JP2008151675A - Device for testing delayed fracture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably maintain test conditions and suppress deviations in the evaluation of delayed fracture in a device for testing delayed fracture. <P>SOLUTION: The device 10 comprises a load testing section 12 for dipping a test specimen 8 into a test liquid using a test vessel 20 and providing a tensile load; a circulation testing liquid tank 40 for circulating the test liquid between the vessel 20 and the tank 40 itself, a new liquid tank 60 for accommodating a new test liquid; and an opening/closing valve provided between the circulation testing liquid tank 40 and the new liquid tank 60; and a heater 60 provided in the circulation testing liquid tank 40 and connected to a thermal source 48 for a heater. The pH adjusting section 72 of a controller 70 controls the opening/closing valve 50 to adjust the pH value of a test liquid 82 based on the detected value of a pH detector 42; a temperature adjusting section 47 adjusts the thermal source 48 for a heater to control the temperature of the test liquid 82 based on the detected value of a test liquid thermometer 44. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a delayed fracture test apparatus, and more particularly to a delayed fracture test apparatus that supplies a test liquid to a test piece to evaluate delayed fracture characteristics of a steel material.

  In high-strength steel materials, when tensile stress is applied in a corrosive environment, a phenomenon called stress corrosion cracking or delayed fracture that causes fracture after a predetermined time is known. The cause of delayed fracture is a model in which hydrogen is introduced into the steel material by pickling, plating, etc., hydrogen accumulates in the stress concentration part, cracks occur, and the cracks propagate along the grain boundaries. Proposed.

  And, as a delayed fracture test device that accelerates evaluation of delayed fracture and predicts danger in advance, it applies a constant tensile stress to the test piece and supplies the test liquid for introducing hydrogen to the stress concentration part etc. of the test piece There are some measures such as providing a means to do this.

  For example, in Patent Document 1, as a device for performing a stress corrosion cracking test assuming a harsh usage environment, a transparent covering airtightly and airtightly covers an intermediate portion of a test piece that can be attached to the upper and lower gripping devices, respectively. A configuration is disclosed that includes an acrylic cover and a liquid supply device that is connected to the cover and supplies a corrosive liquid in a circulating manner. Examples of the corrosive liquid include hydrogen sulfide water, high-temperature seawater, and ammonia water.

JP-A-3-287046

  According to the test apparatus of Patent Document 1, a steady tensile stress can be applied to a test piece, and a corrosive liquid can be circulated and supplied to the test piece. By the way, in the delayed fracture test, since the presence of hydrogen is involved, it is preferable that conditions such as pH and temperature of the test solution are made constant during the test period. In the test apparatus of Patent Document 1, a corrosive liquid is circulated and supplied to a liquid-tight and air-tight acrylic case. However, the pH may change with time, and a temperature change may also occur. Therefore, the evaluation result of delayed fracture may vary.

  An object of the present invention is to provide a delayed fracture test apparatus that can stably maintain test conditions and suppress variations in evaluation of delayed fracture. Yet another object is to provide a delayed fracture testing apparatus that can evaluate delayed fracture in water at room temperature of 50 ° C. or higher, which has been conventionally considered not to be delayed fractured in normal temperature water at 1100 MPa or lower. is there.

  The delayed fracture test apparatus according to the present invention is a container for filling the periphery of a test piece with a test solution, and holds both ends of the test piece outside so as not to leak the liquid. A test container having a discharge port, a load tester that applies a load for delayed fracture testing to both ends of the test piece held in the test container, and a test liquid circulation path between the supply port and the discharge port of the test container A circulating test solution tank that can be connected to the circulating test solution tank through an on-off valve, and can store an unused test solution; A pH detector provided in the circulating test solution tank, and a pH adjusting unit for controlling the opening and closing of the on-off valve based on the detection value of the pH detector and adjusting the pH of the test solution supplied to the test container to a predetermined range; It is characterized by providing.

