JP2002071616A - On-site measuring method for corrosion rate of steel structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the state of corrosion of a steel structure on a portion-by- portion basis continuously in real time by performing alternating-current measurement between a pin made of steel and each of various portions of the steel structure via an insulation layer. SOLUTION: As a sensor electrode to be inserted in a part of the steel structure, the pin manufactured of a steel material with similar electrochemical properties is inserted therein with the insulation layer of a narrow width between. An alternating-current voltage not less than 10 mV and not more than 50 mV is applied between the body of the steel structure and the pin made of steel and alternating-current resistance is measured at two frequencies, not more than 0.01 Hz and not less than 10 kHz, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-situ method of measuring the corrosion rate of a steel structure, and relates to the corrosion rate of a steel structure represented by a bridge or a building, particularly, with the change of environmental factors. The present invention relates to a measuring method capable of measuring a changing corrosion rate continuously and in real time.

[0002]

2. Description of the Related Art Corrosion of a steel structure in an atmospheric environment is affected by various environmental factors, and is very complicated and changes every moment. Therefore, continuous and real-time measurement of the state of corrosion is very important in evaluating the corrosiveness and life of steel structures represented by bridges and buildings. The mainstream of the corrosion resistance evaluation of metallic materials in the air environment is the evaluation based on the exposure of the test piece to the air specified in JIS-Z2381. Although it was possible, it was not possible to capture the change in corrosion phenomena during that time, and it was not a test that could be performed anywhere because it is usually performed at an exposure test site.

On the other hand, when considering a structure, the shape is various, and the micro environment differs depending on each part.
The corrosion also differs for each part, and it is impossible to grasp the corrosion state of all parts of the structure by an exposure test using a conventional cut plate test piece.

[0004] As a method of catching the change of corrosiveness, for example, it is disclosed in Japanese Patent Application Laid-Open No. Hei 7-113740, but this method examines corrosiveness in a very mild corrosion phenomenon in a computer room or the like. In some cases, it is impossible to evaluate corrosion in a place that corrodes greatly depending on the environment such as outdoors.

A method of monitoring a corrosion phenomenon in consideration of each part of a structure is disclosed in, for example,
There is one disclosed in JP-A-9-145698. In this method, a test piece of the same material is placed in the actual use environment,
It is a method of evaluating after actual use, and it was not possible to catch the corrosion phenomena that change every moment like the conventional exposure test.

[0006] On the other hand, the invention of this application measures the corrosion state of each part of the steel structure by performing an alternating current measurement between the steel pin and various parts of the steel structure via an insulating layer. This is a measurement method that enables continuous and real-time measurement.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for in-situ measurement of the corrosion rate of a steel structure in which a sensor electrode is inserted into a part of the steel structure to perform continuous measurement with a two-electrode system. Item 1) is provided.

According to the invention of this application, as a sensor electrode, a pin made of a steel material having similar electrochemical properties is inserted with a narrow insulating layer interposed therebetween, and a steel structure main body and a steel pin are connected. An in-situ method for measuring the corrosion rate of a steel structure in which an alternating current having a voltage of 10 mV or more and less than 50 mV is applied between the two points and a frequency of 0.01 Hz or less and 10 KHz or more is measured. A method for in-situ measurement of the corrosion rate of a steel structure having a steel pin having a cylindrical shape with a diameter of 1 mm or more and less than 50 mm (Claim 3).

In the invention of this application, the width of the narrow insulating layer may be set to 10 μm or more and 100 μm or less (claim 4), or the electrochemical properties may be similar, and the difference in immersion potential in 3% saline may be reduced by 50 mV. The present invention also provides a method for in-situ measurement of the corrosion rate of a steel structure (claim 5).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The steel structure according to the invention of this application includes artificial structures that widely use steel, such as steel bridges and buildings having a steel structure, particularly those that are likely to be deteriorated by corrosion.

The invention of this application is characterized in that a corrosion rate is continuously measured by a two-electrode system by inserting a sensor electrode into a part of a steel structure.

Further, the invention of this application is characterized in that pins having similar electrochemical properties are inserted with an insulating layer interposed therebetween in order to measure the corrosion rate of these steel structures.
The material of the insulating layer at this time is not particularly specified,
It is desirable that the electric resistance is 10 ⁶ Ω or more.

In the invention of this application, an alternating current having a voltage of 10 mV or more and less than 50 mV is applied between the steel structure main body and the steel pin, and a frequency of 0.01 Hz or less and a frequency of 10 KHz or more are applied.
The characteristic is to measure the AC resistance value at the point. As shown in the second embodiment, this is the
It is based on the finding that there is a correlation between the difference in AC resistance value above 0 KHz and the corrosion rate.

