JP2836097B2 - Defect detection device and detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a defect detection device and a detection method for a metal device lined with a corrosion-resistant material. More particularly, the present invention relates to a defect detection apparatus and method capable of quickly and accurately detecting a state of deterioration of a non-conductive corrosion-resistant material layer constituting a lining material before a corrosive substance reaches a metal device by deterioration.

[Conventional technology]

Conventionally, a coating made of a corrosion-resistant material has been used to increase the corrosion resistance of a metal material device, for example, a tower, a tank, a container, and the like.However, the presence or absence of a defect such as chipping or cracking of the film and the degree of damage are determined. Open inspection and destructive inspection were indispensable.

Recently, however, a device for detecting a defect of the glass lining during operation has been commercialized (for example, manufactured by Shinko Faudler Co., Ltd .; trade name "Maison Day P"). In addition, the present applicant has invented a device / system for detecting defects / damages of a non-conductive material film before defects / damages reach a base metal material, and has already filed an application (Japanese Patent Application No. 63-237940, 63-289621). These devices were characterized in that a defect could be detected in an open or non-destructive state of the device during operation or stop.

[Problems to be solved by the invention]

However, the above-mentioned apparatus has the following problems when actually used continuously for a long period of time. First, as defects that can be detected, defects such as cracks with a width of 1 mm or more and a length of 1 cm or more are easy to detect, but defects with minute areas such as minute pinholes, especially pinholes with a diameter of 1 mmφ or less. Is difficult to detect or cannot be detected.
Secondly, if the measurement is continued for a long time while detecting the defect, the presence or absence of the defect cannot be detected again. In particular, there is a problem that the smaller the defect, the greater the possibility.

In addition, the above device puts the electrode in the conductive content liquid,
A voltage is applied between the conductive portions of the base metal or the coating, and if a defect occurs, a conductive liquid enters the defect and a current flows between the two. DC voltage is used as the voltage. It is also conceivable to use a general AC frequency for ease of use of the power supply.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, ascertained the cause and completed the present invention.

That is, gas is generated by electrolysis on the surface of the electrode and the surface of the conductive material portion of the defect, for example, the surface of the metal base material, into which a current flows in the conductive content liquid for the detection of the defect. The gas inside is difficult to discharge, and if the measurement is continued, the gas gradually fills the defect, and finally the liquid stops flowing,
It turned out that it was electrically insulated and could not be detected.
The gas generation due to the electrolysis occurs even when an AC voltage is applied, but becomes remarkable particularly when a DC voltage is applied. In addition, it was found that the time until the measurement became impossible due to generation of gas was faster as the applied voltage was higher and shorter as the defect was smaller.

In addition, due to the presence of gas such as air contained before the start of use of the device in the generated gas and the defect, the cross-sectional area of the conductive content liquid that enables current to flow is reduced, and current flows. It has been found that the equivalent electric circuit has a capacitance component in parallel with a resistance component in the equivalent electric circuit due to the influence of the gas and the like. In addition, it was also found that the above-mentioned effect becomes more remarkable as the defect becomes smaller.

The detection device of the present invention will be described based on the above situation with reference to the drawings. FIG. 1 is an overall view thereof. The target device has a can body 1 made of a conductive material such as a metal and a corrosion-resistant layer 2 made of a non-conductive material lined on the inner surface in contact with the can body. The corrosion-resistant layer 2 may have a multilayer structure of three or more layers made of a non-conductive material and a conductive material. On the other hand, the metal electrode 3 is inserted in a state of being electrically insulated from the device and in contact with a conductive content liquid described later. The electrode 3 may be attached to the surface of the corrosion-resistant non-conductive layer as long as it is immersed in the content liquid. The material of the metal electrode 3 is a material having conductivity and corrosion resistance, and is generally a metal such as platinum or titanium. The size is determined by the mechanical strength and the size of the equipment,
A rod-shaped electrode having a diameter of 1 mmφ or more, preferably 5 mmφ or more is suitably used.