  Further, in the delayed fracture test apparatus according to the present invention, the heater provided in the circulating test liquid tank, the test liquid thermometer provided in the circulating test liquid tank, and energization of the heater are controlled based on the detected value of the test liquid thermometer. And a temperature adjusting unit that adjusts the temperature of the test solution supplied to the test container within a predetermined range.

  Moreover, in the delayed fracture test apparatus according to the present invention, the new liquid tank contains water or acidic liquid as the test liquid, the water or acidic liquid circulates in the circulating test liquid tank and the test container, and the temperature adjusting unit is It is preferable to adjust the temperature of water or acidic liquid as the test liquid supplied to the test container to 50 ° C. or higher and 100 ° C. or lower.

  In the delayed fracture test apparatus according to the present invention, the test container has a specific liquid volume V1 / which is a ratio of the test liquid volume V1 in the test container and the area A where the test piece in the test container contacts the test liquid. It is preferable that A is 30 mm or more and 60 mm or less.

  In the delayed fracture test apparatus according to the present invention, V2 / V1, which is a ratio of the circulating test solution volume V2 accommodated in the circulating test solution tank and the test solution volume V1 in the test container, is 150 times or more and 300 times. The following is preferable.

  With the above configuration, the delayed fracture test apparatus has a test container in which both ends of the test piece are exposed to the outside so as to be applied to a load tester, and the periphery of the test piece is filled with the test solution so as not to leak, Are connected by a test liquid circulation path, and a new liquid tank is connected to the circulating test liquid tank via an on-off valve. Then, the open / close valve is opened / closed according to the pH of the circulating test solution tank, and the pH of the test solution supplied to the test container is adjusted to a predetermined range. As a result, during the delayed fracture test, the test piece is exposed to a test solution that maintains a pH within a predetermined range, and the test conditions can be stably maintained and variations in the delayed fracture evaluation result can be suppressed.

  In addition, the circulating test liquid tank is provided with a heater and a test liquid thermometer, and energization of the heater is controlled based on the detected value of the test liquid thermometer, and the temperature of the test liquid supplied to the test container is set to a predetermined value. Because it is adjusted to the range, during the delayed fracture test, the test piece will be exposed to the test solution that maintains the temperature in the predetermined range, so that the test conditions can be stably maintained, and variation in the delayed fracture evaluation results can be suppressed. .

In particular, when the test solution is water, the temperature of the water is adjusted to 50 ° C. or more and 100 ° C. or less. It is known that when iron is placed in water at about 50 ° C. or higher under atmospheric shutoff, an Fe corrosion reaction and an H ₂ generation reaction occur. Although this phenomenon is called a sicol reaction, a delayed fracture test based on the sicol reaction can be evaluated by maintaining the above conditions.

  Moreover, since the specific liquid amount V1 / A which is the ratio of the test liquid volume V1 in the test container and the area A where the test piece in the test container contacts the test liquid is set to 30 mm or more and 60 mm or less, A sufficient amount of test solution is supplied over the surrounding area. Thereby, even if a local reaction occurs from the surface of the test piece, the test solution is sufficiently uniformed, the test conditions are stably maintained, and the variation in evaluation of delayed fracture can be suppressed. Experience has shown that the change in pH of the test solution in the test container can be suppressed to about 0.5 per day within the range of this specific solution amount.

  In addition, since the ratio V2 / V1, which is the ratio of the circulating test solution volume V2 stored in the circulating test solution tank and the test solution volume V1 in the test vessel, is 150 times or more and 300 times or less, the test in the test vessel The pH of the liquid is kept almost constant. As a result, a local reaction occurs from the surface of the test piece, and even if the pH changes, it is sufficiently uniformed by supplying the test solution from the circulating test solution tank that has a larger capacity than the test vessel, and the test conditions are stabilized. Thus, variation in delayed fracture evaluation can be suppressed. Experience has shown that, within this volume ratio range, the pH change of the test solution in the test container can be suppressed to about 0.5 per 3 days.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The dimensions, materials, and the like in the following are examples for explanation, and can be appropriately changed depending on the application.

