A sealing mechanism for tubesheet in high pressure heat exchanger

Abstract

Disclosed is a sealing mechanism (50) for tube sheet to shell joint in a high-pressure heat exchanger (100) comprises a sealing arrangement for restricting the intermixing of shell side and tube side fluids and a leak detection system for indicating in case detected with leakage of fluid. The mechanism is used for tube bundles in H-H type high-pressure screw plugs or breech lock heat exchangers in refineries and other applications wherein intermixing between shell and tube side fluid is eliminated. The mechanism ensures tube sheet attachment to the channel header to provide leak tightness of the joint yet permits removal of the tube bundle for maintenance purposes.

Description

[0001] A SEALING MECHANISM FOR TUBESHEET IN HIGH PRESSURE HEAT EXCHANGER

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to heat exchangers and more particularly relates to a sealing mechanism for tube sheet in high-pressure heat exchangers that restricts the intermixing of shell side and tube side fluids.

[0004] BACKGROUND OF THE INVENTION

[0005] High-pressure heat exchangers are normally made as shell-and-tube heat exchangers comprising of a shell accommodating a plurality of heating tubes therein. In such arrangements, a first fluid stream flows through the plurality of tubes and similarly, a second fluid stream flows through the shell to exchange heat energy therebetween. Normally, high-pressure heat exchangers are widely used in critical services in process industries such as Hydrocracking units, Hydrotreating units, Hydrowaxing units, Hydrofining units etc. Such heat exchangers are known as Breech Lock or Screw Plug Exchangers and are generally classified based on the operating pressure on the shell side and tube side. The heat exchanger having high pressure fluids on both the shell and tube sides is called H-H (High-High) type heat exchanger. Similarly, the heat exchanger having high pressure on the tube side or channel side and lower pressure on shell side are classified as H-L (High-Low) type heat exchangers.

[0006] A H-H type of high-pressure screw plug or breech lock heat exchanger as shown in figure 1 comprises a channel header (1) wherein the channel header closure comprises of a thread lock ring (2) and a channel cover (3). The heat exchanger further comprises a plurality of tubes receiving a first heat exchanging fluid and a shell (10) receiving a second heat-exchanging fluid therethrough. The plurality of tubes (5) that receives the first heat exchanging fluid is fixed to a tube sheet (4), that is also configured in such a way that it can separate the shell side and tube side fluids. The tube sheet (4) and plurality of tubes (5) together hereinafter described as tube bundle (70) is designed for differential pressure conditions fitted to the channel. The channel (1) is provided with inlet and outlet nozzles (6a&6b) for tube side fluid to enter and exit the heat exchanger respectively. However, the nozzle (6a&6b) can also be used to exit and enter the tube side fluid respectively.

[0007] The heat exchanger is preferably provided with two or more tube passes and accordingly, wherein a first end of the plurality of tubes receives the first heat exchange fluid from the channel side inlet nozzle, while the second end of the plurality of tubes (5) releases the heat exchange fluid through a second nozzle or an outlet nozzle. The tube passes are separated by a plurality of pass partition plates (7) and covers (8). The tube sheet (4) is fixed in the annular shoulder (51) between the shell (10) and the channel header (1). The sealing between the shell side and tube side fluids is obtained by a gasket (9). Further, an internal channel box assembly (11) is provided in the channel header (1), which, houses the aforesaid partition plates (7) and covers (8). The inner cylindrical portion of the channel box assembly (11) rests against the shoulder provided on the front face of the tube sheet. The outer end of the channel box is attached to an annular ring (12). As the force is applied on the annular ring in the axially inward direction, it is transferred to the gasket (9) through the channel box (11) and compression of the gasket (9) configured between the tube sheet and the channel header (1) provides the seal between the tube side and the shell side fluid. The push bolts / rods (17) provided on the channel cover (3), when tightened, press the channel box (11) through the annular ring (12) via the inner compression ring (18), diaphragm (19) and internal sleeve (20). This facilitates the loading of the gasket joint in operation.

