JP2012163478A - Standard test piece for non-destructive test and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a standard test piece for non-destructive test that is used to detect a crack-like defect in a pipe-end weld part through the non-destructive test.SOLUTION: A standard test piece 10 for non-destructive test that is used to detect a crack-like defect in a pipe-end weld part through the non-destructive test comprises: a test piece body 12 that is formed of carbon steel and includes a through-hole 15; a pipe body 14 that is inserted into the through-hole 15 and is formed of Cr-Mo steel; a space 17 that is provided between an outer periphery of the pipe body 14 and an inner periphery of the through-hole 15 in the test piece body 12; and a weld part 18 that welds all over the place between an outer periphery on one longitudinal end side of the pipe body 14 and an inner periphery on one longitudinal end side of the through-hole of the test piece body 12. The weld part 18 is injected with a corrosive liquid of the mixture of NaNOand KNOat a weight ratio of 50% to 50% into the space 17, and includes the crack-like defect induced by stress corrosion cracking.

Description

  The present invention relates to a standard specimen for nondestructive inspection and a manufacturing method thereof, and more particularly, to a standard specimen for nondestructive inspection for detecting crack-like defects in a pipe end weld such as a tube reactor for a chemical plant by nondestructive inspection. The present invention relates to a specimen and a manufacturing method thereof.

  In a tube reactor for a chemical plant, a steam generator for a pressurized water reactor (Pressurized Water Reactor, PWR), etc., a large number of tubes through which a reaction medium, high-temperature water and the like pass are welded and fixed to a tube plate. These many tube bodies are respectively inserted into holes provided in the tube plate, and the tube ends are welded and sealed over the entire periphery of the tube plate.

  In order to inspect defects such as blowholes and inclusions generated in the welded portion of the tube end, which is a welded portion between the tube end and the tube plate, a nondestructive inspection such as a radioactive transmission test is performed. Patent Document 1 describes a radiation transmission test method for inspecting the welded state of a tube body and a tube plate that supports the tube body and the presence or absence of weld defects in a heat exchanger, a multitubular reactor, and the like. Has been.

JP 2009-180647 A

  By the way, in a non-destructive inspection such as a radiation transmission test, a large-volume defect such as a blowhole or an inclusion is relatively easy to detect, but a crack-like defect such as a weld crack or a stress corrosion crack has a small crack volume. Hard to detect. Therefore, the conventional nondestructive inspection method has a problem that it is difficult to specify the size of crack-like defects.

  Therefore, an object of the present invention is to provide a standard specimen for nondestructive inspection and a method for manufacturing the same for detecting a crack-like defect generated in a pipe end welded portion with higher accuracy by nondestructive inspection.

The standard specimen for nondestructive inspection according to the present invention is a standard specimen for nondestructive inspection for detecting crack-like defects in a pipe end welded part by nondestructive inspection, and is formed of carbon steel and has a through hole. And a tube body inserted in the through hole and formed of Cr-Mo steel, between the outer peripheral surface of the tube body and the inner peripheral surface of the through hole in the test body body A welded portion that is welded over the entire circumference between the outer peripheral surface on one end side in the longitudinal direction of the tube body and the inner peripheral surface on one end side in the longitudinal direction of the through hole of the specimen body. And the weld has a crack-like defect introduced by stress corrosion cracking by injecting a corrosion solution in which 50% NaNO ₃ and 50% KNO ₃ are mixed in a weight ratio into the gap. It is characterized by.

A method for producing a standard specimen for nondestructive inspection according to the present invention is a method for producing a standard specimen for nondestructive inspection for detecting a crack-like defect in a pipe end welded portion by nondestructive inspection, wherein a through hole is formed. Forming a specimen body made of carbon steel and forming a tubular body from Cr-Mo steel; inserting the tubular body into the through hole; and an outer peripheral surface of the tubular body and an inner peripheral surface of the through hole. A step of positioning the tube body by providing a gap between the outer peripheral surface of one end side in the longitudinal direction of the tube body and the inner peripheral surface of the one end side of the through hole over the entire circumference. And a step of forming a preliminary specimen, injecting a corrosive solution in which 50% NaNO ₃ and 50% KNO ₃ are mixed in a weight ratio into the gap, and heating the preliminary specimen to 250 ° C. Providing a crack-like defect due to stress corrosion cracking in the weld of the specimen. And butterflies.