  FIG. 1 is a diagram illustrating a configuration of the delayed fracture test apparatus 10. FIG. 1 shows a test piece 8 which is not a constituent element of the delayed fracture test apparatus 10 but is a test target. The delayed fracture test device 10 is a device that applies a constant tensile load to a test piece, holds the test piece immersed in a test solution, and tests how stress corrosion fracture occurs over time. The delayed fracture test apparatus 10 includes a load test unit 12 that immerses the test piece 8 in a test solution and applies a tensile load, a circulating test solution tank 40 for circulating the test solution, and a new solution tank 60 that stores a new test solution. And a control unit 70 for maintaining the state of the test solution at a predetermined condition.

  The load test section 12 holds both ends of the test container 20 that holds both ends to the outside so that the test piece 8 does not leak, and both ends of the test piece that protrudes from the test container 20, and a predetermined tensile force therebetween. And load application units 14 and 16 for applying loads. The load application units 14 and 16 are configured to have a detection function of detecting a change in the length of the test piece 8 while applying a constant tensile force to both ends of the test piece 8 with a load cell, for example. can do.

  FIG. 2 is a diagram showing a detailed configuration of the test container 20. The test container 20 includes a casing 22 having a cylindrical outer shape and a test liquid chamber 23 that is a space for containing a test liquid therein. The outer periphery of the casing 22 communicates with the test liquid chamber 23. A test liquid supply port 24 and a test liquid discharge port 26 are provided. Further, a seal member 28 is provided at a portion for holding the test piece 8 so that liquid does not leak from both ends of the test piece 8. As this test container 20, what shape | molded the transparent acrylic resin can be used so that an internal condition can be observed, for example.

  In the test container 20, the test liquid discharge port 26 is provided at a position close to the upper part, and the test liquid supply port 24 is provided at a position lower than that. Thereby, the test solution 20 can be slowly filled with the test solution 20 without involving air containing oxygen. As shown in FIG. 1, a supply pipe 30 connects between the test solution supply port 24 and a supply port 41 provided at the bottom of the circulating test solution tank 40. The test liquid discharge port 26 is connected to one end of the return pipe 32, and the other end of the return pipe 32 opens at the upper part of the circulating test liquid tank 40. Therefore, the test liquid is supplied from the test liquid supply port 24 of the test container 20 to the test liquid chamber 23 of the test container 20 via the supply pipe 30 from the supply port 41 of the circulating test liquid tank 40. Then, the liquid is guided from the test liquid chamber 23 through the test liquid discharge port 26 to the upper part of the circulating test liquid tank 40 by the return pipe 32 and poured into the circulating test liquid tank 40. In this way, the test liquid circulates between the test container 20 and the circulating test liquid tank 40.

  In addition, as the test piece 8, as shown in FIG. 2, a round bar material that is formed in a cylindrical shape and has a notch portion 4 and that has screw portions 6 and 7 at both ends is used. These screw parts 6 and 7 are connected to load application parts 14 and 16 of the load test part 12, respectively, and a predetermined tensile force load is applied between both ends of the test piece 8 by the function of the load test part 12.

  The test solution chamber 23 of the test container 20 is filled with the test solution 80 as shown in FIG. 1, and the periphery of the test piece 8 is exposed to the test solution. Here, the test solution 80 is filled so that no air remains in the test container 20. The test piece 8 is applied with a tensile load by the function of the load test unit 12 and the test container 20 is kept airtight and liquid-tight as described above. A tensile force load is applied in a state where the test solution is exposed in an oxygen-deficient state. In other words, the test situation facilitates the hydrogen generation reaction and is likely to cause delayed fracture.

