JPH08152291A - Welding structure of tube to header and welding method - Google Patents

Abstract

PURPOSE: To improve the durability against fatigue or creep by interposing a tube of an austenite steel having a predetermined length between a steel tube and a header in a welding structure in which the tube of a ferrite steel is stood on the surface of the header of the ferrite steel and connected. CONSTITUTION: When a ferrite steel tube 2 is connected to a ferrite steel header 1, austenite steel tube 3 is interposed between both the tubes 1 and 2. The tube 3 is set to the length which can be extended to the position separated by 1/2 or more of the outer diameter of the tube from the welding stop end 13 of the tube 3 to the header 1. A route 6 of an annular protrusion partly cut at the tube welding position at the periphery of the position of the header 1 side of the connector of the tube 3 to the header 1, while the end of the tube 3 is formed with a route 6' collided with the route 6. Then, the routes 6 and 6' are butted to form a V-shaped groove 5, and which is welded by using an Ni-based alloy welding material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding structure and welding suitable for welding pipes and pipe heads of heat exchangers in boilers, nuclear power plants, chemical plants, etc. operated at high temperature and high pressure, or welding pipes and pipe sheets. Regarding the method.

[0002]

Boilers, nuclear power plants, and chemical plants are composed of many heat exchangers. In the heat exchanger, a pipe approach structure or a tube plate structure is adopted for distributing the internal fluid from the pipe to the pipe and joining the internal fluid to the internal fluid from the pipe to the pipe.

Ferrite steel having a small coefficient of linear expansion and a large coefficient of heat transfer is generally used for such a pipe head or a tube plate having a large wall thickness from the viewpoint of preventing thermal deformation and thermal stress. On the other hand, a ferritic steel pipe or an austenitic steel pipe is used for the thin-walled pipe depending on the use conditions. A general welded structure example of a ferritic steel pipe header and a ferritic steel pipe will be described. As shown in FIG. 4, the ferritic steel pipe header 1 is ground to form a concave welding groove 5, and the tip of the ferritic steel pipe 2 is directly brought into contact with the welding groove 5 to directly fillet weld both materials 1 and 2. To obtain the structure of FIG. On the other hand, in the case of an austenitic steel pipe, as shown in FIG. 6, a ferrite steel pipe 2 made of the same material as the header is welded to the tip of the austenitic steel pipe 3, and the ferrite steel pipe 2 and the ferrite steel header 1 are filleted. The structure of joining by welding is adopted. This is because when the weld between the pipe and the header is a dissimilar material weld of ferritic steel and austenitic steel,
This is because the following problems occur.

First of all, regarding the structural problem, the structure of the boiler header and heat transfer tube is shown as an example in FIG. The pipe header 9 becomes hot during boiler operation and expands in the longitudinal direction, but the heat transfer pipe 10 fixed to the pipe header 9 is constrained by the ceiling wall pipe 11 and receives a bending load in the direction indicated by the arrow in the figure. For this reason, the welded portion of the header 9 and the heat transfer tube 10 receives the maximum bending moment. Furthermore, in the case of the conventional structure,
Since fillet welding is performed, as shown in FIG.
The portion where the welding groove surface 5 and the tip end surface of the pipe 2 contact each other does not melt, and this unwelded portion 7 remains as a notch. In this way, the pipe header and the welded part of the pipe are the parts with the most severe stress conditions, and the dissimilar material welded structure in which a large thermal stress is generated due to the difference in the linear expansion coefficient of ferritic steel and austenitic steel I could not hire.

Next, regarding the problem of welding work, usually, for dissimilar material welding of ferritic steel and austenitic steel, a Ni-based Inconel welding material having a linear expansion coefficient intermediate between those materials is used. Inconel weld metal has a large surface tension in the molten state and has poor wettability to a narrow groove face. Therefore, in fillet welding with a narrow groove angle as shown in Fig. 5, many fusion defects and blow holes occur at the root part. To do. Furthermore, the unwelded portion 7 shown in FIG. 5 acts as a notch, and high-temperature welding hot cracking starting from the unwelded portion is frequently generated. For the reasons described above, ferritic steel has always been used as the pipe material for the portion directly welded to the ferritic steel header.

[0006]

However, with the recent increase in the size of boilers and the high temperature and high pressure of steam conditions, the stress conditions are becoming severer in the weld portion between the header and the pipe than ever before. In the past experience, it was 10 from the weld toe on the pipe side.
Damage due to high temperature fatigue or creep was concentrated in the range of mm, which sometimes led to cracks. In the future, if the steam temperature rises, the conventional welded structure using a ferritic steel pipe may become insufficient in strength.