In the method for producing a standard specimen for nondestructive inspection according to the present invention, the step of introducing the crack-like defect is performed by placing the preliminary specimen in a metal container, and between the preliminary specimen and the metal container. It is preferable that a heat medium in which 50% NaNO ₂ and 50% KNO ₃ are mixed in a weight ratio is injected into the space and the pipe of the pipe body to heat the preliminary specimen.

According to the above configuration, the corrosive liquid in which 50% NaNO ₃ and 50% KNO ₃ are mixed in a weight ratio is injected into the gap between the tube and the through hole of the sample body, and the tube and the sample body Can produce a standard specimen for nondestructive inspection, in which crack-like defects due to stress corrosion cracking are artificially introduced into the welded part, and the nondestructive inspection result of the pipe end welded part in an actual machine such as a chemical plant tube reactor, By comparing with the non-destructive inspection result of the standard specimen for non-destructive inspection, it is possible to identify the crack-like defect generated in the pipe end weld of the actual machine with higher accuracy.

In embodiment of this invention, it is a perspective view which shows the structure of the standard specimen for nondestructive inspection. In embodiment of this invention, it is sectional drawing which shows the structure of the standard specimen for nondestructive inspection. In embodiment of this invention, it is a flowchart of the manufacturing process in the standard specimen for nondestructive inspection. In embodiment of this invention, it is a figure which shows the state which inserted and positioned the pipe body in the through-hole of the test body main body. In embodiment of this invention, it is sectional drawing which shows the structure of a preliminary test body. In embodiment of this invention, it is a schematic diagram which shows the introduction method of a crack-like defect. In embodiment of this invention, it is sectional drawing which shows the state which put the preliminary specimen into the metal container, and inject | poured the corrosive liquid and the heat medium. In embodiment of this invention, it is a figure which shows the manufacturing method of a welded joint. In embodiment of this invention, it is a graph which shows the hardness distribution of the surface in each site | part of each test piece which changed the cooling conditions after welding. In embodiment of this invention, it is sectional drawing which shows the structure of a bending jig. In embodiment of this invention, it is a graph which shows the result of a stress corrosion cracking test. In embodiment of this invention, it is an external appearance photograph of the test piece which the stress corrosion crack generate | occur | produced. In embodiment of this invention, it is the photograph which expanded the surface of the site | part of the stress corrosion cracking of FIG. In embodiment of this invention, it is a cross-sectional photograph of the site | part of the stress corrosion cracking of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing a configuration of a standard specimen 10 for nondestructive inspection. FIG. 2 is a cross-sectional view showing the configuration of the standard specimen 10 for nondestructive inspection, and FIG. 2A is a cross-sectional view showing the overall configuration of the standard specimen 10 for nondestructive inspection, and FIG. ) Is an enlarged cross-sectional view of a welded portion of the standard specimen 10 for nondestructive inspection.

  The standard specimen 10 for nondestructive inspection is a standard for detecting non-destructive inspection of crack-like defects in pipe end welds in actual machines such as steam generators for pressurized water reactors, heat exchangers or tube reactors for chemical plants. Used as a specimen. The standard specimen 10 for nondestructive inspection includes a specimen body 12 and a tube body 14.

  The specimen body 12 is formed of carbon steel in a rectangular shape or the like. A through hole 15 penetrating from one end surface to the other end surface is formed in the specimen body 12. The through-hole 15 has a circular cross section in a direction perpendicular to the longitudinal direction.

  The tubular body 14 is formed of Cr-Mo steel (chromium-molybdenum steel) in a cylindrical shape or the like. The tube body 14 is inserted into the through hole 15 of the specimen body 12 with the through hole 15 and the axial center aligned.

  The tube body 14 has a protruding portion 16 that protrudes outward in the radial direction. The tube body 14 is positioned on the specimen body 12 by bringing the protruding portion 16 into contact with the inner peripheral surface of the through hole 15. The protrusions 16 are provided at two locations in the circumferential direction. The protrusions 16 are preferably provided so as to face each other on the same circumference in the circumferential direction of the tube body 14. Three or more protrusions 16 may be provided in the circumferential direction of the tube body 14. Since the protruding portion 16 is in contact with the inner peripheral surface of the through hole 15, the displacement of the tubular body 14 is suppressed by friction between the protruding portion 16 and the inner peripheral surface of the through hole 15.

