JPS61279629A - Method for relieving residual stress - Google Patents

Abstract

PURPOSE:To relieve the residual stress in a welded joint at a low heating temp. by placing a heating coil around the joint to heat the joint, arranging electromagnetic coils so that they confront each other on both sides of the joint at an interval, and supplying DC to one of the coils and AC to the other. CONSTITUTION:A high frequency heating coil 3 is placed around a welded joint 2 in a steel pipe 1, and high frequency power is applied to the coil 3 from a high frequency power source 4 to heat the joint 2 to 300-500 deg.C. Electromagnetic coils 5, 7 are arranged so that they confront each other on both sides of the joint 2 at an interval, AC is supplied to the coil 5 from a power source 6 to generate AC magnetic flux 9 in the steel pipe 1, and DC is supplied to the coil 7 from a power source 8 to generate DC magnetic flux 10 in the steel pipe 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for removing or reducing residual stress in a welded joint.

[Conventional technology]

Generally, welded parts undergo distortion due to welding heat, and stress remains inside after welding is completed.

This residual stress induces weld cracking. It also reduces the design allowable stress, causes local corrosion, and causes defects such as deformation during processing and deformation during use.

Conventionally, in order to prevent these defects, stress relief annealing is performed after welding is completed.

[Problem that the invention seeks to solve]

However, this stress relief annealing takes longer at high temperatures □
It requires heating for a long time, and there are methods such as applying it in a heating furnace and applying it on-site by attaching a heating source to the workpiece.
In either method, the heat treatment cost power Z: JtI: tK
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11. Furthermore, we focused only on stress relief in the welded area and
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If heated to
, may have a negative impact of 4°.

[Failure to solve the problem]
・”:′: The present invention was made in order to solve the above problems.1: The present invention was made in order to solve the above problems.
'・j4.1 Heat the welded area and heat the welded joint on both sides.
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Install electromagnetic coils at separate locations, and connect them to one side.
11'1. Characterized by passing direct current and alternating current to the other.
, a method for reducing residual stress is provided.

[Effect]

In the present invention, two sets of coils are installed on both sides of the welding part, and electromagnetic force is generated by passing a direct current through one coil and an alternating current through the other.

Compressive stress and tensile stress are alternately applied to the weld.

Furthermore, the welding area is heated by passing a high-frequency current through a heating coil attached to the welding area. The heating temperature of the welded part by this heating coil can be made considerably lower than the conventional stress relief annealing temperature, and in some cases, it is possible to not heat the welded part at all.

〔Example〕

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

Figure 1 is a diagram showing what was applied to a small diameter steel pipe used for boilers, etc. In Figure 1, 1 is the steel pipe to be welded, 2
It has a welded joint.

Reference numeral 8 denotes a high-frequency heating coil, which is arranged around the outer periphery of the welded part 2. 4 is a high frequency power source that supplies high frequency power to the heating coil 8.

Reference numeral 5 denotes an electromagnetic coil wound around the steel pipe 1, which is disposed on one side away from the welding part 2 and fixed to the steel pipe 1.

Reference numeral 6 denotes an alternating current generation power source for supplying an alternating current to the coil 6. 7 is an electromagnetic coil wound around a steel pipe l,
It is arranged on the other side of the welded part 2 and is fixed to the steel pipe. 8 is a DC power supply for supplying DC current to the electromagnetic coil 7. 9 is an alternating magnetic flux generated by the electromagnetic coil 5, and 1G is a DC magnetic flux generated by the electromagnetic coil 7.

Next, to explain the operation in the eleventh step, high-frequency power is supplied from the high-frequency power source 4 to the heating coil 8 wound over the welded portion 2 of the steel pipe 1 having residual stress, and the welded portion 2 is heated. At this time, electromagnetic
[□ Supply alternating current from power supply 6 to coil 5,
['Magnetic flux 9 is generated in the steel pipe. yet another
DC current is supplied from the power supply 8 to the electromagnetic coil 7 of 1'■
1 and a DC magnetic flux lO is obtained in the steel pipe.

By passing a direct current through one of the two sets of electromagnetic coils wound and fixed to a steel pipe in this way, and an alternating current through the other,
Attractive force 9 repulsive force is generated in the welded part of the steel pipe between the two sets of electromagnetic coils, but at this time the welded part is heated, so the stress inside the steel pipe is rapidly released. The heating temperature of the weld can be significantly lower than the conventional stress relief annealing temperature.

- For example, 650° to 780° for carbon steel and low alloy steel
However, according to the method of the present invention, heating of 80°C was required.
The annealing temperature can be lowered to 0° to 500°C, which shortens annealing time and reduces costs, and furthermore prevents material deterioration due to high-temperature heating.

〔Effect of the invention〕

According to the method of the present invention, residual stress in a welded portion can be reduced and eliminated using a simple device and a low heating temperature.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of one embodiment of the method of the present invention.
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1.1: Steel pipe to be welded, 2: Welded joint, 8: Heating
i::r (ru, 5: electromagnetic coil, 7: electromagnetic coil. 1 ball; embedded ↓ (ma 琥) 11゜i: i' Todo 舊 ? □) Sa,:

Claims (1)

[Claims] A heating coil is placed opposite to the welded joint to heat the welded part, and electromagnetic coils are placed oppositely to each other at separate positions on both sides of the welded joint, and a direct current is passed through one side and an alternating current is passed through the other side. Characteristic residual stress reduction method.