JPS61104028A - Method for improving residual stress of welded part of metallic pipe - Google Patents

Abstract

PURPOSE:To give compressive residual stress to the inner and the outer surface of a metallic pipe by composing one part of the layer of a welding metal to be filled into a welding groove of the metallic pipe of a welding material having a smaller expansion coefficient and a lower stress annealing temp. than the other part of the layer, and stress-annealing at the stress annealing temp. of the one part after welding. CONSTITUTION:A welding metal to be filled into a groove 2 is made to have a 2-layered structure, when the groove 2 of a metallic pipe 1 consisting of carbon steel is welded. Namely, the initial layer part 3 on the inner surface side of the metallic pipe 1 is composed of a carbon steel welding material, and the terminal layer part 4 on the part 3 is welded with a stainless steel welding material having a relatively smaller linear expansion coefficient and a lower stress annealing temp. than the carbon steel welding material. After welding, stress annealing is applied at about 650 deg.C which is the annealing temp. of the carbon steel welding material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for improving residual stress in metal pipe welding, and is particularly suitable for applying compressive residual stress to the inner or outer surface of a metal pipe. This invention relates to a stress improvement method.

"Conventional technology" Conventionally, when metal pipes are connected by welds,
It is known that tensile residual stress is generated near the welded part due to shrinkage of the material after welding, and in the case of steel pipes, for the purpose of removing tensile residual stress, etc.
After welding, annealing is performed at a temperature of 600-650°C.

``Problems to be Solved by the Invention'' However, this method of improving residual stress by annealing involves so-called intermediate layer annealing, and although it can soften the material to some extent and remove some of the internal stress, it is not perfect. Further, in steel pipes and the like, when tensile stress and corrosion factors coexist, there is a problem in that corrosion cracking progresses.

The present invention effectively solves the problems of the prior art.
In addition, the purpose is to apply compressive residual stress to the vicinity of the welds on the four inner surfaces of the metal tube.

[Means for Solving the Problems] The present invention proposes two methods to achieve such an object. One surface layer is made of a weld material with a relatively smaller coefficient of linear expansion and a lower stress annealing temperature than the other surface layers, and stress annealing is performed at the stress annealing temperature of the one surface layer after welding. The second invention applies compressive residual stress to the inner surface of the weld metal tube, and the second invention provides both surface layers of the weld metal filled in the weld groove of the metal pipe with a coefficient of linear expansion that is relatively higher than that of the intermediate layer. It is made of a small weld metal with a low stress annealing temperature, and after welding, stress annealing is applied to both surface layers at a high temperature to impart compressive residual stress to the inner and outer surfaces of the metal tube. .

"Example" Hereinafter, an example of the first invention is shown in FIGS. 1 and 2.
In this example, when welding the groove 2 of the metal tube 1 made of carbon steel, welding is performed so that the weld metal filled in the groove 2 has a two-layer structure. The first layer (one surface layer) 3, which is the inner surface of the tube 1, is made of continuous carbon steel, and the final layer (another surface layer) 4 is made of stainless steel, and then welded. , based on the welding annealing temperature of the initial layer 3, that is, 6
After stress annealing at around 50°C, the material is gradually cooled.

When this series of steps is carried out, the initial layer 3, which is one surface layer of the weld metal filled in the groove 2, becomes an intermediate annealed shape in which thermoplastic deformation due to thermal expansion does not occur at high temperatures due to stress annealing. However, since the final layer 4, which is another surface layer of the weld metal and has a high annealing temperature, maintains an elastically deformed state at a temperature of 650°C, the first layer 3 deforms during cooling.
As shown in FIG. 2, the outer surface of the metal tube 1 has a tensile residual stress +σ, and the inner surface has a compressive residual stress σ. The magnitude of these residual stresses is expressed by the following relational expression.

as=EΔTCas−αc)B/(A+B)−(1)
ac=EΔTCas−αc)(−A)/(A+B)・−
= (2) However, 8 - Cross-sectional area B of the final layer part 4 - Cross-sectional area of the first layer part 3 Linear expansion coefficient αs of the final layer part 4 = +9X 10 - @ Linear expansion coefficient αc of the first layer part 3 = 14X 1G -'.

