JPH07214373A - Welding structure of steel tube plate and steel tube and welding structure of steel tube drawback and steel tube - Google Patents

Abstract

PURPOSE:To provide a welding structure capable of easily welding without generating welding faults such as welding cracking or defective fusion. CONSTITUTION:A ferrite steel tube 3 is welded onto an end of an austenite steel tube 2, the ferrite steel tube 3 is inserted at first onto a groove part of a ferrite tube plate 1 at first, between the ferrite steel tube 3 and the ferrite steel tube plate 1 is welded with ferrite base metal 5, and between the austenite steel tube 2 and the ferrite steel tube plate 1 is welded with Inconel base metal 6.

Description

Detailed Description of the Invention

[0001]

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

[0002]

Boilers, nuclear power plants, and chemical plants are composed of many heat exchangers. In the heat exchanger,
The fluid sent by the pipe is distributed to the pipe, heat exchange is performed between the fluid inside the pipe and the fluid outside the pipe, and the heat-exchanged fluid inside the pipe is merged again and sent to the next process by the pipe. A pipe plate structure or a pipe-side structure is adopted for the distribution of the internal fluid from the pipe to the pipe and the internal fluid from the pipe to the pipe.

In such a tube sheet or tube-sided structure, the distribution of the fluid to the tube is not uniform, so the metal temperature of the tube is also non-uniform. Thus, in the tube, the design temperature is higher than that of the tube sheet or the tube side because the imbalance of the metal temperature is taken into consideration. The material selection and dimensions of the tube sheet and the tube and the tube side and the tube are determined in consideration of such design conditions.

By the way, comparing ferritic steel and austenitic steel, the high temperature strength of austenitic steel is higher, but because of its large linear expansion coefficient and small heat transfer coefficient and its high cost, it has a high thickness. Generally, ferritic steel is used as the material and austenitic steel is used as the thin-walled tube.

[0005]

However, when the ferritic steel pipe sheet and the austenitic steel pipe are directly welded, there are problems described later. Therefore, as shown in FIG. 2, the ferritic steel pipe 3 is welded to the austenitic steel pipe 2 and the ferritic steel pipe is welded. 3 and the ferritic steel tube sheet 1 are welded together. It should be noted that FIG. 4 shows an Inconel weld metal and 5 a ferrite weld metal.

In the present welded structure, when the internal fluid temperature rises, the design temperature of the tube becomes higher than that of the tube sheet, so that the wall thickness of the tube increases and it becomes difficult to manufacture the tube. Further, when the design temperature of the pipe rises and exceeds the upper limit temperature of use of the ferritic steel, the welding structure shown in FIG. 2 can no longer be adopted.

Under these conditions, the austenitic steel pipe is welded directly to the ferritic steel pipe sheet.

FIG. 3 shows a structure in which an austenitic steel pipe 2 is directly welded to a ferritic steel pipe sheet 1 via an Inconel weld metal 6, but this welding structure has the following problems.

In the dissimilar material welding of ferritic steel and austenitic steel, Ni-based Inconel welding material having a linear expansion coefficient intermediate between the two and having a small tendency to form carbides is used. Inconel welding material 6 is also used in the welding structure shown in FIG. 3, but the surface tension of Inconel weld metal is large and the leak property to a narrow groove face is poor. For this reason,
Frequent fusion defects occur at the welding root. Also,
Since the end portion of the pipe and the groove surface of the tube sheet remain unwelded, this unwelded portion acts as a notch, and high-temperature cracking frequently starts from the unwelded portion.

The above-mentioned problems are greatly affected by the shape of the groove where the unwelded portion remains, so that the structure of FIG. 4 which is a butt welding structure is conceivable. In the welded structure shown in the figure, no unwelded portion remains and the groove width is comparatively wide, so no fusion failure or hot cracking occurred. However, since the heat capacities on the tube side and the tube sheet side are significantly different, the back waves were non-uniform. In addition, the welding of the unevenness of the first layer requires that the welding torch be tilted greatly, and welding work became impossible when the pipe pitch became small.

It is an object of the present invention to provide a welded structure which can be simply and easily applied in the welding of a ferritic steel pipe sheet or pipe and an austenitic steel pipe without causing welding defects such as welding cracks and fusion defects. is there.

[0012]

[Means for Solving the Problems] The above-mentioned object is to provide a weld root portion having a narrow groove and an unwelded portion with a welding material of the same composition as ferritic steel so that it can be welded to one side of an austenitic steel pipe. This is achieved by making the ferritic steel pipe into a welded pipe.

[0013]

Function: That is, since the portion corresponding to the welding root portion is the welding of the ferritic steel pipe and the ferritic steel tube sheet, there is no problem as a ferritic steel welding material of the same composition system, and the surface tension of the welding metal is small. Since the high temperature cracking susceptibility is also low, fusion failure and high temperature cracking do not occur. Welding after the height of the ferritic steel pipe is welding of austenitic steel pipe and ferritic steel pipe sheet, so it is an Inconel type welding material, but the groove width is relatively wide and there are no unwelded parts at all Can be obtained.

[0014]

EXAMPLE An example of the present invention will be specifically described below.

