JP5038775B2 - Welding method for structures - Google Patents

Description

  The present invention relates to a method for welding a structure that improves residual tensile stress due to the influence of welding heat during welding of the structure.

  In general, there are thermal expansion due to welding and residual stress due to plastic strain as causes of stress corrosion cracking (SCC) occurrence and progress in welded structures and fatigue strength reduction of welded structures.

  Austenitic stainless steel, which is a material for structures such as containers and pipes in nuclear power plants, tends to precipitate Cr carbide at the grain boundaries by welding, and a Cr-deficient layer is formed near the grain boundaries. It is known that cracking susceptibility (material sensitization) increases. Further, if the welded part (welded metal part and heat-affected part) is exposed to a corrosive environment such as high-temperature water in a state where a high tensile residual stress exists, stress corrosion cracking is likely to occur.

  In order to prevent this stress corrosion cracking, it is necessary to remove one of the three factors of material sensitization, tensile residual stress, and corrosive environment. For this reason, it is strongly required to improve the tensile stress remaining in the vicinity of the surface of the welded part exposed to a corrosive environment such as water to a compressive stress.

As a method for reducing the residual stress resulting from this welding, there is an invention that discloses welding conditions that materialize the material of the weld metal and the heat input conditions during welding.
JP 2006-198557 A JP 2007-21516 A

  As a countermeasure against stress corrosion cracking due to tensile residual stress due to thermal effects during welding of structures, the surface of the welded part is improved by forming surface compressive stress by surface improvement treatment to prevent the occurrence of stress corrosion cracking An attempt is being made.

  Here, the surface improvement treatment means, for example, that shot peening, laser peening, or water jet peening is individually applied to the base material of the structure and the surface of the welded portion, and compressive stress is applied to the surface of the base material and the welded portion to add residual stress. It is to make improvements. Shot peening improves the residual stress by applying small metal balls (shots) to the surface of the base metal and the weld at high speed, and improves the fatigue strength, wear resistance, and stress corrosion resistance of the surface. In laser peening, the surface of the base metal and the welded part is irradiated with a high-energy pulse laser to generate atomic plasma on the surface of the material constituting the base metal and the welded part, and a shock wave due to the reaction force of this plasma generation is generated on the base. Propagating through materials and welds to improve residual stress. Water jet peening improves residual stress by applying water flow at high speed to the surface of the base material and the weld.

  However, in this surface improvement treatment, the depth of the welded portion where the stress is improved is limited to the surface layer portion, the manufacturing cost increases due to an increase in the number of manufacturing steps, the difficulty of implementation for the welded portion that becomes difficult to access after welding, etc. There is a problem, and there is a need for a manufacturing method for providing a reliable welded joint at a lower cost for preventing stress corrosion cracking.

  Moreover, the above-mentioned patent document introduces compressive residual stress as a measure against stress corrosion cracking by setting the welding conditions of a structure that embodies the material of the weld metal and the heat input conditions during welding.

  Therefore, by controlling the distribution of residual stress in the plate thickness (depth) direction and plane direction of the weld due to the influence of welding heat, or by actively introducing compressive residual stress into the weld, It is possible to provide a welded structure having a weld portion with a large margin.

  In the prior art, a method of reducing the tensile residual stress to the inside in the plate thickness direction of the weld by using transformation expansion due to martensitic transformation of the weld metal has been shown. A welded structure used in a corrosive environment such as a furnace internal structure is not suitable for application due to problems such as corrosion resistance.

  In order to solve these problems, the present invention provides a welding method for a structure in which a welding condition in which a residual stress in the vicinity of a weld is made a compressive residual stress is calculated by an analytical method before an actual welding process is performed. provide.

In order to solve the above-described problems, in the present invention, in a method for welding a structure having a weld that is exposed to a corrosive environment, an analysis condition that simulates the thermal effect during welding is set, and the temperature distribution in the vicinity of the weld is determined. After performing the required heat transfer analysis, a thermal elastic-plastic stress analysis is performed based on the temperature distribution to determine the residual stress in the vicinity of the weld, and the residual stress in the vicinity of the weld exposed to the corrosive environment is converted into a compressive stress. The analysis condition is specified, the welding condition reflecting the specified analysis condition is set, and the structure is welded. The analysis condition is calculated from the welding current, welding voltage, and welding speed at the time of welding. Welding heat input per unit, cooling method, preheating method, welding sequence when constructing a plurality of welding passes, and the welding position, these conditions are set and combined as necessary to reduce the residual stress demand, the analysis conditions Upon setting of a representative welding path located less than all of the plurality of welding passes of applying during the welding select the required, the Rukoto determined the residual stress in combination to set the analysis conditions of the representative weld pass position to the required A feature welding method is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the welding method of the structure performed by calculating the welding condition which makes the residual stress of the vicinity of a welding part compressive residual stress by an analytical method before implementing an actual welding process can be provided.

