JP3466341B2 - How to assemble a heat exchanger - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for assembling a heat exchanger such as a superheater or a reheater used in a boiler or the like. . FIG. 10 is a schematic view showing an upper portion of a boiler. As shown in the figure, the secondary superheater 54, the third superheater 55, the fourth superheater 2, the rear water wall 56,
A group of heat exchangers such as a secondary reheater 3, a primary reheater 57, a primary reheater 58, and a economizer 59 are provided, and each heat exchanger has an inlet pipe of the quaternary superheater 2. Drawer 4, outlet drawer 5, upper drawer 6 of rear water wall 56, inlet drawer 7 of secondary reheater 3, outlet drawer 8, outlet drawer 9 above primary reheater 57, primary Outlet header 10 above the superheater 58, economizer 59
An upper outlet header 11 and the like are provided above the ceiling pipe 1. FIG. 11 is a typical view of a conventional heat exchanger which is a part of the boiler shown in FIG.
Is shown. As shown in the figure, an inlet header 7 made of a ferritic steel (which may have a martensitic structure but is hereinafter collectively referred to as a ferritic steel), for example, a fire STBA 28
A plurality of stubs 12 made of ferritic steel are attached to the main body 7a of the main body 7a, and constitute the inlet header 7. Further, the main body 8a of the outlet header 8 made of a ferritic steel pipe.
A plurality of stubs 13 made of a ferritic steel pipe are attached to the outlet pipe header 8. Next, an inlet sleeve 14 made of a ferritic steel pipe is attached to the stub 12 by welding at 21.
An outlet sleeve 15 made of a ferritic steel pipe is attached by welding at 22, and an end piece 16 of the inlet sleeve 14 opposite to the stub 12 is a joint piece 18 made of austenitic stainless steel pipe having a length of about 50 mm. Are attached by welding, and the stub 1
A joint piece 19 made of an austenitic stainless steel pipe and having a length of about 50 mm is attached to the end 17 opposite to 3 by welding, and both ends of a coil 20 made of an austenitic stainless steel pipe are connected to the joint piece 18.
A coil portion is formed by welding at an inlet 19, an inlet sleeve 14, an outlet sleeve 15, joint pieces 18 and 19, and a coil 20. The welding point of the inlet sleeve 14, the outlet sleeve 15, and the joint pieces 18, 19, that is, the material conversion point 1
6 and 17 are located above the ceiling tube 1. FIG. 12 shows another example of the conventional heat exchanger shown in FIG. As shown in the figure, a plurality of stubs 23 made of ferritic steel pipe are attached to the main body 4a of the inlet header 4 made of ferritic steel, and the inlet header 4 is constituted. Also, a plurality of stubs 24 made of ferritic steel pipe are attached to the main body 5a of the outlet header 5 made of ferritic steel, and the outlet header 5 is constituted. Next, an inlet sleeve 25 made of ferritic steel pipe is attached to a part of the stub 23 by welding at 70, and a coil 27 made of ferritic steel pipe is attached to another part of the stub 23 by welding. An outlet sleeve 26 made of a ferritic steel pipe is attached to the stub 24 by welding at 71, and the end 2 of the inlet sleeve 25 on the opposite side to the stub 23.
8, a joint piece 31 made of an austenitic stainless steel pipe is attached by welding, a joint piece 32 made of an austenitic stainless steel pipe is attached to an end 29 of the coil 27 by welding, and an outlet sleeve 26 is provided.
A joint piece 33 made of an austenitic stainless steel pipe is attached to an end 30 of the coil by welding, and both ends of a coil 34 made of austenitic stainless steel pipe are attached to the joint pieces 31 to 33 by welding, an inlet sleeve 25 and an outlet sleeve. Part 26, coil 27, coil 34,
A coil portion is formed by the joint pieces 31 to 33. The welding points between the inlet sleeve 25 and the outlet sleeve 26 and the joint pieces 31 and 33, that is, the material conversion points 28 and 30 are located above the ceiling pipe 1, and the welding points between the coil 27 and the joint pieces 32 and the material The transition point 29 is located below the ceiling tube 1. In these heat exchangers, the coils 2
Austenitic stainless steel pipes are used because steam flows through the steel pipes constituting the pipes 0 and 34 at a temperature of usually 500 ° C. or more and 50 atm or more. However, if stainless steel is used for the headers 4 to 7, the difference in thermal expansion from the boiler body becomes large, and various problems are expected to occur.
