JP6071867B2 - Repair welding method and repair weld structure of welded part - Google Patents

Description

  The present invention relates to a repair welding method and repair weld structure of a welded portion, and is suitable for repairing piping affected by heat, such as a welded portion of a large-diameter piping of a land boiler installed in a thermal power plant. The present invention relates to a welding method of a welded portion and a repair welding structure.

Non-destructive inspections such as structural inspection and ultrasonic inspection are regularly performed on welded parts of large-diameter piping of land boilers installed in thermal power plants, and repair welding is performed on defective parts based on the results. It has been broken. In repair welding, a defective portion is generally excised from both sides or one side, and build-up welding is performed on the excised portion.
In addition, as a repair welding method for the welded portion where the first base material and the second base material are butt welded, both the boundary portion with the first base material and the boundary portion with the second base material are included. After repairing the welded portion where the region having a depth in the thickness direction from the surfaces of the first base material and the second base material is excised so that the bottom surface of the region is along the surface, the region is welded by overlay welding A welding method is known (see, for example, Patent Document 1).
Further, as a repair method for a welded portion in which the first base material and the second base material are welded with a welding material close to the base material component, a material having a larger creep ductility after melting and solidification than the base material ( For example, a repair welding method for a welded portion that is build-up welded with a material having a carbon content smaller than that of a base material is known (see, for example, Patent Document 2).

JP 2011-194458 A JP 2003-326385 A

However, since heat is newly applied to the base material and the weld metal even by repair welding of the welded portion, and a heat affected zone (HAZ (Heat Affected Zone)) is formed in the base material and the weld metal, unintended strength reduction is caused. Sometimes.
In view of the above circumstances, it is an object of the present invention to provide a repair welding method and a repair weld structure for a welded portion that can suppress a decrease in strength due to repair welding.

The present invention provides a repair welding method of the welded parts obtained by a hollow cylindrical first tubular material of the hollow cylindrical second tubular member is subjected to a first welding material circumferentially butt welding, the first The welding material is the same material as the first pipe and the second pipe, and a defect generated in the welded portion is removed including at least one of the first pipe or the second pipe. And, following the excision step , build-up welding with a second welding material having a linear expansion coefficient larger than that of the excised tube material and the first welding material in the excised region. It is characterized by that.
According to the present invention, when internal pressure and heat are applied to the first tube material and the second tube material, the portion welded with the second welding material expands more than the other portions. Thereby, a compressive stress arises in the part which makes the annular | circular shape from which one part (part welded with the 2nd welding material) lacked. This compressive stress relieves tensile stress (hoop stress) generated in the circumferential direction by internal pressure and heat in the first tube material and the second tube material. Thereby, the acting stress which acts on the heat affected zone by welding is reduced. Therefore, according to the repair welding method for welded portions of the present invention, strength reduction due to repair welding can be suppressed.

In the present invention, wherein the first tube and the second tube first welding material, since the same material, the when the pressure and heat is applied to the first tubular member and second tubular member The part welded with the welding material 2 expands more than the part welded with the first welding material. Thereby, a compressive stress arises in the part (part welded with the 1st welding material) which makes the annular | circular shape from which one part was missing. This compressive stress relieves tensile stress (hoop stress) generated in the circumferential direction by internal pressure and heat in the first tube material and the second tube material. Thereby, the acting stress which acts on the heat affected zone by welding is reduced. Therefore, according to the repair welding method for this welded portion, it is possible to suppress a decrease in strength due to repair welding.

In one aspect of the present invention, it is preferable that the second welding material has a higher creep strength than the first pipe member and the second pipe member.
If it does in this way, the creep strength of the part weld-welded with the 2nd welding material can be improved.

The present invention is a repair welding structure for a welded portion in which a hollow tubular first pipe member and a hollow tubular second tubular member are subjected to a butt welding by applying a first welding material in a circumferential direction . The welding material is made of the same material as the first tube material and the second tube material, and has a linear expansion coefficient larger than that of the first tube material or the second tube material in a region where a defect generated in the welded portion is removed. but greatly, and with the first repair welds were overlay clad in linear expansion coefficient larger than the second welding material of the welding material, butt portion after repair part and the repair of the first welding material It is comprised by a welding part, It is characterized by the above-mentioned.
According to the present invention, when internal pressure and heat are applied to the first tube material and the second tube material, the portion welded with the second welding material expands more than the other portions. Thereby, a compressive stress arises in the part which makes the annular | circular shape from which one part (part welded with the 2nd welding material) lacked. This compressive stress relieves tensile stress (hoop stress) generated in the circumferential direction due to internal pressure and heat in the first tube material and the second tube material. Thereby, the acting stress which acts on the heat affected zone by welding is reduced. Therefore, according to the repair welding structure of the welding part of this invention, the strength fall by repair welding can be suppressed.