  A gap 17 is provided between the outer peripheral surface of the tube body 14 and the inner peripheral surface of the through hole 15. The gap 17 is preferably provided with the same width in the circumferential direction. The gap 17 is provided with a width capable of injecting a corrosive liquid 27 described later. The width of the gap 17 (the distance between the outer peripheral surface of the tube body 14 and the inner peripheral surface of the through hole 15) is, for example, 0.2 mm to 0.5 mm.

  One end in the longitudinal direction of the tube body 14 is fixed to the specimen body 12 by welding. The welded portion 18 welds and seals between the outer peripheral surface on one end side in the longitudinal direction of the tube body 14 and the inner peripheral surface on one end side in the longitudinal direction of the through hole 15 of the specimen body 12 over the entire circumference. Is formed.

  The welded portion 18 includes a built-up portion 19 that has been built up by welding, a connecting portion between the built-up portion 19 and the tube body 14, and a connecting portion between the built-up portion 19 and the specimen body 12. It includes not only the built-up portion 19 but also a region that is thermally affected by welding, such as the vicinity of the built-up portion 19. Further, by welding sealing, even if a later-described corrosive liquid 27 is injected into the gap 17, the corrosive liquid 27 does not leak from the welded portion 18.

  A crack-like defect 20 is formed in the welded portion 18 by injecting the corrosive liquid 27 into the gap 17 and introducing it by stress corrosion cracking. For example, the crack-like defect 20 is formed in a connection region between the tubular body 14 and the built-up portion 19. The crack-like defect 20 is formed with a length of 100 μm to 500 μm, for example.

  Next, the manufacturing method of the standard specimen 10 for nondestructive inspection is demonstrated.

  FIG. 3 is a flowchart of the manufacturing process in the standard specimen 10 for nondestructive inspection. The manufacturing process of the standard specimen 10 for nondestructive inspection includes a preparation process (S10) for preparing the specimen body 12 and the tube body 14, a positioning process (S12) for positioning the tube body 14 on the specimen body 12, and A welding step (S14) for welding the tube body 14 to the specimen body 12 and a crack-like defect introduction step (S16) for introducing the crack-like defect 20 into the welded portion 18 are provided.

  The preparation step (S10) is a step of preparing the specimen body 12 and the tube body 14. The specimen body 12 is formed, for example, by cutting out from a carbon steel plate material having a plate thickness of 100 mm into a block shape having a width of 100 mm and a length of 100 mm. For example, SM490, which is a rolled steel material for welded structures, is used as the carbon steel.

  A through-hole 15 is formed by drilling from one end surface of the specimen body 12 to the other end surface facing the one end surface with a drill or the like. The through hole 15 has, for example, a gap 17 of 0.2 mm to 0.5 mm between the inner peripheral surface of the through hole 15 and the outer peripheral surface of the tube body 14 when the tube body 14 is inserted into the through hole 15. It is formed to be provided.

  The tube body 14 is formed of Cr—Mo steel in a tube shape. For example, 2.25Cr-1Mo steel is used as the Cr-Mo steel. The reason why Cr-Mo steel is used for the tube body 14 is that crack-like defects due to stress corrosion cracking are easily introduced because of high sensitivity to stress corrosion cracking (SCC). The tube body 14 is formed by extrusion molding or the like, which is a general plastic processing of a metal material. The tubular body 14 is formed, for example, so that the outer diameter is 20 mm.

  The positioning step (S12) is a step of positioning the tube body 14 by inserting it into the through hole 15 of the specimen body 12. FIG. 4 is a view showing a state in which the tube body 14 is inserted and positioned in the through hole 15 of the specimen body 12, and FIG. 4A shows a state in which the tube body 14 is positioned on the specimen body 12. FIG. 4B is a top view showing a state in which the tube body 14 is positioned on the specimen main body 12.

  The tubular body 14 is positioned by bringing the protruding portion 16 into contact with the inner peripheral surface of the through hole 15. In addition, the tube body 14 is positioned so that one end in the longitudinal direction of the tube body 14 is substantially at the same position as the lower end of the specimen body 12. The protrusion 16 is provided in a part of the circumferential direction in order to secure a flow path for the later-described corrosive liquid 27. The protruding portion 16 is formed, for example, by inserting a metal processing jig into the tube of the tube body 14 and plastically deforming the tube body 14 radially outward. The protrusion 16 is formed such that the gap 17 between the outer peripheral surface of the tube body 14 and the inner peripheral surface of the through hole 15 is substantially the same in the circumferential direction.

