JPH11342493A - Structure and method for welding tube body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize a residual stress generated in a weld zone on an inner side and restrain the occurrence of stress corrosion cracking by forming a groove on inner and outer sides of a pair of tube body edge part and making a groove angle of the tube body outer side smaller than that of the inner side. SOLUTION: Edge parts of the first tube body 1 and the second tube body 2, on which an X-shape groove 13 is formed, are butted. Since the relation ship between an angle θi of a groove 13a on the inner side and an angle θo of a groove 13b on the outer side of the groove 13 is θi>θo, width dimension of a welding 4b on the outer side is smaller than that of a welding 4a on the inner side. After the welding 4a on the inner side is completed, the welding 4b on the outer side is carried out. Therefore, when the metal of the welding 4b is solidified, shrinkage force generated in the tube bodies 1, 2 in an axial direction becomes smaller in a case that the width dimension of the outer side welding 4b is made smaller than that of the inside welding 4a in comparison with shrinkage force generated wherein width dimension of the outer side welding 4b is not made smaller than the welding 4a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe welding structure and a welding method for welding the ends of a pair of joined pipes from an inner surface and an outer surface.

[0002]

2. Description of the Related Art For example, in a nuclear power plant or various energy plants, a pipe is used to transfer a fluid. In such a case, the pipe is often connected by welding. When the pipes are thick, a groove is formed at the welded end of the pair of pipes, and the pipes are welded from the inner surface side and the outer surface side to connect these pipe bodies.

FIG. 5 shows a conventional welding structure. In the figure, reference numeral 1 denotes a first tube, and 2 denotes a second tube. An X-shaped groove 3 is formed at the butted ends of these tubes 1 and 2. The groove 3 is a groove 3 on the inner surface side of the tubes 1 and 2.
a and the angle of the groove 3b on the outer surface side are the same angle θ.
Is set to Then, welding 4 is applied to the groove 3a on the inner surface side.
After performing a, welding 4b is performed on the groove 3b on the outer surface side.

[0004]

However, according to such welding, a very high tensile residual stress is generated in the welded portions on the inner surfaces of the tubular bodies 1 and 2 after the welding, and this is the basis for the welding on the inner surfaces. There was a risk that stress corrosion cracking 5 would occur in the portion. This is because when the metal of the outer surface side weld 4b contracts in the axial direction, a rotational moment M is generated in the direction indicated by the arrow in the figure, and the rotational moment M causes the stress corrosion cracking to occur on the inner surface side weld 4a. 5 would occur.

According to the present invention, when a groove is formed between an inner surface and an outer surface of an end portion of a butted pipe body and welding is performed, a residual welding stress generated in a welded portion on the inner surface can be reduced. An object of the present invention is to provide a welding structure and a welding method for a pipe.

[0006]

According to a first aspect of the present invention, there is provided a welding structure for forming a groove on an inner surface and an outer surface of ends of a pair of pipes and welding the ends. The pipe welding structure is characterized in that the groove angle on the outer surface side of the tube is set smaller than the groove angle on the inner surface side.

According to a second aspect of the present invention, there is provided a welding method in which a groove is formed on an inner surface and an outer surface of ends of a pair of tubes, and these ends are welded. The tip angle is set smaller than the groove angle on the inner side,
A method of welding a tubular body, characterized in that the inner surface side is welded and then the outer surface side is welded.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a welding structure according to the present invention, in which the first tube 1 and the second tube 2 to be joined are joined at the ends where an X-shaped groove 13 is formed. The X-shaped groove 13 is:
Assuming that the angle of the groove 13a on the inner surface side of the tubular bodies 1 and 2 is θi and the angle of the groove 13b on the outer surface side is θo, θi> θo is set.

When the ends of the first tubular body 1 and the second tubular body 2 where the X-shaped grooves 13 are formed abut each other, the inner grooves 13a of the tubular bodies 1 and 2 are welded. Then, the groove 13b on the outer surface side is welded.

As shown in FIG. 2A, the relationship between the angle θi of the groove 13a on the inner surface side of the X-shaped groove 13 and the angle θo of the groove 13b on the outer surface is θi> θo. The width dimension Wo of the inner side weld 4b is smaller than the width dimension Wi of the inner side weld 4a.

On the other hand, the conventional X-shaped groove 3 is shown in FIG.
As shown in (b), the angle of the groove 3a on the inner surface side and the angle of the groove 3b on the outer surface are both set to the same angle θ, so that the width dimension W is also the same.

Therefore, by performing the welding 4a on the inner surface side and then performing the welding 4b on the outer surface side, when the metal of the welding surface 4b on the outer surface solidifies, the axial contraction force generated in the tubular bodies 1 and 2 is generated. As shown in FIG. 3 (b), as shown in FIG. 3 (b), the contraction force C1 of the present invention in which the width dimension of the outer side weld 4b is smaller than the width dimension of the inner side weld 4a as shown in FIG. The contraction force C2 in the case of the conventional structure in which the width dimension of the outer side weld 4b is not reduced is smaller. That is, if the width dimension of the weld is small, the amount of the molten metal is correspondingly reduced, so that the contraction force generated due to solidification of the molten metal is also reduced.