7 are used, followed by stubs 12, 13, 2
3, 24, inlet sleeves 14, 25, outlet sleeves 15, 26,
A ferrite-based steel pipe is also used for the coil 27. Therefore, material conversion points 16, 17, 28, 29, and 30 occur between the ferritic steel pipe and the austenitic stainless steel pipe. The material conversion points 16, 17, 28, 29, 30
In ferrite-based steels and austenitic stainless steels, since they are dissimilar metals and have different physical properties, high-temperature cracking that occurs when welding with ordinary stainless steel or low-alloy steel and the difference in Cr concentration in the material In order to prevent carbon migration at the time, welding is performed with a Ni alloy having intermediate properties. However, in the welding with this Ni alloy, the range of welding conditions is very narrow, and if the Ni concentration in the deposited metal is not less than 39% and the Fe concentration is not more than 44%, the system becomes unstable structurally. Hot cracking occurs at the center of the weld bead. For this reason, the joint pieces 18, 19,
The length of the root face of 31, 32, 33 is increased, the amount of deposited metal is increased by the hot wire method, the amount of Ni is increased, or a ring-shaped Ni alloy is sandwiched between two kinds of metals in advance to form the first layer. Methods such as welding are employed. In any of the methods, the welding condition range is further narrowed in welding with the workpiece fixed (all positions welding), and therefore, in the case of automatic welding, the welding is usually performed by rotating the workpiece downward. The above-mentioned joint pieces 18, 19, 31, 3
In the case where the dissimilar metals 2 and 33 are welded to each other, the sleeve portion 14,
15, 25, 26, and the maximum hardness of the heat-affected zone of the coil 27 increases. In particular, in ferritic steels with a Cr content of 2.25% or more, the temperature increases to about Hv400. In particular, among ferritic steels, such as STBA28, which exhibits a tempered martensite structure, is unstable when welding is performed, and the creep strength of the heat-affected zone decreases. For this reason, the joint pieces 18, 19, 31, 32, 33 are
5, 25, 26, 700 after welding to coil 27
It is necessary to perform heat treatment at 760 ° C. [0007] Austenitic stainless steel has a feature that stress corrosion cracking (SCC cracking) occurs. For this reason, it is necessary to remove the residual stress after welding or bending, and a solution treatment of rapidly cooling after heating to 1050 to 1150 ° C. is performed. This solution treatment also has the purpose of returning the slip line of stress-induced martensite generated by bending stress in the austenite structure to a normal austenite structure. Such a solution treatment is generally performed as a local heat treatment of a bent portion, but may be performed on the entire coils 20 and 34 including a welded portion as necessary. In this case, it is necessary to design the components so that the structure of the weld metal becomes 100% austenite when butt welding of the pipe or welding of parts to the pipe is performed.
In this case, if ferrite is generated even if it is several%, sigma phase embrittlement occurs by solution treatment. Therefore, when a weld metal having good weldability and containing about 4% ferrite is selected, the solution treatment of the welded portion cannot be performed. Further, when the entire coils 20 and 34 are solution-treated, deformation (distortion) occurs in the coils due to overheating and cooling, so that a modification (distortion) correction operation is required. FIGS. 13 to 16 show SUS3.
04H, Tu SUS321J1H, SUS321H, Tu S
A graph showing the relationship between the heat treatment time of US304J1H, the superheat temperature (° C.), and the grain boundary erosion rate (TTS (Time Tempera
ture Sensitization diagram). Here, white circles, asterisks, black triangles, and black circles have grain boundary erosion rates (unit: mm / day) of less than 0.01, 0.01 to less than 0.1, 0.1 to less than 0.5, respectively. It is 0.5 or more. As is apparent from these graphs, the heat treatment at 700 to 760 ° C. for a short period of time increases the grain boundary erosion rate, and the austenitic stainless steel is slightly sensitized, and stress corrosion cracking is likely to occur. You can see that. The sensitization that causes stress corrosion cracking of austenitic stainless steel is generally performed according to JISG.
Confirmed by Strauss test shown in 0575. The welding of the joint pieces 18, 19, 31, 32 without welding the coils 20, 34 directly to the sleeves 14, 15, 25, 26, and the coil 27 is the difference in allowable stress. Sleeves 14, 15, 25, 26, coil 2
7 and the coils 20, 34 are absorbed by the joint pieces to reduce the degree of sensitization and the sensitized area by heat treatment, and to the material conversion points 16, 1 for welding dissimilar metals.