In the present invention, wherein the first tube and the second tube first welding material, since the same material, the when the pressure and heat is applied to the first tubular member and second tubular member The part welded with the welding material 2 expands more than the part welded with the first welding material. Thereby, a compressive stress arises in the part (part welded with the 1st welding material) which makes the annular | circular shape from which one part was missing. This compressive stress relieves tensile stress (hoop stress) generated in the circumferential direction by internal pressure and heat in the first tube material and the second tube material. Thereby, the acting stress which acts on the heat affected zone by welding is reduced. Therefore, according to the repair welding method for this welded portion, it is possible to suppress a decrease in strength due to repair welding.

In one aspect of the present invention, it is preferable that the second welding material has a higher creep strength than the first pipe member and the second pipe member.
If it does in this way, the creep strength of the part weld-welded with the 2nd welding material can be improved.

  As described above, according to the present invention, when internal pressure and heat are applied to the first tube material and the second tube material, the portion welded with the second welding material expands more than the other portions. To do. Thereby, a compressive stress arises in the part which makes the annular | circular shape from which one part (part welded with the 2nd welding material) lacked. This compressive stress relieves tensile stress (hoop stress) generated in the circumferential direction by internal pressure and heat in the first tube material and the second tube material. Thereby, the action stress which acts on the heat affected zone by welding is relieved. Therefore, according to this invention, the strength fall by repair welding can be suppressed.

It is a figure which shows the large diameter piping to which the repair welding method of the welding part which is Embodiment 1 of this invention is applied. It is a figure which shows the outer surface of the welding part repaired with the repair welding method of the welding part which is Embodiment 1 of this invention. It is sectional drawing for demonstrating the repair welding method of the welding part which is Embodiment 1 of this invention. It is a figure which shows the relationship between repair welding length and the action stress of duplication HAZ. It is a figure which shows the relationship between repair welding length and the creep life ratio of duplication HAZ. It is a figure which shows the conditions (calculation conditions) used when examining repair welding. It is a figure which shows the examination result of repair welding. It is a figure which shows the relationship between repair welding length and a strain stress. It is a figure which shows the large diameter piping to which the repair welding method of the welding part which is Embodiment 2 of this invention is applied. It is a figure which shows the outer surface of the welding part repaired with the repair welding method of the welding part which is Embodiment 2 of this invention. It is sectional drawing for demonstrating the repair welding method of the welding part which is Embodiment 2 of this invention.

  Embodiments of a repair welding method and repair weld structure for a welded portion according to the present invention will be described below in detail with reference to the accompanying drawings. Here, the welding part of a large-diameter pipe of a land boiler installed in a thermal power plant will be described as an example, but the present invention is not limited to this, and can be applied to general welding parts of pipes affected by heat. The present invention is not limited to the embodiments.

[Embodiment 1]
FIG. 1 is a diagram showing a large-diameter pipe to which a welded part repair welding method according to Embodiment 1 of the present invention is applied. FIG. 2 is a diagram illustrating an outer surface of a welded portion repaired by the welded portion repair welding method according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view for explaining the repair welding method for welded portions according to the first embodiment of the present invention.

  The welded part repair welding method according to the first embodiment of the present invention is applied to a welded part of a large-diameter pipe of a land boiler. As shown in FIG. 1, a large-bore pipe of a land boiler is configured by being butt welded to hollow tubular large-diameter pipe materials 2 and 3 having the same outer diameter, inner diameter, and same material. In the butt welding, the welding material (first welding material 4) is melted in the circumferential direction of the large-diameter pipe materials 2 and 3. Large-diameter pipes 2 and 3 made of ferritic heat-resistant steel containing chromium (Cr) are used for large-diameter pipes of land boilers. The ferritic heat resistant steel containing chromium is a ferritic heat resistant steel containing 9 to 12 wt% of chromium, and is also referred to as a high chromium heat resistant steel. For the welding material (first welding material 4) to be melted in the circumferential direction of the large-diameter pipe materials 2 and 3, the same welding material as that of the large-diameter pipe materials 2 and 3 is used.