At this time, if the voltage is less than 10 mV, the accuracy of the measured value is inferior. If the voltage is more than 50 mV, either the steel structure or the steel pin is polarized, and the respective surface conditions change, so that the corrosion rate is increased. A resistance value resulting from another reaction different from the above is obtained.

Regarding the shape of the pin of the invention of this application,
Although not particularly limited, such as a square or an ellipse, the cylindrical shape has a feature that in the measurement of the corrosion rate, there is no anisotropy due to the electrode shape and more accurate measurement can be performed.

The size of the diameter is proportional to the opposing portion (perimeter) of the electrode. If the diameter is less than 1 mm, the area to be measured is small, so that the AC resistance is unstable and the accuracy of the measured value is low. On the other hand, if the thickness is 50 mm or more, a current distribution occurs on the electrode surface, so that an accurate resistance value corresponding to the corrosion rate cannot be obtained.

In the invention of this application, the lower limit of the width of the insulating layer is not particularly specified, but if it is less than 10 μm, it is very difficult to insulate the electrodes due to processing problems. In the case of a large value, the measured value is affected by the resistance value of the insulating layer as shown in Example 3, so that the value is specified to be 100 μm or less.

Further, according to the invention of this application, since a two-electrode method is used for measuring impedance, when either the steel structure or the pin electrode corrodes,
A resistance value that does not correspond to the corrosion rate is obtained. Therefore, this method is characterized in that the material of the pin is the same as the corrosion behavior of the steel structure.

Regarding the electrochemical properties, when the difference in immersion potential in a 3% saline solution is less than 50 mV, almost the same corrosion behavior is taken, so the electrochemical properties are defined for the pin material.

Hereinafter, the invention of this application will be described in more detail with reference to examples.

[0021]

(Embodiment 1) FIGS. 1 and 2 show a measurement system according to the invention of the present application.

A sensor electrode (2) is inserted into the center of each part (1) (1) of the steel structure with an insulating layer (3) made of a synthetic resin obtained by polymerizing ethylene tetrafluoride interposed therebetween, and current and voltage are measured. A sinusoidal AC voltage of 10 mV or more and less than 50 mV is applied between the sensor electrode (2) and the steel structure (1) by the device (4).

The voltage and the current flowing between the two electrodes are obtained by a frequency response analyzer (5) to determine the amplitude and phase difference of the voltage and current for each frequency, and to obtain a high frequency side (for example, 10 kHz) and a low frequency side (for example, 0.01 kHz). ) Is obtained, and the corrosion rate of the steel structure can be obtained continuously and in real time using a computer from the reciprocal of the difference.

As shown in FIG. 3, it is understood from the frequency characteristics of the impedance in the aqueous sodium sulfate solution that the frequency to be measured has almost no frequency dependence at 10 KHz or more and 0.01 KHz or less.

Table 1 shows a part of the results of measurement in an actual outdoor environment by this measurement system using a sample sensor. The measurement conditions of the system are a sinusoidal AC voltage of 10 mV and measurement frequencies of 10 KHz and 0.01 Hz. It can be seen that the change in corrosion rate over time can be measured in real time by this system.

[0026]

[Table 1]

Example 2 FIG. 4 shows a graph comparing the measured corrosion depth with the corrosion depth calculated from the corrosion rate. This is a result when an in-situ corrosion rate measurement was performed by the system of FIG. 1 while performing a corrosion test using a 3% NaCl aqueous solution in a constant temperature and humidity chamber using the sample sensor used in Example 1. The measurement conditions of the system are sinusoidal AC voltage 10mV, measurement frequency is 10kHz and 0.01k
Hz.

The calculated corrosion depth is a value calculated from the obtained corrosion rate by integrating the measurement time, and the actually measured corrosion depth is a value obtained by optically measuring the surface irregularities after the corrosion test. The values are proportional to each other, and it can be seen that the measured corrosion amount and the corrosion amount obtained by the measurement method of the present invention match very well. (Example 3) The shape of the inserted pin (2) and the width of the insulating layer were determined using a sample sensor. Table 2 shows the results. When the diameter of the pin (2) is less than 1 mm, the size of the measuring electrode is very small, so that the measuring current with respect to the sinusoidal AC voltage is very small, and the accuracy of the measured value is inferior. Progresses on a water film of the order of μm, the distribution of current flowing between the steel structure and the pin electrode tends to be uneven. Therefore, as in the present invention, the diameter of the pin (2) is 1 mm or more,
It must be less than 0 mm.

For the insulating layer (3), a synthetic resin obtained by polymerizing ethylene tetrafluoride was used. This is because the width of the insulating layer was 100 μm in the sample sensor used in Example 1.
m, 500 μm, and 1000 μm.