This is because welding at 7, 28, 29, and 30 is performed downward before welding with the coils 20 and 34, and after welding, the inside of the first layer is checked. [0010] From the above, the conventional heat exchanger, for example, 2
The method of assembling the secondary reheater 3 is performed as shown in FIG. First, as for the header body 7a, 8a, a hole such as a stub hole is punched, and the circumference of the header body is welded to each other or to the closing plate to manufacture the header body 7a, 8a. The stubs 12, 13 are manufactured by bending a ferritic steel pipe. Next, the stubs 12, 13 are attached to the header body 7a, 8a.
Is welded and then subjected to a post-heat treatment to produce headers 7 and 8. For the coil 20, the austenitic stainless steel pipe is first bent, and the bent portion is subjected to a solution treatment. Next, butt welding of the austenitic stainless steel pipes is performed, parts are assembled, and parts are welded to produce the coil 20. As for the sleeves 61 and 62, the joint pieces 18 and 19 are welded to the ends of the inlet sleeve 14 and the outlet sleeve 15, which are ferritic steel pipes, respectively, and the parts are bent and assembled. After that, heat treatment is performed at 740 ° C. for one hour to produce the sleeves 61 and 62. Next, the sleeves 61 and 62 and the coil 20 are assembled, butt welding is performed, component assembly and component welding are performed, and a coil portion is manufactured. The headers 4 and 5 and the coil part respectively manufactured in the above-described process are assembled on site, and the stub 1 is attached to the welding lines (final welding lines) 21 and 22 after installation.
After welding the second and the 13th and the sleeves 61 and 62 with an inert gas such as an Ar gas while performing back shield and preheating, heat treatment is performed at 740 ° C. for 1 hour. As shown in FIG. 18, the coil 20 is formed by bending an austenitic stainless steel pipe, butting and welding the austenitic stainless steel pipes to each other, and assembling parts before performing a solution treatment. A method of manufacturing the coil 20 by performing a solution treatment locally on a bent portion after performing component welding and correcting a distortion as necessary. Also, sleeve 6
In the manufacture of 1, 62, the heat treatment may be omitted and not performed. In a conventional heat exchanger and a method for assembling the same, a coil portion 20 made of an austenitic stainless steel tube, a sleeve portion 61 made of ferritic steel tubes 14 and 15 and joint pieces 18 and 19 are provided. , 62 must be manufactured separately, the coil 20 and the sleeves 61, 62 need to be assembled and butt-welded, so that the manufacturing is complicated and the construction period is long. The stubs 12, 13 made of ferritic steel pipe and the sleeves 61, 62 are finally welded. This welding requires preheating to prevent low-temperature cracking. Become. In particular, when the stubs 12 and 13, the inlet sleeve 14 and the outlet sleeve 15 are steel pipes having a martensitic structure such as fire STBA 28, the final welding line 21 of the stubs 12 and 13, the inlet sleeve 14 and the outlet sleeve 15 is particularly suitable. , 22 increase the maximum hardness and extremely reduce the toughness of the weld metal, so that post-heat treatment is required in addition to preheating. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide a method of assembling a heat exchanger which is easy to manufacture and whose construction period is not long. [0014] [Means for Solving the Problems] To achieve this object, the present invention, in the method of assembling a heat exchanger having a tube pulling the coil unit, the ferrite to the pipe pulling consisting ferritic steels Weld stubs made of base steel,
After attached by welding joint piece made of austenitic stainless steel to the end of the stub, the tube nearest
And post heat treatment on the stub and the splice piece.
Further, the end of the coil portion made of austenitic stainless steel is welded to the joint piece. FIG. 1 shows a set of heat exchangers according to the present invention.
It is a figure which shows the heat exchanger assembled by the standing method .
As shown in the figure, the ends of the plurality of stubs 12 and 13 are made of austenitic stainless steel and have a length of about 50 mm.
Are welded, and both ends of a coil 45 made of austenitic stainless steel such as SUS321J1H are welded to the joint pieces 43, 44, and the bent portion of the coil 45 has a bending radius of at least twice the pipe outer diameter. The coil 45 constitutes a coil portion. The welding points between the stubs 12 and 13 and the joint pieces 43 and 44, that is, the material conversion points 41 and 42 are located above the ceiling pipe 1. The method of assembling the heat exchanger shown in FIG. 1, that is, the method of assembling the heat exchanger according to the present invention will be described with reference to FIG. First, as for the header body 7a, 8a, a hole such as a stub hole is punched, and the circumference of the header body is welded to each other or to the closing plate to manufacture the header body 7a, 8a. The stubs 12 and 13 are welded with joint pieces 43 and 44 at the ends of the ferritic steel pipe, and those having a bent portion are subjected to a bending process.