  An embodiment of a method for welding a structure according to the present invention will be described with reference to the drawings.

  Note that the stress is treated as positive tensile stress and negative compressive stress.

[First Embodiment]
1st Embodiment of the welding method of the structure based on this invention is described with reference to FIGS.

  1 and 2 are diagrams for explaining the outline of the periphery of the welded portion of the core shroud 1 housed in the reactor containment vessel of the boiling water reactor.

  In the core shroud 1 accommodated in the reactor pressure vessel, a groove 3 is formed on a substantially cylindrical base material 2 made of stainless steel, and the groove 3 is welded by a welding portion 4.

  The groove shape of the groove 3 is a one-side groove. A welder is disposed inside the cylinder of the core shroud 1, and the weld metal 4 is welded from the cylindrical outer surface side to the inner surface side of the core shroud 1.

  The welding method of the structure in this embodiment is a method of welding by setting in advance a welding condition for converting the residual stress generated on the outer surface in the vicinity of the welded portion 4 of the core shroud 1 to a compressive residual stress.

  FIG. 3 is a diagram illustrating a method of setting welding conditions for a structure.

  In FIG. 3, in step S <b> 1, first, the total number of welding passes in the actual welding process is placed on the outer surface (inner surface) of the core shroud 1 that is the reactor internal structure of the reactor pressure vessel and the groove 3 position in the thickness direction of the base material 2. Set fewer welded sections. The welding section selects and sets a required welding pass position representing all the welding passes or a position where a plurality of welding passes are grouped. Next, an analysis condition that simulates the thermal effect of the welding condition of each welded portion of the core shroud 1 constituting the structure is created. Further, a residual stress analysis is performed which includes a heat transfer analysis based on the analysis conditions of each welded portion and a thermoelastic-plastic stress analysis based on the temperature distribution obtained from the heat transfer analysis. Based on the result of the residual stress analysis, parameter analysis is performed to set a plurality of analysis conditions for the welded portion in which the residual stress generated on the outer surface in the vicinity of the welded portion 4 of the core shroud 1 is compressed residual stress.

  In step S2, first, a required analysis condition is selected from the analysis conditions of a plurality of weld construction parts obtained by the parameter analysis in step S1. Next, the welding conditions of the welded part that reflects the analysis conditions of the selected welded part are welded to multiple weld paths (grouped weld paths) in the actual welding process that is performed around the welded part. Condition. Furthermore, appropriate conditions are selected to create analysis conditions that simulate the welding conditions of the grouped welding paths.

  Step S3 is based on the residual stress analysis composed of the heat transfer analysis based on the analysis condition of the welding path created in Step S2 and the thermoelastic-plastic stress analysis based on the temperature distribution obtained from this heat transfer analysis. Perform analysis.

  In step S4, the optimum condition is determined by determining whether or not the residual stress analysis result obtained from the all-pass analysis in step S3 is the residual stress generated on the outer surface in the vicinity of the welded portion 4 of the core shroud 1 as a compressive residual stress. decide. When satisfied, the welding condition of the welding path in the actual welding process reflecting the analysis condition of the welding path is set, and when not satisfied, the process proceeds to Step 2.

  In this parameter analysis, as an example, a welding configuration 6A (FIG. 4 (A)) in which the welding portion 5A is welded to the position of the groove 3 on the outer surface of the core shroud 1, the thickness direction of the base material 2 from the outer surface of the core shroud 1 A welding configuration 6B (FIG. 4B) in which the welding portion 5B is welded to the groove 3 position having a depth of about ¼, and the thickness direction of the base material 2 from the outer surface (inner surface) of the core shroud 1 is about 1 6C (FIG. 4 (C)) in which the welding portion 5C is welded to the groove 3 position at a depth of / 2, and the depth of about 1/4 of the base material 2 from the inner surface of the core shroud 1 A welding configuration 6D (FIG. 4D) in which the welding construction portion 5D is welded to the groove 3 position and a welding configuration 6E in which the welding construction portion 5E is welded to the groove 3 position on the inner surface of the core shroud 1 (FIG. 4). (E)) Residual stress analysis is performed for each welding mode.

  In addition, the welding part 5E on the inner surface of the core shroud 1 which is the final welding part is subjected to residual stress analysis for each pass in order to simulate an actual welding process in which welding is performed in a plurality of passes, such as when performing cosmetic finishing.

  This residual stress analysis is composed of a heat transfer analysis of a welding form 6 that simulates heating by welding of the welding portion 5 and a thermoelastic-plastic stress analysis based on a temperature distribution obtained from this heat transfer analysis. This heat transfer analysis is performed by combining a plurality of analysis conditions for the welding heat input H of the welding construction part 5, the preheating T at the time of welding, and the cooling time S.