  As shown in FIG. 3 (a), a V-shaped groove is provided between one large-diameter pipe 2 and the other large-diameter pipe 3 to be butt-welded, and a welding material along the groove. One large-diameter pipe 2 and the other large-diameter pipe 3 are joined (welded) via a welded material (hereinafter referred to as “welded metal 4”) in which the (first welding material 4) is melted and solidified. Is done. Heat-affected portions (HAZ) 24 and 34 are formed in regions affected by the heat of the first welding material 4 melted in one large-diameter pipe 2 and the other large-diameter pipe 3. . The heat-affected portions 24 and 34 are formed along a boundary surface in contact with the weld metal 4 in one large-diameter pipe 2 and the other large-diameter pipe 3. Specifically, as shown in FIG. 2 and FIG. 3A, it is formed with a substantially constant depth along the groove.

  The large-bore piping of a land boiler causes defects such as cracks in the weld due to fatigue due to internal pressure, thermal stress, and the like. In this case, the repair welding method for the welded portion according to the first embodiment of the present invention is executed.

Here, as shown in FIG. 3A, a method for repairing a defect C generated over the large-diameter pipe material 3 and the weld metal 4 will be described as an example.
In the repair welding method for welded portions according to the first embodiment of the present invention, first, a step of cutting off a portion where a defect C such as a crack has occurred is performed by a mechanical or electrical method (FIG. 3B). reference). Specifically, as shown in FIG. 3 (b), the defect generated in the welded portion is excised including the large-diameter pipe material 3.

  Next, a step of repairing (overlay welding) the area where the defect has been removed with a welding material (second welding material 5) having a larger linear expansion coefficient and a larger creep strength than the large-diameter pipe materials 2 and 3 is executed. (See FIG. 3C). An Inconel (registered trademark) welding material (nickel-based alloy) is used as a material having a larger linear expansion coefficient and a larger creep strength than the large-diameter pipe materials 2 and 3.

  Thus, when the area | region where the defect was excised is repaired with the 2nd welding material 5, as shown in FIG.2 and FIG.3 (c), as shown in FIG.2 and FIG.3 (c), welding material (2nd welding material) is followed. The large-diameter pipe 3 and the weld metal 4 are joined (welded) through a welded material (hereinafter referred to as “repair weld metal 5”) in which the material 5) is melted and hardened. Heat-affected portions (HAZ) 35 and 45 are formed in regions affected by the heat of the second welding material 5 melted in the large-diameter pipe 3 and the weld metal 4. The heat affected portions 35 and 45 are formed along a boundary surface in contact with the repair weld metal 5 in the large diameter pipe material 3 and the weld metal 4. Specifically, it is formed with a substantially constant depth along the region where the defect has been removed. An overlapping heat affected zone (overlapping HAZ) 345 is formed in a region affected by the heat of the first welding material 4 and further affected by the heat of the second welding material 5.

  Thereby, as shown in FIG.2 and FIG.3 (c), the repair welding structure of the welding part which is Embodiment 1 of this invention is one large diameter pipe material 2 and the other large diameter of which are butt-welded. A V-shaped groove is provided between the pipe material 3, and the first welding material 4 is melted along the groove, and the large-diameter pipe material 2 and the other welding pipe 4 are passed through the solidified weld metal 4. The large diameter pipe material 3 is joined (welded). Further, the second welding material 5 is melted along the part where the defect has been removed, and the large-diameter pipe 3 and the weld metal 4 are joined (welded) via the solidified repair weld metal (repair weld portion) 5. Is done. Heat-affected zones (HAZ) 24 and 34 are formed in regions affected by the heat of the first welding material 4 melted in one large-diameter pipe 2 and the other large-diameter pipe 3. Heat-affected portions (HAZ) 35 and 45 are formed in regions affected by the heat of the second welding material 5 melted in the large-diameter pipe 3 and the weld metal 4. In addition, an overlapping heat affected zone (overlapping HAZ) 345 is formed in a region affected by the heat of the first welding material 4 and the heat of the second welding material 5.

  According to the repair weld structure of the welded portion that is the first embodiment of the present invention described above, a repair weld (repair weld metal) that is repair welded when the internal pressure and heat of the land boiler are applied to the large-diameter piping of the land boiler. 5) expands more than other parts (large-diameter pipe materials 2, 3 and weld metal 4). Thereby, a compressive stress arises in the welding part (large-diameter pipe materials 2 and 3 and weld metal 4) which makes the annular shape from which a part (repair weld metal 5) lacked. This compressive stress relieves tensile stress (hoop stress) generated in the circumferential direction by internal pressure and heat in a large-diameter pipe. Thereby, the action stress which acts on the heat affected zone by repair welding is reduced. By reducing the acting stress, strength reduction due to repair welding can be suppressed. As a result, it is possible to extend the creep life of the heat-affected zone by repair welding.

  In addition, since the second welding material 5 is made of Inconel (registered trademark) welding material having a larger creep strength than the large-diameter pipe materials 2 and 3, the repair welding metal 5 can also increase the creep life. Is possible.

FIG. 4 is a diagram showing the relationship between the repair weld length and the acting stress of the overlap HAZ, and FIG. 5 is a diagram showing the relationship between the repair weld length and the creep life ratio of the overlap HAZ.
As shown in FIG. 4, when the weld metal material and the repair weld metal material are the same material repair, the acting stress of the overlapping HAZ is constant even if the repair weld length is increased. Therefore, the working stress of the overlapping HAZ cannot be reduced. On the other hand, in the case of dissimilar material repair having a linear expansion coefficient larger than that of the weld metal material, if the repair weld length is increased, the acting stress of the overlapping HAZ decreases (inversely proportional).

  In addition, as shown in FIG. 5, in the case of repairing the same material, the creep life ratio of the overlapping HAZ is constant even if the repair welding length is increased, so that the creep life of the overlapping HAZ is extended by repair welding. I can't do it. On the other hand, in the case of repairing a different material having a linear expansion coefficient larger than that of the weld metal material, if the repair welding length is increased, the creep life ratio of the overlapping HAZ is increased, and the creep life is increased. This makes it possible to extend the creep life of the heat-affected zone by repairing a different material having a linear expansion coefficient larger than that of the weld metal material.

FIG. 6 is a diagram showing the conditions used when examining repair welding. FIG. 7 is a diagram showing the results of examination of repair welding, and FIG. 8 is a diagram showing the relationship between repair welding length and strain stress.
As shown in FIG. 6, the diameter of the large-diameter pipe is 600 mm, the pipe circumference of the large-diameter pipe is 1885 mm, ferritic heat-resistant steel using 9 to 12 wt% chromium as the weld metal, and Inconel (registered trademark) is used as the repair weld metal. This is the result of the study. The repair welding length R is examined in increments of 50 mm to 10 mm.

According to the conditions shown in FIG. 6, the thermal expansion difference L can be obtained by the following formula 1.

Further, the strain stress S can be obtained by the following formula 2.

  When these are arranged, the results shown in FIGS. 7 and 8 are obtained. 7 and 8, it can be seen that the strain stress S is proportional to the repair weld length.

[Embodiment 2]
FIG. 9 is a diagram showing a large-diameter pipe to which the welded part repair welding method according to the second embodiment of the present invention is applied. FIG. 10 is a diagram illustrating an outer surface of a welded portion repaired by the welded portion repair welding method according to the second embodiment of the present invention. FIG. 11 is a cross-sectional view for explaining a repair welding method for welded portions according to the second embodiment of the present invention.

Here, as shown in FIG. 11A, a method for repairing a defect C generated over the large-diameter pipe material 3 and the weld metal 4 will be described as an example.
In the repair welding method of the welding part which is Embodiment 2 of this invention, while including both the boundary part with the pipe material 2 of one large diameter, and the boundary part with the pipe material 3 of the other large diameter, one large diameter A step of cutting a region having a depth in the thickness direction from the surface of the tube material 2 and the other large-diameter tube material 3 so that the bottom surface of the region is along the surface is executed (see FIG. 11B).

  Next, a step of repairing (building-up welding) with a welding material (second welding material 6) having a larger linear expansion coefficient and a higher creep strength than the removed region is executed (FIG. 11C). reference). An Inconel (registered trademark) welding material (nickel-based alloy) is used as the welding material (second welding material 6) having a larger linear expansion coefficient and a larger creep strength than the cut region.

  Thus, when the area | region in which the defect was excised is repaired with the 2nd welding material 6, as shown in FIG.10 and FIG.11 (c), as shown in FIG.10 and FIG.11 (c), a welding material (2nd welding material) is followed. One large-diameter pipe 2 and the other large-diameter pipe 3 are joined (welded) through a welded material (hereinafter referred to as “repair weld metal 6”) in which the material 6) is melted and solidified. Then, in the region affected by the heat of the second welding material 6 melted in the pipe material 2 and the weld metal 4 on one large diameter and the pipe material 3 and the weld metal 4 on the other large diameter, the heat affected zone ( HAZ) 26, 36 are formed. The heat-affected portions 26 and 36 are formed along a boundary surface in contact with the repair weld metal 6 in one large-diameter tube material 2, the weld metal 4, and the other large-diameter tube material 3. Specifically, it is formed with a substantially constant depth along the region where the defect has been removed. Then, overlapping heat affected zones (overlapping HAZ) 246 and 346 are formed in a region affected by the heat of the first welding material 4 and further affected by the heat of the second welding material 6.