  In this way, the pipe body 14 causes the corrosive liquid 27 to be injected between the outer peripheral surface of the pipe body 14 and the inner peripheral surface of the through hole 15 by bringing the protruding portion 16 into contact with the inner peripheral surface of the through hole 15. A possible gap 17 is provided for positioning. Further, since the protruding portion 16 is in contact with the inner peripheral surface of the through hole 15, the displacement of the tubular body 14 is suppressed by friction.

  The welding step (S14) is a step of welding the tube body 14 to the specimen body 12 to form a preliminary specimen. FIG. 5 is a cross-sectional view showing the configuration of the preliminary specimen 21. A preliminary specimen 21 is formed by welding and sealing between the outer peripheral surface on one end side in the longitudinal direction of the tube body 14 and the inner peripheral surface on one end side of the through hole 15 over the entire periphery. For example, arc welding or TIG welding is used as the welding method. Carbon steel or the like can be used for the welding rod. Moreover, since the pipe body 14 is formed of Cr—Mo steel, it is preferable to increase the heat input and reduce the supply of the welding rod in order to melt the Cr—Mo steel. Welding is performed, for example, in two passes.

  The hardness of the weld 18 is preferably greater than HV400 in terms of Vickers hardness. Since the residual stress of the welded portion 18 is increased by making the hardness of the welded portion 18 higher than HV400, the cracked defect 20 due to stress corrosion cracking using the residual stress as a stress source can be easily put in the welded portion 18. In order to further cure the welded portion 18, it is preferable that the specimen body 12 is sufficiently cooled before welding. For example, the specimen body 12 may be cooled in advance by immersing the specimen body 12 in a bathtub (bath) containing dry ice and liquid nitrogen before welding. Alternatively, the welded part 18 may be cured by water cooling the preliminary specimen 21 immediately after welding. Furthermore, when the hardness of the welded portion 18 is HV400 or less, the welded portion 18 may be hardened by heat-treating the preliminary specimen 21 and baking it.

  The crack-like defect introducing step (S 16) is a step for introducing the crack-like defect 20 into the welded portion 18 of the preliminary specimen 21. The crack-like defect 20 is introduced by causing stress corrosion cracking in the welded portion 18. FIG. 6 is a schematic diagram showing a method for introducing the crack-like defect 20.

  The metal container 24 is formed of carbon steel or the like with a size that can accommodate the preliminary specimen 21. The metal container 24 is formed by, for example, welding a bottom plate to a tube material having a size into which the preliminary specimen 21 can be inserted, and performing stress relief annealing. A heater 26 made of a ribbon heater or the like is provided outside the metal container 24. Further, a temperature measuring instrument (not shown) such as a thermocouple is attached to the metal container 24, and the heater 26 is controlled by a control device (not shown) so that the temperature inside the metal container 24 can be adjusted. Has been. Further, a suspension fitting 22 is attached to the specimen main body 12 so that the preliminary specimen 21 can be easily inserted into and removed from the metal container 24.

  Next, the preliminary specimen 21 is set in the metal container 24. Then, the corrosive liquid 27 is injected into the gap 17 between the outer peripheral surface of the tube body 14 and the inner peripheral surface of the through hole 15. A heat medium 28 is placed in the space between the metal container 24 and the preliminary specimen 21 and in the tube of the tube body 14. FIG. 7 is a cross-sectional view showing a state in which the preliminary specimen 21 is placed in the metal container 24 and the corrosive liquid 27 and the heat medium 28 are injected.

As the corrosive liquid 27, a mixed liquid (molten salt, melting point: about 200 ° C.) in which 50% NaNO ₃ and 50% KNO ₃ are mixed by weight is used. By heating the corrosive liquid in which 50% NaNO ₃ and 50% KNO ₃ are mixed to 250 ° C. and holding it for a predetermined time, stress corrosion cracks can be generated in the welded portion 18. In order to inject the mixed liquid of 50% NaNO ₃ and 50% KNO ₃ into the gap 17 between the outer peripheral surface of the tube body 14 and the inner peripheral surface of the through-hole 15, it is heated to 200 ° C. or higher in advance. It is injected after melting.