  In addition, the thermoelastic-plastic stress analysis in the parameter analysis is performed on the base material 2 of the welded form 6B to which the welded part 5B is welded and the base material 2 of the welded form 6C to which the welded part 7B and the welded part 5C are welded. Base material 2 and welded part 7D of welded form 6D to which welded part 7C and welded part 5D are welded, and base material 2 of welded form 6E and welded part 5E to welded welded part 5E, respectively. 2 and the welded part 7 are analyzed under the condition that no stress remains.

  FIG. 5 shows welding in which a welded portion 5C is welded from the outer surface (inner surface) of the core shroud 1 shown in FIG. It is an example of the result of the residual stress analysis which preheated T at the time of welding and cooling time S were made constant, and the welding heat input H was selected as required for Form 6C, and the residual stress generated on the outer surface near the weld 4 of the core shroud 1 It is a figure which shows the circumferential direction component.

The welding heat input H shown in FIG. 5 has a relationship of [Equation 1].
[Equation 1]
Weld heat input H _C1 > Weld heat input H _C2 > Weld heat input H _C3

From the result of the residual stress analysis in FIG. 5, the vicinity of the welded portion 4 of the core shroud 1 is welded from the outer surface (inner surface) of the core shroud 1 to the position of the groove 3 at a depth in the thickness direction 1/2 of the base material 2. The analysis condition of the welding heat input H that causes the residual stress generated on the outer surface of the steel to be compressive residual stress is the welding heat input H _C1 .

  FIG. 6 shows welding in which a welding portion 5C is welded from the outer surface (inner surface) of the core shroud 1 shown in FIG. It is an example of the result of the residual stress analysis which preheating T at the time of welding and welding heat input H were made constant, and cooling time S was selected suitably about form 6C, and the residual stress produced on the outer surface near the weld 4 of the core shroud 1 It is a figure which shows the circumferential direction component.

The cooling time S shown in FIG. 6 has a relationship of [Equation 2].
[Equation 2]
Cooling time S _C1 <Cooling time S _C2 <Cooling time S _C3

From the result of the residual stress analysis in FIG. 6, the welded portion of the outer surface of the core shroud 1 is welded from the outer surface (inner surface) of the core shroud 1 to the position of the groove 3 at a depth of 1/2 in the thickness direction of the base material 2. The analysis condition of the cooling time S in which the residual stress generated in the vicinity of 4 becomes the compressive residual stress is the cooling time _SC1 .

  FIG. 7 is a diagram showing the relationship between the results of residual stress analysis between the welding heat input amount H and the cooling time S with the preheating T being constant.

  As shown in FIG. 7, when the preheating T is constant, the residual stress generated on the outer surface near the welded portion 4 of the core shroud 1 is compressed if the welding heat input H is large and the cooling time S is small. Residual stress.

  Further, other welding forms 6A, 6B, 6D, and 6E in which the welding portion is welded at the position of the groove 3 having a required depth in the thickness direction of the outer surface (inner surface) of the core shroud 1 and the base material 2, Residual stress analysis is performed with the preheating T during welding constant and the welding heat input H and cooling time S selected as required.

Then, when welding is performed on welding forms 6A, 6B, 6C, 6D, and 6E in which the welding portion is welded to the position of the groove 3 having a required depth in the thickness direction of the outer surface (inner surface) of the core shroud 1 and the base material 2. The residual stress (circumferential component of the outer surface in the vicinity of the welded portion 4 of the core shroud 1 to be evaluated) having as variables the welding heat input H with a constant preheating T and the heat transfer coefficient α which is an index representing the cooling time S (Equation 3) and a suitable analysis condition combining the welding heat input H and the cooling time S can be selected.
[Equation 3]
σ _max = A · H + B · α + C · H · α
σ _max : Maximum residual stress of the circumferential component of the outer surface of the core shroud 1 to be evaluated H: Weld heat input α: Heat transfer coefficient A, B, C: This implementation for welding forms 6A, 6B, 6C, 6D and 6E Constants obtained from the results of residual stress analysis on morphology

  [Equation 3] is an example in which the relationship between the heat input H and the heat transfer coefficient α, which is an index representing the cooling time S, is approximated by the least square method for the residual stress obtained by the parameter analysis. By obtaining a relational expression such as [Equation 3] from a plurality of residual stress analysis results in which welding heat input H, which is an analysis condition of heat transfer analysis, preheating T at the time of welding, and cooling time S are arbitrarily fixed or set. Therefore, it is possible to set a new analysis condition based on an effective prediction that approximates the effect on the residual stress when setting a new analysis condition.

