JP2014202260A - Expansion joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an expansion joint which reduces an internal stress even when a temperature difference is produced on a welding portion for joining constituents of an expansion joint to each other by a temperature change of gas circulating in a gas duct and a repetitionary internal stress is generated, can improve durability of the welded portion and can provide a longer life, regarding the expansion joint of the metallic gas duct.SOLUTION: An expansion joint 10 includes an annular flange 1 and a bellows 2 having a two-layer structure constituted by overlapping two annular freely expansible bellows 2A, 2B. Therein, respective end parts 2Ba, 2Aa of inner side bellows 2B and outer side bellows 2A of the bellows 2 having the two-layer structure are folded to the outer side in the radial direction, the annular flange 1 is arranged between the end parts 2Ba, 2Aa of folded two bellows 2B, 2A, and both surfaces of the annular flange 1 and the respective end parts 2Aa, 2Ba of two bellows 2A, 2B are welded.

Description

  The present invention relates to an expansion joint including a bellows constituting a metal gas duct.

  In a continuous annealing furnace or continuous galvanizing equipment for steel strip, a number of metal gas ducts are arranged, for example, a soaking furnace operating method in a steel strip continuous treatment equipment described in Patent Document 1 and its An example is disclosed in a soaking furnace.

  In the gas duct described above, high-temperature gas fluid and low-temperature gas fluid pass according to the heat treatment cycle such as heating, soaking, and cooling of the steel strip. Therefore, the gas duct is repeatedly heated and cooled according to the heat treatment cycle, and expanded. Thermal deformation such as shrinkage occurs repeatedly. In order to absorb this thermal deformation, a large number of metal bellows (expandable tubes) are disposed in the gas duct, and the stable operation of the equipment is guaranteed by the bellows.

  Here, the concrete structure of the expansion joint provided with the conventional bellows will be described with reference to FIGS. 7 to 9 of Patent Document 2 (these show the prior art in Patent Document 2). As shown in FIG. 7 of Patent Document 2, the expansion joint is configured by connecting a flange and a bellows via a welded portion. As shown in FIG. 8 of Patent Document 2, the structure of the welded portion between the flange and the bellows is that the bellows is inserted into a flange having a different diameter portion into which the bellows is inserted on the inner peripheral side, and the inner peripheral side is welded all around the welded portion. ing.

  In the expansion joint disclosed in Patent Document 2, the flange and the bellows are in direct contact with the gas in an unsteady state (temperature increase or decrease), and the thin bellows has a temperature change more than the thick flange. Since the speed is high, a temperature difference is generated between the bellows and the flange, and the repeated thermal stress caused by the temperature difference is generated in the welded portion, so that the life of the expansion joint is shortened.

  On the other hand, FIG. 9 of Patent Document 2 shows an expansion joint in which a flange and a bellows are welded on the outer peripheral side. In the same figure, the different diameter part formed in the outer peripheral side of the end part of a single pipe is inserted in the parallel part of the end part of a bellows, and the outer peripheral side is welded all around in the welding part. The other end of the single pipe is inserted into a flange having a different diameter portion on the inner peripheral side, and the inner periphery and the outer peripheral side are welded all around the welded portion.

  In the expansion joint of the configuration shown in the figure, although the end pipe is installed for the purpose of securing a space for welding from the outer periphery, there is no disclosure of methods for suppressing thermal stress and the structure of each welded part. Absent.

  By the way, in continuous annealing furnaces and continuous hot dip galvanizing equipment, gas fluids that require careful handling may flow, such as flammable gases such as COG, as gas fluids that circulate in the gas duct. In addition, it is an important subject to detect the breakage of the expansion joint caused by such a gas fluid at an early stage.

  Here, Patent Document 3 discloses an expansion joint including a two-layer bellows, a metal pipe welded to an end portion thereof, and a leak detection hole provided in the metal pipe. However, in the expansion joint disclosed here, the welding point between the bellows inside the two-layer bellows and the metal pipe is located on the gas flow path inside the expansion joint, so the temperature difference between the bellows and the metal pipe increases. The thermal stress resulting from this temperature difference also increases, shortening the life of the expansion joint.

