JP2009085811A - Testpiece and detection apparatus for detection of stress corrosion cracking - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a testpiece for the detection of stress corrosion cracking and capable of detecting and monitoring stress corrosion cracking and easily setting a stress value equivalent to an object to be monitored. <P>SOLUTION: The testpiece 50 for detecting stress corrosion cracking and the state of stress corrosion cracking of a body to be tested which corrodes in contact with a corrosive medium is provided with both a testpiece main body 51 made of the same metallic material as that of the body to be tested and a stress providing mechanism 69 embedded in the testpiece main body 51 for providing a stress for the testpiece main body 51 without coming into contact with the corrosive medium. The testpiece 50 for the detection of stress corrosion cracking includes both a tube 51 made of the same metallic material as that of the body to be tested and having a closed tip and a pressing rod 52 capable of being inserted in the tube 51 and generates a stress specified on the basis of a pressing force of a tip 58 of the pressing rod 52 pressing a wall 57 in the inner part of the tube 51 in the directions of separating both end parts of the tube 51. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a test piece for stress corrosion cracking detection and a stress corrosion cracking detection apparatus.

  For detection of stress corrosion cracking that can be installed in a plant where there is a risk of stress corrosion cracking (SCC) from the internal fluid W side, such as stainless steel welded piping, and for monitoring the occurrence (occurrence) of SCC A sensor and a monitor device are known (Patent Document 1). Specifically, a sensor that applies stress by applying an internal pressure to a film-like metal is formed.

  Specifically, the tip is a hemispherical cylindrical body that holds a working electrode filled with a pressure medium, a reference electrode, a holder for attaching to a monitoring object, and a pressure medium in the working electrode. It has a pressure screw for applying an arbitrary pressure and a detection port for detecting the pressure of the pressure medium in the working electrode. In this stress corrosion cracking detection sensor, a pressure sensor is connected to the detection port, and a corrosion potential measuring device is connected to the working electrode and the reference electrode so as to observe a potential oscillation peculiar to the stress corrosion cracking.

  In addition, stress corrosion cracking (SCC) here refers to a phenomenon in which a metal material placed in a specific corrosive environment causes time-dependent brittle cracking under a continuous tensile stress. In other words, this is a typical environmental embrittlement in which cracking occurs only when a material condition, a corrosive environment, and stress satisfy certain conditions. In addition, stress and corrosive action synergistically damage the target object, which is a necessary condition for the occurrence of SCC. Compared to the case of breaking by stress alone, it is much lower than the yield stress or cracked even in a weak corrosive environment. Will occur. As specific combinations of materials / environments that cause cracking, austenitic stainless steel-chloride aqueous solution, carbon steel-caustic aqueous solution, and brass-ammonia aqueous solution are known.

  Since stress corrosion cracking occurs even at a very low stress as compared with the case of breaking by stress alone, it is desired to detect the stress corrosion reliably. However, there have been few devices for monitoring stress corrosion cracking. In the case of a general corrosion monitoring sensor, there are various types of conventional methods such as an electric resistance method, a polarization resistance method, or an AC impedance method. The crack could not be monitored.

  SCC occurs when a combination of materials, environment, and stress is set as a predetermined condition. For example, it has been elucidated that when stainless steel is sensitized particularly by receiving welding heat input, SCC is generated by applying a condition such as welding residual stress in a chloride environment. .

  However, because there is not necessarily a database on whether or not SCC occurs, such as process fluids in chemical plants, materials such as evaluation of SCC sensitivity of materials accompanying process changes or application of new materials to plant components When changing the environment and stress, it was necessary to conduct an SCC sensitivity test.

