JPS6330754A - Method and apparatus for deteriorating coating metal - Google Patents

Abstract

PURPOSE:To enhance the reliability in the estimation of the life of a coating metal, by deteriorating the coating metal in such a state that overvoltage is held at a predetermined value. CONSTITUTION:A coating metal W, a reference electrode R and an opposed electrode C are immersed in the corrosive liquid L in a container 4 and the metal W is earthed, and the reference electrode R and the opposed electrode C are connected to a potentiostat PO. A pulse applying means Ep and an applying voltage variable means Ev are connected to the potentiostat PO and the current change and potential change of the potentiostat PO are inputted to an operation means CL for operating the values of a polarizing resistor Rr and a coating film resistor Rf while preset overvoltage eta is inputted to the means CL from an overvoltage setting means H. Both of the means CL and the applying voltage variable means Ev are connected by a conductor 9 so that the magnitude of the means Ev can be controlled on the basis of the ratio of the values of the coating film resistor Rf and the polarizing resistor Rr calculated by the means L. Further, a display means REC of overvoltage etais connected to an operation means CL.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for corroding metal coated with paint or lining material.

[Prior Art and Problems Therewith] It is widely known that the deterioration of coated metals coated with paint or lining materials due to corrosion varies depending on the corrosive environmental conditions. However, the rate of deterioration is generally extremely slow. Particularly in the case of metals coated with coatings or the like with excellent corrosion resistance, it is thought that it may not be possible to judge the quality of corrosion resistance with the naked eye until several decades have elapsed. Therefore, it is desired to establish a method for early predicting the corrosion resistance life of a coating film.

In this life prediction method, the current focus is on how to accelerate deterioration. Among them, the so-called electrolytic method, in which a DC voltage is applied to the coated metal, is attracting attention as a method to accelerate the corrosion reaction of the metal surface under the coating.
Yamamotoike: Corrosion Prevention Technology 35.3 (1986)]. or,
There is also a so-called coupling method in which a coated metal and a bare zinc plate are coupled together.

Now, when using the above electrolytic method and applying a DC voltage E of a certain magnitude between the coated metal and the counter electrode (platinum, carbon, etc.) C (so-called between the terminals) through the corrosive liquid, in that case, The electrical circuit formed can be modeled by the equivalent circuit shown in FIG. Here, the metal is coated with paint or lining material. Voltage E. is the electrode potential of the metal, resistance Rr is the polarization resistance near the surface under the coating film of the metal that causes the overvoltage η, and R( is the electrical resistance of the paint or lining material itself applied to the metal or the film It is the electrical resistance of the rust layer or deposited layer in defective parts, etc. Ro is the electrical resistance of the corrosive liquid. Also, the voltage E. 0 is the electrode potential of the counter electrode C, and the resistance Rr is the counter electrode that generates an overvoltage. Rf' is the polarization resistance near the surface of C, and Rf' is the electrical resistance near the surface of the counter electrode C.

The magnitude of the current ■ flowing in this closed circuit is expressed by the following formula.

1 = (E-Ey□-Eco)/(R, +Rf+Ro×Rf'+Rr')... (1) If the concentration of the electrolytic solution (corrosive solution) L is constant, the liquid resistance R
0 is almost constant. Also, considering that the resistances Rf', R,' are small and can be virtually ignored, the above (1
) formula is as follows.

1=(E-EWo-E(0)/(Rr+Rf+Ro)
・(1') However, in general, the electrical resistance Rf of a paint film coated with paint or lining material (hereinafter collectively referred to as a paint film) is determined by water absorption or dehydration of the paint film, or water droplets in the paint film. It does not always show a constant value due to factors such as formation or temperature changes in the corrosive environment. Also,
Even when a defect such as a scratch or a pinhole exists in the coating film, corrosion reaction products of the metal under the coating film, so-called rust, are deposited in the defective portion, and the electrical resistance Rf of this rust layer also changes. Furthermore, when a coated metal is electrolyzed in seawater, more specifically, if the coated metal is electrolyzed in such a way that a reduction reaction occurs, deposits such as calcium ions present in seawater are deposited on the coated metal. .

The electrical resistance R of this deposited layer changes depending on the temperature of the seawater, the state of deposition, etc. In this way, R4 changes with changes in the properties of the coating film and progress of corrosion.