Therefore, A and B are set in consideration of the magnitude of the required compressive residual stress, and according to a trial calculation, for example, the weld metal is carbon steel, stainless steel weld metal, A=B, and the operating temperature of the metal pipe 1 is 288. ℃, stress annealing temperature is 650℃
In this case, the σC valve is 1 Bkg/am'.

Further, FIG. 3 shows another embodiment of the first invention, in which the cross-sectional area of the final layer portion 4 is increased to expand the range of compressive residual stress generation on the inner surface of the metal tube 1. Compressive residual stress is applied to all parts estimated to be affected by heat input.

Next, an embodiment of the second invention will be explained with reference to FIGS. 4 and 5. When welding the groove 2 of a metal tube made of carbon steel, the weld metal filled in the groove 2 is As a layer structure, the first layer 3 is made of carbon steel series,
The intermediate layer 5 thereon is welded with a stainless steel welding material, and the final layer 4 is welded with an Inconel welding material, and then the temperature based on the initial layer 3 and the final layer 4 is set to 65.
Stress annealing is performed at around 0°C and then gradually cooled. In the case of this embodiment, the Inconel-based final layer 4 can be welded onto a stainless steel weld material like a high nickel alloy such as Inconel, so it has a stress annealing temperature and linear expansion coefficient similar to that of carbon steel. It is required to be a welding material. In the case of Inconel welding material, linear expansion coefficient αi-
Since it is about 12X 10-', the initial layer part 3 and the final layer part 4 each have a compressive residual stress -σC as shown in FIG.
and −σ! can be granted.

"Effects of the Invention" As explained above, the present invention provides a layer of weld metal that is filled into a welding groove of a metal tube, which has a relatively smaller coefficient of linear expansion than other layers and which is under stress. It is made of a weld material with a low annealing temperature, and after welding, stress annealing is performed on some layers at the stress annealing temperature described in 1iii, and the inner and outer surfaces of the metal tube are At least one of them can be in a state where compressive residual stress is applied. Therefore, in cases where corrosion factors exist on the inner and outer surfaces of steel pipes, etc., it is possible to effectively prevent the progression of corrosion cracking in the welded portion and its vicinity, which are likely to cause defects, thereby improving the reliability of the metal pipe. It has the following effects:

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of the residual stress improvement method of the first invention, FIG. 2 is an explanatory diagram of the residual stress, and FIG. 3 is an explanatory diagram of another embodiment of the first invention. FIG. 4 is an explanatory diagram of an embodiment of the residual stress improvement method of the second invention, and FIG. 5 is an explanatory diagram of the residual stress. !・Metal tube, 2. ・Bevel, 3. ・Chip+]<(one surface layer), 4 Final layer (other surface layer), 5. Intermediate layer. Applicant: Ishikawajima Harima Heavy Industries Ajishikikai Tsuji, Figure 1, Field 3

Claims (1)

[Claims] (i) One surface layer of the weld metal filled into the weld groove of the metal tube is made of a weld material having a relatively smaller coefficient of linear expansion and a lower stress annealing temperature than other surface layers. . A method for improving residual stress in a metal pipe welded part, characterized in that stress annealing is performed at a stress annealing temperature of the one surface layer after welding. (ii) Both surface layers of the weld metal filled into the welding groove of the metal tube are composed of a weld metal having a relatively smaller coefficient of linear expansion and a lower stress annealing temperature than the intermediate layer, and after welding, both surface layers of the weld metal are A method for improving residual stress in a metal pipe weld, characterized by carrying out stress annealing at a stress annealing temperature.