JP4915251B2 - Clad welded structure of low alloy steel base metal - Google Patents

Description

  The present invention relates to a clad welded structure of a low alloy steel base material used in an environment where PWSCC (Primary Water Stress Corrosion Cracking) resistance is required.

  As shown in FIG. 2, in a pressurized water reactor, in an environment in contact with primary system reactor water (high-temperature and high-pressure water) such as a steam generator 23, a reactor pressure vessel 21, and a pipe 22, they are configured. Clad welding is applied to the wetted surface of the structural material to prevent corrosion.

  For example, as shown in FIG. 3, the bottom surface 32 of the water chamber 31 in the steam generator 23 has been formed on the surface of the base material (structural material) 11 made of low alloy steel as shown in FIG. -By welding a 52 alloy (alloy having almost the same composition as a 690 Ni-base alloy) which is a weld metal of a Cr-Fe alloy, a clad weld layer (lining layer) 16 is provided, so that the low alloy steel base material 11 It was anticorrosive. Here, the reason why the 52 alloy is used as the weld metal is that it has excellent characteristics as a PWSCC countermeasure material.

JP-A-5-293661

  By the way, while 52 alloy is excellent as a PWSCC countermeasure material, when the clad weld layer 16 of 52 alloy is welded to the surface of the low alloy steel base material 11 made of low alloy steel, solidification cracking and delayed cracking occur in the welded portion. There is a risk of reheat cracking. Conventionally, when such a crack occurs, a sound welded part has been obtained by removing the welded area of the poorly welded part and re-welding again.

  However, repeatedly applying welding heat to the low alloy steel base material 11 has a negative effect on the heat-affected zone, so it is not suitable as a structural material for primary cooling system equipment (under a radioactive environment) in a pressurized water reactor. It is not preferable. In addition, in order to obtain a sound welded portion, it is necessary to use advanced welding techniques such as strict management of heat input and purge (gas shield).

  Accordingly, an object of the present invention is to provide a clad welded structure of a low alloy steel base material which is excellent in welding workability and excellent in PWSCC resistance.

In order to achieve the above-mentioned object, the invention of claim 1 is directed to a Ni—Cr—Fe system on the surface of a base material made of low alloy steel so as to be used in contact with the primary system water of a pressurized water reactor. In a clad weld structure provided with a clad weld layer made of an alloy weld metal, an inner layer side clad weld layer is formed by welding 82 alloy, which is a weld metal of the Ni-Cr-Fe alloy , to the surface of the low alloy steel base material. A low-alloy steel base material characterized in that an outer-layer-side clad weld layer is provided on the inner-layer-side clad weld layer by welding 52 alloy, which is a weld metal of the Ni-Cr-Fe-based alloy. This is a clad welded structure.

  In the invention of claim 2, when the thickness of the low alloy steel base material is 1, the thickness of the inner layer side cladding weld layer is 0.02 to 0.06, and the thickness of the outer layer side clad weld layer is The clad welded structure of a low alloy steel base material according to claim 1, which is 0.08 to 0.12.

  The invention of claim 3 is the clad weld structure of the low alloy steel base material according to claim 1 or 2, wherein the low alloy steel constituting the low alloy steel base material is SA508.

  According to the present invention, the inner layer side clad weld layer is provided by welding 82 alloy on the surface of the low alloy steel base material, and the outer layer side clad weld layer is welded on the inner layer side clad weld layer. By providing the above, it is possible to obtain a clad welded structure of a low alloy steel base material which is excellent in welding workability and excellent in PWSCC resistance.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1 (c), the clad welded structure of the low alloy steel base material according to a preferred embodiment of the present invention is formed on the surface (welded surface) of the base material 11 made of low alloy steel with the 82 alloy 13 Is welded to provide an inner-layer-side clad weld layer 14, and an outer-layer-side clad weld layer 16 is provided on the inner-layer-side clad weld layer 14 by welding 52 alloy 15. Moreover, when the thickness of the low alloy steel base material 11 is 1, the thickness of the inner layer side cladding weld layer 14 is 0.02 to 0.06, preferably 0.025 to 0.05, and the outer layer side cladding weld layer. The thickness of 16 is 0.08 to 0.12, preferably about 0.1. Here, the “inner layer side” indicates the side close to the low alloy steel base material 11, and the “outer layer side” indicates the side away from the low alloy steel base material 11. The “surface” indicates the inner surface of the base material 11 (for example, a container or a tube).