It is an object of the present invention to provide a highly reliable pipe head and pipe welding structure and welding method, which have improved resistance to fatigue or creep.

[0008]

SUMMARY OF THE INVENTION In general, the present invention uses an austenitic steel pipe in the vicinity of a welded portion with a header and forms a weld groove by cutting the header side or a Ni-based alloy. The ring is inserted into the weld groove and butt-welded using a welding material of Ni-based alloy.

In order to achieve the above object, the welded structure of the pipe and the header of the present invention is a welded structure of the pipe and the header in which a ferritic steel pipe is erected on a plate surface of the ferrite steel header and connected. An austenitic steel pipe is interposed between the steel pipe and the header, and the austenitic steel pipe is separated from the weld toe of the pipe and the ferrite steel header by at least ½ of the pipe outer diameter. The ferritic steel header and austenitic steel pipe joints are machined around the pipe weld side on the plate side of the header to form an annular protrusion. In addition, the tip of the austenitic steel pipe is processed to form a groove including a protrusion facing the protrusion of the header, and these protrusions are butted to form a butt groove. It is formed by welding.

The butt groove has a trapezoidal shape in which the cross section expands outward, and both of the projections forming the bottom of the trapezoid are used as the welding roots, and the root side of the austenitic steel pipe side is the ferritic steel side. It is preferable to make it longer than the root part of the. Alternatively, a ring made of austenitic steel or Ni-based material having a Ni content higher than that of an austenitic steel tube may be inserted between both protrusions and welded.

In order to achieve the above object, the welding method of the pipe and the header of the present invention uses a welding material made of a Ni-based alloy for the header of the ferritic steel and the pipe of the austenitic steel in the above welded structure. It is characterized by welding.

[0012]

[Operation] Since the weld toes of pipes and pipe headers are made of austenitic steel, which has better high-temperature strength than ferritic steel, is used at the weld toe where the stress conditions are the most severe, damage due to fatigue and creep can be reduced. . Then, the austenitic steel pipe is extended from the weld toe portion by 1/2 or more of the pipe outer diameter to cover a severe range of stress conditions.
Further, since the butt welding is performed, the groove angle can be widened as compared with the case of the fillet, and the welding can be performed without causing a welding defect even in the welding work using the Ni-based welding material such as Inconel system.

[0013]

EXAMPLE An example of the present invention will be specifically described below. Figure 1 shows ferritic steel pipe 2
2 is a sectional view of a welded structure in the case of joining via an austenitic steel pipe 3. FIG. An austenitic steel pipe 3 excellent in high-temperature strength is butt-welded to the tip of the ferritic steel pipe 2 using an Inconel welding material. A welding groove 5'for butt welding is machined on the other end of the austenitic steel pipe 3, but the groove angle α is as large as possible,
5 ° or more. On the other hand, on the outer surface of the pipe welding position of the ferritic steel pipe header 1, a concave welding groove 5 is processed by grinding,
A convex root portion 6 is provided in the center so as to match the root portion 6 ′ of the austenitic steel pipe 3. At this time, the width (w ₃ ) of the route portion 6 ′ is preferably wider than that (w ₁ ) of the route 6, preferably about 3 times the width of the route 6 (w ₃ ≈).
w ₁ ) to be processed. A Ni-based welding material such as an Inconel welding material is used as the welding material. Weld so as to melt the root portions 6 and 6'in the first layer. Further, the weld metal is laminated so as to fill the inside of the groove to obtain a completely melted welded structure shown in FIG. By the way, the length of the austenitic steel pipe 3 is from the end 14 (welding toe) of the Inconel weld metal 4 between the ferrite steel pipe 2 and the ferrite steel pipe 1
It is preset so that the distance to the end 13 (welding toe) of the weld metal 4 ′ between and is at least ½ of the pipe outer diameter.

In the case of the present embodiment, first, in terms of welding work, the groove angle is made large and the root portion on the side of the austenitic steel pipe 3 is also made wide so that the welding torch is easy to enter and despite the welding of a narrow portion. Can be constructed relatively easily. Further, the root portion 6 ′ on the austenitic steel pipe 3 side is preferentially melted, and it is also effective in preventing the strength from being reduced due to the dilution of the Ni component in the weld metal, which tends to cause a problem particularly in the first layer. Next, also in terms of the shape, the completely welded portion does not have the unwelded portion 7 as shown in FIG. 5, and the reliability of the dissimilar material weld portion where thermal stress is likely to occur is greatly improved. Since the austenitic steel with excellent high-temperature strength is present in the vicinity of the weld toe of the pipe where stress is the most severe, such as bending, the yield strength is of course improved compared to conventional ferritic steel.