In addition, U-shaped bending specimens (specified in the JIS G0576 boiling salt mug test) are collected from a given material (select alloy type, welded, heat treated, etc.) and immersed in plant piping, storage tanks, etc. for a certain period of time. SCC sensitivity is determined by
In addition, if necessary to clarify the stress dependence, an experimental loop branched from the system is provided, or a laboratory test apparatus is provided, a constant load test is performed, and the SCC generation time (constant load test piece The stress dependence of the SCC occurrence time (representing the SCC occurrence time with the rupture time), the SCC occurrence limit stress, and the like are obtained. Alternatively, evaluation is performed by performing a constant strain bending test such as a four-point bending test.

In addition to the test piece, the reference electrode and electrometer (potentiometer), or counter electrode and non-resistance ammeter are used to continuously record the potential of the test piece or the short-circuit current with the counter electrode, and time-series data Attempts have also been made to monitor the occurrence of SCC by analysis (electrochemical noise analysis, ENA).
JP 2000-266661 A

  However, in a sensor that applies stress by applying an internal pressure to a film-like metal (metal foil) without contacting the load applying mechanism disclosed in Patent Document 1, the verifiability as a simulation experiment is uncertain. There was a drawback. That is, although a general plant component material is a thick member, the sensor using the metal foil is a metal foil, so the material characteristics are different, so the SCC sensitivity needs to be considered different. There was a problem. In addition, there is a problem that special machining such as collecting a metal foil having a large area from a thick member is difficult.

  In addition, the constant load test requires a load application mechanism, the setting of a corrosion cell surrounding the test piece, and the supply of process fluid. Therefore, the test equipment becomes large, so the bending jig should be exposed to the process fluid environment. However, there is a problem that a difficult mounting test is difficult to realize (dimension of the entire jig, fluid obstruction, jig corrosion, etc.).

  The present invention has been made in view of the above-described circumstances, and is capable of detecting and monitoring stress corrosion cracking, and for detecting stress corrosion cracking that can easily set a stress value equivalent to a subject to be monitored. An object is to provide a test piece and a stress corrosion cracking detection device.

In the test piece for stress corrosion cracking detection and the stress corrosion cracking detection apparatus according to the present invention, the following means are adopted in order to solve the above problems.
A test piece for stress corrosion cracking detection according to the first invention is a test piece for stress corrosion cracking detection for detecting a stress corrosion cracking state of a specimen that corrodes in contact with a corrosion medium, and is the same as the specimen. A test piece body made of a metal material; and a stress applying mechanism that is built in the test piece main body and applies stress to the test piece main body without being in contact with the corrosive medium.

According to the stress applying mechanism in the test piece for detecting stress corrosion cracking of the present invention, it is possible to apply stress to the test piece main body without being in contact with the corrosion medium. The test piece for detecting stress corrosion cracking that includes such a stress applying mechanism can set the tensile stress with the test piece for detecting stress corrosion cracking itself made of the same metal material as the specimen. It is possible to detect the state of stress corrosion cracking of the corroding specimen by maintaining the state of imparting the contact with the corrosive medium.
Therefore, in the stress corrosion cracking detection test, a large-scale stress generator that has been necessary in the past, that is, a load applying mechanism, a bending jig, a process fluid supply, and the like surrounding the test piece become unnecessary.

  In the second invention, the stress applying mechanism includes a push rod that can be inserted into the cylindrical test piece main body having a closed tip, and the tip of the push rod is disposed on the inner wall of the tube. A stress defined based on a pressing force to be pressed is generated in a direction in which both end portions of the cylinder are pulled apart.

  According to the stress application mechanism in the test piece for detecting stress corrosion cracking of the present invention, the tip of the push rod inserted from the opening end of the cylinder hits and presses the back wall of the cylinder, Since stress is generated in a direction away from the open end, it is possible to apply stress in a direction in which both ends of the cylinder are pulled apart by a set stress corresponding to the pressing force of the push rod.