  The volume of the test solution chamber 23 of the test container 20 is such that when the outer periphery of the test piece 8 is sufficiently exposed to the test solution 80 and a corrosion reaction occurs on the outer periphery, the resulting pH changes particularly for the acidic test solution. It is preferable that a sufficient amount can be secured so that it is difficult. That is, it is preferable that the ratio of (volume of the test solution 80 in the test solution chamber 23) V1 / (peripheral area where the test piece 8 is exposed to the test solution 80) A is sufficiently large. When this V1 / A is called a specific liquid amount, the specific liquid amount has a thickness dimension, and indicates the liquid thickness of the test liquid 80 from the outer surface of the test piece 8.

As an example of specific dimensions, the outer diameter of the test piece 8 can be 8 mm, the inner diameter of the test liquid chamber 23 can be 38 mm, and the height can be 55 mm. At this time, (the outer peripheral area where the test piece 8 is exposed to the test solution 80) A is calculated by π × 8 mm × 55 mm and is about 1380 mm ² . On the other hand, (volume of the test solution 80 in the test solution chamber 23) V1 is calculated by (π / 4) × {(38) ² − (8) ² } mm ² × 55 mm, and about 59,580 mm ³ . is there. The specific volume (V1 / A) in this case is about 43 mm. That is, the outer periphery of the test piece 8 is surrounded by the thickness of the test solution 80 of about 43 mm.

  When the test piece 8 is exposed to the test solution 80, particularly in the case of an acidic test solution, the pH of the test solution 80 changes due to a corrosion reaction. it can. When the relationship between the pH change of the test liquid 80 in the test container 20 and the specific liquid amount is examined in a state where there is no circulation of the test liquid between the circulating test liquid tank 40 and the test liquid 80 is an acidic test liquid. When the specific liquid amount is 30 mm or more and 60 mm or less, the pH change of the test solution 80 in the test container 20 can be suppressed to about 0.5 per day.

  Further, when the stress corrosion test is to be performed with the temperature of the test solution 80 higher than room temperature, the distance from the outer wall portion of the test container 20 where the heat is dissipated to the test piece 8 becomes longer as the specific volume increases. As a result, the decrease in the temperature of the test solution 80 can be reduced.

  Returning to FIG. 1, the circulating test solution tank 40 is a test solution buffer tank having a function for maintaining the state of the test solution supplied to the test container 20 at substantially the same condition during the test period. This function is realized by two methods.

One is to circulate the test liquid between the test container 20 and uniformize the change in the state of the test liquid caused by the corrosion reaction in the test container 20. Therefore, the volume V2 of the test liquid stored in the circulating test liquid tank 40 is set sufficiently larger than the volume of the test liquid chamber 23 of the test container 20. As an example, taking the size of the test container 20 as the above example, the size of the test liquid volume portion of the circulating test liquid tank 40 is a rectangular shape of 235 mm in length, 135 mm in width, and 350 mm in height, and its volume V2 is It is calculated by 235 mm × 135 mm × 350 mm, and becomes about 11,103,750 mm ³ . When V1 is used, (the test liquid volume of the circulating test liquid tank 40) V2 / (the test liquid volume of the test container 20) V1 is about 186 times.

  If V2 / V1 is sufficiently large by circulating the test liquid 80 in the test container 20 between the test liquid 80 and the test liquid 82 in the circulating test liquid tank 40, the pH of the test liquid 80 in the test container 20 will be described. Can be suppressed. When the relationship between the change in pH of the test liquid 80 in the test container 20 and the magnitude of V2 / V1 is examined in a state where the test liquid is circulated between the test container 20 and the circulating test liquid tank 40, the test liquid 80 is obtained. In the case of an acidic test solution, when V2 / V1 is 150 times or more and 300 times or less, the pH change of the test solution 80 in the test container 20 can be suppressed to about 0.5 per three days.

  Similarly, when the stress corrosion test is performed with the temperature of the test solution 80 higher than room temperature, the temperature drop of the test solution 80 in the test container 20 can be reduced as V2 / V1 increases. For example, if the test liquid 82 higher than room temperature is stored in the circulating test liquid tank 40 and the test liquid is circulated between the test container 20 and the circulating test liquid tank 40, the larger V2 / V1 is, Even if the temperature of the test solution 80 is lowered, the whole temperature can be made uniform by returning it to the circulation test solution tank 40 and circulating it.