[0008] However, shortcomings associated with the H-H type heat exchangers include:

[0009] • Intermixing between shell side and tube side fluid has been observed in a few H-H type heat exchangers at the tube sheet gasket (9) immediately after the plant is restarted subsequent to the occurrence of an upset condition. Typically, the shell side fluid in the heat exchangers is fed to the Reactor comprising a two-phase mixture of hydrocarbon liquid and gas which is primarily hydrogen. The tube side fluid in the heat exchangers is Effluent from the Reactor, which may contain low Sulphur content. The Reactor Effluent is further processed in equipment located downstream of the heat exchangers to produce the final product. An upset condition occurs when either the Feed Pump or the Recycle Gas Compressor trips. During this scenario, the temperature of the Reactor Effluent rises rapidly (of the order of 100 °C or more) within a short span of time. As the Reactor Effluent flows on the tube side of the heat exchangers, different channel side components made of different materials having different coefficients of thermal expansion, are prone to expand rapidly and generate high thermal stresses. The result is sudden raise in pressure on gasket (9) and subsequent loss of sealing at the tube sheet to the shell joint. The Reactor Feed being at a higher pressure than the Reactor Effluent, any intermixing results in the deterioration of the quality of the final product, which is not acceptable.

[0010] • Recent or proposed environmental norms or laws require the products quality to be much more stringent. Thus, even minor intermixing between shell side and channel side fluids is not acceptable.

[0011] • Though there is a provision to externally tighten the gasketed joint by online tightening of the push bolts / rods (17) provided on the channel cover (3), yet intermixing once initiated, makes it very difficult to achieve the leak tightness. Also, every upset operating condition encountered during plant operation initiates the intermixing, which requires frequent external tightening and eventually leading to shut down.

[0012] In H-L type heat exchangers, tube sheets and tube bundles are designed for full pressure acting independently from the shell side and tube side. However, the exchanger usually experiences higher pressure on the channel side and lower pressure on the shell side. Referring to figure 2, an HL type of high-pressure screw plug or breech lock heat exchanger having a tube sheet (1) welded or integral with channel (4) and bolted with shell flange (14). Sealing of shell-side fluid against the outside atmosphere is achieved by a shell flange gasket (12). The shell assembly is a removable type for facilitating maintenance or cleaning of the tube bundle. In order to address the shortcomings of the prior art design of H-H type heat exchangers, some of the refineries have opted for H-L type construction for the Feed / Effluent Exchanger service.

[0013] The shortcomings associated with H-L type of heat exchangers when used in Feed / Effluent service include: shell side fluid is sealed by a shell flange gasket (12) which is exposed to the atmosphere. In case of leakage through this gasket joint, shell side fluid will directly leak into the atmosphere. Since this equipment contain high-pressure, high-temperature flammable fluids (such as hydrogen), any leakage into the atmosphere may have safety hazards.

[0014] Hence, use of H-L type of heat exchangers are not advisable for Feed / Effluent service and there exists a need to provide a heat exchanger with reliable sealing mechanism for tube sheet to shell joint in the high pressure heat exchanger which would be alternate to above mentioned configurations and overcome the associated shortcomings.

[0015] OBJECTS OF THE INVENTION

[0016] An object of the present invention is to eliminate intermixing of shell side and tube side fluids when the plant is restarted after the occurrence of upset conditions.

[0017] Another object of the present invention is to provide a reliable sealing arrangement for tube sheet to shell joint in H-H type heat exchangers, which can eliminate intermixing of shell side and tube side fluids.

[0018] Yet, another object of the present invention is to eliminate the safety hazard condition that can arise due to the leakage of fluid which can occur in H-L type heat exchangers due to the exposure of the sealing mechanism to the atmosphere under normal operating conditions. Yet, another object of the present invention is to provide a warning signal when the sealing arrangement in a heat exchanger fails due to occurrence of any upset conditions.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The objects and advantages of the present invention will become apparent when the disclosure is read in conjunction with the following figures, wherein

[0021] Figure 1 illustrates a pictorial view of general arrangement of H-H type high pressure screw plug or breech lock heat exchanger, in accordance with a prior art technique;

[0022] Figure 2 illustrates a pictorial view of a tube side arrangement of H-H type high pressure screw plug or breech lock heat exchanger, in accordance with the prior art technique;

[0023] Figure 3 illustrates a pictorial view of tube side arrangement of H-L type heat exchanger with sealing mechanism exposed to the atmosphere, in accordance with the prior art technique.