Further, in the test piece for detecting stress corrosion cracking according to the third invention, the stress applying mechanism is provided on the outer periphery of the female screw engraved on the inner periphery in the vicinity of the opening end of the cylinder and the proximal end portion of the push rod. The engraved male screw is screwed together, and the stress is defined by the degree of tightening of the screwed screw.
The inside of the cylinder constituting the test piece for detecting stress corrosion cracking according to the present invention is substantially uniform from the opening end to the end of the innermost end except that an internal thread is engraved on the inner periphery near the opening end. A cylindrical shaft hole is provided. On the other hand, the push-in rod is also a cylindrical rod without unevenness, which is cut narrower than the valley diameter of the male screw until reaching the tip, except that a male screw is engraved at the base end.

The insertion depth from the threaded portion of the female screw and the male screw to the tip of the push rod is adjusted depending on the screw tightening torque and / or screw tightening angle of the push rod inserted from the open end of the cylinder. Then, the deeper the tip of the push rod is inserted, the more strongly the set stress in the direction of pulling away from the opening end to the innermost wall is generated. By this action, it is possible to arbitrarily set a tensile stress in the test piece for detecting stress corrosion cracking itself.
Therefore, it is possible to set the set stress according to the screw tightening torque and / or screw tightening angle of the push-in bar with the test piece itself for detecting stress corrosion cracking.

Moreover, the test piece for stress corrosion cracking detection according to the fourth invention has a central constricted portion in which the outer diameter of the central portion with respect to the longitudinal direction of the cylinder is narrower than the outer diameters of both end portions of the cylinder.
According to the present invention, since the peripheral wall of the narrowest constricted portion is thin, in addition to the influence of corrosion due to contact with the corrosive medium, it is remarkably easily affected by the application of stress due to tensile force, and in a relatively short time. Since it breaks clearly, it is suitable for a test piece.

  The test piece for detecting stress corrosion cracking according to a fifth aspect of the present invention is the test object, wherein the metal material constituting the pipe or container in the apparatus for contacting and circulating the corrosive medium is the subject, and the pipe or container is perforated. It is characterized by being tightly fitted and fixed in a provided mounting hole.

  According to the present invention, it is possible to grasp the degree of deterioration of the equipment by mounting the test piece for detecting the stress corrosion cracking in a part of the operating equipment. In other words, the stress corrosion cracking test piece itself can generate and maintain a specified tensile stress without using a load applying mechanism or bending jig surrounding the test piece, so a small and simple test piece for stress corrosion cracking detection Only need to be exposed to the process fluid environment. Therefore, it is possible to realize a mounting test for the stress corrosion cracking detection test simply and easily. And it is possible to grasp | ascertain the deterioration degree of an installation by removing and confirming the test piece for a stress corrosion cracking detection mounted in a part of said operation equipment regularly.

A stress corrosion cracking detection apparatus according to a sixth aspect of the present invention includes a plurality of measurement electrodes that are wire-connected so that the stress corrosion cracking state of the subject can be detected electrochemically, and currents between the measurement electrodes and / or A stress corrosion cracking detection apparatus comprising a measuring instrument for measuring a potential difference, wherein the test piece for detecting stress corrosion cracking is used for at least one of the measurement electrodes.
According to the present invention, in the electrochemical stress corrosion cracking detection apparatus, tensile stress can be generated and maintained in the test piece for stress corrosion cracking detection itself without using other equipment. It is possible to detect cracks.

According to the present invention, the following effects can be obtained.
First, according to the test piece for detecting stress corrosion cracking according to the present invention, in the test for detecting stress corrosion cracking, a large-scale stress generator that was conventionally necessary, that is, a load applying mechanism and a bending jig surrounding the test piece, and The supply of process fluid to them is no longer necessary, and the stress corrosion cracking state of the corroding specimen can be detected by maintaining the stress generated state in the stress corrosion cracking detection specimen itself and bringing it into contact with the corrosion medium. Is possible.