  As a second method for maintaining the state of the test liquid supplied to the test container 20 at substantially the same condition during the test period, the circulating test liquid tank 40 adjusts the pH of the test liquid 82 therein, Further, the temperature of the test solution 82 is adjusted.

  In FIG. 1, a new liquid tank 60, an on-off valve 50, and a pH detector 42 are for adjusting the pH of the test liquid 82 in the circulating test liquid tank 40. The heater 46, the heater heat source 48, and the test liquid thermometer 44 are for adjusting the temperature of the test liquid 82 in the circulating test liquid tank 40. The control unit 70 has a function of performing pH adjustment and temperature adjustment, and controls the on-off valve 50 based on the detection value of the pH detector 42 to adjust the pH of the test solution 82; A temperature adjustment unit 74 that adjusts the temperature of the test liquid 82 by adjusting the heater heat source 48 based on the detected value of the test liquid thermometer 44 is configured. Here, the new solution is an unused neutral test solution when the test solution is neutral, and is hydrochloric acid, nitric acid or sulfuric acid when the test solution is acidic.

  The new liquid tank 60 is a container for storing an unused test liquid 84. The unused test solution is the above-described new solution, and is an unused neutral test solution, hydrochloric acid, nitric acid, or sulfuric acid. The on-off valve 50 is an electromagnetic fluid control valve provided between the flow path connecting the new liquid tank 60 and the circulating test liquid tank 40. The open / close valve 50 opens and closes in response to a command from the control unit 70 and opens the new liquid tank 60. The unused test solution 84 can be supplied to the circulating test solution tank 40. The pH detector 42 is an electric signal type measuring device that detects the pH of the test solution 82 and outputs the detected value to the control unit 70.

  The heater 46 has a function of heating the test liquid 82 in the circulating test liquid tank 40 by heat supplied from the heater heat source 48. When the heater heat source 48 is used as a power source, a resistance heating heater is used. It can be. When the heater heat source 48 is a high-temperature fluid medium such as hot water, the heater 46 can be a heat exchanger that exchanges heat between the heating fluid and the test liquid 82. The test liquid thermometer 44 is an electric signal thermometer that detects the liquid temperature of the test liquid 82 and outputs the detected value to the control unit 70.

  Based on the detected value of the pH detector 42, the pH adjusting unit 72 of the control unit 70 opens the on-off valve 50 when the detected value exceeds a predetermined threshold range, and the test solution in the circulating test solution tank 40 is opened. It has a function of maintaining the pH of 82 within a predetermined threshold range. When the corrosion reaction occurs, the pH of the test solution 80 in the test container 20 changes, and the pH of the test solution 82 in the circulating test solution tank 40 changes accordingly, and is stored in the new solution tank 60. There is a difference between the pH of the unused test solution 84, that is, the pH of the unused neutral test solution, or the pH of hydrochloric acid, nitric acid, and sulfuric acid. Therefore, the change in pH is suppressed by opening the on-off valve 50 and refilling the circulating test solution tank 40 with an unused neutral test solution that is an unused test solution 84 or hydrochloric acid, nitric acid, and sulfuric acid. be able to.

  In addition, the volume of the test liquid 82 accommodated in the circulation test liquid tank 40 increases by replenishing the unused neutral test liquid that is the unused test liquid 84 or hydrochloric acid, nitric acid, and sulfuric acid. In order to prevent the excess, it is preferable to open a drain valve (not shown) as appropriate to discharge the test solution 82 in the circulating test solution tank 40 to the outside.