Produce 4. Next, stubs 23 and 24 are attached to the header body 7a and 8a by welding.
After the time, heat treatment is performed. Next, after bending the austenitic stainless steel pipe for the coil 45 having a bent portion, butt welding is performed.
The coil 45 is manufactured by performing component assembly and component welding. Further, the headers 7 and 8 and the coil 45 are assembled on site, a back shield is implemented, and the welding wire 4 is installed after installation.
At steps 6 and 47, the joint pieces 43 and 44 and the coil 45 are butt-welded. In the method of assembling the heat exchanger in the present embodiment, the coil and the sleeve as in the conventional example are separately manufactured,
Since there is no need to assemble the coil and the sleeve and perform butt welding, the production is easy and the construction period is not long. Further, since the joint pieces 43 and 44 made of austenitic stainless steel and the coil 45 made of the same material are finally welded, preheating and post heat treatment are not required in the final welding, and there is no need to perform heating and temperature control by a burner. Finally, the final welding performed on site is very easy, and the construction period is not long. After the joint pieces 43 and 44 are attached to the stubs 12 and 13, post-heat treatment is performed. However, by increasing the heat treatment time to 3 hours, the degree of sensitization is reduced.
Stress corrosion cracking does not occur in the joint pieces 43 and 44. Further, since heat treatment for reducing the hardness of the ferritic steel is not performed after the bending of the coil 45, sensitization does not occur and stress corrosion cracking does not occur, so that stress corrosion cracking of the bent portion of the coil 45 is prevented. Therefore, it is not necessary to perform a solution treatment for performing the heat treatment, the production of the coil 45 is easy, and the construction period is not long. FIGS. 3 to 5 show SUS321H and Tuesday S.
US304J1H, SUS321J1H with 10% reduction in wall thickness
3 is a graph showing the creep rupture strength when the processing of No. was added. The sample shown in FIG. 7 is obtained by subjecting the sample shown in FIG. 6 to a process of reducing the wall thickness by 10% using a tensile tester and then performing a cutting process to obtain a smooth surface. Here, the case where the sample shown in FIG. 7 is heated to 650 ° C. is represented by a white circle, the case where the sample shown in FIG. 7 is heated to 700 ° C. is represented by a white triangle, and the sample shown in FIG. 7 is heated to 750 ° C. If done, it will be a white square. The sample shown in FIG. 8 is obtained by subjecting the sample shown in FIG. 6 to a process of reducing the wall thickness by 10% using a tensile tester, and then performing a cutting process to provide a notched portion. Here, the case where the sample shown in FIG. 8 is heated to 650 ° C. is defined as a black circle, and the case where the sample illustrated in FIG. 8 is heated to 750 ° C. is defined as a black square. The solid line shows the average creep rupture strength of the unprocessed sample. As is clear from these graphs, the creep rupture strength when a process with a working ratio (thinning ratio) of 10% is added is equal to or greater than the average creep rupture strength of the unprocessed sample. Here, when the steel pipe is bent at a bending radius twice as large as the pipe outer diameter (2DR), the working ratio becomes 10%. Therefore, in the embodiment of the present invention, when the austenitic stainless steel pipe is bent with a bending radius of at least twice the outer diameter of the pipe, the pipe has a sufficient creep rupture strength and is generated by bending stress in the austenitic structure. No solution treatment is required to return the stress-induced martensite slip line to a normal austenitic structure. For example, if the coil 45 is SUS347 system, SUS321 system, fire SUS
When it is made of 321J1 or SUS304J1 austenitic stainless steel, it is possible to reliably prevent the creep strength of the coil 45 from lowering without performing the solution treatment. FIG. 9 is a diagram showing another embodiment according to the present invention. This embodiment is an example in which the present invention is applied to the conventional example shown in FIG. As shown in the drawing, joint pieces 50 and 51 made of austenitic stainless steel and having a length of about 50 mm are welded to the ends of the plurality of stubs 23 and 24, and a coil 52 made of austenitic stainless steel is provided.
Are welded to the joint pieces 50 and 51, and the coil 5
The bent portion of No. 2 is manufactured by bending with a bending radius of twice or more the outer diameter of the tube, and a coil portion is constituted by the coil 52.