Further, according to the test piece for stress corrosion cracking detection according to the present invention, the inner wall of the cylinder is pressed with the tip of a push rod that can be inserted into the cylinder made of the same metal material as the subject and closed at the tip. It is possible to provide a test piece for detecting stress corrosion cracking that is extremely simple and easy to handle.
Further, according to the test piece for detecting stress corrosion cracking according to the present invention, it is possible to set the set stress corresponding to the screw tightening torque and / or the screw tightening angle of the push-in rod with the stress corrosion crack detecting test piece itself. Therefore, it is possible to provide a test piece for detecting stress corrosion cracking that is extremely simple and easy to handle.

  Further, according to the test specimen for detecting stress corrosion cracking according to the present invention, since the peripheral wall of the narrowest constricted portion is thin, in addition to the influence of corrosion due to contact with the corrosive medium, stress applied by tensile force can be applied. The test piece is suitable for a test piece because it is also easily affected and breaks clearly in a relatively short time.

  Further, according to the test piece for detecting stress corrosion cracking according to the present invention, it becomes possible to easily, simply and easily realize a mounting test for the test for detecting stress corrosion cracking. Then, it is possible to grasp the degree of deterioration of the equipment by periodically removing and checking the test pieces for detecting stress corrosion cracking mounted on a part of the operating equipment.

  Further, according to the stress corrosion cracking detection apparatus and / or the stress corrosion cracking monitoring method according to the present invention, in the electrochemical stress corrosion cracking detection apparatus, the stress corrosion cracking test piece itself without using other equipment. Therefore, it is possible to easily detect and monitor stress corrosion cracking with a simple and inexpensive device.

Hereinafter, a stress corrosion cracking (SSC) test piece, a stress corrosion cracking (SSC) detection device, and a stress corrosion cracking (SSC) monitoring method according to embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an explanatory view of an SCC (stress corrosion cracking) test piece 50 including a stress applying mechanism 69 according to an embodiment of the present invention, (a) a perspective view and (b) a partial sectional schematic view.

  2 is a detailed view of the SCC test piece 50 shown in FIG. 1, (a) a side view of a round bar test piece (test piece main body, cylinder) 51, (b) a front view of the round bar test piece 51, c) A front view of a bolt (stress applying mechanism, push-in rod) 52, and (d) a side view of the bolt 52. Although specific numerical values are illustrated in FIG. 2 for ease of explanation, the dimensions are not necessarily limited to these dimensions.

As shown in FIGS. 1 and 2, the SCC test piece 50 is configured such that a bolt 52 is screwed into the shaft hole 59 from the open end 60 of the round bar test piece 51. The round bar test piece 51 is formed by drilling a cylindrical shaft hole 59 at the axial center of a test piece having a central constricted portion 55 near the center in the longitudinal direction of the metal bar.
Inside this round bar test piece 51, a female screw Q (stress applying mechanism) is engraved on the inner periphery in the vicinity of the opening end 60, and extends from the opening end 60 to the farthest end, that is, the wall 57 at the end. A substantially uniform cylindrical shaft hole 59 is formed. On the other hand, the bolt 52 is also a cylindrical rod having no irregularities, which is cut to be narrower than the valley diameter of the male screw R until reaching the tip 58 except that the male screw R (stress applying mechanism) is engraved on the base end portion 56. is there.

Therefore, the insertion depth from the threaded portion of the female screw Q and the male screw R to the tip 58 of the push rod 52 is adjusted depending on the screw tightening torque and / or screw tightening angle of the push rod 52. Then, as the tip 58 of the push-in bar 52 is inserted deeper, a set stress in the direction of separating the opening end 60 to the innermost wall 57 is generated more strongly. With this action, it is possible to arbitrarily set the tensile stress in the SSC test piece 50 itself.
That is, by tightening the bolt 52 strongly from the open end 60 of the round bar test piece 51 to the end of the shaft hole 59, the tensile stress X in the direction of extending the round bar test piece 51 (arrow X in FIG. 1B). It is comprised so that it can be given and maintained.

  If the SCC test piece 50 having the stress applying mechanism 69 with this configuration is used, the SCC test piece 50 maintaining an arbitrary stress generated by itself without contacting a large load applying mechanism (not shown). A test can be conducted.

As shown in FIG. 2, a shaft hole 59 having an inner diameter φ4.5 + α (mm) is formed at the center with respect to the outer diameter φ5 (mm) of the central constricted portion 55 in the round bar test piece 51. The cross-sectional area of the tube thickness due to the difference in diameter is about 3.7 mm ² , and the tensile load is handled by the cross-sectional area. If a stress corresponding to the hydraulic pressure P (see FIG. 6) of the process fluid W is applied as the tensile load on the SCC test piece 50, an appropriate test can be set. Incidentally, the cross-sectional area is based on the following equation.
The cross-sectional area = π (φ5 / 2) ² −π (φ4.5 / 2) ² = about 3.7 mm ²
Further, a female thread Q is engraved on the inner periphery of the base end portion (large diameter portion) 54 on the opening end 60 side with an M5 tap standing, and a male screw engraved on the outer periphery of the base end portion 56 of the bolt 52. It is configured to be screwable with R.

On the other hand, as shown in FIGS. 2 (c) and 2 (d), the bolt 52 is formed to have a diameter of φ4.5−α (mm) toward the base end portion 56 by 16 mm from the tip 58 of the high-strength bolt of M5. It is formed so that it can be inserted into the shaft hole 59 of the bar test piece 51.
Prior to the test, a strain gauge is attached to the central constricted portion 55 of the round bar test piece 51, and the relationship between the rotation angle of the bolt 52 and the strain is obtained while the bolt 52 is screwed in, and a conversion table or the like (or graph). It is desirable to create.

  In a subsequent test, the pressing force that presses the inner wall 57 of the round bar test piece 51 with the front end 58 of the bolt 52 coming into contact with it can be defined based on the tightening angle of the screws Q and R, etc. The strain applied to the SSC specimen 50 can be estimated. Further, since the load stress can be estimated from the relationship between the stress and strain on the material, it is still preferable to complete the conversion table as “stress to be applied based on the tightening angle of the screws Q and R” (not shown). .

  In addition, when the SSC test piece 50 raises SCC, since the screw Q and R part becomes a boundary (water stop boundary), the seal structure in consideration of the water stop in this part is designed. Further, when the SSC test piece 50 is completely broken, a small piece at the tip 53 of the round bar test piece 51 flows out together with the process fluid W, and therefore a screen 34 (see FIG. 6) like a colander is provided at the outflow destination. Measures such as these are necessary.

Next, the SSC detection apparatus 1 using the SCC test piece 50 and the SSC monitoring method for monitoring the change with time will be described more specifically and in detail with reference to FIGS.
FIG. 3 is a schematic explanatory view showing a partial cross section of the SCC detection device 1 according to the embodiment of the present invention, which is (a) a bipolar type and (b) a tripolar type. This test is performed by immersing the SCC test piece 50 in the corrosive medium 3 filled in the transparent glass cells 30 and 31 in order to visually confirm the occurrence of SCC from the outside.

  The SCC detectors 1 and 2 include measuring probes 24 and 25 immersed (contacted) in the corrosive medium 3, a measuring instrument 20 including a potentiometer / ammeter connected to the measuring probes 24 and 25, and the measuring instrument 20. The detection output is acquired, and this detection data is recorded (accumulated) every arbitrary time. Further, the data logger 22 that can be output to the outside and various data output from the data logger 22 are processed and displayed and recorded. The personal computer 23 etc. that perform etc.

The bipolar SCC detection apparatus 1 shown in FIG. 3 (a) includes a bipolar measurement probe 24. The bipolar measurement probe 24 includes an SSC test piece 50 and a bipolar electrode 8 corresponding to the SSC test piece 50. The measurement electrode is fixed by the insulating portion 32 so as to maintain an appropriate positional relationship.
The tripolar SCC detection device 2 shown in FIG. 3B includes a tripolar measurement probe 25, and the tripolar measurement probe 25 includes three electrodes, that is, an SSC test piece 50, a counter electrode 8, and a reference electrode 10. The configured measurement electrode is fixed by the insulating portion 33 so as to maintain an appropriate positional relationship.
It should be noted that the SSC state is detected electrochemically by the SCC test piece 50 made of the same metal as the subject in both the bipolar SCC detection device 1 and the tripolar SCC detection device 2. It is possible.

  More specifically, in addition to the SSC test piece 50, the counter electrode 8 is also immersed in the corrosion medium 3 of the cells 30, 31, and a potentiometer // measures the potential difference and / or current between the SSC test piece 50 and the counter electrode 8. The ammeter 20 is wired. In addition to the SSC test piece 50 and the counter electrode 8, the reference electrode 10 is also immersed in the corrosion medium 3 of the cell 31 to provide a reference potential for measuring the potential difference between the SSC test piece and the counter electrode 8. ing. A method of monitoring the occurrence of SCC (electrochemical noise analysis, ENA) depending on the configuration of these SCC detection devices 1 and 2, that is, continuously recording the potential of the SSC test piece or the short-circuit current with the counter electrode 8, It is configured to be able to analyze time series data.

That is, by continuously measuring the potential generated between the SCC test piece 50 and the reference electrode 10, that is, electrochemical noise, and analyzing the signal indicated as potential fluctuation, the state in which SCC occurs in the test piece is obtained. It can be monitored.
The reference electrode 10 is a reference electrode that always gives a constant potential by placing Ag / AgCl in a constant environment such as saturated KCl, and is a glass tube (see FIG. (Not shown) etc. to ensure a liquid junction.

  In addition, a stable metal that does not corrode in the system, for example, titanium or the like can be substituted for the reference electrode 10 as a reference electrode. Then, an SSC test piece 50 made of a material different from that of the reference electrode 10 serving as the reference electrode is inserted into the system as an electrode, and the potential is measured. The measured potential shows a high potential when no SCC occurs, the potential decreases when the SCC occurs, maintains a low potential during the progress of the SCC, and increases when the SCC stops. it can.

The occurrence of SCC can also be monitored by analyzing the short circuit current between the counter electrode 8 and the counter electrode 8. The counter electrode 8 is basically made of the same material as the SSC test piece 50 or a stable metal such as Pt. A stainless steel cylinder or the like may be provided around and insulated from the SCC test piece 50, or the pipe itself may be the counter electrode 8. If the SCC test piece 50 and the counter electrode 8 are in the same state, basically no short-circuit current flows (equilibrium state), but when SCC occurs in the SCC test piece 50, metal dissolution due to cracking, that is, the following electrochemical reaction equation The occurrence of SCC can be detected by the corresponding current flowing.
Fe → Fe ²⁺ + 2e

  Further, according to the SCC detection devices 1 and 2 according to the present invention, the time series data of the potential or short-circuit current is taken into the data logger 22 and the personal computer 23 (see FIG. 3), and the potential / current change is detected. Allows online monitoring of SCC. Furthermore, according to the present invention, it is possible to collect and test the SCC test piece 50 from the actual structural component material including the welded portion, such as piping, and by applying an arbitrary stress, SCC sensitivity can be evaluated under the conditions to be evaluated. Further, according to the SCC detection devices 1 and 2, since it is possible to generate and maintain the tensile stress in the SCC test piece 50 itself without using a large-scale spring-type load applying mechanism or the like, SCC is detected simply and inexpensively. It is possible.

  FIG. 4 is a graph showing changes over time of the short-circuit currents 62I and 64I / potential differences 61E and 63E during the test in the SCC detection apparatus 1 according to the embodiment of the present invention. (A) 15-hour measurement data, (b) 2 hours Measurement data. As shown in FIG. 4, since the absolute values of the short-circuit current, the potential difference with time, the potential differences 61E and 63E, and the short-circuit currents 62I and 64I during the test move relatively large and protrude from the graph, only the change is extracted. Thus, it is preferable to display differentially (see FIG. 5) so that SCC can be detected more easily.

  FIG. 5 shows two-hour measurement data obtained by measuring the change over time in the differential values of the short-circuit currents 62I and 64I / potential differences 61E and 63E under test in the SCC detection apparatus 1 according to the embodiment of the present invention. As shown in FIG. 5, a remarkable spike (electrochemical noise) is recognized in both the potential 65E and the short-circuit current 66I around 0.7 h after the start of the test, and it can be detected that SCC has occurred at this point. According to such a stress corrosion cracking monitoring method, a highly sensitive test result can be obtained.

6A and 6B are explanatory diagrams of the SCC monitoring method according to the embodiment of the present invention, in which FIG. 6A is a cross-sectional view in which the SCC test piece 50 is directly attached to the existing pipe 100, and FIG. 2 is a cross-sectional view of a state in which an SCC test piece 50 is attached to a bypass pipe (hereinafter referred to as “piping”) 201 provided.
As shown in FIG. 6, the subject whose SCC sensitivity is to be evaluated is piping 100 and 200 through which the process fluid W flows while maintaining the fluid pressure P. In the test piece mounting hole 101 in the pipes 100 and 200, the SCC test piece 50 with the insulating seal 21 interposed is supported by the base end portion 54 (see FIG. 2) and directed toward the pipes 100 and 201. It has been planted. Further, as shown in FIG. 6B, by disposing the screen 34, it is possible to collect the broken pieces due to the occurrence of SCC without flowing out into the piping system.

  As described above, the SCC test piece 50 is implanted from the test piece mounting hole 101 of the pipes 100 and 200 through which the process fluid W flows into the pipes 100 and 200, and is brought into contact with the corrosive medium 3. You can start. Specifically, when a screw is engraved on a part of the base end portion 54 of the round bar test piece 51 and the inner periphery of the test piece mounting hole 101 and the both are screwed together, the metals are in direct contact with each other, so that they are in an electrically conductive state. Is maintained. However, it is necessary to distinguish whether the piping 100 and the SCC test piece 50 are electrically insulated from each other or to maintain the conduction state depending on the purpose of the test. In FIG. 6, insulation is performed with an insulating seal 21 interposed.

Next, ENA will be supplementarily described.
As described above, the occurrence of SSC is an environmental embrittlement phenomenon in which a metal material placed in a specific corrosive environment undergoes time-dependent brittle cracking under a continuous tensile stress. The conditions for the occurrence of the SSC are that the material structure, the corrosive environment, and the stress are satisfied to a considerable extent.

  In the SSC test piece 50, the SSC detectors 1 and 2 and the SSC monitoring method of the present invention, the necessary condition that stress and corrosive action are simultaneously applied to the SSC test piece 50 is satisfied. Thus, cracks occur even in much lower stresses below the yield stress and in weak corrosive environments. Therefore, according to the test piece for stress corrosion cracking detection and the stress corrosion cracking detection apparatus according to the present invention, it is possible to obtain a highly sensitive test result.

  In addition, in the SCC detection device having a conventional spring-type load application mechanism (not shown), a simulation experiment was performed instead of a mounting test by applying a load of about 500 kgf to a rod-shaped SSC test piece. Since the detecting devices 1 and 2 generate and maintain a desired tensile stress X (see FIG. 1) in the SSC test piece 50 itself without using a conventional large-scale spring-type load applying mechanism or the like, in plant piping or the like Simple, inexpensive and easy to perform mounting tests. Needless to say, the SSC test piece 50 is also effective for a simulation experiment in a laboratory or the like.

