JPS6167566A - Residual stress improving method of pipe joint weld zone - Google Patents

Abstract

PURPOSE:To reduce a residual stress of a weld zone by providing an additional torch and executing heating from the peripheral side part of a pipe body, when a welding torch is positioned at the upper half part of the pipe body to be welded. CONSTITUTION:Welding is executed by making the end parts of two pipe bodies 7, 8 abut on each other, and moving a welding torch along its joint line 9. In this case, when the torch 4 is positioned on the upper half part of the pipe bodies 7, 8, heating of cooling water W is executed through the pipe wall by providing an additional torch 10 on the peripheral side part of the pipe bodies 7, 8. By heating the additional torch 10, circulating flows 11, 13 are generated, and a vapor phase of the uppermost part of the pipe body is made to flow. Accordingly, the colling efficiency of this part is improved, and a residual stress value can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a method for improving residual stress in a welded part of a pipe joint, and in particular, the present invention relates to a method for improving residual stress in a welded part of a pipe joint, and in particular, the method involves filling the inside of a pipe with cooling water and passing a welding torch along the outer periphery. When welding by moving around the circumference, even when the welding torch is positioned on the upper semicircle of the tube, especially at the top, the cold n1 water is naturally circulated in the circumferential direction of the tube to form a vapor phase, i.e. steam. The present invention relates to a method for improving residual stress in pipe joint welds, which can remove superheated water containing water and obtain a sufficient water cooling effect.

[Prior Art] Generally, when circumferential welding is required, such as when joint welding pipes together or when performing so-called external buttering, cooling water is filled into the pipe to reduce welding residual stress on the inner surface of the pipe. Cooling is performed. In this case, in order to improve the cooling efficiency, the filled cooling water is usually forced to circulate, but it may be difficult to do such forced circulation depending on the location.

Here, based on FIG. 2, a conventional method of welding a pipe body in a case where forced circulation of cooling water is not possible will be described. The illustrated example shows a case where pipe bodies are welded together, and the end of another pipe body 2 (indicated by a phantom line in the figure) to be connected is brought into contact with the end of pipe body 1 supported almost horizontally. Then, one welding torch 4 is moved circumferentially along this connecting portion 3 to perform circumferential welding.

At this time, the tubes 1 and 2 are filled with cooling water W to cool the inner surfaces of the tubes. In addition, tube body 1,
Of course, both ends of the tube 2 are closed to prevent leakage of cooling water.

[Problem to be solved by the invention 1] However, in this type of conventional welding method, when welding the side of the tube, for example at the 3 o'clock or 9 o'clock position, steam generated inside this No problem occurs because the phase immediately rises and a circulating flow of cooling water is formed to obtain sufficient cooling efficiency. However, when the welding torch 4 is In particular, when the cooling water is located at the top (12 o'clock position) as shown in the figure, the cooling water is almost at a standstill, and the vapor phase 5 generated inside this part does not move and stagnates in this part. This leads to a decrease in heat transfer coefficient and insufficient cooling of this top layer, resulting in rl! There was a tendency for the U retention stress to increase. For this reason, high tensile residual stress causes problems such as stress corrosion cracking, which has been a major problem particularly in the fields of nuclear power and chemical equipment.

[Object of the Invention] The present invention has focused on the above-mentioned problems and has been devised to effectively solve the problems.

An object of the present invention is to fill cooling water inside a tube and move the welding torch along the outer periphery to perform welding, when the welding torch is located on the upper semicircle of the tube, especially at the top. It is an object of the present invention to provide a method for improving residual stress in a welded joint of a pipe joint, in which the vapor phase is removed by natural circulation of cooling water, and a sufficient water cooling effect can be achieved by 1q.

[Summary of the Invention] The configuration of the present invention that achieves the above object is such that when welding along the outer periphery of a tube filled with cooling water and supported substantially horizontally, the welding torch moves at least around the tube. When the cooling water is placed on the upper semicircular part, it is heated from the circumferential side of the tube with a heating torch or the like to cause natural convection of the cooling water in the circumferential direction within the tube, thereby removing the vapor phase. The gist of this is to improve cooling efficiency.

[Embodiment] A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram for explaining the method of the present invention, and FIG. 3 is a cross-sectional view taken along the line T in FIG.