As the heat medium 28, a mixed liquid (molten salt, melting point is about 150 ° C.) in which 50% NaNO ₂ and 50% KNO ₃ are mixed by weight is used. A mixed liquid obtained by mixing 50% NaNO ₂ and 50% KNO ₃ does not cause stress corrosion cracking in the weld 18 when heated at 250 ° C. In addition, a mixed solution obtained by mixing 50% NaNO ₂ and 50% KNO ₃ has excellent thermal conductivity, and has a low vapor pressure even when heated to 250 ° C., and can be heated in an open system under atmospheric pressure. So it is easy to handle. A mixed liquid in which 50% NaNO ₂ and 50% KNO ₃ are mixed is prepared by putting each reagent in a solid state in a metal container 24 and then heating it to 150 ° C. or higher with a heater 26 to melt it.

Thus, the use in combination with 50% NaNO ₃ the etchant 27 with a mixture obtained by mixing a 50% KNO _3, a heat medium 28 by 50% NaNO ₂ and liquid mixture and 50% KNO ₃ Thus, the preliminary specimen 21 can be heated to 250 ° C., and the crack-like defect 20 due to stress corrosion cracking can be introduced into the welded portion 18. The holding time at 250 ° C. for introducing the crack-like defect 20 by stress corrosion cracking is, for example, 500 hours. Further, the size of the crack-like defect 20 can be changed by adjusting the holding time at 250 ° C. In order to form the crack-like defect 20 larger, the holding time at 250 ° C. may be made longer.

  Next, after the preliminary specimen 21 is held at 250 ° C. until the crack-like defect 20 is introduced into the welded portion 18, the preliminary specimen 21 is pulled up by the hanging bracket 22 and cleaned. If necessary, the gap 17 between the outer peripheral surface of the tube body 14 and the inner peripheral surface of the through-hole 15 is closed by expanding the tube body 14 radially outward (full thickness expansion). Also good. Thus, the manufacture of the standard specimen 10 for nondestructive inspection is completed.

  Next, a nondestructive inspection method using the standard specimen 10 for nondestructive inspection will be described. As the nondestructive inspection method, a radiation transmission test method, an ultrasonic flaw detection test method, or the like can be used. First, a nondestructive inspection is performed on the standard specimen 10 for nondestructive inspection under the same conditions as the nondestructive inspection conditions of the pipe end weld of the actual machine, and the crack-like defect 20 introduced into the standard specimen 10 for nondestructive inspection is inspected. Get the data. The inspection data may be stored in a database for each size of the crack-like defect 20.

  In the case of the radiation transmission test, radiation is irradiated to the welded portion 18 of the standard specimen 10 for nondestructive inspection, and the film is exposed to the radiation transmitted through the welded portion 18. In the cracked defect 20 portion, the intensity of transmitted radiation is higher than that of the surroundings, so that the film is strongly exposed. For each size of the crack-like defect 20, the inspection data made of the exposed film is acquired. In the case of an ultrasonic flaw detection test, ultrasonic waves are propagated from the surface of the welded portion 18 of the standard specimen 10 for nondestructive inspection. Then, the ultrasonic wave reflected by the crack-like defect 20 is detected. For each size of the crack-like defect 20, inspection data obtained from the ultrasonic wave reflected by the crack-like defect 20 is acquired.

  Next, a radiation transmission test or an ultrasonic flaw detection test is performed on the actual pipe end welded portion, and inspection data of the pipe end welded portion is acquired. Then, the inspection data of the pipe end welded part of the actual machine and the inspection data of the crack-like defect 20 of the standard specimen 10 for nondestructive inspection are compared to quantitatively determine the size of the defect of the pipe end welded part of the actual machine. evaluate. In this way, crack-like defects such as weld cracks and stress corrosion cracks in the pipe end welds of the actual machine can be detected with high accuracy. Although the radiation transmission test and the ultrasonic flaw detection test have been described, the detection accuracy of crack-like defects is improved by performing other nondestructive inspection test methods in the same manner as described above.

