JPH0246654B2 - CHUKUTAINOZANRYUORYOKUKAIZENHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving residual stresses in butt circumferential weld joints of hollow bodies such as pipes or tubular vessels.

Tensile residual stress exists in both the circumferential and axial directions on the inner surface of butt circumferential welds of hollow bodies such as piping or tubular containers, and the presence of this inner surface tensile residual stress affects fatigue strength and stress corrosion cracking resistance. Therefore, it is desired to reduce the degree of tensile residual stress or bring it into a compressed state.

Various residual stress improvement methods have been proposed to achieve this purpose.The outer surface heating/inner surface cooling method heats the outer surface and simultaneously cools the inner surface with water to create a temperature difference between the inner and outer surfaces. This method attempts to make the residual stress state of the inner surface into a compressive state by thermal stress, but this method requires cooling the inner surface and cannot be applied in cases where cooling is difficult. There are disadvantages such as the need for a large capacity device.

In addition, the Linde method heats both sides of the weld line and immediately cools the weld line, processing the process sequentially along the weld line, but this method also has the disadvantage of requiring cooling. In addition, the effect is uncertain because heating and cooling are performed sequentially in the direction of the weld line.

All of these methods require heating and cooling at the same time, but among the previously proposed methods, one method that does not require cooling is to place weld beads on both sides of the weld line and utilize the resulting residual stress distribution. There is a method that attempts to improve the residual stress distribution in the period. However, this method has the drawback that material changes occur due to welding, and, like the Linde method, it lacks reliability because heating is not done all at once, and it also has a fundamental flaw in that residual stress in the axial direction is difficult to improve.

The present invention does not have the drawbacks of the conventional methods as described above, that is, there is no need for cooling after or during the treatment, so the capacity of the heating device is small, and the residual stress improvement effect is reliable and reliable. This method aims to provide a method for uniformly heating annularly with an appropriate width in the axial direction according to the dimensions of the hollow body on both sides of the weld line of a butt circumferential weld joint of a hollow body, and thereby creating a temperature distribution in the axial direction. After the heating is stopped and the hollow body is allowed to cool, the tensile residual stress is reduced or compressed in both the circumferential and axial directions of the inner surface of the butt-circumferential welded part of the hollow body. Suggest a method.

An embodiment of the method of the present invention will be described with reference to the drawings.

First, in FIG. 1, a specific position according to the pipe dimensions on both sides of the butt circumferential weld joint 2 of the pipes 1, 1, for example,
In the case of a pipe made of SUS304 steel with an outer diameter of approximately 100 mm and a plate thickness of 6 mm, the distance from the welding line is 10 to 30 mm or 20 to 40 mm.
The area is simultaneously heated in an annular manner by a heating device 3 such as a gas flame or high-frequency induction heating to create a high-temperature area and after creating an axial temperature distribution, the heating is stopped and allowed to cool. Heating is sufficient to produce temperature distribution, and after heating, there is no need for forced cooling such as water cooling during heating.

By heating in this manner, the welded structure of the tubes 1, 1 exhibits a temperature distribution in the axial direction as shown in FIG. 2, and as a result is deformed into the shape shown in FIG. 3.

Due to this deformation, the circumferential stress becomes tensile stress near the weld line as shown in FIG. 4, and becomes compressive stress in the heated area as shown in FIG. 5. On the other hand, in the axial direction, since the circumferential surface is heated at the same time, thermal expansion causes a discrepancy in the diameter in the axial direction, resulting in a bending moment.As a result, the axial stress near the weld line is as shown in Figure 6. As shown in Figure 2, the outer surface of the tube is under compressive stress, the inner surface of the tube is under tensile stress, and in the heating section, the seventh
As shown in the figure, the outer surface of the tube is under compressive stress, and the inner surface of the tube is under tensile stress.

However, after such a stress distribution occurs during heating, when the thermal stress is unloaded by cooling after heating, these stresses decrease or reverse, resulting in a decrease in tensile residual stress near the weld. Or compressive stress.

The results of numerical experiments (simulations) using the thermoelastic-plastic finite element method, which were conducted to confirm the effects of the method of the present invention, will be explained below with reference to FIGS. 8 to 18.

The specimen is made of SUS304 steel with an outer diameter of 114.3 mm and a wall thickness of 6 mm.
A butt circumferential welded joint for pipes was used.

FIG. 8 shows the outer surface residual stress distribution as it is after welding, and FIG. 9 shows the inner surface residual stress distribution.

FIG. 10 shows the inner surface temperature distribution during heat treatment when heating of 0.1 cal/mm ³ ×60 sec with a gas flame is applied to an area 10 to 30 mm from the weld line. FIG. 11 shows the outer surface residual stress distribution after the heat treatment, and FIG. 12 similarly shows the inner surface residual stress distribution.

Next, Fig. 13, Fig. 14, and Fig. 15 show that heating at 0.1 cal/mm ³
The inner surface temperature distribution during heat treatment, the outer surface residual stress distribution after heat treatment, and the inner surface residual stress distribution when applied to an area of ~40 mm are shown, respectively.

Furthermore, Fig. 16, Fig. 17, and Fig. 18 show that heating at 0.1cal/mm ³ ×60sec with a gas flame is performed from the welding line at 40°C.
The inner surface temperature distribution during the heat treatment, the outer surface residual stress distribution after the heat treatment, and the inner surface residual stress distribution when applied to an area of ~60 mm are shown, respectively.

From the figures shown above, it can be seen that in Fig. 8, the inner surface residual stress after welding was in a tensile state of 20 kgf/mm2 or ^more in both the circumferential and axial directions, but by heating the appropriate heating area, only the circumferential direction can be reduced. It can be seen that the residual stress in the axial direction is also largely removed.
In other words, as shown in Figure 18, 40 mm from the weld line
When heating an area of ~60mm, the residual stress becomes larger than the original residual stress, but when heating an area of 20~40mm as shown in Figure 15, or 10~30mm as shown in Figure 12, the residual stress increases. , has the effect of removing residual stress. Among them, 20 to 40 mm is the most appropriate for this pipe diameter.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the method of the present invention, and FIG.
3 and 3 are explanatory diagrams of the temperature distribution and deformation state in the same as above, FIGS. 4 to 7 are residual stress state diagrams in the same as above, and FIGS. 8 to 18 are experimental examples of the method of the present invention. In the explanatory diagrams, Figures 8 and 9 are residual stress distribution diagrams during welding, Figures 10 to 12 are temperature distribution diagrams and residual stress distribution diagrams in the case of heating in an area of 10 to 30 mm from the weld line, Figures 13 to 15 are temperature distribution diagrams and residual stress distribution diagrams for heating an area 20 to 40 mm from the weld line, and Figures 16 to 18 are temperature distribution diagrams and residual stress distribution diagrams for heating an area 40 to 60 mm from the weld line. It is a residual stress distribution diagram. 1: Pipe, 2: Butt circumferential weld joint, 3: Heating device.

Claims (1)

[Claims] 1 Apply uniform heating to an annular shape with an appropriate width in the axial direction according to the dimensions of the hollow body on both sides of the weld line of the butt circumference weld joint of the hollow body to create a temperature distribution in the axial direction, and then stop the heating. A method for improving residual stress in a hollow body, characterized by reducing or compressing tensile residual stress in both the circumferential and axial directions of the inner surface of a butt circumferential welded part of the hollow body by allowing the hollow body to cool.