JP 2007-92140 A JP 2001-263563 A JP-A-3-294003

  The present invention has been made in view of the above-described problems, and relates to an expansion joint of a metal gas duct applied to a continuous annealing furnace, a continuous hot dip galvanization facility, etc., and an expansion joint according to a temperature change of gas flowing in the gas duct Even if a temperature difference occurs in the welded part that connects the structural members of each other, and repeated internal stress occurs due to this temperature difference, the durability of the welded part can be improved, thereby realizing a long life The purpose of this invention is to provide an expansion joint. It is another object of the present invention to provide an expansion joint provided with a simple configuration means capable of detecting leakage of impure gas or the like.

  In order to achieve the above object, an expansion joint according to the present invention includes an annular flange and a two-layered bellows formed by superposing two annular bellows that can be stretched and contracted. The end portions of the inner bellows and the outer bellows are bent radially outwardly, and the annular flange is disposed between the ends of the two folded bellows. Each end of the bellows is welded.

  In the expansion joint of the present invention, the end portions of the inner bellows and the outer bellows of the two-layered bellows are radially outwardly folded, and an annular flange is sandwiched between the end portions of the two folded bellows. The flanges are connected to the respective bellows by welding, and with this configuration, the welded portion of the bellows and flange is set at a position away from the gas flow path inside the expansion joint. It is possible to effectively reduce the thermal stress that may occur at the welded part due to the temperature change. The annular flange is fastened to a flange such as a metal gas duct in a manner in which sealing performance is guaranteed.

  Here, the position of the welded part, that is, the distance from the inside of the annular flange (the part in contact with the gas) to the welded part is the influence of welding when a general bellows with a height of about 40 mm is used. In order not to affect the bellows, the height of the bellows should be set to a height of about 45 mm to 50 mm, which is 40 mm or more, or 50 mm or more.

  In addition, by using austenitic stainless steel as the flange material and heat-resistant alloy such as incoloy as the bellows material, the resistance to embrittlement of each member under severe conditions where the temperature rises and falls frequently is improved. be able to.

  In another embodiment of the expansion joint according to the present invention, in the flange, a through hole is provided from an annular inner side toward a radial outer side, and the gas flowing through the expansion joint is inside the expansion joint. It is a leak detection hole for detecting leakage from the bellows.

  In the present embodiment, in addition to the configuration in which the flange is sandwiched between the two-layered bellows, a through hole is provided from the inner side of the annular flange toward the outer side in the radial direction. If combustible gas or the like leaks from the inner bellows that is in direct contact, the combustible gas or the like enters a space surrounded by the two-layered bellows and the flange.

  And since the end opening of the through-hole established in the bellows faces the space surrounded by the two-layer structure bellows and the flange, the combustible gas or the like passes through this end opening and the through-hole. Is discharged from the other end opening of the through hole, and leakage is detected.

  As described above, the main factor of the two-layer structure of the bellows is that the flange together with the flange forms a space for accommodating the leaked gas, and the leaked gas accommodated in the space is effectively derived through the through hole. It is to detect.

  The leakage detection means constituting the present embodiment is a simple configuration in which one or a plurality of through holes are opened for the flange, and if the through holes are formed in a straight line extending in the radial direction, Because it's good, it doesn't take much work.

  In a preferred embodiment of the expansion joint according to the present invention, one end of the flange and an annular plate sandwich the end of the inner bellows.

  In this embodiment, an annular plate member is arranged on one surface of the flange, and the end portion of the inner bellows is sandwiched between the plate member and the flange so that the inner side directly exposed to the gas having a temperature change. When the bellows of this product is thermally deformed, especially when it is about to expand due to thermal expansion, this bulge can be suppressed by the plate material, which prevents the pulling force from being applied to the welded part of the inner bellows due to this bulge. Moreover, the problem that the cross section of the gas flow path is lost due to the swelling of the inner bellows cannot occur.

