifically, the mating surfaces of the first gasket 64 and the second gasket 65 are both concave to form an annular positioning groove 66. The sealing ring 67 is embedded in the positioning groove 66, and under the action of the locking component 68, the sealing ring 67 is squeezed and deformed, so that the first gasket 64 and the second gasket 65 fit together.

[0038] Specifically, the first flange 61 and the second flange 62 extend outwards with annular flanges 63. Multiple locking holes 631 are circumferentially spaced on the flanges 63, and the locking assembly 68 passes through each locking hole 631. The locking assembly 68 includes a stud 681 and a nut 682. The stud 681 passes through the locking holes 631 of the first flange 61 and the second flange 62, and the nut 682 is threaded onto the stud 681 and abuts against the corresponding end face of the flange 63. Similarly, in practice, the locking assembly can be changed to a bolt and nut combination, or it can be changed to a bolt hole with a screw thread, where the bolt is tightened into the bolt hole. Both methods can achieve the application of similar locking forces to the first flange and the second flange.

[0039] Specifically, the flange 63 of the first flange 61 and the flange 63 of the second flange 62 face outwards in an flared shape, providing space for welding the outer sides of the first gasket 64 and the second gasket 65.

[0040] Specifically, there are two sealing rings 67, arranged separately inside and outside each other. Of course, the actual number can be changed to other quantities as needed.

[0041] In this embodiment, the wall thickness of the first flange 61 increases downwards, while the wall thickness of the transition cylinder 31 and the second flange 62 increases upwards, thus meeting the strength requirements.

[0042] like Figures 1 to 3 This high-pressure steam superheater body serves as a hydrostatic test structure. The hydrostatic test is conducted, and only after passing the test is the welding process implemented. The outer sides of the first gasket 64 and the second gasket 65 are then circumferentially sealed by welding, forming a structure as shown below. Figure 4 The state shown.

[0043] In the description of this invention, it is obvious that the described embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the embodiments of the invention described and illustrated herein can generally be arranged and designed in various different configurations.

[0044] Therefore, the above detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0045] In the description of this invention, it should be noted that the terms "middle," "upper," "lower," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0046] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection. They can refer to a mechanical connection or an electrical connection. They can refer to a direct connection or an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

Claims

1. A manufacturing and testing method for a high-pressure steam superheater, characterized in that, Includes the following steps: Prefabrication steps: manufacture the high-pressure steam superheater body, which includes an upper tube box (1), tube sheet (2), shell-side cylinder (3), and lower tube box (4) arranged from top to bottom. The shell-side cylinder (3) and the upper tube box (1) are separated by the tube sheet (2). The upper tube box (1) is equipped with a manifold (14) inside. The space between the inner side of the upper tube box (1) and the outer side of the manifold (14) serves as the tube flow in chamber (11). The upper tube box (1) is equipped with a tube inlet pipe (12) that connects to the tube flow in chamber (11). The manifold (14) is connected to a tube outlet pipe (13) that extends out of the upper tube box (1). The shell-side cylinder (3) is provided with multiple U-shaped heat exchange tubes (5). One end of the heat exchange tube (5) is connected to the tube side inflow chamber (11), and the other end of the heat exchange tube (5) is connected to the manifold (14). The shell-side cylinder (3) is provided with a central tube (7), the upper end of which extends to near the tube sheet (2). The lower tube box (4) is provided with a shell-side inlet tube (41) and a shell-side outlet tube (42), and the shell-side inlet tube (41) is connected to the lower end of the central tube (7). The tube sheet (2) and the shell-side cylinder (3) are connected by a flange assembly structure (6). The flange assembly structure (6) includes a first flange (61), a second flange (62), a first gasket (64), and a second gasket (65), all of which are annular metal parts. The upper end of the first flange (61) is fixed to the tube sheet (2), and the lower end of the second flange (62) is fixed to the shell-side cylinder (3). The annular first gasket (64) and the second gasket (65) are stacked on the mating surfaces of the first flange (61) and the second flange (62). The inner side of the first gasket (64) is circumferentially sealed and welded to the end face of the first flange (61), and the inner side of the second gasket (65) is circumferentially sealed and welded to the end face of the second flange (62). The outer sides of the first gasket (64) and the second gasket (65) remain unwelded. An annular sealing ring (67) is provided between the first gasket (64) and the second gasket (65); the first flange (61) and the second flange (62) are provided with a plurality of locking components (68) arranged in a circumferentially spaced manner to lock the two together, so as to squeeze the sealing ring (67) to deform and seal the mating surfaces of the first gasket (64) and the second gasket (65). Water pressure test steps: Input liquid into the shell side cylinder (3) to make the water pressure inside reach the preset range value, and monitor whether the flange substructure (6) leaks water and the location of the leak; Adjustment steps: If leakage occurs in the flange substructure (6) during the water pressure test, loosen the locking assembly (68), address the leakage location, and repeat the water pressure test. If no leakage occurs in the flange assembly (6) during the water pressure test, the test is passed and can then proceed: Welding steps: Disassemble part of the locking assembly (68) to make room for welding, while always keeping part of the locking assembly (68) locked to prevent the sealing ring (67) from loosening and plastic deformation; then perform circumferential sealing welding on the outer side of the first gasket (64) and the outer side of the second gasket (65), and finally reassemble the disassembled locking assembly (68).

2. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: During the welding process, the disassembled locking components and the locking components that remain locked are distributed alternately.

3. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: in In the prefabrication step, a positioning groove (66) is machined on the mating surface of the first gasket (64) and the second gasket (65), and the sealing ring (67) is embedded in the positioning groove (66). Under the action of the locking assembly (68), the sealing ring (67) is squeezed and deformed, so that the first gasket (64) and the second gasket (65) fit together.

4. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: in In the prefabrication step, the first flange (61) and the second flange (62) extend outward with an annular flange (63), and the flange (63) is circumferentially spaced with a plurality of locking holes (631), and the locking assembly (68) passes through each locking hole (631).

5. The manufacturing and testing method for a high-pressure steam superheater according to claim 4, characterized in that: The locking assembly (68) includes a stud (681) and a nut (682). The stud (681) passes through the locking hole (631) of the first flange (61) and the second flange (62). The nut (682) is threaded onto the stud (681) and abuts against the end face of the corresponding flange (63).

6. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: The flange (63) of the first flange (61) and the flange (63) of the second flange (62) face outwards and are flared.

7. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: in In the prefabrication step, a transition cylinder (31) is provided at the upper end of the shell-side cylinder (3). The upper end of the transition cylinder (31) is circumferentially sealed and welded to the second flange (62), and the lower end of the transition cylinder (31) is circumferentially sealed and welded to the shell-side cylinder (3).

8. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: The lower end face of the tube sheet (2) has a convex ring (21) extending downwards, and the upper end of the first flange (61) is circumferentially sealed and welded to the convex ring (21).

9. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: The wall thickness of the first flange (61) increases downwards, and / or the wall thickness of the transition cylinder (31) and the second flange (62) increases upwards.

10. The manufacturing and testing method for a high-pressure steam superheater according to claim 1, characterized in that: Two or more of the aforementioned sealing rings (67) are arranged with inner and outer separation.

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