The measurement conditions were a sinusoidal AC voltage of 10 mV, measurement frequencies of 10 kHz and 0.01 kHz, and a temperature of 25 ° C. and a relative humidity of 95% in a constant temperature and humidity chamber.
% NaCl aqueous solution. Under the conditions in the thermo-hygrostat, the water film formed on the sample sensor is so thick that it can be confirmed with the naked eye. At an impedance value of 10 kHz, the width of the insulating layer is 500 μm and 1000 μm.
The value at μm is larger than the value at 100 μm, and resistance occurs due to the width of the insulating layer.

On the other hand, the impedance value at 0.01 kHz is proportional to the reciprocal of the difference between the impedance value at 0.01 Hz and the impedance value at 10 kHz. Must be sufficiently large compared to the value.

[0032]

[Table 2]

In Table 2, the difference is that the width of the insulating layer is 10
In the case of 0 μm, it showed about 550Ω, but there was almost no difference in other corrosion sensors.

The lower limit of the width of the insulating layer is 10 μm
If it is less than 1, the resistance between the two electrodes becomes 1 KΩ or less and insulation is insufficient, so that a resistance value not corresponding to the corrosion rate is obtained. (Example 4) With respect to the material of the inserted pin, Table 3 shows measurement data when a commercially available carbon steel pin and a commercially available stainless steel pin were used as electrodes in this measurement system.

The commercially available carbon steel pins are made of the same material as the steel structure used, and have a difference in immersion potential in a 3% saline solution of 50 mV or more from the stainless steel pins. The pin electrode used was 25 mm in diameter and 100 μm in width. The measurement conditions were a sinusoidal AC voltage of 10 mV and a measurement frequency of 10 kHz.
And 0.01 Hz.

[0036]

[Table 3]

When a stainless steel pin electrode is used,
At 10 kHz, the impedance value hardly changes, but at 0.01 Hz, the impedance value of the stainless steel pin electrode itself is measured, and a value much smaller than the actual corrosion rate of the steel structure is measured. .

On the other hand, a commercially available pin electrode made of carbon steel having an electrochemical property similar to that of a steel structure provides an accurate corrosion rate of the steel structure.

[0039]

According to the invention of this application, it is possible to constantly monitor the corrosion state in various parts of a structure without destroying the structure, so that a new corrosive property different from the conventional exposure test is used. And it can be expected as a life evaluation method.

Conventionally, when investigating the corrosion of a structure, a method of evaluating after destruction or a method of evaluating by partial sampling has been used, which has required a huge amount of labor and cost. According to the invention of this application, it is possible to continuously monitor the corrosion state of a structure in a non-destructive manner, and it is also possible to remotely control the use of a computer. The measurement can be performed easily and with a minimum of labor, and the economic effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view when a pin electrode is inserted into a steel structure of the present invention.

FIG. 2 is a diagram showing a measurement system according to the invention of this application.

FIG. 3 is a diagram showing frequency characteristics of impedance measured in an aqueous solution of sodium sulfate by the measuring method of the present invention.

FIG. 4 is a graph comparing the amount of corrosion calculated from the measured corrosion rate with the optically measured corrosion depth according to the measurement method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel structure 2 Pin electrode 3 Insulation layer 4 Current / voltage measuring device 5 Frequency response analysis device 6 Computer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Yamamoto 1-2-1 Sengen, Tsukuba, Ibaraki Pref. EA05 EA08 HA02 HC10

Claims (5)

[Claims] 1. A method for in-situ measurement of corrosion rate of a steel structure, wherein a continuous measurement is performed by a two-electrode system by inserting a sensor electrode into a part of the steel structure. 2. A pin made of a steel material having electrochemical properties similar to those of a steel structure with a narrow insulating layer interposed therebetween as a sensor electrode to be inserted into a part of the steel structure according to claim 1. Insert and apply a voltage of 1 between the steel structure body and the steel pin.
An alternating current of 0 mV or more and less than 50 mV is applied, and a frequency of 0.0
An in-situ method for measuring the corrosion rate of a steel structure, comprising measuring two points of AC resistance at 1 Hz or less and 10 KHz or more. 3. The method according to claim 2, wherein the steel pin has a cylindrical shape having a diameter of 1 mm or more and less than 50 mm. 4. The method according to claim 2, wherein the width of the narrow insulating layer is 10 μm or more and 100 μm or less. 5. The corrosion of a steel structure according to claim 2, wherein the similarity in the electrochemical properties is that a difference in immersion potential in a 3% saline solution is less than 50 mV. In-situ measurement of speed.