Nuclear power plant steam generator heat transfer tube welding plug and using method thereof

Abstract

The invention provides a nuclear power plant steam generator heat transfer tube welding plug, the length of the welding plug is 3.8 D, the inner diameter value is D, the wall thickness t of the plug is 0.2 D and is smaller than or equal to 2.3 mm, the welding plug is hollow, D is the inner diameter value of a heat transfer tube, and the inner diameter value range is 12.6 mm > D > = 19.05 mm. The invention further provides a using method of the nuclear power plant steam generator heat transfer tube welding plug. The welding plug can meet the requirement for blocking welding of heat transfer pipes of steam generators of various reactor types in a nuclear power plant, is suitable for blocking welding of heat transfer pipes of evaporators of various reactor types in the nuclear power plant, and meanwhile can meet the pressure bearing requirement and reduce the influence on a primary side flow field as much as possible.

Description

Technical Field

[0001] The invention relates to the technical field of heat transfer tube plugging, and in particular to a heat transfer tube welding plugging for a steam generator in a nuclear power plant and a use method thereof. Background Art

[0002] The steam generator heat transfer tube is the main nuclear safety pressure boundary of the primary circuit of a nuclear power plant. Due to the large number of heat transfer tubes, small tube diameter, thin wall thickness and large surface area, it is affected by structural materials, manufacturing process and operating environment. It is also the equipment component with the weakest primary circuit pressure boundary and the highest probability of defects.

[0003] The heat transfer tubes of steam generators in nuclear power plants are operated under the erosion and evaporation of high-temperature and high-pressure media for a long time, which is prone to mechanical or chemical damage. Once the heat transfer tubes are damaged, it may directly cause the primary circuit medium and the radioactive substances in it to enter the secondary circuit and then be released into the environment. Since 1971, there have been more and more accidents of rupture of heat transfer tubes of steam generators in nuclear power plants in many countries.

[0004] The existing nuclear power plant steam generator mechanical plugging or welding plugging lacks the analysis of the impact of the new plug on the internal flow field of the primary side of the steam generator. The new plug structure may cause erosion and thinning of the heat transfer tube or tube sheet. The existing nuclear power plant steam generator welding plugging also lacks the integrated design of the plug, heat transfer tube and tube sheet welding structure. At the same time, the wall thickness of the existing welding plug is quite different from that of the heat transfer tube, which easily leads to uneven stress distribution of the welding joint. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects described in the prior art, thereby providing a nuclear power plant steam generator heat transfer tube welding plug and a method of using the same, which optimizes the internal flow field on the primary side of the steam generator and the residual stress distribution of the welded joint after the plug is added, and alleviates the erosion corrosion of the heat transfer tube and the tube sheet and the stress corrosion cracking tendency at the welded joint.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A welding plug for a heat transfer tube of a steam generator in a nuclear power plant, wherein the welding plug has a length of 3.8D, an inner diameter value of D, a plug wall thickness t=0.2D and less than or equal to 2.3mm, and the welding plug is hollow inside, wherein D is the inner diameter value of the heat transfer tube, and the value range of the inner diameter is 12.6mm>D≥19.05mm.

[0008] As an implementable manner, the length of the hollow portion of the welding plug is 3D.

[0009] As an practicable manner, the surface roughness of the welding plug is 6.3.

[0010] As an implementable manner, the upper deviation of the outer diameter value is 0 mm, and the lower deviation is -0.2 mm.

[0011] As an practicable manner, the material of the welding plug is 690TT nickel-based material.

[0012] As an practicable manner, the inner diameter of the heat transfer tube is 12.7 mm or 19.05 mm.

[0013] A method for using a welding plug for a heat transfer tube of a steam generator in a nuclear power plant comprises the following steps:

[0014] Step 1: Place the solid part of the welding plug downward in the heat transfer tube, and the upper end of the welding plug is higher than the steam generator tube sheet;

[0015] Step 2: spot-fixing the welding plug and the heat transfer tube;

[0016] Step 3: Weld the welding plug to the nickel-based cladding layer on the upper part of the evaporator tube sheet, and use welding wire to fill and cover the weld; during welding, melt the part of the heat transfer tube protruding from the tube sheet to form a fillet weld between the welding plug and the heat transfer tube sheet.