The welding points between the stubs 23, 24 and the joint pieces 50, 51, ie, the material conversion points 48, 49, are located above the ceiling pipe 1. In this embodiment, the same effects as in the above embodiment can be obtained. Here, in the conventional heat exchanger shown in FIG. 12, the coil portion is constituted by an inlet sleeve portion 25, an outlet sleeve portion 26, a coil 27 made of ferritic steel and a coil 34 made of austenitic stainless steel. On the other hand, in the heat exchanger shown in FIG. 9, the entire coil portion is made of a coil 5 made of austenitic stainless steel.
Since the price per unit weight of the austenitic stainless steel is higher than the price per unit weight of the ferritic steel, the material cost may increase. However, in the heat exchanger shown in FIG. 9, when the coil 52 is made of fire SUS321J1H,
In the case of the reheater, the thickness of the coil 52 is reduced to 4 mm or less, and the allowable stress of the fire SUS321J1H at 600 ° C. is 1.2 times or more the allowable stress of the SUS347H. The increase in the material cost compared to the container is small, and the merit of the reduction in the production cost due to the ease of production is greater than the increase in the material cost. When the coil 52 is made of fire SUS304J1H, the allowable stress of the fire SUS304J1H at 600 ° C. is about 1.4 times the allowable stress of SUS347H. Therefore, the thickness of the coil 52 can be considerably reduced. The increase in material costs as compared to the heat exchangers shown in the above is almost negligible. As described above, the heat exchange according to the present invention
In the method of assembling the heat exchanger, there is no need to separately manufacture the coil and the sleeve, assemble the coil and the sleeve, and perform butt welding. In addition, since the joint piece made of austenitic stainless steel and the coil made of the same material are finally welded, preheating,
No post heat treatment is required, making the final welding very easy.
Further, since it is not necessary to perform heat treatment to reduce the hardness of the ferritic steel after bending the coil, no sensitization occurs and no stress corrosion cracking occurs, so the stress at the bent portion of the coil is reduced. There is no need to perform a solution treatment for preventing corrosion cracking. Thus, the coil can be easily manufactured, and the construction period does not become long. [0029]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is assembled by a method for assembling a heat exchanger according to the present invention.
It is a figure which shows the heat exchanger taken. FIG. 2 is an explanatory view of a method of assembling a heat exchanger according to the present invention. FIG. 3 is a graph showing the creep rupture strength of stainless steel. FIG. 4 is a graph showing the creep rupture strength of stainless steel. FIG. 5 is a graph showing the creep rupture strength of stainless steel. FIG. 6 is a diagram illustrating a sample used to create the graphs shown in FIGS. 3 to 5; FIG. 7 is a diagram showing a sample used for creating the graphs shown in FIGS. 3 to 5; FIG. 8 is a diagram showing a sample used for creating the graphs shown in FIGS. 3 to 5; FIG. 9 is assembled by a method of assembling a heat exchanger according to the present invention.
It is a figure which shows the other heat exchanger assigned . FIG. 10 is a schematic view showing an upper portion of a boiler. FIG. 11 is a view showing a conventional heat exchanger. FIG. 12 is a view showing another conventional heat exchanger. FIG. 13 is a graph showing the relationship between the heat treatment time, the superheating temperature, and the grain boundary erosion rate of stainless steel. FIG. 14 is a graph showing the relationship between the heat treatment time, the superheating temperature, and the grain boundary erosion rate of stainless steel. FIG. 15 is a graph showing the relationship between the heat treatment time, the superheating temperature, and the grain boundary erosion rate of stainless steel. FIG. 16 is a graph showing the relationship between the heat treatment time, the superheating temperature, and the grain boundary erosion rate of stainless steel. FIG. 17 is an explanatory diagram of a conventional heat exchanger assembling method. FIG. 18 is an explanatory view of another conventional heat exchanger assembling method. [Description of Signs] 4 ... Inlet header 5 ... Outlet header 7 ... Inlet header 8 ... Outlet header 12 ... Stub 13 ... Stub 23 ... Stub 24 ... Stub 43 ... Piece piece 44 ... Piece piece 50 ... Piece piece 51 ... Joint piece 45 ... Coil 52 ... Coil

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F28F 1/00 F28F 9/26 F28F 21/08 F22G 3/00 F22B 37/22

Claims (1)

(57) [Claim 1] In a method for assembling a heat exchanger having a header and a coil part, the method comprises assembling a ferrite-based steel header .
A stub made of ferritic steel is welded, and a joining piece made of austenitic stainless steel is attached to an end of the stub by welding .
Post heat treatment of the tab and the joint piece
Method of assembling a heat exchanger, characterized in that welding the ends of the coil portion made of austenitic stainless steel該継technique piece.