  The 82 alloy 13 is a Ni—Cr—Fe alloy having almost the same composition as a 600-based Ni-based alloy (for example, Inconel 600 (registered trademark)), and the 52 alloy 15 is a 690-based Ni-based alloy (for example, Inconel 690). (Registered Trademark)) is a Ni—Cr—Fe alloy having almost the same composition as that of the alloy 52, and the 52 alloy 15 has a higher Cr content than the 82 alloy 13 and has improved corrosion resistance.

  Since the constituent material of the low alloy steel base material 11 is finally clad welded to form an anticorrosion layer, it is sufficient that it has only strength against pressure (pressurized primary system reactor water). For this reason, as a constituent material of the low alloy steel base material 11, a low alloy steel having higher strength and lower cost than stainless steel is preferable, and examples thereof include SA508 (ASME (American Society of Mechanical Engineers) standard). In addition to SA508, all steel materials conventionally used as low alloy steels for nuclear reactors are applicable.

  Next, a method for forming a clad welded structure of a low alloy steel base material according to the present embodiment will be described.

  First, as the low alloy steel base material 11, for example, a structural material constituting the bottom surface 32 of the water chamber 31 in the steam generator 23 shown in FIG. 3 is prepared. This structural material is composed of, for example, SA508 (ASME standard) having excellent strength.

  Thereafter, as shown in FIG. 1A, clad welding is performed on the entire surface (the upper surface in the drawing) of the low alloy steel base material 11 using a 82 alloy 13 as a welding material and a TIG welding machine 12. Since the structural material constituting the low alloy steel base material 11 is a large member having a diameter of about 4 m, for example, the bottom surface 32 is substantially flat. For this reason, as a welding material, it is preferable to use the thing of a flat plate shape (sheet shape) rather than a rod shape (wire shape). Further, when performing the clad welding, if the welding object is small, the low alloy steel base material 11 may be fixed and the TIG welding machine 12 may be rotated and moved. However, if the welding object is large, the TIG welding machine 12 may be used. Is fixed and the low alloy steel base material 11 is preferably rotated and moved.

  By this clad welding, the 82 alloy 13 is melted and melted into the surface of the low alloy steel base material 11, and the inner layer side that is a melting and solidifying portion (bead) of the 82 alloy 13 is formed on the entire surface of the low alloy steel base material 11. A clad weld layer 14 is provided. One layer is sufficient for the number of the melted / solidified portions constituting the inner-layer-side clad weld layer 14.

  Next, as shown in FIG. 1B, clad welding is similarly performed on the inner-layer-side clad weld layer 14 using a 52 alloy 15 and a TIG welder 12 as welding materials. As a result, the 52 alloy 15 is melted and melted into the surface of the inner layer side cladding weld layer 14, and the outer layer side clad weld layer 16, which is a melting / solidified portion of the 52 alloy 15, is formed on the entire surface of the inner layer side clad weld layer 14. Provide. The number of layers of the melted / solidified portion constituting the outer layer side clad weld layer 16 is appropriately adjusted according to the target thickness, and the thickness of the outer layer side clad weld layer 16 is adjusted by the number of layers of the melted / solidified portion. To do. For example, when the thickness of the low alloy steel base material 11 made of SA508 is about 40 mm, the thickness of the inner layer side clad weld layer 14 made of 82 alloy 13 is about 1 to 2 mm, and the outer layer side clad weld made of 52 alloy 15 The thickness of layer 16 is adjusted to about 4 mm.

  Thereafter, the surface of the outer-layer-side clad weld layer 16 is appropriately ground with a grinding tool such as a grinder to smooth the surface, and as shown in FIG. 1C, the clad of the low alloy steel base material according to the present embodiment A welded structure is obtained. This grinding may be performed on the inner-side clad weld layer 14.

  Unlike the outer clad weld layer 16 made of 52 alloy 15, the inner clad weld layer 14 made of 82 alloy 13 has good weldability to the low alloy steel base material 11. For this reason, when the inner layer side clad weld layer 14 is clad welded to the surface of the low alloy steel base material 11, there is no possibility that solidification cracks, delayed cracks, reheat cracks, etc. will occur in the welds. Moreover, since the 82 alloy 13 and the 52 alloy 15 are the same Ni-Cr-Fe type alloys although the compositions are somewhat different, the weldability of the outer-layer-side clad weld layer 16 to the inner-layer-side clad weld layer 14 is good. For this reason, even when the outer-layer-side clad weld layer 16 is clad-welded on the inner-layer-side clad weld layer 14, there is no possibility that solidification cracks, delayed cracks, reheat cracks, etc. will occur in the welded portion.

  By adopting such a clad welding structure, when clad welding the anticorrosion layer (PWSCC layer) to the surface of the low alloy steel base material 11, various cracks do not occur and it is not necessary to repeat the welding (or Therefore, a clad weld structure with excellent weldability can be obtained.

  Further, when clad welding is performed on the surface of the low alloy steel base material 11, particularly when the first layer clad welding is performed, welding is not repeated and only one heat input of the welding heat is required for each welded portion. For this reason, the adverse effect of the heat-affected zone on the low alloy steel base material 11 is reduced, and the clad weld quality of the weld layer can be greatly improved. As a result, the reliability of the primary cooling system equipment, which is an important equipment in the PWR nuclear power plant, can be further ensured.

  Furthermore, since the anticorrosion layer (PWSCC layer) provided on the surface of the low alloy steel base material 11 is the outer layer side clad weld layer 16 of the 52 alloy 15 having excellent characteristics as a PWSCC countermeasure material, it is excellent in PWSCC resistance. It becomes a clad weld structure.

  In addition, SA508, which constitutes the low alloy steel base material 11, is a steel that is susceptible to weld cracking. Therefore, it is necessary to strictly manage welding conditions such as heat input management and purge (gas shield), and advanced welding technology. Need. However, in order to form the clad welded structure of the low alloy steel base material according to the present embodiment, a new welding technique is not particularly required, and an already established conventional welding technique can be applied. For this reason, a new capital investment is not required, the existing welding equipment can be used, and a cost increase can be suppressed.

It is a cross-sectional view showing a clad weld structure of a low alloy steel base material according to a preferred embodiment of the present invention. FIG. 1A is a diagram for explaining the formation state of the inner-layer-side clad weld layer, FIG. 1B is a diagram for explaining the formation state of the outer-layer-side clad weld layer, and FIG. 1C is a clad weld. It is a cross-sectional view of the subsequent low alloy steel base material. It is a schematic diagram in the reactor containment vessel in a pressurized water reactor. It is a fragmentary sectional view of a steam generator. It is a cross-sectional view which shows the clad welding structure of the conventional low alloy steel base material.

Explanation of symbols

11 Low alloy steel base material 13 82 alloy (welding material)
14 Inner layer side clad weld layer 15 52 alloy (welding material)
16 Outer layer side cladding weld layer

Claims (3)

In a clad welding structure in which a clad weld layer made of a weld metal of a Ni-Cr-Fe alloy is provided on the surface of a base material made of low alloy steel to be used in contact with the primary water of a pressurized water reactor . , the surface of the low alloy steel base metal, the inner side cladding welding layer is provided by welding a 82 alloy is a weld metal of the Ni-Cr-Fe-based alloy, on the inner side cladding welding layer, said Ni A clad welded structure of a low alloy steel base material, wherein an outer clad weld layer is provided by welding 52 alloy which is a weld metal of a Cr—Fe alloy .   When the thickness of the low alloy steel base material is 1, the thickness of the inner layer side clad weld layer is 0.02 to 0.06, and the thickness of the outer layer side clad weld layer is 0.08 to 0.12. The clad welded structure of a low alloy steel base material according to claim 1.   The low alloy steel base metal clad welded structure according to claim 1 or 2, wherein the low alloy steel constituting the low alloy steel base material is SA508.

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