Here, the welding heat input H, which is the analysis condition of the heat transfer analysis of the welding forms 6A, 6B, 6C, 6D, and 6E, the preheating T and the cooling time S at the time of welding, respectively, H _An , T _Am , S _Al , H _Bn , T _Bm , S _B1 for welding form 6B, H _Cn , T _Cm , S _Cl for welding form 6C, H _Dn , T _Dm , S _D1 for welding form 6D, H _En , T _Em for welding form 6E , S _El .

  Further, as shown in FIG. 8, a plurality of welding paths around the position of the groove 3 on the outer surface of the core shroud 1 are grouped to form a welded portion 8 </ b> A, from the outer surface of the core shroud 1 in the thickness direction of the base metal 2. A plurality of weld paths around the groove 3 at a depth of 3 mm are grouped to form a groove 3 position at a depth of about 1/2 of the thickness of the base metal 2 from the outer surface (inner surface) of the welded portion 8B and the core shroud 1. A plurality of surrounding weld paths are grouped to weld the welded portion 8C and a plurality of weld paths around the groove 3 position at a depth of about 1/4 of the thickness direction of the base metal 2 from the inner surface of the core shroud 1. A portion 8D and a plurality of weld passes around the position of the groove 3 on the inner surface of the core shroud 1 are grouped to form a weld portion 8E.

  The welding heat input H, which is an analysis condition, is a welding heat input per unit calculated from the welding current, welding voltage, and welding speed in the actual welding process. In addition, the cooling time S, which is an analysis condition, is determined by a cooling method such as water cooling in the actual welding process, water cooling with a changed flow velocity, forced air cooling with a fan or air jet, water cooling with water jet, or cooling with dry ice jet. To reflect. Further, the preheating T which is an analysis condition is reflected in the welding condition by high-frequency heating or a heating method using a gas burner or the like in the welded part in the actual welding process.

Appropriate conditions are selected, for example, as H _An , T _Am and S _Al as analysis conditions for the welded portion 8A, H _Bn , T _Bm and S _B1 as analysis conditions for the welded portion 8B, and H _Cn , T _Cm as analysis conditions for the welded portion 8C. And S _Cl , H _Dn , T _Dm and S _Dl are selected as analysis conditions for the welded portion 8D, and H _En , T _Em and S _El are selected and combined as the analysis conditions for the welded portion 8E.

  In the all-pass analysis, heat transfer analysis is performed on the welded portions 8A, 8B, 8C, 8D, and 8E based on the analysis conditions combined by selecting appropriate conditions, and the results of this heat transfer analysis are actually welded corresponding to each welded portion. Thermo-elasto-plastic analysis of all weld passes is performed as analysis conditions for thermo-elasto-plastic analysis of weld passes in the process.

  From the results of this all-pass analysis, it is determined whether or not the residual stress generated on the outer surface in the vicinity of the welded portion 4 of the core shroud 1 is a compressive residual stress, and the optimum condition is determined. If satisfied, this analysis condition is set as the welding condition of the welding path in the actual welding process. If not satisfied, the process returns to the selection of the appropriate condition, and the residual generated on the outer surface near the weld 4 of the core shroud 1 Repeat until stress assessment is required.

  FIG. 9 is a diagram illustrating an example of the result of all path analysis obtained from a combination of required analysis conditions performed according to the present embodiment.

H _A1 , T _A1 and S _A1 as analysis conditions for the welded part 8A, H _B1 , T _B1 and S _B1 as analysis conditions for the welded part 8B, H _C1 , T _C1 and S _C1 as analysis conditions for the welded part 8C, and welded parts As a result of selecting and combining H _D1 , T _D1 and S _D1 as analysis conditions for 8D and H _E1 , T _E1 and S _E1 as analysis conditions for welded portion 8E, residuals generated on the outer surface of welded portion 4 of core shroud 1 The stress is a compressive residual stress in both the circumferential component and the axial component.

  FIG. 10 is a diagram showing another method for setting the welding conditions of the present embodiment.

  In FIG. 10, in step S <b> 1 </ b> A, first, a plurality of welded portions less than the number of welding passes in the actual welding process are set at the outer surface (inner surface) of the core shroud 1 and the groove 3 position in the thickness direction of the base material 2. Next, a simulated test body simulating each welding part is manufactured. Furthermore, the welding conditions of each welding construction part are set. Based on these welding conditions, each simulated specimen is welded and the change in residual stress before and after welding is measured. From the results obtained from the measurement of this change in residual stress, a plurality of welding conditions were obtained for the welded portion where the residual stress generated on the outer surface in the vicinity of the welded portion 4 of the core shroud 1 was compressed residual stress, and this welding condition was simulated. Parameter acquisition is performed using a mock specimen that prepares multiple analysis conditions.