In the constant potential method, which has been conventionally used for life prediction, a constant DC voltage is applied to allow the reaction to proceed. In other words, despite the change in the electrical resistance R of this coating film,
Electrolysis is carried out with a constant voltage E between terminals. Therefore, even if a constant voltage E between the terminals is applied, the overvoltage η changes.

The overvoltage η is a voltage required to cause a current to flow between the metal W and the counter electrode C, and changes depending on the current density and the like.

If the overvoltage η changes during electrolysis, it does not mean that deterioration is caused by a constant corrosion force.

Also, a potentiostat, a so-called constant potential electrolysis device, is widely used, and the same can be said for electrolysis using this device. If this device is explained with reference to FIG. 2, J' and Rr' related to the counter electrode C.

In order to make Eco negligible, a reference electrode (a so-called reference electrode that exhibits a stable electrode potential in the corrosive solution) is inserted into the solution, and electrolysis is performed using a three-electrode system. but,
In this case as well, although the metal can be held (electrolyzed) with a constant potential difference when viewed from the reference electrode, Rr and E. 0 changes, it is not possible to control the overvoltage η that governs the corrosion of the coated metal at a constant level. Therefore, the conventional early life prediction method is not effective because the corrosion reaction does not occur under the application of a constant force. ,
Paint film life prediction results are unreliable as they depend on unknown factors. In order to accelerate the corrosion reaction by applying a constant force, it is necessary to keep the magnitude of the overvoltage η near the metal surface of the coated metal constant.

An object of the present invention is to provide a method and apparatus for deteriorating coated metals that maintain constant overvoltage.

[Means for Solving the Problems] The coated metal deterioration method according to the present invention includes immersing the coated metal coated with paint or lining material and a counter electrode in a corrosive liquid;
In a coated metal deterioration method in which a voltage is applied between the coated metal and the counter electrode to deteriorate the coated metal, the resistance of the electric circuit between the coated metal and the counter electrode is determined by the overvoltage or the applied polarization resistance. Measure the resistance other than the polarization resistance above,
A feature of the present invention is that the above-mentioned voltage is controlled so that the overvoltage reaches a predetermined level based on this measurement result.

The coated metal deterioration device according to the present invention includes a sample electrode made of a coated metal coated with paint or a lining material, a counter electrode for the sample electrode, a reference electrode for the sample electrode, and a sample electrode set between the sample electrode and the counter electrode. A variable voltage electrolytic means for applying a voltage, a pulse voltage applying means for setting a voltage so as to apply a pulse voltage to the variable voltage electrolytic means, and a variable voltage electrolytic means for applying a voltage so that almost no current flows between the coated metal and the counter electrode. Set the voltage in the means and measure by pulse polarization method,
The present invention is characterized by comprising applied voltage setting means for setting the voltage variable electrolysis means to a voltage value at which a predetermined overvoltage calculated from the measurement results can be applied.

[Function] In the coated metal deterioration method according to the present invention, corrosion can be promoted by polarizing while maintaining the overvoltage at a predetermined level.

In the coated metal deterioration device according to the present invention, measurement can be performed using a pulse polarization method, and overvoltage can be maintained at a predetermined level.

[Example] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the deterioration device according to the present invention, electrolysis is performed using a three-electrode method. That is, as shown on the left side of FIG. 1, the coated metal W, the counter electrode C, and the reference electrode R are immersed in a container 4 containing a corrosive liquid. Then, a voltage E is applied between the covered electrode W and the counter electrode C so that the potential difference between the covered electrode W and the reference electrode R becomes E+E9°. The equivalent circuit diagram of this container 4 is the same as that shown in FIG. The feature of this embodiment is that the applied voltage E is corrected and the coating metal is In other words, the magnitude of J+Ro and the magnitude of Rr are detected, and E is changed according to the ratio of the two so that η added to Rr becomes constant. To apply with the magnitude of Rr and Rf+H
Voltage drop due to □ and E,. It is necessary to constantly grasp the value of +Eco and change the magnitude of E according to the amount of change in these values.

Next, concrete numerical values will be given and explained. Now, overvoltage η
Assume that electrolysis is performed while maintaining the voltage at 0.005V to progress the deterioration. Measure R4 and the resistances Rf and Ro of the pond at predetermined intervals (Rr' and Rr' can be ignored).