FIG. 1 is a sectional view of a welding structure according to an embodiment of the present invention. In the figure, 1 is a ferrite-based SCMV4 (2.25Cr-1Mo) whose chemical composition is shown in FIG.
Steel) Steel tube sheet, 2 is austenitic SUS321HT
B steel pipe. 3 is STBA24 of the same composition system as SCMV
As the steel pipes, the SUS321HTB steel pipe 2 and the STBA24 steel pipe 3 were previously dissimilarly welded with the Inconel-based TIG welding material 4 shown in the fourth stage of FIG. After the pipes 2 and 3 were welded to each other by dissimilar materials, the STBA24 steel pipe 3 was cut into a length equivalent to the groove depth of the tube sheet 1 and set in the welding groove processed into the SCMV4 steel tube sheet 1 to perform temporary welding.

From the first layer, at the height of the STBA24 steel pipe 3, after welding using the 2.25Cr-2Mo system (ferrite system) welding material 5 shown in FIG. 5, the subsequent steps are shown in the fifth stage of FIG. Inconel Welding Material 6 was used to weld the closure to a shape that provided a low throat thickness.

After welding, a cross-section structure inspection and a side bending test were carried out, and it was confirmed that no defect or crack occurred and a sound welded portion was obtained.

If the length of the ferritic steel pipe 3 is set to 0.5 times or less than the groove depth, the groove portion at the time of starting welding with the Inconel welding material 6 is narrow, and fusion failure may occur. It was Further, if the length of the ferritic steel pipe 3 is set to be 1.5 times or more the groove depth, the number of layers for welding up to the height of the ferritic steel pipe 3 or more increases and the welding man-hour increases. Therefore, the length of the ferritic steel pipe 3 welded to the austenitic steel pipe 2 is preferably in the range of 0.5 to 1.5 times the groove depth.

In the welded structure of the present invention, since the ferritic steel pipe 3 is completely reinforced by welding, it is not necessary to make it thicker than the austenitic steel pipe as shown in FIG. Things are enough.

[0020]

As described above, according to the present invention, the welding of the ferritic steel pipe sheet or the pipe side and the austenitic steel pipe is carried out by the welding workability equivalent to that of the ferritic alloy welding by solving the problems of the prior art. It is possible, and it is possible to improve the reliability of the plant operated at high temperature and high pressure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a welded structure of a ferritic steel pipe sheet and an austenitic steel pipe according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a welded structure of a conventional ferrite steel tube sheet and a ferrite steel tube.

FIG. 3 is a sectional view showing a welded structure of a conventional ferritic steel tube sheet and an austenitic steel tube.

FIG. 4 is a sectional view showing a welded structure of a conventional ferritic steel tube sheet and an austenitic steel tube.

FIG. 5 is a diagram showing chemical compositions of various materials used in Examples of the present invention.

[Explanation of symbols]

 1 Ferrite Steel Tube Sheet 2 Austenitic Steel Tube 3 Ferrite Steel Tube 4 Inconel Weld Metal 5 Ferrite Weld Metal 6 Inconel Weld Metal

Front Page Continuation (72) Inventor Kazutaka Susaki 3 36 Takara-cho, Kure City, Hiroshima Prefecture Bab Kotsk Hitachi Kure Research Institute

Claims (8)

[Claims] 1. A ferritic steel pipe is welded to one end of an austenitic steel pipe, the ferritic steel pipe side is first inserted into a groove formed in the ferritic steel pipe sheet, and a ferritic metal is welded between the ferritic steel pipe and the ferritic steel pipe sheet. A welded structure of a steel tube sheet and a steel tube, wherein the austenitic steel tube and the ferritic steel tube sheet are welded with an Inconel metal. 2. The steel pipe sheet and pipe according to claim 1, wherein the length of the ferritic steel pipe is regulated within a range of 0.5 to 1.5 times the depth of the groove portion. Welded structure. 3. The welded structure for a steel pipe sheet and a steel pipe according to claim 1, wherein the austenitic steel pipe and the ferritic steel pipe are welded with an Inconel-based metal. 4. The ferrite steel pipe according to claim 1, wherein the ferritic steel pipe, the ferritic steel pipe and the ferritic metal for welding between the ferritic steel pipe and the ferritic steel pipe are both chrome molybdenum based metals. Welded structure of steel pipe and steel pipe. 5. A ferritic steel pipe is welded to one end of an austenitic steel pipe, the ferritic steel pipe side is first inserted into a groove formed near the ferritic steel pipe, and a ferritic metal is used between the ferritic steel pipe and the ferritic steel pipe. A welded structure of a steel pipe and a steel pipe, characterized in that welding is performed, and an austenitic steel pipe and a ferritic steel pipe are welded with an Inconel metal. 6. The steel pipe side and the steel pipe according to claim 5, wherein the length of the ferritic steel pipe is restricted to a range of 0.5 to 1.5 times the depth of the groove portion. Welded structure. 7. The welded structure of a steel pipe side and a steel pipe according to claim 5, wherein the austenitic steel pipe and the ferritic steel pipe are welded with an Inconel-based metal. 8. The ferrite steel pipe according to claim 5, wherein the ferrite steel pipe and the ferrite metal for welding the ferrite steel pipe and the ferrite steel pipe are both chrome molybdenum metal. Welded structure of steel pipe and steel pipe.