  As can be understood from the above description, according to the expansion joint of the present invention, the end portions of the inner bellows and the outer bellows of the two-layered bellows are bent radially outward, and the two bellows folded An annular flange is sandwiched between the end portions and connected to the bellows on both sides of the flange by welding, so that the welded portion of the bellows and the flange is separated from the gas flow path inside the expansion joint. Therefore, it is possible to effectively reduce the thermal stress that can occur at the weld location due to the temperature difference of the gas and improve its durability, thereby realizing a long life of the expansion joint. can do.

It is a longitudinal cross-sectional view of Embodiment 1 of the expansion joint of this invention. It is a longitudinal cross-sectional view of Embodiment 2 of the expansion joint of this invention. It is a longitudinal cross-sectional view of Embodiment 3 of the expansion joint of this invention. It is the figure which showed the temperature change of the gas and bellows which were applied in stress analysis. It is the schematic diagram explaining the outline | summary of the forced displacement applied in stress analysis. It is the schematic diagram explaining the welding location in a stress analysis model. It is the figure which showed the analysis result regarding the temperature difference of the flange and bellows in a measurement position (welding location 1, 2, 3, 4). It is the figure which showed the stress analysis result in the measurement position (welding location 1, 2, 3, 4).

  Hereinafter, the first to third embodiments of the expansion joint of the present invention will be described with reference to the drawings. The illustrated example shows a form in which the bellows constituting the expansion joint is connected to the intermediate pipe, but various forms of gas ducts to which the expansion joint composed of the illustrated flange and the bellows of the two-layer structure is applied, For example, it goes without saying that the bellows constituting the expansion joint may be connected to a separate flange instead of the intermediate pipe.

(Embodiment 1 of expansion joint)
FIG. 1 is a longitudinal sectional view of the first embodiment of the expansion joint of the present invention. The expansion joint 10 shown in the figure is generally composed of a flange 1 connected to a flange 3 to be connected (a flange such as a metal gas duct) and a bellows 2 having an expandable and two-layer structure connected to an intermediate pipe 4. Has been. The expansion joint 10 is preferably applied to some or all of a number of metal gas ducts constituting a continuous annealing furnace (not shown), a continuous hot dip galvanizing facility, or the like through which a gas having a large temperature change flows. .

  The ring-shaped and two-layered bellows 2 has a structure in which an outer bellows 2A and an inner bellows 2B are stacked. The ends 2Aa and 2Ba of both bellows 2A and 2B are separated from each other at one end of the bellows 2 and radially outward. The annular flange 1 is disposed between the bent end portions 2Aa and 2Ba, and both ends of the annular flange 1 and the two end portions 2Aa and 2Ba are connected via an annular welded portion 5. It is.

  Here, when the bellows 2 having a general height of about 40 mm is used, the position of the welded portion 5, that is, the distance from the inside of the annular flange 1 to the welded portion 5 is affected by the bellows 2. From the viewpoint of not affecting the height, the height of the bellows 2 is set to about 45 mm to 50 mm, which is 40 mm or more, or 50 mm or more.

  The material of the flange 1 is austenitic stainless steel (SUS321, SUS310, etc.) and the material of the bellows 2 is a heat-resistant alloy (Incoloy 800HT, Inconel 600, 601, 625, etc.). The resistance to embrittlement of each member under severe conditions can be improved. The above heat-resistant alloys have a high chromium content and nickel content, and chromium forms an oxidation protective film on the surface of the bellows, and nickel improves the durability of the oxidation protective film at high temperatures and precipitates the σ phase. Since it has the inhibitory effect, the corrosion resistance and brittleness resistance of the bellows can be improved, and the life of the expansion joint 10 can be extended.