  Steps subsequent to step S2 are based on the analysis conditions of the plurality of weld construction parts obtained by parameter acquisition by the simulated specimen in step S1A, and the outer surface in the vicinity of the weld part 4 of the core shroud 1 as in the step shown in FIG. Welding conditions to make the residual stress generated in the compression compressive residual stress are set beforehand by analysis.

  In the parameter acquisition by the simulated specimen, first, as an example, a weld form 6A (FIG. 4A) in which the welding portion 5A is welded to the position of the groove 3 on the outer surface of the core shroud 1, the base material from the outer surface of the core shroud 1 is used. 2 in the welding configuration 5B (FIG. 4B) in which the welded portion 5B is welded to the groove 3 at a depth of about ¼ of the thickness direction of the plate thickness 2 of the base material 2 from the outer surface (inner surface) of the core shroud 1. A welded form 6C (FIG. 4C) in which a welded portion 5C is welded to a groove 3 position having a depth of about 1/2 in the plate thickness direction, from the inner surface of the core shroud 1 to about 1 in the plate thickness direction of the base material 2. Weld form 6D (FIG. 4 (D)) in which the welded part 5D is welded to the groove 3 position at a depth of / 4 and welding in which the welded part 5E is welded to the groove 3 position on the inner surface of the core shroud 1 Welding based on welding conditions was performed for each welding form of Form 6E (FIG. 4E). Measuring the residual stress generated in the welded portion 4 near the outer surface of the core shroud 1.

  Note that the welding site 5E on the inner surface of the core shroud 1, which is the final welding site, measures the residual stress for each pass in order to simulate an actual welding process for welding in a plurality of passes.

  This welding condition is set by combining a plurality of conditions of the welding heat input H of the welding work part 5, the preheating T and the cooling time S during welding.

  The residual stress is measured by a measuring method such as a residual stress measurement by an X-ray diffraction method, a cutting release method, a drilling method, or the like.

  In the cutting release method, for example, a strain gauge is attached to a mock specimen, the initial value of strain before welding is measured, and the periphery of the strain gauge is cut into a dice shape (about 10 mm × 10 mm × 5 mm) after welding. The strain is measured, the amount of strain released by cutting is obtained from the change in strain before and after cutting, and the residual stress is calculated from the amount of strain released.

  In the drilling method, for example, a strain gauge is affixed to a mock specimen, the initial value of strain before welding is measured, the area around the strain gauge is drilled after welding, and strain is released by cutting from changes in the strain before and after drilling. The amount is obtained, and the residual stress is calculated from the strain release amount. The holes are made deeper and the strain is measured each time.

  From the result of the residual stress measurement in the parameter acquisition by this simulated specimen, the welded part is welded at the groove 3 position of the required depth in the thickness direction of the outer surface (inner surface) of the core shroud 1 and the base material 2. Residual stress (welding of core shroud 1 for evaluation) with variables of heat transfer coefficient α, which is an index representing welding heat input H, preheating T, and cooling time S during welding for forms 6A, 6B, 6C, 6D and 6E The relationship with the maximum value of the circumferential component of the outer surface in the vicinity of the portion 4 can be expressed as a mathematical expression (Equation 3), and an appropriate analysis condition combining the welding heat input H and the cooling time S can be selected.

  Then, appropriate conditions are selected (step S2) and all-pass analysis (step S3) from the analysis conditions obtained by parameter acquisition by the simulated specimen, and the residual stress generated on the outer surface near the weld 4 of the core shroud 1 is compressed. Welding conditions for residual stress are obtained (step S4).

  Also, by using parameter analysis and parameter acquisition together and surveying the results of parameter analysis by parameter acquisition, it is possible to improve the accuracy of all-path analysis.

  According to the present embodiment, the residual stress generated on the outer surface near the welded portion 4 of the core shroud 1 can be made the compressive residual stress, and the stress corrosion cracking susceptibility is improved.

  In addition, the residual stress in the vicinity of the welded portion 4 of the core shroud 1 can be made the compressive residual stress without performing the residual stress improving process by the surface improving process performed in the conventional welding process, thereby shortening the process. And the cost reduction effect accompanying this is obtained.

  Furthermore, the residual stress in the vicinity of the welded portion, particularly the welded portion that is difficult to access easily after welding, can be made the compressive residual stress before the actual welding process is performed by the analytical method.

[Second Embodiment]
A second embodiment of the welding method for a welded structure according to the present invention will be described with reference to FIGS. 11 to 13.

  In the present embodiment, the same components as those of the structure welding method according to the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The structure welding method in the present embodiment is a welding method in which welding conditions are set in advance by analysis so that the residual stress generated on the outer surface near the welded portion 4 of the core shroud 1A is a compressive residual stress.

  11 and 12 are cross-sectional views for explaining the outline of the welded portion 4 of the core shroud 1A in the present embodiment.

