JPS59166786A - Method of improving residual stress of piping - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving welding residual stress in pipe joints that causes stress corrosion cracking.

When butt welding is performed all around to connect pipes, a strong tensile residual stress exceeding the yield point is generated in the weld and its heat-affected zone. If this residual stress is left untreated, stress corrosion cracking will occur, causing serious defects and even accidents.
Usually, measures are taken to improve the residual stress, that is, measures are taken to make the residual stress at least in the weld zone and its heat-affected zone compressive stress.

The conventional residual stress improvement method is to flow cooling water into the pipe, heat the welded part and its heat-affected zone with a high-frequency heater, and reduce the residual stress to a compressive state due to the difference in thermal expansion between the inner and outer circumference of the pipe. It is to be made so that.

Such conventional residual stress improvement methods require a high-frequency heating machine, and it may be difficult to bring a high-frequency heating machine into a small space, and a generator for high-frequency heating is also required, making the work difficult. There were problems in terms of labor and cost as it required a lot of people.

The present invention has been made to solve the above problems,
The welded area is secured with a ring that has sufficient rigidity, a thermal fluid is flowed inside the pipe, and the thermal expansion of the welded area due to the thermal fluid is mechanically restrained, and when the ring is removed, the welded area and its heat-affected zone are The residual stress is improved.

The present invention will be described in detail below with reference to the drawings.

In Fig. 1, 1.2 indicates the joined pipes, and 3 indicates the welded part.

A ring 4 is attached around the entire circumference of the welded part 3 to secure it.

The ring 4 has sufficient rigidity to restrain the thermal expansion of the pipe in the radial direction, and has a groove 5 cut into its inner peripheral surface for escaping the overlay of the welded portion 3.

When the attachment of the ring 4 is completed, a thermal fluid (for example, a fluid with a temperature of about 280° C.) is made to flow through the pipes 1 and 2. Due to this thermal fluid, the pipes 1 and 2 thermally expand in the axial and radial directions, but the thermal expansion in the radial direction is restrained by the ring 4, and the welded part 3 and its vicinity are deformed as shown in Fig. 2. .

Due to the deformation, compressive plastic deformation occurs on the outer periphery of the pipes 1 and 2, and tensile plastic deformation occurs on the inner periphery, and when the ring 4 is removed, tensile residual stress is generated in the welded part 3 and the heat affected zone. will occur.

Changes in this residual stress are shown in the graph of FIG.

In the graph, the vertical axis t represents the residual stress, the positive value is the tensile pressure, the negative value is the compressive pressure, the horizontal axis represents the position, and the dashed line in the graph represents the center of the weld.

When the pipes 1 and 2 are still welded, high positive residual stress occurs in both the axial and circumferential directions around the welded part 3, as shown by the broken line in the graph. When this is done, the residual stress in the axial direction becomes a negative value, and the residual stress in the circumferential direction is also significantly reduced (indicated by the solid line in the graph).

In addition, if the fluid to be handled is thermal fluid, such as boiler piping or nuclear reactor piping, it is sufficient to secure the welded part with a ring, operate it steadily, and then remove the ring after the required time has elapsed. The work is extremely simple.

Furthermore, water or the like may be allowed to flow through the groove 5 to prevent heat transfer from the pipes 1 and 2 to the ring 4, and furthermore, a passage for cooling water may be formed in the knob to actively cool the ring. You may.

As described above, according to the present invention, it is possible to improve residual stress with an extremely simple device, and it exhibits the excellent effects of being easy to operate and having low running costs.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams of the present invention, and FIG. 3 is a graph showing the state of residual stress before and after implementing the present invention. 1.2 is a pipe, 3 is a welded part, 4 is a ring, and 5 is a groove. Patent application person Ishikawajima Harima Heavy Industries Co., Ltd. Patent applicant agent

Claims (1)

[Claims] 1) A method for improving residual stress in piping, which comprises securing the welded portion with a ring having sufficient rigidity, flowing a thermal fluid into the interior of the piping, restricting thermal expansion of the welded portion with the ring, and then removing the ring.