  Here, the test solution used for the delayed fracture test, its pH adjustment, and temperature adjustment will be described. As described above, the delayed fracture phenomenon is considered to be caused by the presence of hydrogen. Accordingly, a liquid that can introduce hydrogen into steel by a corrosion reaction with steel is used as a test liquid used in the delayed fracture test. For example, in addition to corrosive test solutions such as hydrogen sulfide water, high-temperature seawater, and ammonia water listed in Patent Document 1, water, hydrochloric acid, nitric acid, sulfuric acid, or acid is added to adjust to an appropriate pH. Water or the like is used. Further, in order to check whether or not delayed fracture occurs under the environmental conditions where the test piece is actually placed, a liquid close to acid rain, a liquid close to lubricating oil, or the like on which the test piece is placed is used.

It has been pointed out that a delayed fracture phenomenon occurs in steel materials, particularly high-strength steel, as test specimens. Here, when a delayed fracture test is performed, the steel material is corroded and discolored by the test solution, and it has been found that there are two types of discoloration. One is Fe ₂ O ₃ red rust and the other is Fe ₃ O ₄ black rust. The formation of black rust is due to the Sicol reaction. Here, the Sicol reaction was pointed out by Mr. Sikor. 1) Under atmospheric blocking, 2) Above 50 ° C., 3) In the presence of moisture, in the hydrolysis reaction of Fe, H ₂ A generation reaction occurs, and a larger amount of hydrogen is generated than a reaction in which red rust is generated. FIG. 3 shows the reaction of red rust and black rust corrosion.

  As described above, when evaluating delayed fracture, even a steel material having a strength level that does not cause delayed fracture in water at room temperature is accompanied by a hydrogen generation reaction in water at 50 ° C. or higher where a sicol reaction occurs. Therefore, it is necessary to perform the test. In this case, as described above, it is necessary to expose the test piece loaded with a tensile force to water at 50 ° C. or higher under an atmospheric cutoff. In this case, the test solution is water at 50 ° C. or higher.

  Therefore, as a test solution used in the delayed fracture test, for example, an acidic solution, salt water, water at 50 ° C. or higher is preferable, assuming an actual environment.

  When using hydrochloric acid, nitric acid, sulfuric acid, etc. as the test solution, the pH changes due to the corrosion reaction.To maintain the corrosion conditions constant over the test period, keep the pH within the specified range. It is preferable to adjust. For example, when the pH is adjusted to about 3 ± 0.5, the unused test solution in the new solution tank 60 in FIG. 1 is hydrochloric acid, nitric acid, sulfuric acid or the like having a pH of 1 or less. 72, when the detected value of the pH detector 42 exceeds the range of 3 ± 0.5, the on-off valve 50 is opened to replenish the circulating test solution tank 40 with an unused test solution 84 having a pH of 1 or less. Adjust.

  Further, the temperature adjustment unit 74 of the control unit 70 can adjust the temperature of the test solution 82 within a predetermined range using the heater 46 according to the detection value of the test solution thermometer 44. When strong acids such as hydrochloric acid, nitric acid, sulfuric acid, etc. are used for the test solution, if these are heated to high temperatures, the risk of the test environment may increase. Therefore, the predetermined temperature range is preferably about room temperature ± 5 ° C.

  When the test solution is salt water, the pH of the unused test solution 84 can be set to about 6, and the threshold range for the operation of the on-off valve 50 can be set to about 6 ± 0.5. Regarding temperature adjustment, it is considered that the test conditions become unstable when boiling, so a test temperature is set between room temperature and below the boiling point, and a predetermined temperature range for the operation of the heater 46 (test temperature ± 5) is set. ° C) degree.

  When water is used as the test solution assuming a Sicol reaction, the pH of the unused test solution 84 is between 7 and 8, and the threshold range for the operation of the on-off valve 50 is pH (7 to 8). It can be about ± 0.5. For temperature adjustment, a test temperature can be set between 50 ° C. and 100 ° C., and a predetermined temperature range for the operation of the heater 46 can be set to about (test temperature ± 5 ° C.). The reason for setting the test temperature to 100 ° C. or less is to avoid instability of test conditions such as evaporation of the test liquid due to boiling.