In this embodiment, the case where the pipe side is the ferritic steel pipe has been described. However, even when the pipe side is originally the austenitic steel pipe, the groove shape shown in FIG. If another single austenitic steel pipe having a high temperature is welded to the ferritic steel header, and the austenitic steel pipe is welded through this, a welded structure with even better strength can be obtained.

Another embodiment according to the present invention is shown in FIG. The present embodiment has a groove shape similar to that of FIG. 1 and aims for the same effect, but the root portion 6'on the austenitic steel pipe side is provided.
Ring 8 of austenitic steel or Ni-based material having a high Ni content between the root part 6 on the side closer to the ferritic steel pipe
And the ring 8 is welded so as to melt. After that, welding is carried out by laminating the weld metal so as to fill the inside of the groove. In the present embodiment, the amount of Ni in the weld metal can be increased by the Ni contained in the ring 8 and the high temperature strength of the weld metal can be further improved, as compared with the case of the weld structure shown in FIG.

Although the embodiment of the butt welding structure according to the present invention has been described above with reference to FIGS. 1 to 3, even in the case of the fillet welding shown in FIG. It can also be installed by inserting a ring of austenitic steel or Ni-based material with a high content and welding the Ni-based welding material such as Inconel-based welding material so that the root part and the ring are melted in the first layer. is there. In this case, although the unwelded portion remains, there is an advantage that the same groove structure as the conventional structure can be adopted.

[0018]

According to the present invention, since the austenitic steel having excellent high temperature strength is used for the welded portion of the pipe under severe stress conditions and the welded portion of the pipe, the damage of the welded portion due to fatigue and creep can be reduced. In addition, since the welded portion uses a butt groove that allows a large groove angle, welding is facilitated and problems in welding work do not occur, and the performance and reliability of equipment such as a heat exchanger having the welded structure of the present invention are improved. It has a great effect on improving the sex.

[Brief description of drawings]

FIG. 1 is a sectional view showing a welded structure of a header and a pipe according to the present invention.

FIG. 2 is a cross-sectional view showing a welded portion between a ferritic steel pipe header and an austenitic steel pipe in a welded structure according to the present invention.

FIG. 3 is a sectional view showing another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a conventional pipe header and pipe welding structure.

FIG. 5 is a cross-sectional view showing fillet welding for joining a header and a pipe with a conventional welding structure.

FIG. 6 is a cross-sectional view showing a conventional welded structure of a header and a pipe.

FIG. 7 is a diagram showing an example of the structure of a tube drawer and a heat transfer tube.

[Explanation of symbols]

 1 Ferrite Steel Pipe Head 2 Ferrite Steel Pipe 3 Austenite Steel Pipe 4 Inconel Weld Metal 5 Weld Groove 6,6 'Root 8 Ring 9 Pipe Head 13,14 Weld Toe

Claims (5)

[Claims] 1. A welded structure of a pipe and a pipe in which a ferritic steel pipe is erected on a plate surface of a ferritic steel pipe header and connected thereto, and an austenitic steel pipe is interposed between the steel pipe and the pipe header. The austenitic steel pipe has a half of the pipe outer diameter from the weld toe of this pipe and the ferritic steel header.
A welded structure of a pipe and a pipe head, which is characterized in that it is extended to a position separated from the above. 2. The ferritic steel pipe header plate surface is machined around the position of the welded portion of the pipe to form an annular protrusion, while the austenitic steel pipe is processed by processing the tip end of the pipe. 2. The pipe according to claim 1, wherein a groove including a protrusion facing the protrusion is formed, the protrusions are butted to form a butt groove, and the butt groove is welded. Welded structure. 3. The butt groove has a trapezoidal shape with an outwardly expanding cross section, the protrusion forming the base of the trapezoid is used as a welding root, and the pipe-side root of the austenitic steel is used as the ferritic steel. 3. The welded structure according to claim 2, wherein the welded structure is made longer than the root portion on the pipe drawing side. 4. The welded structure according to claim 2, wherein a ring made of an austenitic steel having a Ni content higher than that of the austenitic steel or a Ni-based material is inserted between the both protrusions. 5. The welded structure of the ferritic steel and the austenitic steel in the welded structure according to claim 1, wherein the welded material is made of a Ni-based alloy. Welding method for pipe and header.