Initially Rr=IOkΩ, R=50Ω, Ro=0.2Ω, then Rr/(J+Ro)−10150,2
= 115.02, and each voltage applied to Rr and Rf+R0 is I xO, o05V and 5.02X0.005
V, that is, 0.005V and 0.0251Vi:

Therefore, the applied voltage E is 0.005+0.0251. =0
．． It is sufficient to set it to 030+V. Next, after a predetermined period of time has elapsed, only the electrical resistance Ftf of the coating film changes due to water absorption, etc., and decreases by 30KO+, J-/(Rr
+Ro)=10/30.2=1/3.02, and the applied voltage E is 0.005+O,0151=0.020tv
, that is, it may be varied so that it becomes 0.020 tV. Furthermore, suppose that a predetermined period of time has elapsed and, for example, due to deterioration of the adhesion between the paint film and the metal, paint film blistering occurs, R7 decreases, and IkΩ is detected.

If we continue electrolysis with R(=30Ω and Ro=0.2Ω, then Rr/(Rf+R0)=I/(30+0.
2)=t/30.2, so the size of E is l×0
．． 005+ 30.2X O,QO5= 0.005+
0.0151= O,0156V, therefore E=
Electrolysis can be performed at 0.0 I 56V.

The present invention thus detects Rrh Rf, R0 and changes the magnitude of the applied voltage E to maintain the overvoltage η applied to Rr at a predetermined value, thereby deteriorating the coated metal. It is. However, if the amount of change in Ro is small, or if the magnitude of R8 is negligibly small compared to Rr, it is sufficient to detect R (and Rr. Also, the sum of J and Ro Rr may also be detected.

As explained using the above numerical values, there is a metal with almost no difference in the magnitude of the overvoltage η and the magnitude of the applied voltage E, that is, there is a coating film on the metal surface and a deposited film of rust on the defective parts of the coating film. Metals that do not have a .

(b) Resistance measurement method J+R0 (hereinafter abbreviated as R4) and Rr are determined. There are two known methods: pulse polarization method and sweep polarization method. In this example, it was determined by the pulse polarization method.

This is because R' and R4 are determined by short-term polarization.As will be explained later, during the time when R4 and Rr are to be detected, the overvoltage η applied to Rr is set to a predetermined magnitude. For example, in the pulse polarization method, the value of the original applied voltage E must be set to zero and only the pulse applied voltage V must be applied, so in principle the overvoltage η is changed. Also in the polarization method, the overvoltage η is changed during the sweep with the applied voltage V. In this case,
Since the pulse polarization method can be executed in a much shorter time than the sweep polarization method, it is advantageous to use the pulse polarization method in order to minimize the influence of the voltage V applied to determine Rf and Rr. be. Note that measurements using the pulse polarization method are performed at appropriate intervals, and R[ and R4
If a change is observed in Rf and R2, Rf and Rr
The magnitude of E may be changed in accordance with the magnitude of E so that the overvoltage η can be kept constant.

Next, two methods for determining Rf and Rr will be explained.

First, the pulse polarization method used in this example will be explained. Assume now that the electrical equivalent circuit of the coated metal is the circuit shown in FIG. The difference from the circuit shown in FIG. 2 is that the electric double layer capacitance ff1Cdl of the metal surface is taken into consideration. When the overvoltage η is small and Rr is a constant value, the voltage pulse V shown in the upper part of FIG.
When applied across the circuit of the figure, in response to this voltage pulse V, the current changes along the curve shown at the bottom of FIG. 4**. The curve for 0≦t≦t and the curve for E≧t can be expressed by the following equations, respectively.

* * Here, t and I are the time and current value when the voltage pulse V is interrupted. Dividing both sides by V...(4) The I/V value becomes a function only of time, which is unrelated to the magnitude of the voltage pulse. Therefore, by setting Cd1.R".Rr2JO3X R"V and taking the logarithm of both sides of equation (5), it can be rewritten as the following equation.

l*log(-r/V)=logY--Q-L
)...(6)* Therefore, from the slope of the graph of lOg (-I /V) and (t-t) * * the values of X and Y can be found from the intercept (I, t
is determined from Figure 4). Therefore, the following values can be calculated.