  In this manner, the expansion joint 10 has two end portions 2Aa and 2Ba which are bent by radially bending the end portions 2Aa and 2Ba of the outer bellows 2A and the inner bellows 2B of the two-layered bellows 2, respectively. The annular flange 1 is sandwiched between the flanges 1 and the ends 2Aa and 2Ba are connected to both ends of the flange 1 by welding so that the welded portion 5 of the bellows 2 and the flange 1 is connected to the expansion joint 10. The temperature difference between the flange 1 and the bellows 2 in the vicinity of the welded portion 5 becomes small. Therefore, it is possible to effectively reduce the thermal stress that may occur at the welded portion 5 due to the temperature change of the gas and improve the durability thereof, and thus it is possible to realize the extension of the life of the expansion joint 10.

(Embodiment 2 of expansion joint)
FIG. 2 is a longitudinal sectional view of a second embodiment of the expansion joint of the present invention. The expansion joint 10A shown in the figure is obtained by modifying the expansion joint 10 shown in FIG. 1 and applying a flange 1A provided with a through hole 1Aa from the inside of the ring toward the outside in the radial direction.

  The through hole 1Aa is a leak detection hole that detects that gas flowing through the expansion joint 10A leaks from the inner bellows 2B.

  In addition to the configuration in which the flange 1A is sandwiched between the two-layered bellows 2, the through-hole 1Aa is provided from the inner side of the annular flange 1A to the outer side in the radial direction. If flammable gas or the like leaks from the inner bellows 2B in contact, the flammable gas or the like first enters the space G surrounded by the two-layered bellows 2 and the flange 1A (X1 direction). Since the end opening 1Aa ′ of the through hole 1Aa opened in the flange 1A faces the space G surrounded by the two-layered bellows 2 and the flange 1, through this end opening 1Aa ′, A combustible gas or the like is discharged from the other end opening 1Aa ″ of the through-hole 1Aa through the through-hole 1Aa (in the X2 direction), and leakage is detected. Thus, the configuration of the bellows 2 has a two-layer structure. The main factor is to form a space G for accommodating leakage gas together with the flange 1A, and to effectively derive and detect the leakage gas accommodated in the space G through the through hole 1Aa. The leakage detection means constituting 10A is a simple configuration in which one or a plurality of through holes 1Aa are opened with respect to the flange 1A, and if the through holes 1Aa are formed in a linear shape extending in the radial direction. Good In less than processing time from the.

(Third embodiment of expansion joint)
FIG. 3 is a longitudinal sectional view of a third embodiment of the expansion joint of the present invention. The expansion joint 10B shown in the figure is an improvement on the expansion joint 10A shown in FIG. 2, and an annular plate 6A is arranged on one surface side of the flange 1A, and the end of the inner bellows 2B between the plate 6A and the flange 1A. The configuration is such that the portion 2Ba is sandwiched.

  More specifically, a bulge prevention member 6 composed of an annular plate member 6A and a tubular member 6B extending in the gas flow direction is disposed inside the inner bellows 2B, and a recess 1b on one surface of the flange 1A. The plate member 6A is disposed so as to sandwich the end 2Ba of the inner bellows 2B, and at this time, the bulge prevention member 6 is assembled so that the end surface of the plate member 6A and the end surface of the protruding portion 1c of the flange 1 are flush with each other. ing.

  When the inner bellows 2B that is directly exposed to a gas having a temperature change is thermally deformed, particularly when it tries to expand due to thermal expansion (swells in the Z direction in the state of the one-dot chain line in the figure), this swelling is used as a plate material. 6A and the cylindrical material 6B can be prevented, and it is possible to prevent the inner bellows 2B from being given a pulling force to the welded portion 5 due to the swelling, or the gas bellows cross section is caused by the swelling of the inner bellows 2B. The problem of missing can be suppressed.

  In addition, the end portion 2Ba of the inner bellows 2B is accommodated in the recessed portion 1b on one side of the flange 1A and welded here, and a plate member 6A for preventing the swelling of the inner bellows 2B is also accommodated in the recessed portion 1b. By forming the end face of the plate member 6A and the end face of the projecting portion 1c of the flange 1A flush with each other, it is possible to easily fasten the joint target flange 3 in a manner in which the sealing performance is guaranteed.