  As an example, the welded portion 4 of the core shroud 1A is welded by setting the number of welding passes of the groove 3 in the actual welding process to 23, for example (FIG. 11), and then the final welding to be performed on the innermost peripheral surface of the core shroud 1A. The number of welding passes of the layer 10 is welded, for example, as 15 passes (FIG. 12), and the weld portion 4 as a whole is composed of 38 weld passes in total. The environment during welding of the core shroud 1A is, for example, an atmospheric environment from 1 to 3 passes, and an environment in which water is filled outside the core shroud 1A from 4 to 38 passes. The number of passes from the first pass to the third pass may be a required thickness that can maintain the water pressure when water is filled outside the core shroud 1A, and if this thickness is about 5 mm, water is placed outside the core shroud 1A. By satisfying the above, even if the welding heat input, which is a welding condition, is about 30 kJ / cm, the thermal effect on the outer surface in the vicinity of the welded portion 4 of the core shroud 1 is small.

  That is, in the present embodiment, the cooling time S, which is the analysis condition for the heat transfer analysis in the parameter analysis and the all-pass analysis, is reduced for the four to 38 passes that are welded in an environment where the outside of the core shroud 1A is filled with water. .

  In the present embodiment, first, similarly to the first embodiment, the parameters of the welding forms 6A, 6B, 6C, 6D, and 6E are analyzed for the welding portions 5A, 5B, 5C, 5D, and 5E shown in FIG. Select the optimum condition.

  Next, all path analysis is performed. In consideration of the case where the welding metal supply amount increases due to the welding heat input H, the welding passes from 1 to 20 shown in FIG. 11 are grouped approximately every 2 passes, and the number of analysis passes is reduced to about half. It is also possible to perform all path analysis.

  Further, by changing the number of welding passes of the final weld layer 10 to be applied to the innermost surface of the core shroud 1A as necessary, the final welding that changes the residual stress generated on the outer surface near the welded portion 4 of the core shroud 1A to compressive residual stress. The optimum axial weld width D of the layer 10 can be determined.

  FIG. 13 is a diagram showing an example of the result of residual stress analysis in the present embodiment.

  The core thickness of the core shroud 1A to be analyzed is about 50 mm, the groove has a groove shape of 4 to 6 mm at the bottom, and the opening is 10 to 15 mm. The base metal and the weld metal of the core shroud 1A are austenite. Stainless steel.

  As an analysis condition, when the outer surface of the core shroud 1A is filled with water after the first to third passes of the weld 4 are welded, the welding pass after the fourth pass is about 10 kJ / cm or more and about 30 kJ / cm or less ( The residual stress in the vicinity of the welded portion 4 of the core shroud 1A can be made a compressive residual stress by welding at a welding heat input of about 20 kJ / cm or more. Further, by setting the width D of the axial welded portion of the final weld layer 10 applied to the innermost surface of the core shroud 1A to 50 mm or more, the residual stress near the welded portion 4 of the core shroud 1A can be made the compressive residual stress.

  According to the present embodiment, the residual stress generated on the outer surface near the welded portion 4 of the core shroud 1A can be made the compressive residual stress, and the stress corrosion cracking susceptibility is improved.

  Further, the residual stress on the outer surface near the welded portion 4 of the core shroud 1A can be made the compressive residual stress without performing the residual stress improving process by the surface improving process carried out in the conventional welding process, thereby shortening the process. And the cost reduction effect accompanying this is obtained.

[Third Embodiment]
A third embodiment of the welding method for a welded structure according to the present invention will be described with reference to FIGS. 14 to 17.

  In the present embodiment, the same components as those of the structure welding method according to the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The welding method of the structure in this embodiment is a method in which welding is performed by setting in advance a welding condition in which the residual stress generated on the inner surface in the vicinity of the welded portion 4 of the pipe 12 made of stainless steel is a compressive residual stress.

  FIG. 14 and FIG. 15 are diagrams for explaining the outline around the welded portion of the pipe 12 where the inner surface used in a nuclear power plant or the like is exposed to a corrosive environment.

  In the pipe 12, a groove 3 is formed on a substantially cylindrical base material 2 made of stainless steel, and the groove 3 is welded by a welding portion 4.

  The groove shape of the groove 3 is a V-shaped joint. A welder is disposed outside the cylinder of the pipe 12, and weld metal is welded from the cylinder inner surface side to the outer surface side of the pipe 12 to constitute the welded portion 4. The pipe 12 uses a V-shaped joint as a joint of the base material 2, but may be composed of a joint such as a butt joint, a metal joint, or a lap joint. A groove such as a mold can be used.