  Moreover, the standard specimen 10 for nondestructive inspection is a weld crack and stress in the pipe end weld part which combined the carbon steel pipe plate and the Cr-Mo steel pipe mainly used for the tube reactor for chemical plants. It can be used not only for non-destructive inspection such as corrosion cracking but also for non-destructive inspection of a pipe end welded portion in which a tube sheet and a tube body formed of other metal materials are combined. This is because in the nondestructive inspection test, the influence of crack-like defects is greater than the influence of the material of the tube sheet and the tube body.

  For example, the standard specimen 10 for nondestructive inspection is a tube in which a Ni-based alloy (Alloy 52) clad tube plate and a Ni-based alloy (Alloy 690) tube used in a steam generator for a pressurized water reactor are combined. It can also be used for nondestructive inspection of end welds. Since the pipe end weld used in the steam generator for a pressurized water reactor is expanded in full thickness, the tube 14 of the standard specimen 10 for nondestructive inspection is expanded in full thickness to close the gap 17. You can use what is.

Furthermore, according to the standard specimen 10 for non-destructive inspection, a cracking defect is artificially introduced by stress corrosion cracking by injecting a corrosive solution 27 in which 50% NaNO ₃ and 50% KNO ₃ are mixed by weight. Therefore, it is possible to simulate a crack-like defect having substantially the same form as an actual stress corrosion cracking rather than putting a defect in the welded part by machining or the like, so that the detection accuracy of the crack-like defect due to the stress corrosion cracking or the like is improved.

  The stress corrosion cracking properties for welds between carbon steel and Cr-Mo steel were evaluated.

  First, a welded joint was manufactured by welding a carbon steel sheet material and a Cr—Mo steel sheet material. FIG. 8 is a diagram illustrating a method for manufacturing the welded joint 32, FIG. 8A is a diagram illustrating the shape of the welded joint 32, and FIG. 8B is a diagram illustrating welding conditions.

  The weld joint 32 has a rectangular shape with a length of 115 mm and a width of 100 mm. As the carbon steel sheet material 34, SM490, which is a rolled steel material for welded structures, was used. 2.25Cr-1Mo steel was used for the Cr—Mo steel sheet material 36. And the site | part 38 which faced | matched the carbon steel sheet material 34 and the Cr-Mo steel sheet material 36 was TIG-welded. TGS-50 was used as a TIG welding rod. The current value was changed from 60 (A) to 100 (A), and the arc voltage was changed from 9 (V) to 11 (V).

  After TIG welding, the cooling conditions were changed in order to change the hardness of the weld. In the first cooling condition, air cooling was performed after welding. Under the second cooling condition, the sample was placed in a water bath immediately after welding and cooled with water. In the third cooling condition, air cooling was performed after welding, and then held at 900 ° C. for 15 minutes.

  Next, a test piece was cut out from each weld joint 32. The shape of the test piece was a rectangular shape having a width of 20 mm, a length of 50 mm, and a plate thickness of 2 mm. Moreover, about each test piece, it cut out from each weld joint 32 so that a welding part might be located in the approximate center of the width direction of a test piece, and along the longitudinal direction of a test piece.

  The surface hardness of each test piece with different cooling conditions after welding was measured by the Vickers hardness test. FIG. 9 is a graph showing the hardness distribution of the surface at each part of each test piece with different cooling conditions after welding. The horizontal axis of the graph shown in FIG. 9 represents the position of the test piece in the width direction, and the vertical axis of the graph represents Vickers hardness (HV).

  In the test piece under the first cooling condition (air cooling after welding), high hardness was obtained particularly in the connection region between the built-up portion and the Cr—Mo steel. In the test piece of the second cooling condition (water cooling immediately after welding), the hardness increases in the built-up portion and the connection region between the built-up portion and the Cr—Mo steel. A hardness greater than HV400 was obtained in the connection region. In the third cooling condition (after air cooling after welding, holding at 900 ° C. for 15 minutes and water cooling), the hardness increases from the carbon steel side to the Cr—Mo steel side. A hardness greater than HV400 was obtained in the connection region between Cr and Mo steel.

  As described above, by cooling under the second cooling condition or the third cooling condition, the residual stress in the weld becomes larger than that under the first cooling condition. The result is that the hardness is higher in the connection region with steel.

  Next, stress corrosion cracking was evaluated in a state in which a test piece was set on a bending jig and a constant strain bending was applied.