[Stress analysis and results]
The inventors of the present invention have an expansion joint (example) according to the present invention and a conventional expansion joint (comparative example), in which a single bellows is welded and joined inside the annular flange instead of a two-layer structure. Model) was created in a computer, and a coupled analysis of thermal stress due to heat transfer and stress due to mechanical displacement (forced displacement) was performed. Regarding thermal stress analysis, FIG. 4 is a diagram showing temperature changes of the gas and bellows applied in this analysis. Further, regarding stress analysis by forced displacement, FIG. 5 is a schematic diagram illustrating an outline of forced displacement applied in this analysis. FIG. 6 shows the present stress analysis model, and is a schematic diagram illustrating the welding location (stress analysis target site) in this model.

  First, in FIG. 4, a simulation was performed on a change in stress at each welding location with a time change in a section up to time T1, a time period T1 to T2, a time period T2 to T3, and a time period after time T4 in FIG.

  Here, the section up to time T1 shows a steady state in which the gas fluid heated to about 650 ° C. passes through the expansion joint for a sufficient time and the temperature of the expansion joint is uniform. Also, during the period from time T1 to T2, the internal gas fluid is cooled to about 500 ° C. from the period up to time T1, and the temperature of the expansion joint is decreasing following the temperature change of the internal gas fluid. There is an unsteady state in which the temperature distribution in the expansion joint varies. Moreover, the time T2-T3 area has shown the steady state in which the gas fluid of about 500 degreeC passed sufficient time, and the temperature of the expansion joint became uniform. Furthermore, the time period T3 to T4 is a state in which the internal gas fluid is heated to about 650 ° C. and the temperature of the expansion joint is rising following the temperature change of the internal gas fluid. An unsteady state in which the temperature distribution varies.

  On the other hand, with respect to FIG. 5, the expansion joint is installed for the purpose of absorbing the thermal deformation of the gas duct provided in various directions in the continuous annealing furnace or continuous galvanizing equipment of the steel strip. Causes axial displacement and axial displacement. Therefore, in this analysis, axial displacement and axial displacement were forcibly added, and a simulation of the stress state at each weld location was performed when the expansion joint had a broken line shape.

  Further, with reference to FIG. 6, the analysis model is composed of a flange, a bellows, and an intermediate pipe. Here, the thickness of the flange is 25 mm, and the thickness of both the outer and inner bellows is 0.8 mm. In this analysis, attention was paid to the stress generated at the welded portion of the bellows and flange and the intermediate pipe in the expansion joint, and these portions were set as stress analysis target portions.

  Table 1 below shows the material and physical properties of each constituent member in this analysis.

  The analysis results are shown in FIGS. Here, FIG. 7 is a diagram showing an analysis result regarding the temperature difference between the flange and the bellows at the measurement position (welding points 1, 2, 3, 4), and FIG. 8 is a measurement position (welding points 1, 2, 3). FIG. 4 is a diagram showing a stress analysis result in 4).

  The analysis result regarding the temperature difference between the flange and the bellows shown in FIG. 7 shows that the flange and bellows at the welding point in the state of time T1 to T2, which is an unsteady state when the temperature is lowered, among the state changes shown in FIG. It shows the temperature difference.

  As is clear from the figure, it can be seen that the temperature difference at the welded portion of the example is significantly reduced at any measurement location as compared with the comparative example.

  On the other hand, the stress analysis result shown in FIG. 8 shows that the axial displacement and the direction perpendicular to the axis shown in FIG. 5 are obtained in the state T1 to T2 which is an unsteady state at the time of temperature reduction in the state change shown in FIG. The stress analysis result in the welding location when displacement is forcibly added is shown.

  As is apparent from FIG. 8, it can be seen that the stress value at the welded portion of the example is significantly reduced at any measurement location as compared with the comparative example. From this result of FIG. 7, this is considered to be due to the reduction of the repeated thermal stress generated at the welded part because the temperature difference at the welded part between the flange and the bellows was relaxed.