  As an example, the welded portion 4 of the pipe 12 is constructed by welding the number of welding passes in an actual welding process, for example, as 5 passes (FIG. 15). Moreover, the environment at the time of welding of the pipe 12 is, for example, an atmosphere environment from the first pass to the third pass, and an environment in which the inside of the pipe 12 is filled with water from the fourth pass to the fifth pass. The number of passes from the first pass to the third pass may be a required thickness that can maintain the water pressure when water is filled in the pipe 12.

  That is, in the present embodiment, the cooling time S, which is the analysis condition of the heat transfer analysis in the parameter analysis and the all-pass analysis, is reduced for 4 to 5 passes that are welded in an environment where the inside of the pipe 12 is filled with water. Further, in order to increase the cooling effect of the water filled in the pipe 12, the cooling time S reflecting the heat transfer coefficient α in consideration of the water flow is used as an analysis condition, and the pipe 12 is welded from the heat transfer coefficient α. The flow rate of water at which compressive residual stress is generated on the inner surface in the vicinity of the portion 4 can be obtained.

  In the present embodiment, as in the first embodiment, first, parameter analysis of each welding mode is performed on the welding passes from 1 to 5 shown in FIG. 15, then optimum conditions are selected, and further, all pass analysis is performed. I do.

  16 and 17 are diagrams showing an example of the result of the residual stress analysis in the present embodiment.

  As an analysis condition for all-pass analysis, when the inside of the pipe 12 is filled with water after the end of the first to third passes of the weld 4, the inside of the pipe 12 is filled for four to five passes. By setting the water flow rate to 0.01 m / second or more, the residual stress on the inner surface of the pipe 12 in the vicinity of the welded portion 4 can be made the compressive residual stress.

  According to this embodiment, the residual stress generated on the inner surface in the vicinity of the welded portion 4 of the pipe 12 can be made the compressive residual stress, and the stress corrosion cracking susceptibility is improved.

BRIEF DESCRIPTION OF THE DRAWINGS The 1st Embodiment of the welding method of the structure which concerns on this invention is shown, and the figure explaining the outline around the welding part of the core shroud accommodated in the reactor pressure vessel of a boiling water reactor. Sectional drawing explaining the outline around the welding part of the core shroud accommodated in the said reactor pressure vessel. The flowchart which shows the method of setting the welding conditions in 1st Embodiment of the welding method of the structure which concerns on this invention. It is a figure explaining the conditions of parameter analysis among the methods of setting the welding conditions in the first embodiment of the welding method of the structure according to the present invention, and (A) is welded to the position of the outer surface of the groove portion of the core shroud. Sectional drawing which shows the outline of the welding form by which a construction part is welded, (B) is a welding construction part welded to the depth position of about 1/4 of the thickness direction of a base material from the outer surface of the groove part of a core shroud. Sectional drawing which shows the outline of a welding form, (C) is a welding form in which the welding construction part was welded from the outer surface (inner surface) of the groove part of a core shroud to the depth position of about 1/2 of the thickness direction of the base metal. Sectional drawing which shows outline, (D) is sectional drawing which shows the outline of the welding form by which the welding construction part was welded from the inner surface of the groove part of a core shroud to the depth position of about 1/4 of the thickness direction of a base material, (E) is a welded form in which the weld construction part is welded to the position of the inner surface of the groove part of the core shroud. Sectional view showing a schematic. It is a figure explaining the conditions of parameter analysis among the methods of setting the welding conditions in the first embodiment of the welding method of the structure according to the present invention, and the welding mode shown in FIG. The figure which shows an example of the result of the residual stress analysis (circumferential component) which made the preheating and cooling time constant, and selected the welding heat input as required. It is a figure explaining the conditions of parameter analysis among the methods of setting the welding conditions in the first embodiment of the welding method of the structure according to the present invention, and the welding mode shown in FIG. The figure which shows an example of the result of the residual stress analysis (circumferential component) which selected precooling and welding heat input constant and cooling time required. It is a figure explaining the conditions of parameter analysis among the methods of setting the welding conditions in the first embodiment of the welding method of the structure according to the present invention, and the residual stress analysis of the welding heat input and the cooling time with constant preheating The figure which shows the relationship of the result of. The figure which shows an example of the combination of the analysis conditions obtained by parameter analysis among the methods of setting the welding conditions in 1st Embodiment of the welding method of the structure which concerns on this invention. The figure which shows an example of the result of all pass analysis among the methods of setting the welding conditions in 1st Embodiment of the welding method of the structure which concerns on this invention. The flowchart which shows the method of setting the welding conditions in 1st Embodiment of the welding method of the structure which concerns on this invention. The figure explaining the outline around the welding part of the core shroud accommodated in the reactor pressure vessel of the boiling water reactor welded by 2nd Embodiment of the welding method of the structure which concerns on this invention. The figure explaining the outline around the welding part of the core shroud accommodated in the reactor pressure vessel of the boiling water reactor welded by 2nd Embodiment of the welding method of the structure which concerns on this invention. The figure which shows an example of the result of all the paths analysis among the methods of setting the welding conditions in 2nd Embodiment of the welding method of the structure which concerns on this invention. The figure explaining the outline of the welding part periphery of piping welded by 3rd Embodiment of the welding method of the structure which concerns on this invention. Sectional drawing explaining the outline of the welding part periphery of piping welded by 3rd Embodiment of the welding method of the structure which concerns on this invention. The figure which shows an example of the result (pipe longitudinal-axis direction component of a residual stress) of all the paths analysis among the methods of setting the welding conditions in 3rd Embodiment of the welding method of the structure which concerns on this invention. The figure which shows an example of the result (pipe circumferential direction component of a residual stress) of all the paths analysis among the methods of setting the welding conditions in 3rd Embodiment of the welding method of the structure which concerns on this invention.