[0017] Compared with the prior art, the nuclear power plant steam generator heat transfer tube welding plug and the use method thereof provided by the present invention have the following beneficial effects:

[0018] The welding plug of the present invention can meet the requirements of pipe plugging welding of heat transfer pipes of steam generators of various reactor types in nuclear power plants. Field practice has verified that the welding plug of the present invention is suitable for pipe plugging welding of heat transfer pipes of evaporators of various reactor types in nuclear power plants, and can meet the pressure requirements and minimize the impact on the primary side flow field.

[0019] After welding, the test pieces are visually inspected, penetrated and metallographically inspected to ensure that the quality of the weld meets the requirements. At the same time, in the maintenance of automatic welding pipe blockage, the risk of high-dose radiation exposure for welders can be reduced, and the probability of irreversible defects such as heat transfer pipe melting through and surrounding heat transfer pipe damage caused by traditional manual welding can also be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A cross-sectional view of a welding plug for a heat transfer tube of a steam generator in a nuclear power plant provided by an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of the assembly of a welding plug for a heat transfer tube of a steam generator in a nuclear power plant provided by an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the structure of the heat transfer pipe opening after cutting and polishing provided in an embodiment of the present invention.

[0024] Description of reference numerals:

[0025] 1. Heat transfer tube; 2. Carbon steel substrate; 3. Welding plug; 4. Nickel-based alloy cladding layer. DETAILED DESCRIPTION

[0026] The following is further explained in detail through specific implementation methods.

[0027] like Figure 1 As shown, the present invention provides a welding plug for a heat transfer tube of a steam generator in a nuclear power plant (hereinafter referred to as welding plug 3), and welding plug 3 is a wire-filled welding plug for a heat transfer tube of a steam generator in a nuclear power plant. Welding plug 3 is a wire-filled welding plug for a heat transfer tube of a steam generator in a nuclear power plant. The welding plug 3 is hollow inside, the length of welding plug 3 is 3.8D, and the length of the hollow part is 3D. The outer diameter value of welding plug 3 is D, the upper deviation is 0mm, and the lower deviation is -0.2mm. The wall thickness of the plug t=0.2D and not less than 2.3mm, and the value is accurate to 0.1mm. In the above parameters, D is the inner diameter value of the heat transfer tube 1, and the inner diameter value D of the heat transfer tube is 12.6mm>D≥19.05mm. The inner diameter value of the heat transfer tube is, for example, 12.7mm, 19.05mm, and the surface roughness of the welding plug is 6.3. The chamfer of the hollow part of the welding plug is R0.8, and the chamfer of the lower part of the welding plug is C0.8.

[0028] The welding wire used for welding the welding plug 3 provided by the present invention is ERNiGrFe-7A with a diameter of φ1.6 mm.

[0029] According to the material matching principle, the welding plug material is processed with 690TT nickel-based material, which is used for assembly with the SG branch pipe material Incoloy-800 (SB-163UNS N08800) iron-nickel alloy tube. On this basis, the internal fluid mechanics model of the primary side of the steam generator is established to optimize the design of the heat transfer tube structure and the plugging welding joint structure. The original steam generator heat transfer tube plug is a solid plug, which is optimized to a dummy tube plug. Through the fluid mechanics analysis of the water chamber tube sheet area on the primary side of the steam generator, it is determined that the plug length is 3.8D, the plug hole inner diameter range is 12.6mm>D≥19.05mm, and the plug hole depth is 3D. The dummy tube plug optimizes the internal flow field of the primary side of the steam generator after plugging, and alleviates the erosion and corrosion damage of the heat transfer tube or tube sheet.

[0030] Ensure that the welding plug 3 can meet the pressure requirements and minimize the impact on the primary side flow field.

[0031] The plug material and size are determined according to the needs of automatic welding maintenance of pipe plugging, combined with the structure, material properties, vibration load, welding process parameters, etc. of the maintenance object. The welding structure of the plug and the tube sheet is designed according to the welding structure of the steam generator tube sheet and the size of the plug. After the hardness test and micro-punching shear test of the simulated parts of the welded joint, the welding residual stress of the plug welding structure designed by this patent is significantly reduced compared with the solid plug welding structure. The microscopic characterization of the cladding metal precipitates in the weld joint also shows that the precipitation of the metal grain boundary of the weld metal in the plug welding structure designed by this patent is effectively suppressed, thereby effectively reducing the cracking of the weld.