  FIG. 10 is a cross-sectional view showing the configuration of the bending jig. A CBB (Creviced Bent Beam) test jig was used as the bending jig. By setting the test piece on the CBB test jig, 2% bending strain is applied to the test piece.

With the test piece set on the CBB test jig, the test piece was placed in a carbon steel container containing the corrosion candidate solution, and the test piece was immersed in the corrosion candidate solution. Corrosion candidate solutions include NaNO ₂ reagent (Showa Chemical Co., Ltd., sodium nitrite, code number 1950-4260) _, NaNO ₃ reagent (Showa Chemical Co., Ltd., sodium nitrate, code number 1949-8289), KNO ₃ reagent A mixed solution (molten salt) obtained by mixing Showa Chemical Co., Ltd. (potassium nitrate, code number 1642-4280) at a predetermined mixing ratio was used. In addition, the first grade reagent was used for each reagent. Moreover, the heating temperature of the carbon steel container was set to 150 ° C. to 550 ° C., and the immersion time was set to 500 hours. And after immersion for 500 hours, the CBB test jig was taken out from the carbon steel container, and the test piece was observed.

FIG. 11 is a graph showing the results of the stress corrosion cracking test. The horizontal axis of the graph shown in FIG. 11, NaNO ₂ reagent and NaNO ₃ Reagents and KNO _3, represents the proportion of a weight ratio of NaNO ₂ reagent to the sum of the reagent, the vertical axis of the graph represents the heating temperature ing. The white circle data indicates that no stress corrosion cracking occurred, and the black rhombus (large) data and the black rhombus (small) data indicate that stress corrosion cracking occurred. .

  The white circle data and black rhombus (large) data are the test results for the test piece of the first cooling condition (air cooling after welding), and the black rhombus (small) data are the second cooling condition. The test results are shown for the test piece (water-cooled immediately after welding) and the third cooling condition (air-cooled after welding, then water-cooled by holding at 900 ° C. for 15 minutes). .

As apparent from the graph of FIG. 11, stress corrosion cracking occurred at a heating temperature of 250 ° C. in the case of a mixed liquid containing NaNO ₃ reagent, KNO _3, and a reagent without containing the NaNO ₂ reagent. In addition, when the welded part is further cured, it does not include the NaNO ₂ reagent, not only in the case of the mixed solution in which the NaNO ₃ reagent, KNO _{3 and the} reagent are mixed, but also the mixture that includes 5% NaNO ₂ reagent. Even in the liquid, stress corrosion cracking occurred at a heating temperature of 250 ° C. In other cases, the occurrence of stress corrosion cracking was not observed.

Table 1 is a table in which a part of the data in the graph of FIG. 11 is summarized. Which was heated at 250 ° C. using a mixture obtained by mixing 50% NaNO ₃ and 50% KNO _3, the stress corrosion cracking occurs in the Cr-Mo steel side of the weld. Further, when a mixed solution in which 50% NaNO ₂ and 50% KNO ₃ were mixed was used, stress corrosion cracking did not occur even when the heating temperature was 200 ° C. to 300 ° C.

FIG. 12 is an appearance photograph of a test piece in which stress corrosion cracking has occurred. FIG. 13 is an enlarged photograph of the surface of the site of stress corrosion cracking in FIG. FIG. 14 is a cross-sectional photograph of the site of stress corrosion cracking in FIG. Thus, 50% NaNO ₃ and is 50% KNO ₃ and those heated at 250 ° C. using a mixed mixture, intergranular stress corrosion cracking in the weld heat affected zone of the Cr-Mo steel grit (HAZ) A crack-like defect occurred.

From the above evaluation test results, it is possible to introduce the crack-like defect 20 into the welded portion 18 by using a mixed liquid in which 50% NaNO ₃ and 50% KNO ₃ are mixed as the corrosive liquid 27 that causes stress corrosion cracking. It becomes possible. Further, when a mixed solution in which 50% NaNO ₂ and 50% KNO ₃ are mixed is used, stress corrosion cracking does not occur, so that it can be used as the heat medium 28.

  Next, the standard specimen 10 for nondestructive inspection was manufactured.

  A carbon steel block (specimen body 12) was cut from a plate material of 100 mm thickness formed of carbon steel SM490 with a width of 100 mm and a length of 100 mm. A substantially center of the carbon steel block was drilled with a drill to form a through hole having an inner diameter of 21 mm. A Cr-Mo steel pipe (pipe 14) was formed from 2.25Cr-1Mo steel by extrusion. The outer diameter of the Cr-Mo steel pipe was 20 mm and the length was 150 mm.