During operation, the apparatus contains, as the liquid 4 having conductivity, acids such as sulfuric acid and hydrochloric acid, alkalis such as caustic soda and other conductive liquids or aqueous solutions thereof. In the case where the content liquid is a liquid having no conductivity, detection during operation is impossible, but detection can be performed by periodically stopping and introducing a conductive liquid. Further, even when the content liquid used in the normal operation has conductivity, a liquid having a low liquid resistance can be supplied during a periodic stop to detect the liquid, in order to improve the accuracy of detection. In this case, a 30% sulfuric acid aqueous solution having a low liquid resistance is recommended. If the expected defect is small, an alcohol-based liquid that allows the liquid to easily penetrate the defect is recommended.

Next, a voltage is applied between the electrode 3 inserted in the conductive liquid 4 and the conductive layer 11 or 12 between the can 1 or the conductive layer in the corrosion resistant layer. When a defect 5 such as a crack or a crack occurs in the non-conductive corrosion-resistant layer of the coating 2, the electrode 3 → the conductive liquid 4 → the conductive liquid in the defect 5 → the conductive layer in the can 1 or the corrosion-resistant layer. A current path is created and current flows. The defect is detected by a current detection circuit such as converting the voltage into a voltage by the current detection resistor 7.

As described above, the voltage applied here is significantly affected by gas generation due to electrolysis as described above. Also, for applying an alternating current, 10 kHz to 1000 kHz, preferably 10 kHz to 100 kHz is used. The reason is that it has been confirmed by experiments and the like that in the case of an alternating current of 1 KHz or less, the above-mentioned electrolysis progresses remarkably, gas is generated sharply, and the resistance value rises quickly. Also, it has been confirmed that the higher the frequency, the larger the flowing current and the better the noise resistance can be measured due to the capacitance of the gas or the like existing in the defect.

On the other hand, when a frequency of 1000 KHz or more is used, the dielectric current of a non-conductive material that is not a defect, the leakage current due to a surface wave becomes remarkable, the current that flows even in a non-defect becomes large, and cannot be ignored compared to the current that flows when a defect occurs. Therefore, the noise is large.

Considering defects with a diameter of 10 ^-1 mmφ or more as a defect, the AC impedance of the defect, which can be measured from the current flowing due to its occurrence, has been obtained from experiments to be 500 KΩ or less. The upper limit of the frequency to be applied is 1000 KHz, preferably 100 KHz.

The voltage to be applied next varies depending on the type of electrolysis of the content liquid 4. If the voltage is equal to or lower than the electrolysis start voltage of 0.1 V or less, the electrolysis does not occur and the above-mentioned problem is solved. Since the current flowing with the voltage is small, the noise resistance is considerably reduced. From this point and the point of safety, the voltage to be applied is desirably 10 V to 0.1 V, preferably 5 to 1 V.

As a method of applying the voltage, it is preferable to perform the intermittent measurement periodically or irregularly without continuously applying the voltage in order to reduce the influence of the electrolysis. Depending on the anticorrosion speed, the frequency is from once a day to once a week.
Within minutes. The frequency and application time are selected according to the contents of the liquid, the condition of the measuring instrument, and the like.

Next, the measurement and calculation circuit 8 measures and calculates the AC impedance from the applied voltage and the flowing current. This includes a combination of a device for measuring the amplitude and phase difference of current and voltage and a circuit for calculating impedance from the device. Further, a general high-resistance AC resistance meter or an automatic AC bridge may be used. Further, the circuit 8 may calculate the capacitance from the AC impedance, detect the influence of liquid permeation, correct an error due to stray capacitance and leak current, and the like. The measured values calculated by the circuit 8 are sent to the judgment circuit 9 and accumulated for a long time, and the occurrence / detection of the defect is judged by comparing with the past value, and the operator is notified by an alarm or the like. As a comparison method, a method of processing by an analog circuit including a differential amplifier or the like can be considered, but a method of processing by software in a computer is simple.