[0024] Figure 4 illustrates a pictorial view of a tube side arrangement of H-H type high pressure heat exchanger with sealing mechanism, in accordance with an embodiment of the present invention;

[0025] Figure 5 illustrates a closer view of the sealing mechanism of Figure 3 in accordance with an embodiment of the present invention; and

[0026] Figure 6 illustrates a pictorial view of leak detection arrangement for detecting deterioration in sealing at the tube sheet to channel header, in accordance with an embodiment of the present invention.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] The foregoing objects of the invention are accomplished, and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiments. The present invention provides a sealing mechanism for tube sheet in a high- pressure heat exchanger. The tube sheet is configured to seal the open ends of removable tube bundles thereon. The mechanism is used for tube bundles in H-H type high-pressure screw plug or breech lock heat exchangers in refineries and other applications wherein intermixing between shell and tube side fluid is eliminated. The mechanism ensures tube sheet attachment to the channel header to provide leak tightness of the joint, yet permits removal of the tube bundle for maintenance purposes.

[0029] In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.

[0030] Furthermore, connections between components and / or modules within the figures are not intended to be limited to direct connections. Rather, these components and modules may be modified, re-formatted or otherwise changed by intermediary components and modules.

[0031] Throughout this application, with respect to all reasonable derivatives of such terms, and unless otherwise specified (and / or unless the particular context clearly dictates otherwise), each usage of:

[0032] “a” or “an” is meant to read as “at least one.”

[0033] “the” is meant to be read as “the at least one.”

[0034] References in the present invention to “one of the embodiments” or “an embodiment” mean that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. If the specification states a component or feature "may1can", "could", or "might" be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.

[0035] In the description of the present disclosure, it's important to clarify that terms such as "top," "bottom," "left," "right," "vertical," "horizontal," "inside," "outside," and similar expressions are used within this context to describe directions or positional relationships. They are based on the orientation or positioning depicted in the accompanying drawings or the standard orientation commonly observed when using the invention's product. These terms are employed for the sake of clarity and simplifying the description rather than indicating any requirement for the device or elements referred to having specific orientations or operating exclusively in particular orientations. Thus, it is important not to interpret these terms as limiting the scope of this disclosure. Furthermore, terms like "first," "second," and so forth are solely used for distinction and should not be interpreted as signifying relative importance. Moreover, it's essential to clarify that when terms like "horizontal" or "vertical" are used, they do not strictly imply absolute flatness or sheer perpendicularity. Rather, these terms can encompass subtle inclinations. For example, "horizontal" indicates a direction more aligned with the horizontal axis than the vertical, without insisting on complete flatness; it may still involve a slight incline.

[0036] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this invention will be thorough and complete and will fully convey the scope of the invention to those of ordinary skilled in the art. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).

[0037] The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding elements in the various figures. These reference numbers are shown in brackets in the following description.

[0038] Referring to the figures from 4 to 6, a sealing mechanism (50) for tube sheet to channel header joint in high-pressure heat exchangers (100) is disclosed in accordance with the present invention. The sealing mechanism of the present disclosure is applicable for the tube bundles arranged in H-H type high-pressure screw plug or breech lock heat exchangers in refineries and other applications to eliminate intermixing of the shell and tube side fluid.

[0039] The high-pressure heat exchangers (100) in accordance with an embodiment of the present invention includes a channel header (1), a tube bundle comprises of a' plurality of tubes (5) filled with a first fluid therein, a shell (10) filled with a second fluid therein, a tube sheet (4) and a channel box assembly. The heat exchangers (100) further includes an internal apparatus containing an annular ring (12), a partition cover (8), and heat exchanger fluid inlet and outlet nozzles (6a&6b).