  Thereby, as shown in FIG.11 (c), the repair welding structure of the welding part which is Embodiment 2 of this invention has one large diameter pipe material 2 and the other large diameter pipe material 3 which are butt-welded. A V-shaped groove is provided between the first large-diameter pipe 2 and the other large-diameter pipe via the weld metal 4 in which the first welding material 4 is melted along the groove. The pipe material 3 is joined (welded). Further, the second welding material 6 is melted along the portion where the defect has been removed, and the large-diameter pipe materials 2 and 3 are joined to the weld metal 4 via the solidified repair weld metal 6 (repair weld). Welding). Heat-affected zones (HAZ) 24 and 34 are formed in regions affected by the heat of the first welding material 4 melted in one large-diameter pipe 2 and the other large-diameter pipe 3. Heat-affected zones (HAZ) 26 and 36 are formed in regions affected by the heat of the second welding material 6 melted in the large-diameter pipe materials 2 and 3 and the weld metal 4. In addition, overlapping heat affected zones (overlapping HAZ) 246 and 346 are formed in regions affected by the heat of the first welding material 4 and the heat of the second welding material 6.

  According to the repair weld structure of the weld portion according to the second embodiment of the present invention described above, a repair weld (repair weld metal) that is repair welded when the internal pressure and heat of the land boiler is applied to the large-diameter pipe of the land boiler. The portion) expands more than the other portions (the large-diameter pipe materials 2, 3 and the weld metal 4). As a result, a compressive stress is generated in an annular portion (large diameter pipe materials 2 and 3 and weld metal 4) in which a part (repair weld metal portion) is missing. This compressive stress relieves tensile stress (hoop stress) generated in the circumferential direction by internal pressure and heat in a large-diameter pipe. Thereby, the action stress which acts on the heat affected zone by repair welding is reduced. Moreover, the reduction in strength due to repair welding can be suppressed by reducing the acting stress. As a result, it is possible to extend the creep life of the heat-affected zone by repair welding.

  In addition, since the second welding material 6 is an Inconel (registered trademark) welding material having a creep strength larger than that of the large-diameter pipe materials 2 and 3, the repair welding metal 6 also increases the creep life. Is possible.

  As described above, since the present invention can suppress a decrease in strength due to repair welding, repair of a welded portion of a pipe affected by heat, such as a welded portion of a large-diameter pipe of a land-use boiler installed in a thermal power plant. It is suitable for.

2 First pipe material 24 Heat affected zone (HAZ)
26 Heat affected zone (HAZ)
3 Second pipe material 34 Heat affected zone (HAZ)
345 Overlap heat affected zone (overlap HAZ)
346 Overlap heat affected zone (overlap HAZ)
35 Heat-affected zone (HAZ)
36 Heat affected zone (HAZ)
4 First welding material (welded metal)
45 Heat-affected zone 5 Second welding material (repair weld metal) (repair weld zone)
6 Second welding material (repair weld metal) (repair weld)

Claims (4)

A repair welding method for a welded portion in which a first tubular material having a hollow cylindrical shape and a second tubular material having a hollow cylindrical shape are subjected to butt welding by applying the first welding material in the circumferential direction,
The first welding material uses the same material as the first pipe material and the second pipe material,
A step of cutting out defects generated in the welded portion including at least one of the first pipe material and the second pipe material, and the cutting step and the first pipe material and the first pipe after the cutting step . And a step of build-up welding with a second welding material having a linear expansion coefficient larger than the linear expansion coefficient of the welding material. 2. The repair welding method for a welded portion according to claim 1 , wherein the second welding material has a higher creep strength than the first pipe material and the second pipe material. A repair welding structure for a welded portion in which a first tubular material having a hollow cylindrical shape and a second tubular material having a hollow cylindrical shape are subjected to a first welding material in a circumferential direction and butt-welded,
The first welding material is made of the same material as the first pipe material and the second pipe material,
The first tubular member or said second linear expansion coefficient greatly than tubing in the region was resected defects generated on the welded portion, and said first weld material linear expansion coefficient larger than the second welding material A repair weld structure for a welded portion, comprising a repair weld portion that has been welded and welded, wherein the repaired butt portion is constituted by the first weld material portion and the repair weld portion . The repair welding structure for a welded portion according to claim 3 , wherein the second welding material has a higher creep strength than the first pipe material and the second pipe material.

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