* ■ Rr-(y +-)-+...(7)
■ φ However, Rr is a constant value only when the overvoltage η is small. If voltage dependence is observed in the I/V vs. time curve by sequentially setting the voltage pulses to larger values, this means that the overvoltage η has changed and a corrosion reaction of the coated metal has been detected.

Next, the sweep polarization method will be explained.

When the coating film resistance component Rf of the coated metal is large, the relationship between potential and current (polarization curve) when swept polarization becomes a "nearly linear relationship" when ■ is small (polarization resistance region), and The polarization behavior of electrochemically reactive components near the surface of the coated metal is included on the curve of this "sublinear relationship". Therefore, by always subtracting the slope value of the potential (E)-current (1) curve corresponding to the total resistance component at the initial stage of the sweep by the total electrolytic current r, the electrochemically related minute current (△i) -Potential△
E) A curve is obtained. Then, J and R2 can be calculated from Δ1 as follows.

Now, the natural electrode potential is Er5t, and the electrode potential is E.

When the electrolytic current is I, the coating resistance is Rf, and the polarization resistance is R7, the relationship between E and I in the polarization resistance region is expressed as E-1 (Rf + R,) = I - R (... (9) , Rf is constant and is outside the polarization resistance range*, then Rr changes (represented by Rr), and the relationship between E and I is *E=I(Rf+Rr)...(10
), and the difference between formulas (9) and (10) is *ΔE=I(Rr−Rr)·(H). From Figure 5, which conceptually represents the relationship between equations (9) and (10), the relationship between △E and △i is △E - △i (R "+Rr) = △i - J - (12)
From equations (11) and (12), * △i= l /Rt-I (RrRr) ”・
(13). By the way, the following Terfel formula * Rr = η/I = (a+blogI)/I = (1
4) can be applied to coated metal, then equation (14) can be changed to (1
3) Substituting the formula, △1=(1/Rt-1-Ry-) L/RL・(a+
b Logl) - (15). Since Δi, r, and E are measured values, R can be estimated from the intercept of the asymptote of the relationship between Δi/I・town and ■. Also, Rr=Rt
-R.

Therefore, Rf can be found.

(C) Deterioration device Next, a deterioration device that embodies the deterioration method described above will be described.

FIG. 1 shows the basic configuration of the deterioration device. As explained above, the coating metal W and the reference electrode R1 are placed in the corrosive liquid in the container 4.
Immerse the counter electrode C. The covering metal W is grounded by an electric conductor (hereinafter referred to as a conductor) l, and the reference electrode R1 and the counter electrode C are tangential to the potentiostat PO by a conductor 2.3. A pulse application means Ep and an applied voltage variable means Ev are connected to the potentiostat PO by conductive wires 5 and 6, and
The current change and potential change of the potentiostat Po are determined by the polarization resistance R2 and the coating resistance R4 (hereinafter, B refers to the total resistance between the metal W and the counter electrode C, excluding Rf). Means for calculating values (hereinafter referred to as calculation means) CL
It is manually powered by conductor 7. On the other hand, the magnitude of the preset overvoltage η is input from the overvoltage setting means I to the calculation means CL through a conductor 8.

Further, it is connected to the applied voltage variable means Ev by a conductive wire 9 so that the magnitude of the applied voltage variable means Ev can be controlled by the ratio of the coating film resistance Rr and the polarization resistance R7 calculated by the calculation means CL. Furthermore, current, potential, overvoltage η, coating film resistance Rf,
A display means REC is tangentially connected to the calculation means CL by a conducting wire 10 so that polarization resistance Rr or elapsed time can be displayed. On the other hand, the potentiostat PO is grounded through a conductor 11. However, if the container 4 is a river or the sea, for example,
If the conductor 11 is grounded, measurement will not be possible, so the potentiostat PO is made floating with respect to the ground.

The coated metal W may be coated with a paint or lining material by any conventional method such as spraying, dipping, brushing, rolling or electrodeposition. Furthermore, the type of metal is not limited.

The reference electrode R only needs to have its own electrode potential stable in the corrosive solution used, and may be a commonly used electrode such as a calomel electrode or a silver-silver chloride electrode.