[0040] The tube sheet (4) is configured as a separating element having particularly a shell side face (4a) facing the shell and a tube side face (4b) holding the open ends of the plurality of tubes (5) thereon. The tube sheet (4), annular ring (12), channel box (11) face and the partition cover (8) together form a first heat exchanger fluid chamber therebetween. The first heat exchanger fluid chamber (15) is connected with an inlet nozzle and an outlet nozzle. The chamber is further separated by a pass partition plate (7) and the partition cover (8) to form an inlet fluid chamber (15a) and an outlet fluid chamber (15b) with at least one nozzle. The inlet chamber (15a) receives the first heat exchanger fluid therein via an inlet nozzle (6a), allows to circulate the fluid through the tube bundle and the outlet chamber (15b) receives the circulated fluid and flows out through the outlet nozzle (6b). The tube sheet (4) thus attached to the open ends of the plurality of tubes (5) in the tube bundle and allows the tubes in fluid communication with the first heat exchanger fluid chamber.

[0041] In one of the embodiments of the present invention, the plurality of the tubes in the tube bundle are ‘U’ shaped tubes.

[0042] The tube sheet (4) is provided with the sealing mechanism (50) at the point of contact with the channel header (1). The sealing mechanism (50) in accordance with the present invention provides fluid sealing for the tube bundle and the channel header (1) hence eliminates intermixing of the first and the second fluids, thus provides reliable sealing when the heat exchanger is subjected to upset conditions. The sealing mechanism comprises a sealing assembly, particularly an assembly of sealing components configured between the channel header (1) and the tube sheet (4), and a gasket (9).

[0043] In an embodiment of the present disclosure, the sealing assembly includes a first gasket (26) and a second gasket (27) secured in separate grooves configured on the channel header (1). Specifically, the first gasket (26) and a second gasket (27) are configured within a first and a second groove (28&29) respectively. In the sealing mechanism of the present disclosure, the second gasket (27) provides redundancy and safety margin to absorb the thermal loads arising during any upset conditions without loss of sealing.

[0044] In an embodiment of the present disclosure, the first and the second grooves (28&29) are configured as concentric grooves located at a radial distance “d” between the axial lines passing through the center thereof.

[0045] In an embodiment of the present disclosure, the sealing mechanism further includes a tube sheet (4) attachment to the channel header (1) that ensures leak tightness of the joint yet permits removal of the tube bundle for maintenance purposes. The tube sheet (4) is provided with a first shoulder (4d) that is extended in the radial direction so as to cover both the first and the second gaskets (26, 27). In one of the exemplary embodiments of the present disclosure, the first and the second gaskets (26 & 27) are made of Kammprofile or grooved metal gasket type.

[0046] In one of the exemplary embodiments of the present disclosure, the tube sheet (4) at the tube side (4b) is configured with a second shoulder (4e) which is in contact with the channel box assembly. The channel box assembly comprises a channel box (11) provided with a first face particularly an inner face resting on the second shoulder (4e) on outer diameter of the tube sheet (4) while a second face particularly an outer face of the channel box (11) resting against an annular ring (12). The second face of the channel box (11) is provided with a reduced diameter and arranged to align with the centerline of a first push bolt (13). In an embodiment of the present invention, the first push bolt (13) is internal flange push bolt. The first push bolt (13) being provided in the threaded holes in the internal flange (14) such that upon tightening the threads the push bolt (13) loads the annular ring (12) from its outer side in turn loading the sealing assembly through the channel box (11) and tube sheet (4). The reaction to this load in outward direction is taken by a split ring (15). Further, a plurality of gussets (23) are provided in the annular ring (12) for full circumferences and fixed to both channel box (11) and annular ring (12) for stiffening. The channel box assembly is further provided with a second push bolt (17), via an inner compression ring (18), a diaphragm (19), and an internal sleeve (20). In an embodiment of the present invention, the second push bolt (17) is a channel cover push bolt (17), which, upon tightening, the second push bolt (17) may load the annular ring (12) through the compression ring (18), diaphragm (19), and the internal sleeve (20), the internal flange and the first push bolt (13). Thus, the load on annular ring (12) may get transmitted to channel box (11) and ultimately to the tube sheet (4).

