JP2001124693A - Method and device for evaluating weather resistance of steel product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device capable of non-destructively, quickly and quantitatively evaluating the weather resistance of a steel product having rust on the surface, particularly, with an actual stature as the subject. SOLUTION: The resistance of the steel product having rust on the surface is measured, and the corrosion speed of the steel product is determined on the basis of this. This method can be executed by use of this device comprising a means for infiltrating an electrolytic solution into the rust 2 on the surface of the steel product 3, a counter electrode 5 for carrying a current to the steel product having the electrolytic solution infiltrated into the rust 2 on the surface, a constant current device 6 and a voltmeter 7, the counter electrode 5 and voltmeter 7 being connected to one terminal of the constant current device 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a weather resistance of a steel material having a rust layer (hereinafter simply referred to as "rust") formed in the air, particularly a steel material used for an actual structure. The present invention relates to an evaluation method and an apparatus used for the method.

[0002]

2. Description of the Related Art Generally, phosphorus (P), copper (Cu),
By containing elements such as chromium (Cr) and nickel (Ni), the corrosion resistance of the steel in the air can be improved. These low-alloy steels are referred to as weatherable steels, and rusts that have a steel material protection effect (hereinafter referred to as “protective rusts”) are formed on the surface of the low-temperature steels in a few years outdoors.
After that, it is a so-called maintenance-free steel that does not require any corrosion-resistant treatment such as painting.

[0003] However, the period until the protective rust is formed depends not only on the material of the steel (base material) but also on the use environment. There is also. Therefore, it is necessary to evaluate how much rust formed on the surface of the base material has a steel material protecting effect, that is, whether or not the rust has a protective property.

Conventionally, methods for evaluating the protection of rust include: (a) a method of measuring the change in corrosion loss of steel over time to measure the corrosion rate; and (b) collecting rust on the surface of steel. And X
The amount of α-FeOOH in the rust was measured by the line diffraction method,
The ratio of the amount of α-FeOOH to the total amount of rust (α-FeOOH
(Amount of OH / total amount of rust) and a method for evaluating it (see Japanese Patent No. 2718337) (c) Powdering rust collected from the surface of a steel material and evaluating it by the average crystal grain size of α-FeOOH in the rust (See the above-cited publication) and the like have already been used.

[0005] However, all of these evaluation methods involve the removal of rust formed on the surface of the base material,
It is a so-called destructive inspection that involves sampling, and has problems in that it lacks promptness and that quantitative evaluation is difficult.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and its object is to evaluate the protection of rust formed on the surface of a base material, that is, a steel material having rust on the surface. The present invention provides a method capable of non-destructively, quickly and quantitatively evaluating the weather resistance of a steel material used in an actual structure in situ, nondestructively, and an apparatus used for the method. It is in.

[0007]

The gist of the present invention resides in the following (1) a method for evaluating the weather resistance of a steel material and (2) an apparatus therefor.

(1) A method for evaluating the weather resistance of a steel material in which the polarization resistance of a steel material having rust on its surface is measured and the corrosion rate of the steel material is determined based on the measured polarization resistance.

(2) An apparatus used for carrying out the weather resistance evaluation method for a steel material according to the above (1), wherein a means for impregnating the rust on the surface of the steel material with the electrolyte solution; An apparatus for evaluating the weather resistance of steel, comprising a counter electrode for flowing an electric current through a steel material impregnated, a constant current device and a voltmeter, wherein the counter electrode and the voltmeter are connected to one terminal of the constant current device.

Here, "polarization resistance" means a ratio of a potential or a voltage change (a change in potential or voltage caused by flowing a current) to a current (polarization current) passed through a steel material, as will be described in detail later.

[0011] Further, "steel material" means, unless otherwise specified.
A steel material having rust on the surface, that is, a steel material having rust formed on the surface of the base material.

To solve the above problems, the present inventor has
Rust protection was evaluated using various electrochemical techniques. As a result, the measurement is simple, excellent in quickness and quantitativeness, and it is possible to apply it to the actual structure on the spot, so the polarization resistance method protects rust, and thus the weather resistance of steel materials. It was confirmed that it was effective as a method for evaluating sex. The value obtained by this polarization resistance method is the "corrosion rate"
However, it is also desirable that a value having a direct relationship with rust protection be used as an evaluation method. The above-mentioned polarization resistance method is generally a method of measuring the polarization resistance of a steel material (bare steel material) having no rust formed on the surface, and obtaining the corrosion rate of the steel material based on the measured polarization resistance. This will also be described later in detail.

The findings obtained by applying the polarization resistance method to the evaluation of rust protection are as follows, and the present invention has been made based on these findings.

(A) For steel materials having a rust on the surface, the corrosion rate obtained from the actual corrosion weight loss and the corrosion rate obtained by the polarization resistance method have a high correlation, and the polarization resistance method is applied to the steel material having a rust on the surface. To determine the corrosion rate.

(B) The polarization resistance mainly corresponds to the rust defect rate. Since the rust defect rate is correlated with the long-term life, the polarization resistance method can be applied to the long-term life prediction of steel having rust on the surface.

(C) When considering application to an actual structure, the polarization resistance of steel having a protective rust on the surface is much larger than the ground resistance. It is possible to evaluate the protection of rust by measuring the polarization resistance when a current is passed through an actual structure through the structure.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for evaluating the weather resistance of a steel material of the present invention (the method of the present invention) and an apparatus therefor (the apparatus of the present invention) will be described in detail.

The method of the present invention is a method of measuring the polarization resistance of a steel material having a rust on its surface, determining the corrosion rate of the steel material based on the measured resistance, and evaluating the protection of the rust (ie, the weather resistance of the steel material). .

Generally, in a bare steel material having no rust formed on the surface, the polarization resistance R is represented by the following equation, and the corrosion current i _corr can be obtained by using the polarization resistance R by the following equation. (For example, see “Corrosion Protection Technology Handbook” edited by the Corrosion and Corrosion Prevention Association (issued on December 20, 1978)), and is called the polarization resistance method. Note that ΔE
(Potential change of steel material) is a range of change in the potential of a test piece measured by a current (polarization current i _{x, a} ) as described above in a spontaneously corroded state with reference to a saturated luster electrode or the like. It is. Further, Tafel coefficients beta _c of the Tafel coefficients beta _a and cathodic polarization curves of the anode polarization curve of the equation is determined from the measured data.

[0020]

(Equation 1)

When the corrosion current i _corr is obtained, the corrosion rate is calculated by multiplying the corrosion current i _corr by the electrochemical equivalent of the metal ion eluted in the anodic reaction (in the case of the steel material of the present invention, Fe ²⁺ ). be able to. In this case, the potential change ΔE of the steel material (bare steel material) in the above equation is at most ± 50 mV so as not to disturb the natural corrosion state so much.
It is necessary to stop the change to a small degree. The present inventor studied the protection of rust on the surface of various steel materials. As a result, as shown in an example (see FIG. 2) described later, the polarization resistance method described above was applied to steel materials having rust on the surface. We confirmed that it could be applied. The corrosion current of steel having rust on the surface is determined by the polarization resistance method, the corrosion rate is calculated from this corrosion current, and based on that,
By comparing the magnitude of the corrosion rate, the weather resistance of the steel material can be quantitatively evaluated.

FIG. 1 is a schematic view showing the structure of an example of an apparatus for evaluating the weather resistance of a steel material used in the method of the present invention (that is, the apparatus of the present invention).

As shown in FIG. 1, this apparatus is a means for impregnating an electrolyte solution into a rust 2 of a steel material 3 having a rust 2 on the surface of a base material 1 (in this example, a sponge 4 containing an electrolyte solution). Is used in contact with the steel material 3), and the steel material 3 having the rust 2 on the surface impregnated with the electrolyte solution by the above-described means.
And a counter electrode 5 for flowing a current through the counter, a constant current device 6 and a voltmeter 7. The counter electrode 5 and the voltmeter 7 are connected to one terminal of the constant current device 6.

In order to carry out the method of the present invention using this apparatus, for example, as shown in the drawing, a sponge 4 containing an electrolyte solution is brought into contact with the rust 2 on the surface of the steel material to impregnate the rust 2 with the electrolyte solution. Then, the counter electrode 5 connected to one terminal of the constant current device 6 is brought into contact with the electrolyte solution portion (refer to the sponge 4 containing the electrolyte solution), and the other terminal of the constant current device 6 is connected to the steel material. 3 is connected to a ground wire 8 electrically connected to the base material 1, and a current flows between the counter electrode 5 and the ground wire 8 using a constant current device 6. On the other hand, the other terminal of the voltmeter 7 connected to the counter electrode 5 is directly connected to the base material 1 to measure a voltage change when a current flows through the rust 2 between the counter electrode 5 and the ground wire 8. . As described below, the polarization resistance of a steel material having rust on the surface can be determined from the applied current and voltage change.

In the polarization resistance method performed on a bare steel material having no rust formed on the surface, a potential change ΔE
And the current (polarization current) i _{x, a} flowing in the steel at that time
Is measured (referred to as “potentiostatic polarization method”), or a current (polarizing current) i _{x, a} is applied to the steel using a galvanostatic device.
And a change in potential ΔE of the steel material due to the flow is measured (referred to as “constant current polarization method”). However, in the case of a steel material having a rust on the surface used for an actual structure, it is difficult to set a reference potential which is a reference of the potential change ΔE applied to the steel material, so that it is difficult to apply the above-described constant potential polarization method. .

Therefore, when the polarization resistance is measured by applying the method of the present invention to a steel material used for an actual structure, a constant current polarization method is used. In this case, a steel material having a rust on the surface is used. Since the polarization resistance is much larger than the ground resistance, the constant current device 6 is connected to the counter electrode 5 and the ground line 8 and the polarization current ix _{, a is} passed through the ground line 8 as shown in FIG. It can flow on the steel material 3. The constant current device 6 may be connected to the counter electrode 5 and the base material 1, and the polarization current ix _{, a} may be directly passed through the base material 1. However, the use of the ground wire 8 makes it easier to measure the polarization resistance. .

It is not necessary to determine the potential change .DELTA.E at that time, and the voltage change .DELTA.E 'is measured by the voltmeter 7 connected to the counter electrode 5 and the base material 1, and this voltage change .DELTA. The polarization resistance can be obtained using ΔE ′. In this case, the polarization current ix _{, a} flowing through the steel material 3 is changed _{by a} voltage change ΔE ′ so that the natural corrosion state is not disturbed.
Is desirably set to a current value such that the current value stops at a minute change of about ± 30 mV or less.

In the apparatus of the present invention, the means for impregnating the steel material 3 with the electrolyte solution is required in order to carry out the method of the present invention on an actual structure. This makes it possible to impregnate the electrolyte solution into the rust 2 and measure the polarization resistance of the steel material 3 having the rust 2 on the surface. In the example shown in FIG. 1, a sponge 4 containing an electrolyte solution is used as a means for impregnating the rust 2 on the surface of the steel material with the electrolyte solution, but this is a simple and preferable means. However, not limited to sponge, any porous material that can contain an electrolyte solution can be used.

As the electrolyte solution, a conductive aqueous solution may be used. It is preferable to avoid using an aqueous solution that greatly affects the corrosion of the steel structure, and to use a neutral aqueous solution such as an aqueous sodium sulfate solution. The concentration is 0.001 to 1
mol / l (liter) is appropriate.

The counter electrode 5 is an electrode required to allow the current sent from the constant current device 6 to flow through the steel material 3 and may be any conductive material, but is usually a copper wire having a high electrical conductivity.
It is preferable to use a platinum wire or the like.

The constant current device 6 is a device for supplying a direct current to the steel material 3 through the counter electrode 5, and may be a device normally used for electrochemical measurement.

As the voltmeter 7, a digital voltmeter driven by a dry battery, a potentiostat, or the like can be used. Those having a large internal resistance are preferred.

The grounding wire 8 may be a wire already buried or, if newly installed, a copper plate or a stainless steel plate having high conductivity and good corrosion resistance is suitable.

If the steel material having a rust on the surface is small enough to be used for the measurement of ordinary polarization resistance, it is immersed in an electrolyte solution and subjected to an electric potential (for example, with reference to a saturated agar electrode or the like). The measured potential) is determined, the potential is changed (that is, a potential change ΔE is given), the polarization current ix _{, a} flowing at that time is measured, and the constant potential polarization method for determining the polarization resistance R by the above equation is used. It is possible to apply. If the polarization resistance R is determined, the corrosion current i _corr is determined by the above equation.

According to the method of the present invention described above, it is possible to evaluate the weather resistance of a steel material having a rust on the surface. In particular, when the above-described apparatus of the present invention is used, the rust on the surface constituting an actual structure is obtained. The non-destructive, rapid, and quantitative evaluation of the weather resistance of a steel material having the following can be performed.

The polarization resistance mainly corresponds to the rust defect rate, while the rust defect rate is said to be correlated with the long-term life of the steel material. The value corresponds to the long-term life of a steel material having rust on the surface, and can be said to be applicable to the prediction thereof.

[0037]

(Example 1) A base material steel having the chemical composition shown in Table 1 was exposed to the air for 30 years, and a steel material (dimensions: 100 mm x 60 mm, thickness 5 mm) having a rust on the surface was 15 m in length.
cut into a size of mx 15 mm, and the part to be measured (10 mm x
10 mm) was used as a test piece, and the polarization resistance was measured in an aqueous solution of sodium sulfate, the corrosion current was calculated, the corrosion rate was calculated, and the corrosion rate was actually measured. The weight loss was measured to determine the corrosion rate.

In the measurement of the polarization resistance, the test piece was placed at 0.
Stabilize the potential by immersing it in an aqueous solution of 01 mol / l sodium sulfate for 1 hour or more, polarize ± 40 mv from that potential (ΔE is +40 mv or −40 mv), and then flow the current (polarization current i _{x , a} ) was applied. The polarization resistance was determined from the slope of the polarization curve in the polarization current-potential diagram (potential change ΔE / polarization current ix _{, a} ).

[0039]

[Table 1]

FIG. 2 is a diagram showing the corrosion rate calculated by using the polarization resistance and the corrosion rate obtained by actually measuring the corrosion weight loss on coordinates using both axes. Incidentally, upon obtaining the corrosion current i _corr from the equation using the polarization resistance, the Tafel coefficients beta _c of the Tafel coefficients beta _a and cathodic polarization curves of the anode polarization curve, both 0.
It was set to 1. As a result of measuring many samples, β _a =
This is because it was confirmed that when β _c = 0.1, a corrosion rate having a high correlation with the corrosion rate obtained from the actual corrosion weight loss can be obtained.

As shown in FIG. 2, the corrosion rate obtained by the polarization resistance method and the corrosion rate obtained by actually measuring the corrosion weight loss show a very good correlation. It can be seen that the determination can be made quantitatively by determining the corrosion rate which has a direct relationship with the protection.

(Embodiment 2) Using the apparatus of the present invention having the structure shown in FIG. 1 and applying the method of the present invention, each part of a bridge installed in a mountainous area or an area 10 km away from the coast The polarization resistance of the steel material having rust on the surface used for the measurement was measured, and the corrosion rate was calculated from the obtained corrosion current to evaluate the weather resistance of the steel material. When measuring the polarization resistance, a sponge containing a 0.01 mol / l aqueous solution of sodium sulfate was brought into contact with the portion to be measured of the bridge, and the voltage change of the steel material was +5 between the steel material and the ground wire.
An electric current was supplied so as to be mv or −5 mv.

FIG. 3 shows the corrosion rate determined by the polarization resistance method. In the horizontal axis of the figure, A is a bridge in a mountainous area 20 years after construction, B is a bridge 10 km away from the coast, 15 years after construction, and C is a bridge 25 km in the area 10 km away from the coast. Old bridge, D is a bridge in the mountainous area 15 years after construction, E is a mountainous building 1
The bridge has passed 0 years. In the figure, “-” indicates which part of the bridge was measured. That is,
And are the front and back sides of the top (ie, bridge plate) of the bridge, respectively, is the front side of the bridge girder, and is the back side of the bridge girder. In addition, the front side of the bridge girder is the outside of the bridge girder (the side corresponding to both sides in the width direction of the bridge) or close to the outside, which is appropriately exposed to wind and rain, and where weather-resistant rust is easily formed,
The back side of the bridge girder refers to a portion of the inside of the bridge girder (a side corresponding to a position closer to the center in the width direction of the bridge), which is not exposed to wind and rain and is less likely to form weather-resistant rust. Further, in the figure, 〜 indicates the corrosion rate of the site by the position in the figure (position with respect to the vertical axis).

As shown in FIG. 3, the corrosion rate obtained by the method of the present invention is higher in both the mountainous area and the area 10 km away from the coast from the back side of the bridge plate> the back side of the bridge girder> Bridge plate front side> Bridge girder front side ”. In addition, the corrosion rate relatively decreases as the number of years elapsed after construction increases. Since the evaluation target is steel used for actual structures, actual measurement values of corrosion rates cannot be obtained.However, the generally accepted ranking of corrosion susceptibility for each part of a bridge is as follows: Back side> Back side of bridge girder> Front side of bridge plate> Front side of bridge girder, and the order of corrosion rate obtained by the method of the present invention coincides with this general order of susceptibility to corrosion. The order of symbols in the upper right frame (from the top,...) In the figure indicates the general order of susceptibility to corrosion.

From the above results, the method of the present invention makes it possible to estimate the corrosion rate at the time of a steel material having rust on the surface used in an actual structure, and to evaluate the weather resistance of the steel material based on the corrosion rate. It can be seen that the evaluation can be performed quickly and quantitatively.

[0046]

According to the method of the present invention, the evaluation of the protection of the rust formed on the surface of the base material, that is, the evaluation of the weather resistance of the steel material, is carried out, in particular, for an actual structure.
It can be performed nondestructively and quickly and quantitatively. This method can be easily performed using the apparatus of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an example of a steel weather resistance evaluation device of the present invention.

FIG. 2 is a diagram showing a corrosion rate calculated using polarization resistance and a corrosion rate obtained by actually measuring corrosion weight loss on coordinates using both axes as axes.

FIG. 3 is a diagram showing corrosion rates obtained by a polarization resistance method for a steel material having a rust on a surface used in each part of a bridge installed in a mountainous area or an area 10 km away from a coast.

[Explanation of symbols]

 1: Base metal 2: Rust 3: Steel 4: Sponge 5: Counter electrode 6: Constant current device 7: Voltmeter 8: Ground wire

Claims (3)

[Claims] 1. A method for evaluating the weather resistance of a steel material, comprising: measuring a polarization resistance of a steel material having a rust on its surface, and calculating a corrosion rate of the steel material based on the measured polarization resistance. 2. A constant current is applied between a counter electrode brought into contact with the electrolyte solution part and a base material of the steel material or a ground wire electrically connected to the base material by impregnating an electrolyte solution into rust on a steel material surface. The steel material according to claim 1, wherein a current is passed by using a device, a voltage change is measured using a voltmeter connected between the counter electrode and the base material, and a polarization resistance of the steel material is obtained. Weather resistance evaluation method. 3. An apparatus for use in carrying out the method for evaluating the weather resistance of steel according to claim 1 or 2, wherein means for impregnating the rust on the surface of the steel with an electrolyte solution, and applying the electrolyte to the rust on the surface. A counter electrode for flowing an electric current through the impregnated steel material, and a constant current device and a voltmeter, wherein the counter electrode and the voltmeter are connected to one terminal of the constant current device. Evaluation device.