Explanation of symbols

1, 1A Core shroud 2 Base material 3 Groove 4 Welded part 5A, 5B, 5C, 5D, 5E, Welded part 6A, 6B, 6C, 6D, 6E, Welding form 7B, 7C, 7D, 7E Existing welded part 8A , 8B, 8C, 8D, 8E Welded part 10 Final weld layer 12 Piping

Claims (9)

In a method for welding a structure having a weld that is exposed to a corrosive environment,
After conducting heat transfer analysis to determine the temperature distribution in the vicinity of the weld by setting analysis conditions that simulate the thermal effect during welding,
Perform thermal elastic-plastic stress analysis based on the temperature distribution to determine the residual stress in the vicinity of the weld,
Identify the analysis conditions where the residual stress on the surface near the weld exposed to the corrosive environment becomes compressive stress,
Welding the structure by setting a welding condition that reflects the specified analysis condition,
The analysis conditions include welding heat input per welding, welding voltage, welding heat input per unit calculated from welding speed, cooling method, preheating method, welding sequence when constructing a plurality of welding passes, A welding position, and set and combine these conditions as required to determine the residual stress,
When setting the analysis conditions, select a representative welding pass position smaller than the total number of the plurality of welding passes to be applied during welding, as required,
The representative weld pass position welding method configured creation you, characterized in that the analysis conditions in combination set the required obtaining the residual stress. When setting the analysis conditions, select a representative welding pass position smaller than the total number of the plurality of welding passes to be applied during welding, as required,
Preparing a welding test specimen that simulates the representative welding pass position, welding the welding test specimen by setting and combining the welding conditions as required,
The residual stress is obtained by measuring the residual stress generated in the weld specimen by this welding and then setting the analysis conditions simulating the welding conditions at the representative welding pass positions in combination as required. 2. A method for welding a structure according to 1 . For the calculation result of the residual stress at the evaluation target position of the structure for each representative welding pass position, prepare a mathematical expression using the analysis condition as a variable, and determine the influence on the residual stress when setting a new analysis condition from the mathematical expression. welding method of the structure according to claim 1 or 2, characterized in that estimated to set the analysis conditions. The structure is a pipe or a container, and the groove shape of the welded portion is a one-sided groove, and cooling is performed when welding from the first welding pass to a required welding pass among all the welding passes in an atmospheric environment. A first analysis condition for simulating a method and a second analysis condition for simulating a cooling method when the back surface of the first welding pass is set in a water environment from the required welding pass to the final welding pass are set. welding method of the structure according to any one of claims 1 to 3, characterized in that determining the residual stress and. The method for welding a structure according to claim 4 , wherein the water environment on the back surface of the first welding pass has a water flow rate of 0.01 m / sec or more. The structure is a pipe or a container, and the groove shape of the welded portion is a one-sided groove, and in the setting of the analysis conditions, the welding path of the welding portion constructed in the welded portion is substantially perpendicular to the welding line. welding method of the structure according to any one of claims 1 to 5, by setting the number of welds paths simulating the width of the final welding layer to the required and obtains the residual stress. The structure welding method according to claim 6 , wherein the width of the final weld layer in a direction substantially perpendicular to the weld line is set to 50 mm or more with the approximate center of the weld line as a center. After the thickness from the first welding pass to be applied first to the required welding pass among the welding passes to be applied to the welded portion is set to 5 mm or more, the welding heat input is included in the analysis conditions of the subsequent welding pass. The welding method for a structure according to any one of claims 1 to 7 , wherein the welding heat input is 10 kJ / cm or more and 30 kJ / cm or less. The structure is a structure made of stainless steel or a nickel base alloy, and welding conditions are set such that a residual stress in a range of 10 mm or more from the weld boundary of the surface of the weld exposed to the corrosive environment becomes a compressive stress. welding method of the structure according to any one of claims 1 to 8, characterized in that welding the structure after.

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