[0047] This arrangement of the tube sheet (4) attachment eliminates intermixing of the fluid in the shell side and the tube side of the tube sheet (4) that observed in H-H type high pressure heat exchangers. The sealing mechanism (50) in accordance with the present invention comprises a sealing arrangement for restricting the intermixing of shell side and tube side fluids and a leak detection unit for producing warning signals in case detected with leakage of fluid from any one of the first and the second gaskets (26 & 27).

[0048] In one of the exemplary embodiments, the sealing mechanism also associated with a leak detection unit is provided for generating alert signals in case of a leakage detected at any one of the first and second gasket (26&27). The leak detection unit comprises a pair of cavities drilled on the channel header (1) connecting a leak detection pipe (56). The pair of cavities include a first cavity (55a) drilled in the axial direction with respect to the shell connecting the solid metallic zone between the first and the second gaskets (26&27) to a second cavity (55b). The second cavity (55b) is drilled in the radial direction through the thickness of the channel header (1) connecting the leak detection pipe (56). The leak detection pipe (56) is firmly fitted on the outer face of channel header ( 1) at the location where the second cavity (55b) emerges out of the channel header (1). The open end of the leak detection pipe can be coupled to a monitoring device that generates alarm upon flow of fluid through the pair of cavities. In a preferred embodiment, the monitoring device is a gas sensor coupled to an electronic circuitry such as a buzzer module.

[0049] In another aspect of the present disclosure, an operation of the sealing mechanism is explained with respect to the diagrams from 4 to 6. During upset conditions in the heat exchanger such as feed Pump or Recycle Gas Compressor trip, the temperature of the Reactor Effluent rises rapidly almost by 100°C within a short span of time. As the Reactor Effluent flows on the tube side of the heat exchangers, different channel side components made of different materials having different coefficients of thermal expansion may be prone to generate high thermal stresses and ultimately leads to rapid rise in pressure on gasket (26). Subsequently failure of the single gasket located as the sealing between the first fluid chamber and the second fluid chamber. In such situations, the sealing arrangement particularly the second gasket (27) provides redundancy and a safety margin by absorbing the thermal loads during upset condition without loss of sealing. Further, the loading on each of the first and the second gaskets (26&27) is effectively reduced to 50% of that in the conventional techniques.

[0050] List of Components:

[0051] Component Name Component Component Name Component

[0052] Number Number

[0053] Channel header 1 Channel cover push 17 bolts

[0054] Thread lock ring 2 Diaphragm 19

[0055] Channel cover 3 Internal sleeve 20

[0056] Tubesheet 4 Gussets 23

[0057] Shell side face of 4a First gasket 26 tubesheet

[0058] Tube side face of 4b Second gasket 27 tubesheet

[0059] First shoulder 4d First groove 28

[0060] Second shoulder 4e Second groove 29

[0061] Tubes 5 Sealing mechanism 50

[0062] Channel side inlet / 6a / 6b Annular shoulder 51 outlet nozzle

[0063] Pass partition plate 7 First cavity 55a

[0064] Partition Cover 8 Second cavity 55b

[0065] Gasket at tube sheet to 9 Leak detection pipe 56 channel header joint

[0066] Shell 10 Tube bundle 70

[0067] Channel box 11 Tubesheet for HL type 81 exchanger

[0068] Annular ring 12 Channel header for HL 82 type exchanger Internal flange push 13 Shell flange for HL 83 bolts type exchanger

[0069] Internal flange 14 Shell flange gasket for 84

[0070] HL type exchanger

[0071] Split ring 15

[0072] ADVANTAGES OF THE INVENTION

[0073] 1. The tube bundle with the first and the second gaskets (26&27) in the sealing mechanism (50) provides a solution to eliminate the risk of intermixing of the fluids in H-H type heat exchangers (100).