(Operation)

The following is a specific description based on the apparatus shown in FIG. In the figure, 1 is a metal tube having a capacity of about 1, 2 is a corrosion-resistant non-conductive material layer made of polyvinyl chloride (thickness 0.5 mm), 4 is 30% sulfuric acid, 3 is a Pt electrode (1 mmφ), 6 is impedance Each of the analyzers is shown. Four kinds of pinholes having a diameter of 0.2 mmφ or more as indicated by 5 in this corrosion-resistant non-conductive material layer 2, 0.2 mm ×
Four types of cracks of 1 cm or more were made, and the changes in frequency and admittance were measured. FIG. 3 shows an example using a 0.4 mmφ pinhole. At measurement points with a frequency of 10 ³ Hz or less, a downward arrow indicates that the admittance temporarily rises but rapidly decreases (resistance increases).
Indicates that the admittance drops quickly.

At 10 ⁶ Hz or higher, the admittance rises sharply for devices with no defect (marked by x).

In each of these cases, it is difficult to detect a defect.

〔The invention's effect〕

According to the apparatus of the present invention, a high-frequency alternating current of 10 kHz to 1000 kHz is intermittently applied to the insertion electrode and the conductive layer in the can body or the corrosion-resistant coating, and the current flowing through the defect detects the defect in the protective coating, thereby detecting the state of the protective coating. Can be stabilized for a longer period of time, and a finer defect can be detected with high accuracy. As a result, the reliability of the detection device has been improved, and the damage to the can body can be predicted more quickly, and it is possible to estimate the time for replacing the coating without opening or destroying it.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of an apparatus for carrying out the method of the present invention. 1: Metal can body, 2: Corrosion resistant non-conductive material layer, 3: Electrode, 4: Conductive content liquid, 5: Defect, 6: High frequency oscillator, 7: Current detection circuit,
8: AC impedance measurement / calculation circuit, 9: Judgment circuit, 1
1: Conductor, 12: Conductor Fig. 2 shows test equipment, Fig. 3 shows test data 1
Here is an example.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/00-27/24

Claims (5)

(57) [Claims] An apparatus for detecting a defect of a corrosion-resistant non-conductive material layer of a metal device by using electrical conduction, wherein the corrosion-resistant non-conductive material layer is laminated on an inner surface of the device made of a metal material,
Conduction between the conductive wire (11) connected to the metal material and the conductive wire (12) connected to the electrode immersed in the conductive liquid inside the metal device is conducted to the outside of the device, and the conductive wire (11) and the conductive wire (12) And a power supply applied to the defect detection device is a high-frequency alternating current of 10 to 1000 kHz. 2. A patent comprising a corrosion-resistant conductive material layer between a metal material and a corrosion-resistant non-conductive material layer, wherein the conductive wire (11) is connected to the metal material or the corrosion-resistant conductive material layer. The defect detection device according to claim 1. 3. A conductive wire formed by laminating a corrosion-resistant non-conductive material layer, a corrosion-resistant conductive material layer, and a corrosion-resistant non-conductive material layer on a metal material in this order.
2. The defect detection device according to claim 1, wherein the first electrode is connected to a metal material or a corrosion-resistant conductive material layer. 4. A defect of a corrosion-resistant non-conductive material layer of a metal device in which a corrosion-resistant non-conductive material layer is laminated on an inner surface of a device made of a metal material and contains a conductive liquid therein by utilizing electric conduction. When detecting, 10 ~ on both sides of the corrosion resistant non-conductive material layer
A defect detection method characterized by intermittently applying a 1000 kHz high frequency AC voltage. 5. When detecting a defect in a corrosion-resistant non-conductive material layer of a metal device in which a corrosion-resistant non-conductive material layer is laminated on an inner surface of a device made of a metal material by utilizing electric conduction, the metal material is subjected to The conducting wire (11) and the conducting wire (12) connected to the electrode immersed in the conductive liquid inside the metal device are electrically connected to the outside of the device, and the conducting wire (11) and the conducting wire (12) are connected to each other. Ten~
A defect detection method characterized by intermittently applying a 1000 kHz high frequency AC voltage.