  The difference in temperature difference between the measurement points in the comparative example and the example can be considered as follows. That is, in the comparative example, when the temperature of the gas flowing through the inside decreases due to the change of the heat treatment cycle, heat transfer (hereinafter referred to as heat transfer A) occurs between the low temperature gas fluid and the welded portion, Heat transfer (hereinafter referred to as heat transfer B) occurs between the flange connected to the bellows and the welded portion, and the heat transfer A tries to compensate for the amount of heat lost to the welded portion by heat transfer A. It is considered that the temperature difference between the flange and the bellows increases because the temperature change between the bellows and the welded part due to the heat transfer is faster than the temperature change of the flange due to heat transfer B, and the thermal stress also increases. When the temperature of the gas flowing through the heat treatment cycle changes, the amount of heat moves from the bellows to the low-temperature gas fluid by heat transfer (hereinafter referred to as heat transfer C). Due to this heat transfer C, the amount of heat lost by the bellows is compensated for by heat transfer from the flange connected to the bellows, the flange to be connected to the bellows, and the welding location (hereinafter referred to as heat transfer D). This heat transfer D is performed so that the temperatures of the flange connected to the bellows, the flange to be connected, and the welded portion are uniform, and therefore the temperature difference between the flange connected to the bellows and the welded portion. Is smaller than the comparative example, and as a result, the generation of thermal stress is considered to be reduced.

[Real machine introduction test and results]
The present inventors further applied the expansion joint of the present invention to a continuous annealing furnace (actual machine) in which the gas flowing in the gas duct repeatedly raises and lowers the temperature, and shows the material of each component of the expansion joint as shown in the table below. In three cases shown by No. 2, the degree of corrosion of the bellows due to cracking of the welded part due to repeated stress and the gas fluid property in the gas duct was observed, and the effect of the expansion joint of the present invention was verified. The verification results are shown in Table 3 below.

  With regard to cracks in welded parts, the expansion joints of cases 1 to 3 introduced in the actual machine test have reduced thermal stresses generated in the welded parts, and even now several years after the introduction of expansion joints in any case No cracks have been confirmed at the welded part.

  Regarding the corrosion of the bellows, the expansion joint of Case 1 uses SUS321 (austenitic stainless steel) for the bellows. Since brittleness resistance cannot be obtained, corrosion occurs in about half a year, leading to breakage. In contrast, in the expansion joints of cases 2 and 3, Incoloy 800HT and Inconel 625 are used for the bellows, but Incoloy 800HT and Inconel 625 have a chromium amount and a nickel amount that are higher than austenitic stainless steel such as SUS321. Many of them are excellent in corrosion resistance and embrittlement resistance, and no corrosion was confirmed even after several years after installation.

  Therefore, it can be seen from the actual machine introduction test that each constituent member of the expansion joint is preferably formed from the material of the cases 2 and 3.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1,1A ... Flange, 1a ... Notch location, 1b ... Depression location, 1c ... Projection location, 1Aa ... Through-hole, 1Aa ', 1Aa "... End opening, 2 ... Bellows (two-layer structure bellows), 2A ... Outer bellows, 2B ... Inner bellows, 3 ... Flange to be joined, 4 ... Intermediate pipe, 5 ... Welding point, 6 ... Expansion prevention material, 6A ... Plate material (annular plate material), 6B ... Cylinder material, 10, 10A , 10B ... Expansion joint, G ... Space

Claims (3)

It is composed of an annular flange and a two-layered bellows formed by overlapping two annular bellows that can be stretched and contracted.
The ends of the inner and outer bellows of the two-layer structure are folded radially outward, and the annular flange is disposed between the two bent bellows, and the annular flange is disposed. An expansion joint in which both sides of each and the end of two bellows are welded.   In the flange, a through hole is provided from the inner side of the ring toward the outer side in the radial direction, and this through hole serves as a leak detection hole for detecting the gas flowing through the expansion joint leaking from the inner bellows. The expansion joint according to claim 1.   The expansion joint according to claim 1 or 2, wherein one surface of the flange and an annular plate sandwich an end of the inner bellows.

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