[0074] 2. The tube bundle with the tube sheet (4), provides a solution to eliminate external gasketed joint in the conventional heat exchangers specifically the H- L type heat exchangers.

[0075] 3. The loading on each of the first and the second gasket (26&27) is effectively reduced to 50% of that in the existing techniques. Further, locating the gasket in a groove provides backing support to the gasket from crushing / deformation.

[0076] 4. The tube bundle with tube sheet (4) is configured as a removable component permitting easier removal for maintenance or cleaning purposes.

[0077] 5. The detection system configured within the heat exchanger (100) provides a warning in case of leakage occurred in any one of the first and second gaskets (26&27).

[0078] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the scope of the present invention.

Claims

We claim:

1. A sealing mechanism (50) for tube sheet in high-pressure heat exchanger (100), the sealing mechanism comprises: a sealing assembly configured at the tube sheet (4) to channel header (1) joint; and a channel box assembly configured at a second shoulder (4e) of the tube sheet (4); wherein the sealing assembly and the channel box assembly restricts the intermixing of shell side and tube side fluids.

2. The sealing mechanism as claimed in claim 1, wherein the sealing assembly includes, a first gasket (26) secured in a first groove (28) configured on the channel header (1); and a second gasket (27) secured in a second groove (29) configured on the channel header (1).

3. The sealing mechanism as claimed in claim 2, wherein the first and second grooves (28&29) are configured as concentric grooves located at a radial distance “d” between the axial lines passing through the center thereof.

4. The sealing mechanism as claimed in claim 2, wherein the first and second gaskets (26, 27) rest on a first shoulder (4d) configured on the shell side face of the tube sheet (4).

5. The sealing mechanism as claimed in claim 2, wherein the first and second gaskets (26 & 27) are made of Kammprofile or grooved metal gasket type.

6. The sealing mechanism as claimed in claim 1, wherein the channel box assembly includes, a channel box (11) having a first face resting on the second shoulder (4e) of the tube sheet (4) and a second face resting against an annular ring (12);a first push bolt (13) arranged to align with the centerline of the channel box (11) at the annular ring (12) end; and an internal flange (14) with threaded hole for receiving the first push bolt(13) therein; wherein the first push bolt (13) is configured within the threaded hole in the flange such that upon tightening the threads the first push bolt (13) loads the annular ring (12) from the outer side in turn loading the sealing assembly through channel box (11) and the tube sheet (4).

7. The sealing mechanism as claimed in claim 1, wherein the channel box assembly includes a second push bolt (17) coupled to the annular ring (12) via a compression ring (18) a diaphragm (19), an internal sleeve (20), the internal flange(14) and the first push bolt (13).

8. The sealing mechanism as claimed in claim 1, wherein the tube sheet is configured with the second shoulder (4e) for receiving the first face of the channel box (11).

9. The sealing mechanism as claimed in claim 1, wherein the channel box (11) having an outer face is provided with a reduced diameter and arranged to align with the centerline of the first push bolt (13).

10. The sealing mechanism as claimed in claim 1, wherein the channel box (11) is supported by a gusset (23) secured between the channel box (11) and the annular ring (12).

11. The sealing mechanism as claimed in claim 1 includes a leak detection unit configured on a channel header (11) close to the sealing assembly to produce warning signals in case detected with leakage of fluid.

12. The sealing mechanism as claimed in claim 11, wherein the leak detection unit includes, a first cavity (55a) drilled on the channel header (1) connecting to the solid metallic zone between the first and the second gaskets (26&27),a leak detection pipe (56) firmly fitted on the outer face of channel (1) at a location where a second cavity (55b) emerges out of the channel (1), and a monitoring device located at an open end of the leak detection pipe (56).

13. The sealing mechanism as claimed in claim 12, wherein the first cavity (55a) is drilled in the axial direction with respect to the shell connecting the solid metallic zone between the first and the second gaskets (26&27) to the second cavity (55b).

14. The sealing mechanism as claimed in claim 12, wherein the second cavity (55b) is drilled in the radial direction through the thickness of the channel header (1) connecting the leak detection pipe (56).

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