  The results of testing using the delayed fracture test apparatus 10 will be described below. In the following description, the reference numerals in FIGS. 1 and 2 are used.

  As a material of the test piece, as shown in FIG. 4, a steel material having a component conforming to JIS G4105 was used. As shown in FIG. 5, the mechanical properties of the test piece are 11.9T class high strength steel. Here, 11.9T indicates a tensile strength of 1100 MPa or more. As shown in FIG. 5, the tensile strength of the test piece is 1190 MPa. The 0.2% proof stress indicates an offset stress when the strain is 0.2%, and is 1082 MPa in FIG. Particle size No. Is the size of the crystal grain represented by the method defined in JIS. The larger the is, the finer the crystal grains.

  As shown in FIG. 2, the shape of the test piece is a round bar having a diameter of 8 mm, in which a notch portion 4 for stress concentration is provided at the center portion, and M8 screw portions 6 and 7 are formed at both ends.

  As the test solution, water at normal temperature and water at 80 ° C. were used. For each, the operation of the heater 46 is controlled, the temperature of the test liquid 82 in the circulating test liquid tank 40 is adjusted, and the temperature of the test liquid supplied to the test container 20 is set to room temperature ± 5 ° C., 80 ° C. ± 5 ° C. It was. As room temperature, it can be 25 degreeC, for example. For each, the operation of the on-off valve 50 is controlled to adjust the pH of the test liquid 82 in the circulating test liquid tank 40 so that the pH of the test liquid supplied to the test container 20 is 7 ± 0.5, or 8 ± 0.5.

  In the load test section 12, a tensile force corresponding to a stress ratio of 0.95σ, that is, a stress of 95% of the tensile strength is applied between the screw sections 6 and 7 at both ends of the test piece 8 and held for several hundred hours. . As a result, when water at 80 ° C. was used as the test solution, the test piece was broken in 100 hours or less, and when normal temperature water was used as the test solution, the test piece was not broken even after several hundred hours.

  FIG. 6 is a diagram schematically showing the state of the test piece after the test. FIG. 6A shows a case where 80 ° C. water is used as the test solution, and FIG. 6B shows that normal temperature water is used as the test solution. Is the case. As shown in FIG. 6, black rust is generated in the case of FIG. 6A using 80 ° C. water as the test solution, whereas FIG. 6B using normal temperature water as the test piece. Then, black rust has not occurred.

  FIG. 7 is a diagram showing the results of measuring the amount of diffusible hydrogen for the test piece after the test. Here, the abscissa indicates the rupture time when the test piece is ruptured, and the ordinate indicates the amount of diffusible hydrogen in mass ppm. Here, ◯ indicates the experimental result of a test piece using 80 ° C. water as the test solution, and Δ indicates the experimental result of the test piece using normal temperature water as the test solution. The reason why the arrow mark is added to the data indicated by Δ is to indicate that no fracture occurred during the test time, and that the fracture time is longer or not broken. This experimental result is different from that in the conventional definition of delayed fracture as shown in FIG. 7, in the steel material having the strength level of 11.9T class, delayed fracture does not occur in water. This indicates that delayed destruction occurs in water at 50 ° C. or higher where a sycol reaction occurs.

  The amount of diffusible hydrogen is measured by placing the test piece in a heating furnace in an argon atmosphere and heating it at a constant heating rate to change the temperature range. Measured by the method detected by As shown in FIG. 7, the test piece that was ruptured in several tens of hours using 80 ° C. water as the test solution was more intensive than the test piece that was not broken in several hundred hours using normal temperature water as the test solution. However, the amount of diffusible hydrogen is large.

From the results of FIG. 6 and FIG. 7, the test piece to which the load of the tensile force was applied in the test vessel sealed with 80 ° C. water as the test solution broke in tens of hours, and after the break It was found that black rust was generated on the test piece and a large amount of diffusible hydrogen was detected. The cause of this breakage is presumed to be due to the H ₂ generation reaction due to the Sicol reaction in relation to FIG.