[0032] like Figure 2 and Figure 3 As shown, the present invention also provides a method for using a welding plug for a heat transfer tube of a steam generator in a nuclear power plant, comprising the following steps:

[0033] Step 0 (preparation step): Cut and grind the heat transfer tube 1 before assembling the welding plug 3. Take precautions against foreign matter before grinding to prevent debris from falling into the heat transfer tube during grinding. The heat transfer tube 1 after grinding should be smooth and burr-free. The heat transfer tube 1 after grinding should be 1.3mm higher than the evaporator tube sheet, with an upper deviation of +0.2mm and a lower deviation of -0.1mm. The upper part of the evaporator tube sheet is a nickel-based alloy cladding layer 4, and the lower part is a carbon steel substrate 2.

[0034] Step 1: Figure 3 As shown, the solid part of the thread-filled plug with a surface roughness of 6.3 is placed downward in the heat transfer tube, and the upper end of the welding plug 3 (thread-filled plug) is 5.2 mm higher than the steam generator tube sheet, with an upper deviation of +0.13 mm and a lower deviation of -0.12 mm.

[0035] Step 2: Use ERNiGrFe-7A high nickel-chromium welding wire with a diameter of φ1.6 mm to spot-fix the wire-filling plug and the heat transfer tube 1.

[0036] Step 3: Then weld the wire-filling plug to the nickel-based cladding layer 4 on the upper part of the evaporator tube sheet, using ERNiGrFe-7A welding wire with a diameter of φ1.6mm to fill and cover the weld. During welding, the part of the heat transfer tube 1 that protrudes above the tube sheet should be melted to form a fillet weld between the welding plug 3 and the heat transfer tube sheet.

[0037] Step 4: After welding is completed, conduct a visual inspection of the weld appearance. The weld surface should be smooth without obvious bumps and the weld size should be no less than 2.5mm. There should be no defects such as cracks, lack of fusion, pores, slag inclusions, etc.

[0038] Step 5: Finally, liquid penetration test is performed on the weld area between the welding plug 3 and the heat transfer tube 1. No linear display or circular display with a diameter greater than 0.5 mm is allowed on the outer surface, otherwise local repair should be performed; if defects exceeding the standard are found, they need to be repaired and eliminated.

[0039] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A welding plug for a heat transfer tube of a steam generator in a nuclear power plant, characterized in that: The length of the welding plug is 3.8D, the outer diameter is D, the wall thickness of the plug is t=0.2D and is less than or equal to 2.3mm, and the inside of the welding plug is hollow, wherein D is the inner diameter of the heat transfer tube, and the value range of the inner diameter is 12.6mm>D≥19.05mm.

2. The welding plug for heat transfer tube of steam generator of nuclear power plant according to claim 1, characterized in that: The length of the hollow portion of the welding plug is 3D.

3. The welding plug for heat transfer tube of steam generator of nuclear power plant according to claim 1, characterized in that: The surface roughness of the welding plug is 6.

3.

4. The welding plug for heat transfer tube of steam generator of nuclear power plant according to claim 1, characterized in that: The upper deviation of the outer diameter value is 0 mm, and the lower deviation is -0.2 mm.

5. The welding plug for heat transfer tube of steam generator of nuclear power plant according to claim 1, characterized in that: The material of the welding plug is 690TT nickel-based material.

6. The welding plug for heat transfer tube of steam generator of nuclear power plant according to claim 1, characterized in that: The inner diameter of the heat transfer tube is 12.7 mm or 19.05 mm.

7. A method for using the welding plug for heat transfer tube of a steam generator in a nuclear power plant according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Place the solid part of the welding plug downward in the heat transfer tube, and the upper end of the welding plug is higher than the steam generator tube sheet; Step 2: spot-fixing the welding plug and the heat transfer tube; Step 3: Weld the welding plug to the nickel-based cladding layer on the upper part of the evaporator tube sheet, and use welding wire to fill and cover the weld; during welding, melt the part of the heat transfer tube protruding from the tube sheet to form a fillet weld between the welding plug and the heat transfer tube sheet.

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