As shown, FIG. 1 shows a case in which two tube bodies 7 and 8 are jointly welded together, and the tube bodies 7 and 8 having the same diameter are supported in a substantially horizontal state with their respective ends abutting each other. Then, welding is performed by moving the welding torch 4 circumferentially along the joining line 9 of these tube ends. At this time, the other ends of each of the tubes 7 and 8 are closed by a closing member (not shown) or the like, and the inside is filled with cooling water W to cool the inner surface of the tubes. When the welding torch 4 is located on the inside of the lower half of the cross section of the joining line 9 of the pipe body, the cooling water moves along with the upward flow of steam generated inside, and the cooling water moves in the circumferential direction of the pipe body 7.8. Since a circulating flow is formed that flows along the pipe, the generated vapor phase immediately separates from that part and sufficient cooling efficiency can be obtained. When it is located, the momentum of the circulating flow becomes weak and the generated vapor phase may not be removed immediately. In particular, when the welding torch 4 is located at the top P of the tube joint 5iI9, the circulation flow disappears and the vapor phase tends to stay inside (see FIG. 2). Therefore, in the present invention, when the welding torch 4 is located at the top, the circumferential side of the tubes 7, 8, for example, at the 3 o'clock or 9 o'clock position (in FIG. 3, the 3 o'clock position ) is fixedly provided with an additional torch 10 as a heating means,
The cooling water located in this area is heated. As a result, the cooling water inside the side part of the tube joining line 9 expands and its density decreases, and due to natural convection, circulation flows 11 and 13 convect along the circumferential and axial directions of the tube as shown by the arrows in the figure. is formed. Therefore, the vapor phase 1 generated on the inner surface of the top of the tube
2 flows along with the circulation flows 11 and 13 generated by the additional torch 10, and is immediately removed from the inner surface of the top of the tube. Therefore, the state in which the cooling water is constantly in contact with the inner surface of this uppermost portion is maintained, and the cooling efficiency of this portion can be sufficiently improved.

Further, even if the welding torch 4 is not located at the top of the tubes 7 and 8, if it is located on the upper semicircular section of the tubes, the momentum of the circulating flow 11 will be weakened, so the additional torch 10 as described above will be used.
is provided to heat the cooling water W, thereby increasing the momentum of the circulating streams 11 and 13 to a velocity sufficient to remove the boiling vapor or vapor phase 12. In this case, the additional torches 10 are arranged so that the respective cooling water circulation directions generated by the welding torch 4 and the additional torches 10 are in the same direction.

Although the heat m generated by the additional torch 10 depends on the wall thickness of the tube, it is set to a value that can generate sufficient circulating flow momentum to remove the generated vapor phase within a time range that does not reduce the cooling efficiency.

When starting welding, do not start from the top P of the tubes 7 and 8, but start from the 3 o'clock or 9 o'clock position of the tubes 7 and 8 and work your way to the top, as shown in Figure 4. It is effective to allow sufficient natural convection to occur before welds 1 to 4 reach the top P.

In the above embodiment, the additional torch is fixed at the 3 o'clock or 9 o'clock position in order to form an effective circulating flow, but the present invention is not limited to this, and for example, the additional torch may be used as a welding torch. Welding may be performed at the same time using two 1--chis. In this case, the torch spacing will vary somewhat depending on the diameter of the pipe, but it is best to space them approximately 90 degrees apart. Welding starts with the first welding torch at 3 o'clock, and the second welding torch (additional welding) at 6 o'clock. It is best to start from a position where you can

In this embodiment, an additional torch is used as the heating means, but the present invention is not limited to this, and any heating means can be used as long as it can form circulating convection in the circumferential direction within the tube.

Furthermore, although the embodiments have been described with respect to the case where pipe bodies are connected by joints, it is of course applicable not only to this but also to the case where other members are welded and connected along the outer periphery of the pipe bodies. It is.

[Effects of the Invention] As described above, according to the present invention, the following excellent effects can be exhibited.

(1) When the welding torch is positioned at least above the upper semicircle of the tube, the additional torch heats the cooling water to form a circulating flow due to natural convection, so the vapor phase generated inside the weld is quickly removed. can be removed. In particular, even if the welding torch is located at the top of the pipe body and the generated vapor phase tends to be most difficult to accumulate at the bottom thereof, the vapor phase can be reliably removed by the circulating flow due to the above-mentioned natural convection.

(B) Therefore, the cooling water is constantly in contact with the inner surface of the welded part, and the heat transfer coefficient in this area does not decrease, so the cooling effect can be improved as much as possible.

(3) Since the cooling effect can be sufficiently improved, welding residual stress can be extremely reduced, and problems associated with residual stress such as stress corrosion cracking can be solved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram for explaining a preferred embodiment of the method of the present invention, Fig. 2 is an explanatory diagram for reprinting the conventional pipe body welding method, and Fig. 3 is an explanatory diagram for explaining a preferred embodiment of the method of the present invention. [[[A sectional view taken along the line, FIG. 4 is an explanatory diagram for explaining the start of welding. In the figure, 4 is a welding torch, 7 and 8 are tube bodies, and 10 is an additional 1.
--H, 12 is a vapor phase, and W is cooling water.

Claims (1)

[Claims] When the pipe is supported substantially horizontally and the welding torch is moved along the outer periphery of the pipe while filling the inside with cooling water, the welding torch is positioned at least above the upper semicircular part of the pipe. A method for improving residual stress in a welded joint of a pipe joint, characterized in that the cooling water is heated from the circumferential side of the pipe body to cause the cooling water to convect in the circumferential direction within the pipe body when