  In this test, the pH of the test solution is maintained in a certain range during the test period, and the temperature of the test solution is also maintained in a certain range. Therefore, as shown in FIG. Few. As described above, according to the delayed fracture test apparatus 10 described above, it is confirmed by reducing the variation in evaluation that delayed fracture occurs in high-strength steel when water having a temperature of 50 ° C. or higher and lower than 100 ° C. is used. I was able to.

In embodiment which concerns on this invention, it is a figure which shows the structure of a delayed fracture test apparatus. In embodiment concerning this invention, it is a figure which shows the detailed structure of a test container. In embodiment which concerns on this invention, it is a figure explaining the mode of reaction about corrosion when it estimates that it is a Sicol reaction about red rust type corrosion and black rust type. It is a figure explaining the material of the test piece used in embodiment which concerns on this invention. It is a figure explaining the mechanical characteristic of the test piece used in embodiment which concerns on this invention. In embodiment which concerns on this invention, it is a figure which illustrates typically the state of the test piece after a delayed fracture test. In embodiment which concerns on this invention, it is a figure which shows the result of having measured the amount of diffusible hydrogen about the test piece after a delayed fracture test.

Explanation of symbols

  4 Notch part, 6, 7 Thread part, 8 Test piece, 10 Delayed fracture test device, 12 Load test part, 14, 16 Load application part, 20 Test container, 22 Case, 23 Test liquid chamber, 24 Test liquid supply port , 26 Test solution outlet, 28 Seal member, 30 Supply pipe, 32 Return pipe, 40 Circulating test solution tank, 41 Supply port, 42 pH detector, 44 Test solution thermometer, 46 Heater, 48 Heat source for heater, 50 Open / close Valve, 60 fresh solution tank, 70 control unit, 72 pH adjustment unit, 74 temperature adjustment unit, 80, 82, 84 test solution.

Claims (5)

A container for filling the periphery of the test piece with the test solution, holding the test piece at both ends so as not to leak, and having a test solution supply port and a discharge port;
A load testing machine that applies a load for delayed fracture testing to both ends of a test piece held in a test container;
A circulating test solution tank connected between the supply port and the discharge port of the test vessel via a test solution circulation path and capable of storing a larger amount of test solution than the inner volume of the test vessel;
A new liquid tank that is connected to the circulating test liquid tank via an on-off valve and stores unused test liquid;
A pH detector provided in the circulating test liquid tank;
a pH adjusting unit that controls the opening and closing of the on-off valve based on the detection value of the pH detector, and adjusts the pH of the test solution supplied to the test container to a predetermined range;
A delayed fracture test apparatus comprising: In the delayed fracture test apparatus according to claim 1,
A heater provided in the circulating test liquid tank;
A test liquid thermometer installed in the circulating test liquid tank;
A temperature adjusting unit that controls energization of the heater based on the detected value of the test liquid thermometer, and adjusts the temperature of the test liquid supplied to the test container to a predetermined range;
A delayed fracture test apparatus comprising: In the delayed fracture test apparatus according to claim 2,
The new liquid tank contains water or acidic liquid as the test liquid,
Water or acidic liquid circulates in the circulating test liquid tank and test container,
The temperature adjustment unit adjusts the temperature of water or an acidic solution as a test solution supplied to a test container to 50 ° C. or more and 100 ° C. or less, and a delayed fracture test apparatus characterized in that: In the delayed fracture test apparatus according to claim 1,
The test container is
Delayed fracture characterized in that the specific liquid volume V1 / A, which is the ratio of the test liquid volume V1 in the test container to the area A where the test piece in the test container contacts the test liquid, is 30 mm or more and 60 mm or less. Test equipment. In the delayed fracture test apparatus according to claim 1,
Delayed fracture test apparatus characterized in that V2 / V1, which is the ratio of the circulating test liquid volume V2 accommodated in the circulating test liquid tank and the test liquid volume V1 in the test container, is 150 to 300 times .

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