  Next, a Cr-Mo steel pipe is inserted into the through hole of the carbon steel block, a processing jig is inserted from the inside of the Cr-Mo steel pipe, and a part of the circumferential direction is radially outward. The protrusion was formed by projecting to. The protrusions were provided at two locations on the same circumference with an interval in the circumferential direction. And the protrusion part was made to contact | abut to the internal peripheral surface of a through-hole, and the positioning of the Cr-Mo steel pipe was performed. Further, the route gap (gap 17) between the outer peripheral surface of the Cr-Mo steel pipe and the inner peripheral surface of the through hole was set to 0.2 mm so that the route gaps were substantially equal in the circumferential direction.

  Next, the outer peripheral surface on one end side in the longitudinal direction of the Cr-Mo steel tubular body and the inner peripheral surface on one end side in the longitudinal direction of the through hole of the carbon steel block are TIG welded and sealed in the circumferential direction. Thus, a mock-up (preliminary specimen 21) was formed. TGS-50 was used for the welding rod. The welding conditions were substantially the same as the welding conditions shown in FIG.

  Next, the mock-up was put into a carbon steel container, and crack-like defects due to stress corrosion cracking were introduced. The carbon steel container had a bottomed cylindrical shape with an inner diameter of 200 mm. The mock-up was set in a carbon steel container.

After putting a mixture of 50% NaNO ₂ and 50% KNO ₃ in a weight ratio into the space between the carbon steel container and the mock-up and the inside of the Cr—Mo steel pipe, the carbon steel The container was heated and melted to obtain a heat medium. Next, a corrosive liquid composed of a mixture of 50% NaNO ₃ and 50% KNO _{3 in} a weight ratio that was previously heated to 200 ° C. or higher and melted was applied to the outer peripheral surface of the Cr—Mo steel pipe and the through hole. Injected into the root gap between the inner peripheral surface of each of the two. And by hold | maintaining at 250 degreeC for 500 hours, the crack-like defect was introduce | transduced into the welding part and the standard specimen for nondestructive inspection was manufactured.

  10 Standard specimen for nondestructive inspection, 12 Specimen main body, 14 Tube body, 15 Through hole, 16 Protruding part, 17 Clearance, 18 Welded part, 19 Overlay part, 20 Cracked defect, 21 Preliminary specimen, 22 Hanging Hardware, 24 Metal container, 26 Heater, 27 Corrosive liquid, 28 Heat medium

Claims (2)

A standard specimen for nondestructive inspection for detecting crack-like defects in a pipe end weld by nondestructive inspection,
A specimen body formed of carbon steel and having a through hole;
A tube inserted into the through hole and formed of Cr-Mo steel;
With
A gap is provided between the outer peripheral surface of the tubular body and the inner peripheral surface of the through hole in the specimen body,
Having a welded portion welded over the entire circumference between the outer peripheral surface on one end side in the longitudinal direction of the tube and the inner peripheral surface on one end side in the longitudinal direction of the through hole of the specimen body;
The weld has a crack-like defect introduced by stress corrosion cracking by injecting a corrosion solution in which 50% NaNO ₃ and 50% KNO ₃ are mixed in a weight ratio into the gap. Standard specimen for nondestructive inspection. A method of manufacturing a standard specimen for nondestructive inspection for detecting crack-like defects in a pipe end weld by nondestructive inspection,
Forming a specimen body having a through hole with carbon steel and forming a tube with Cr-Mo steel;
Inserting the tubular body into the through hole, positioning the tubular body by providing a gap between an outer peripheral surface of the tubular body and an inner peripheral surface of the through hole;
Welding between the outer peripheral surface on one end side in the longitudinal direction of the tubular body and the inner peripheral surface on one end side of the through-hole over the entire circumference, and forming a preliminary specimen;
A corrosion solution in which 50% NaNO ₃ and 50% KNO ₃ are mixed in a weight ratio is injected into the gap, the preliminary specimen is heated to 250 ° C., and the welded portion of the preliminary specimen is cracked due to stress corrosion cracking. Introducing a defect,
A method for producing a standard specimen for nondestructive inspection, comprising: