JP5510020B2 - Wet atmospheric stress corrosion cracking sensor - Google Patents

Description

  The present invention relates to a wet atmospheric stress corrosion cracking sensor.

Non-patent document 1 below describes wet atmospheric stress corrosion cracking (ASCC) of a member that occurs in an environment (humid oceanic environment, humid oceanic climate) in a humid atmosphere containing salt, such as near the sea. -Corrosion Cracking) is disclosed. In this technique, a Pt (platinum) electrode is brought into contact with a U-bend test piece made of SUS304 stainless steel placed in an environment simulating a wet marine environment, and the U-bend test piece is passed through the Pt electrode. The surface potential is measured, and it is determined whether wet atmospheric stress corrosion cracking has occurred in the U-bend test piece based on the change in the measured value (surface potential). That is, when wet atmospheric stress corrosion cracking occurs in the U-bend test piece, the surface potential of the U-bend test piece rapidly decreases at the occurrence timing, and the surface potential continues while the wet atmospheric stress corrosion cracking continues to progress. Since it returns to the stage where it has lost its progressability (returns to the potential range before the decrease in surface potential), the occurrence of wet atmospheric stress corrosion cracking is detected by judging the sudden decrease in the surface potential. Is possible.
Non-Patent Document 2 below also discloses a technique for evaluating the SCC resistance of a stainless alloy based on the same detection principle as in Non-Patent Document 1.

135th Corrosion Protection Symposium “Examination of ENA Applicability to ASCC Occurrence Monitoring Technology in Wet Marine Environment”, Corrosion Protection Association (2001) The 49th Materials and Environment Conference C-211 Lecture Proceedings, "Dependence of Alloy Species on SCC Resistance of Stainless Alloys Subjected to Heating in Sea Salt Particles and the Effect of Welding", Corrosion Protection Association (2002) )

  By the way, the techniques disclosed in Non-Patent Documents 1 and 2 are of the laboratory level and do not consider practicality. For example, the experimental apparatus described in Non-Patent Document 1 is for evaluating the validity of the detection principle, and is a stainless steel welded structure (for example, a stainless steel tank) that is exposed to a wet marine environment. ) Is not intended for wearing. Against this background, development of a wet atmospheric stress corrosion cracking sensor that can be applied to actual machines has been eagerly desired.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a wet atmospheric stress corrosion cracking sensor that can be easily applied to an actual machine.

  In order to achieve the above object, in the present invention, as a first solving means, a frame whose one surface is a mounting surface for a detection object, and a breathable electrode provided on the other surface of the frame And a contact electrode provided on the frame and in contact with a detection object of wet atmospheric stress corrosion cracking.

  As the second solving means, the means in the first solving means described above is further provided with a reagent containing chloride provided inside the frame.

  As a third solving means, in the first or second solving means, a means is adopted in which the air-permeable electrode is a mesh electrode formed from a platinum wire.

  As a fourth solving means, in the above first or second solving means, a means is adopted in which the reagent is a compression-molded dry powder of bitter juice.

  According to the present invention, since the frame, the breathable electrode, and the contact electrode are integrated, the handleability is good and the attachment of the detection object to the surface is extremely easy. Therefore, according to the present invention, unlike the conventional experimental level, it can be easily applied to an object to be detected as an actual machine and used for evaluation of stress corrosion cracking.

It is the perspective view (a), B-B 'arrow view (b), and bottom view (c) which show the structure of the wet atmospheric stress corrosion cracking sensor A which concerns on one Embodiment of this invention. The block diagram (a) which shows the detection system of the wet atmospheric stress corrosion cracking sensor using the wet atmospheric stress corrosion cracking sensor A which concerns on one Embodiment of this invention, and the mounting state to the detection target object of the wet atmospheric stress corrosion cracking sensor A It is a side view (b) shown. It is a graph which shows the example of an electric potential measurement using the wet atmospheric stress corrosion cracking sensor A which concerns on one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The wet atmospheric stress corrosion cracking sensor A according to this embodiment includes a frame 1, a mesh electrode 2 (breathable electrode), a reagent 3, a contact electrode 4, as shown in FIGS. 1 (a) to 1 (c). The first lead wire 5, the second lead wire 6, and the adhesive 7 are included. In the following description, the wet atmospheric stress corrosion cracking sensor A is simply referred to as sensor A.

  The sensor A is a detector that detects an atmospheric stress-corrosion cracking (ASCC) of an object to be detected that occurs in a wet marine environment (humid ocean climate). As is well known, salt (chloride) and moisture adhere to the surface of a detection object exposed to a wet marine environment. Stress corrosion cracking (SCC: Stress-Corrosion Cracking) may occur in a portion where the internal stress stays in such an object to be detected, for example, a welded portion, due to the corrosive action of salt (chloride). This sensor A detects a stress corrosion crack generated in a detection object placed in such a wet marine environment.

  The detection object of the sensor A is a structure made of a passive metal such as stainless steel, for example, a passive metal such as stainless steel which is a welded structure made of stainless steel. The surface potential rises and reaches a predetermined steady-state potential, but if active impurities such as chloride exist in the aqueous solution, the passive state is broken by the action of these impurities and local corrosion occurs, resulting in surface corrosion. The potential drops. Furthermore, if stress acts, local corrosion becomes stress corrosion cracking (SCC). When the surface of the passive metal is repassivated, the surface potential returns to the steady potential. Wet atmospheric stress corrosion cracking is a phenomenon of local corrosion caused by the action of moisture and salt contained in the atmosphere of such a passive marine environment, and is detected by capturing the change in surface potential. can do. The term “passive state” is synonymous with “passive state”, but the term “passive state” is used in this specification.

  As shown in FIGS. 1A to 1C, the frame 1 is a square frame member having a constant frame width and a constant frame thickness. For example, one side of the outer shape is about 10 mm, and the frame width is 1 mm. The frame thickness is set to about 0.5 mm. The frame 1 is made of an insulating material, for example, a resin material such as Teflon (registered trademark), and one frame surface (the lower plane in FIG. 1B) is a mounting surface to the detection target. Further, a flat mesh electrode 2 is fixed to the other frame surface (upper plane in FIG. 1B) of the frame body 1 with an adhesive or the like, and a contact electrode 4 is formed on one side surface of the frame body 1. Similarly, it is fixed by an adhesive or the like, and a reagent 3 is fixed inside the frame 1 (inside the frame), that is, on the frame 1 side of the mesh electrode 2.

  The mesh electrode 2 is an electrode having air permeability (breathable electrode) by braiding platinum wires (conductive material wires) having a wire diameter of about 0.02 mm vertically and horizontally into a mesh shape. As shown, it is cut into the same shape as the outer shape of the frame 1. Such a mesh electrode 2 is fixed to the upper plane of the frame body 1 so as to match the outer shape of the frame body 1. In addition, the material of the mesh electrode 2 should just be a thing which functions stably as an electrode in a humid marine environment, Therefore It is not limited to platinum (Pt).

The reagent 3 is obtained by compression molding a dry powder of bitter juice (eg, chloride, eg, NaCl, MgCl ₂ , CaCl _2, etc.), which is a main component, into a square shape having the same thickness as the frame thickness of the frame 1. As shown in the figure, the reagent 3 is provided in the frame 1 while being supported by the mesh electrode 2, and the outer shape is set slightly smaller than the inner shape of the frame 1. That is, the outer shape of the reagent 3 and the positional relationship with respect to the frame body 1 are set so that a certain amount of gap is formed with the frame body 1 at all the outer peripheral portions of the reagent 3. Such a reagent 3 is fixed to the mesh electrode 2 as shown in FIGS. 1A to 1C, for example, with an adhesive or the like partially provided at four corners.

Although details will be described later, such a reagent 3 functions when the dry powder of bitter juice absorbs moisture in the atmosphere and exhibits conductivity in a wet marine environment. The component of the reagent 3 in this embodiment is a dry powder of bitter juice, but any other dry powder of chloride such as NaCl, MgCl ₂ , CaCl ₂ contained in the atmosphere of the marine environment. There may be.

  The contact electrode 4 is a strip-shaped thin film made of a highly corrosion-resistant metal material such as a conductive Ni—Cr—Mo alloy (registered trademark: Hastelloy). As shown in FIG. 1A and FIG. 1C, the contact electrode 4 has a width substantially equal to the sum of the frame thickness and the frame width of the frame 1, and one side surface (in the figure, the figure). It is provided in an L shape from the short surface to the lower surface (mounting surface) of the frame 1. Further, as shown in FIGS. 1A and 1C, the contact electrode 4 is set to have a length slightly shorter than the length of one side surface (short surface in the figure) of the frame body 1. Such a contact electrode 4 contacts the detection target in a state where the sensor A is mounted on the surface of the detection target.

  The first lead wire 5 is a conductive wire having one end connected to the end of the mesh electrode 2, and an insulating sheath is provided on the surface. The second lead wire 6 is a conductive wire having one end connected to the end portion of the contact electrode 4, and an insulating sheath is provided on the surface like the first lead wire 5. As shown in FIGS. 1B and 1C, the adhesive 7 is provided as a thin film in a region where the contact electrode 4 does not exist on the lower plane (mounting surface) of the frame 1. This adhesive 7 is provided to fix the sensor A to the surface of the object to be detected, and when not in use, a protective seal having the same shape as the lower flat surface (mounting surface) of the frame 1 is provided on the surface. ing. The unused sensor A is housed in a sealed capsule in order to prevent moisture from entering the reagent 3.

  Next, a method for detecting wet atmospheric stress corrosion cracking using the sensor A configured as described above will be described in detail with reference to FIGS.

  When wet atmospheric stress corrosion cracking using this sensor A is detected, as a preparatory preparation, the surface of the stress concentration part (for example, weld heat affected zone (HAZ)) of the detection object exposed to the atmosphere is polished and soiled. And smoothing. Then, as shown in FIG. 2B, the sensor A is attached (adhered) to the surface of the polished stress concentration portion by removing the protective seal. In such a mounting state, a portion of the contact electrode 4 located on the lower plane (mounting surface) of the frame 1 is in contact with the surface of the detection target, and the contact electrode 4 and the detection target are electrically connected. It becomes a conductive state. 2A, the open ends of the first lead wire 5 and the second lead wire 6 are connected to an electrometer (electrometer), and the electrometer is connected to a data logger (data recording display device). ).

  Now that the preparation for detection has been completed, the electrometer and the data logger are connected to the power source and detection of wet atmospheric stress corrosion cracking is started. In a wet marine environment, the dry powder of bitter juice (chloride) that is a component of the reagent 3 absorbs moisture in the atmosphere that has passed through the mesh electrode 2 and becomes wet. In other words, moisture in the air that has passed through the mesh electrode 2 is condensed on the surface of the detection object to form condensed water, and is absorbed by the reagent 3 present in the vicinity.

  When the amount of condensed water exceeds a certain amount, a liquid pool X of liquid bitter juice straddling the surface of the detection object and the mesh electrode 2 is formed in the frame 1 as shown in FIG. That is, since gaps are formed around the reagent 3 around the entire circumference of the frame 1, stress concentration sites are exposed around the reagent 3 around the whole circumference. Since the dew condensation water is generated in this exposed portion, it is effectively absorbed by the reagent 3 present in the vicinity and contributes to the formation of the liquid bitumen pool X.

  Since this liquid pool X is a liquid bitter juice having conductivity, it is indirectly connected to the mesh electrode 2 through the portion where the contact electrode 4 contacts and the conductive bitum liquid pool X in the stress concentration portion of the detection target. A portion in contact with (that is, a portion where stress corrosion cracking can occur due to the corrosive action of bitter juice (chloride)) is in a state of electrical conduction through the liquid reservoir X. That is, the contact electrode 4 and the mesh electrode are electrically connected because the mesh electrode 2 and the surface of the detection object are bridged by the liquid reservoir X.

  Here, the frame 1 formed of Teflon (registered trademark) is stable in shape without being deformed even when exposed to a wet marine environment. Further, since the mesh electrode 2 is formed of a platinum wire, the mesh electrode 2 is stable as an electrode even when exposed to a wet marine environment. Therefore, the performance of the frame body 1 and the mesh electrode 2 is maintained even when used for a long time.

  As described above, when the contact electrode 4 and the mesh electrode are brought into conduction, the sensor A has a portion where stress corrosion cracking cannot occur in the stress concentration portion of the detection target (a portion where the contact electrode 4 contacts). The potential difference between the portion where stress corrosion cracking can occur due to the corrosive action of bitter juice (chloride) (the portion that indirectly contacts the mesh electrode 2) is output to the electrometer as a detection signal.

  The electrometer sequentially measures the potential difference indicated by the detection signal in time series and outputs it as a measurement signal to the data logger. Further, the data logger converts the measurement signal into a digital signal and sequentially stores it as time-series measurement data, and displays an image of the measurement data, that is, the time-series change in the potential difference according to an instruction from the operator.

The potential of the corrosion site detected by the sensor A, that is, the potential measurement data recorded in the data logger via the electrometer is as shown in the graph of FIG. 3, for example. This graph shows the potential measurement data with the horizontal axis representing time and the vertical axis representing potential. In this graph, the portion where the potential is temporarily reduced corresponds to the occurrence of stress corrosion cracking. In particular, since the temporary decrease in potential occurring at the time when 6 × 10 ⁵ (s) has elapsed from the start of measurement is larger than the temporary decrease in other potentials and the decrease period is longer, This shows that a large stress corrosion crack has occurred.

  According to the present sensor A, since the frame body 1, the mesh electrode 2, the reagent 3 and the contact electrode 4 are integrated in a compact manner, the handling property is good and the detection object can be mounted on the surface. Very easy. Therefore, according to the present sensor A, unlike the conventional experimental level, it can be easily attached to an object to be detected as an actual machine and used for evaluation of stress corrosion cracking.

  Further, according to the present sensor A, since it is configured in a very small size of about 10 mm square when viewed from the front, handling is good even in terms of size. Further, since the first lead wire 5 is connected to the mesh electrode 2 in advance and the second lead wire 6 is connected to the contact electrode 4 in advance, connection to an electrometer (electrometer) is easy. Furthermore, since the adhesive 7 is attached in advance to the lower surface (mounting surface) of the frame body 1, it is not necessary to separately prepare an adhesive necessary for mounting, so that the detection object can be mounted on the surface extremely. Easy.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the said embodiment, although the reagent 3 which consists of dry powder of a bitter juice (chloride) was used, this invention is not limited to this. Reagent 3 is used to facilitate wet atmospheric stress corrosion cracking (ASCC). For example, in areas with strong sea breeze, wet atmospheric stress corrosion cracking (ASCC) can be applied without artificially applying bitter juice. Therefore, a sensor configuration without the reagent 3 is also conceivable.

(2) In the above embodiment, the mesh electrode 2 is employed as the breathable electrode, but the present invention is not limited to this. For example, other modes may be used as long as the conductivity and air permeability through which moisture in the atmosphere can pass are changed, such as a conductive fiber or a punching metal in which a plurality of holes are formed. Further, the material of the breathable electrode is not limited to platinum. Any material other than platinum may be used as long as it is stable and conductive even when in contact with chloride.

(3) In the above-described embodiment, the dry powder of bitter juice (chloride) is compression-molded to make the reagent 3 a fixed body so that it can be fixed to the mesh electrode 2. However, the present invention is not limited to this. . Reagent 3 only has to absorb condensed water to form liquid pool X. For example, bitter juice (chloride) is applied to a film (for example, an oblate) or a capsule (gelatin capsule such as a medicine capsule) that dissolves with moisture. It is good also as a fixed body by storing the dry powder of.

(4) In the above embodiment, the gap is positively formed between the reagent 3 and the inside of the frame 1, but the present invention is not limited to this. Since the humidity is relatively high in a humid marine environment, the reagent 3 made of dry powder of bitter juice absorbs moisture in the atmosphere without actively forming a gap between the reagent 3 and the inside of the frame 1. The liquid is gradually absorbed and finally a liquid pool X is formed. In order to encourage such a reagent 3 to directly absorb moisture in the atmosphere, for example, a water-absorbing powder may be mixed into the reagent 3.

(4) In the above-described embodiment, the contact electrode 4 is provided in an L shape from one side surface of the frame body 1 to the lower flat surface (mounting surface), but the present invention is not limited to this. The contact electrode 4 should just be provided in the state which can contact a detection target object, and may be provided in the frame 1 in the other aspect.

(5) In the said embodiment, although the frame 1 was set to the square shape, this invention is not limited to this. For example, it may be a circle, an ellipse, or a polygon other than a rectangle. In addition, the shape of the reagent 3 may be appropriately set according to the shape of the frame 1.

(6) Further, the adhesive 7 may be omitted, and the adhesive 7 may be attached to the surface of the object to be detected with an adhesive that is separately required. Furthermore, the first lead wire 5 and the second lead wire 6 may not be provided in advance but may be separately connected during use.

  DESCRIPTION OF SYMBOLS 1 ... Frame body, 2 ... Mesh electrode (breathable electrode), 3 ... Reagent, 4 ... Contact electrode, 5 ... 1st lead wire, 6 ... 2nd lead wire, 7 ... Adhesive, X ... Liquid reservoir

Claims (4)

A frame having an inner space while one surface is a mounting surface with the detection target;
A breathable electrode provided on the other surface of the frame so as to face the internal space ;
Wet atmosphere stress corrosion cracking sensors, characterized in that provided on the frame body comprises a contact electrode in contact with the object to be detected.   The wet atmospheric stress corrosion cracking sensor according to claim 1, further comprising a reagent containing chloride provided in the internal space.   The wet air stress corrosion cracking sensor according to claim 1 or 2, wherein the breathable electrode is a mesh electrode formed from a platinum wire. 4. The wet atmospheric stress corrosion cracking sensor according to claim 2 , wherein the reagent is a compression-molded dry powder of bitter juice.

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