It is explanatory drawing of the SCC (stress corrosion cracking) test piece which included the stress provision mechanism which concerns on embodiment of this invention, (a) Perspective view, (b) It is a partial cross section schematic diagram. FIG. 2 is a detailed view of the SCC test piece shown in FIG. 1, (a) a side view of the round bar test piece, (b) a front view of the round bar test piece, (c) a front view of the bolt, and (d) a side face of the bolt. FIG. It is the schematic explanatory drawing which showed the partial cross section of the SCC detection apparatus which concerns on embodiment of this invention, (a) Bipolar type, (b) Tripolar type. It is a graph which shows a time-dependent change of the short circuit current / potential difference during a test in the SCC detection device concerning the embodiment of the present invention, (a) 15 hours measurement data, (b) 2 hours measurement data. It is a graph which shows the differential value time-dependent change of the short circuit current / potential difference under test in the SCC detection device concerning the embodiment of the present invention, (a) 15 hours measurement data, (b) 2 hours measurement data. It is explanatory drawing of the SCC monitoring method which concerns on this embodiment, (a) Sectional drawing of the state which attached the SCC test piece directly to existing piping, (b) SCC test to the bypass pipe provided by shunting from existing piping It is sectional drawing of the state which attached the piece.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... SCC detection device 3 ... Corrosion medium 8 ... Counter electrode (measurement electrode) 10 ... Reference electrode (measurement electrode) 20 ... Measuring instrument 50 ... SCC (corrosion cracking) test piece 51 ... Round bar test Piece (test piece main body, tube), 52 ... Bolt (stress applying mechanism, push-in rod), 53 ... Tip end (both ends), 54 ... Base end (both ends), 55 ... Center constriction, 56 ... Base end , 57 ... back wall, 58 ... tip, 60 ... open end, 61E, 63E, 65E ... potential (potential difference), 62I, 64I, 66I ... short circuit current, 69 ... stress applying mechanism, Q ... female screw (stress applying mechanism) ), R ... male screw (stress applying mechanism), W ... process fluid (corrosion medium)

Claims (6)

A test piece for stress corrosion cracking detection that detects the state of stress corrosion cracking of a specimen that corrodes in contact with a corrosive medium,
A specimen body made of the same metal material as the subject;
A stress applying mechanism that is built in the test piece body and applies stress to the test piece body without contacting the corrosive medium;
A test piece for detecting stress corrosion cracking. The stress applying mechanism is
A push rod that can be inserted into the cylindrical test piece main body having a closed tip,
2. The stress corrosion according to claim 1, wherein a stress defined based on a pressing force with which a tip of the push-in rod presses the inner wall of the cylinder is generated in a direction in which both ends of the cylinder are separated. Test specimen for crack detection. The stress applying mechanism is
The internal thread engraved on the inner periphery near the opening end of the cylinder and the external thread engraved on the outer periphery of the base end of the push rod are screwed together,
The test piece for detecting stress corrosion cracking according to claim 2, wherein the stress is defined by a tightening degree of the screwed screw.   The stress corrosion cracking detection according to claim 2 or 3, wherein a central constriction portion is formed in which an outer diameter of a central portion with respect to a longitudinal direction of the tube is smaller than an outer diameter of both end portions of the tube. Test piece.   The test piece for detecting stress corrosion cracking according to any one of claims 1 to 4, wherein the test piece is tightly fitted and fixed to a mounting hole formed in a pipe or a container as the object. . A plurality of measurement electrodes wired to enable electrochemical detection of the state of stress corrosion cracking of the specimen;
A measuring instrument for measuring the current and / or potential difference between the measuring electrodes;
In the stress corrosion cracking detector with
A stress corrosion cracking detection apparatus using the stress corrosion cracking test piece according to any one of claims 1 to 5 as at least one of the measurement electrodes.

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