As described above, if the contraction force C1 generated along the axial direction of the pipes 1 and 2 becomes smaller, the rotational moment M1 that generates a tensile force on the inner surface side of the welded portion as shown in FIG. Since it is smaller than the rotational moment M generated by the conventional structure shown in FIG. 5, stress corrosion cracking is less likely to occur in the weld 4a on the inner surface side.

Further, the width Wo of the outer side weld 4b is made smaller than the width Wi of the inner side weld 4a. Stress is also reduced. As a result, the amount of deformation in the radial direction is also greater when the structure of the present invention is employed as shown by the dashed line X in FIG. 3C than when the conventional structure shown by the dashed line Y in FIG. Can be smaller.

FIG. 4 shows inner and outer grooves 13a, 13a.
6 is a graph showing a relationship between an angle ratio (θo / θi) and a residual stress remaining in a pair of welded pipes 1 and 2. As the residual stress, the residual stress in the axial direction and the circumferential direction was measured. In the figure, curve A indicates the residual stress in the axial direction, and curve B indicates the residual stress in the circumferential direction.

As a result, the angle ratio (θo / θi) is 1
It was confirmed that both the residual stress in the axial direction and the residual stress in the circumferential direction decreased as the diameter became smaller. That is, it can be seen that the residual stress decreases as the angle θo of the outer groove 13b becomes smaller than the angle θi of the inner groove 13a.

When the pair of pipes 1 and 2 are welded, the inner groove 13a having a large angle is welded, and then the outer groove 13b having a small angle is welded. The generated contraction force C1 is reduced and the inner side 4
a can be prevented from generating stress corrosion cracking.

In other words, by performing welding 4b on the outer surface having a small groove angle with less generation of contraction force after welding 4a on the inner surface, the generation of contraction force is reduced and the occurrence of stress corrosion cracking is prevented. can do.

The welding of the outer groove 13b is hardly restricted in terms of workability as compared with the welding of the inner groove 13b, but the inner welding cannot secure a sufficient working space. It is often limited by workability. Therefore, as in the present invention, the outer groove 13
Even if the angle θo of b is small, there is almost no trouble in the welding operation.

The present invention is not limited to the above embodiment. For example, instead of the X-shaped groove, a K-shaped groove is used.
The present invention can be applied to a groove having a shape for welding the inner surface side and the outer surface side of the pipe body, respectively.

[0022]

According to the first aspect of the present invention, when welding the ends of the pair of pipes where the grooves are formed, the angle of the groove on the outer surface of the tube is adjusted to the groove on the inner surface. Smaller than the angle.

Therefore, since the amount of molten metal in the weld on the outer surface side can be reduced, the residual stress generated in the weld on the inner surface side can be kept low, thereby suppressing the occurrence of stress corrosion cracking in that portion. be able to.

According to the second aspect of the present invention, the groove angle on the outer surface side of the tube is made smaller than the groove angle on the inner surface side, and the inner surface side of the groove is welded before the outer surface side is welded. I made it.

[0025] Therefore, since the welding on the outer surface side with a small amount of molten metal is performed later, the residual stress generated in the welded portion on the inner surface side can be suppressed low, and the occurrence of stress corrosion cracking can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a welding structure for a pair of pipes, showing one embodiment of the present invention.

FIGS. 2A and 2B are explanatory views of a groove angle in a conventional welding structure of the present invention.

FIGS. 3 (a) and 3 (b) are explanatory diagrams of a state of generation of a contraction force and a rotational moment in a conventional welding structure of the present invention, and FIGS. 3 (c) and 3 (d) are explanatory diagrams of a deformation amount in a radial direction. .

FIG. 4 is a graph showing a relationship between a ratio of a groove angle between an inner side and an outer side and a residual stress.

FIG. 5 is a cross-sectional view showing a conventional pipe welding structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st pipe 2 ... 2nd pipe 13 ... X type groove 13a ... Inner side groove 13b ... Outer side groove

Claims (2)

[Claims] 1. A welding structure for forming a groove on each of an inner surface and an outer surface of an end of a pair of tubes and welding the ends, wherein the groove is formed on an outer surface of the tube. A welding structure for a tubular body, wherein a tip angle is set smaller than a groove angle on an inner surface side. 2. A welding structure for forming a groove on an inner surface side and an outer surface side of an end portion of a pair of tubes, and welding these ends, wherein a groove angle on an outer surface side of the tube is adjusted to an inner surface side. A method for welding a tubular body, wherein the angle is set smaller than the groove angle of the pipe, and the inner surface side is welded and then the outer surface side is welded.