The counter electrode C may be made of the same material as the metal W to be coated,
Alternatively, a carbon plate or rod may be used. Preferable materials for the counter electrode include inert materials such as platinum and gold, but are not particularly limited. However, when the amount of corrosive liquid is small, it is desirable to use an inert counter electrode such as platinum.

Botenyostat P○ A commonly used constant potential electrolyzer is sufficient, but there are no defects in the coating film.
When Rf is large, the magnitude of the input impedance of this Botennoyostat PO is equal to the membrane resistance Rf in the corrosive liquid.
It is desirable that the value is 100 times or more greater than the sum of the polarization resistance Rr and the polarization resistance Rr.

The pulse application means Ep overlaps pulsed voltages of a certain magnitude in order to electrolyze (so-called polarization) the coated metal with a pulsed voltage of a certain magnitude using a potentiostat PO. It is a generator of

The calculation means CL is for calculating the magnitude of R4 and the magnitude of Rr, grasps the values of J and Rr, and determines the variable amount of the applied voltage E in Fig. 2 based on these values. It is for the purpose of

The overvoltage setting means H is used to set the overvoltage η to a certain level in advance, so that even if R, . . . Rf changes, η can be maintained at the preset level.

The applied voltage variable means Ev varies the magnitude of the applied voltage E (FIG. 2) based on the above-mentioned calculation means CL.

The display means RFC is a recorder or a printer, and the above E, l'J, Rr, i.

It displays and records η, etc.

Now, assuming that the potential of W (natural electrode potential Er5t (vs, R) of W itself) as seen from the reference electrode R is -IV (vs, R), first, +IV is applied by the applied voltage variable means Ev, and C- The current between W is made almost zero. In other words, it becomes electrolyzed near the natural electrode potential of W itself. Next, the voltage pulse V is applied by the pulse application means El) as shown in Fig. 4 above. Then, from equations (2) to (8), calculation means C
The coating film resistance R4 and the polarization resistance Rr are determined by L. Now, if the overvoltage η is to be electrolytically maintained at 0.005V (the W pole itself is cathodically polarized), the overvoltage setting means H is set to 0.005V. If Rr is IOkΩ and Rr is 50Ω (for example, in the case of seawater, the relationship of Ro is Rr>>RO, and Ro can be almost ignored), then if you calculate as described above, , the applied voltage is +〇,
It becomes 006v. Therefore, +0°006V may be added so that the magnitude of the applied voltage variable means Ev becomes +1.006V.

Next, after a certain period of time has elapsed, Rf and Rr are determined again. That is, stop the electrolysis once, repeat the above operations, measure the potential of W seen from R, and if it is -1.2V, first apply +1.2V by the applied voltage variable means Ev, and then Electrolysis is carried out near the natural electrode potential of W itself by setting the current between them to approximately zero, and then a voltage pulse V is applied by the pulse application means Ep to find the values of Rf and R2, and if the magnitude of the ratio of J and R2 If there is a change in the applied voltage, the magnitude of the applied voltage is set in advance by the applied voltage variable means Ev.
You can change it so that In this way, while sequentially measuring the values of R (and Rr) at certain time intervals, the applied voltage E is varied to a constant overvoltage η.Then, each time,
Each value is displayed or recorded on the display means RFC.

FIG. 6 shows a specific example of the deterioration device. Counter electrode 0 in container 4
1 reference electrode R and coated metal W are installed, and container 4
There is a corrosive liquid inside. The reference electrode R is tangentially connected to the input (1) of the differential amplifier 23DA of the potentiostat PO, and the counter electrode C is connected to its output (3) via an ammeter (2). Also, the metal W is grounded and the base? The $ electrode R is grounded via the voltmeter ■. On the other hand, the other input (2) of the differential amplifier DA of the potentiostat PO is connected to the switch SWI, the applied voltage variable power supply Ev, and the switch S
It is grounded via W2 or via the pulse application means El). Further, the outputs of the voltmeter (2) and the ammeter (2) are input to the calculating means CL, and the overvoltage set value of the overvoltage setting means H is also manually input to this means CL. Furthermore, the output of this calculation means CL is sent to the display means RFC and the servo motor M.
The servo motor M changes the magnitude of the power supply of the applied voltage variable means Ev.

If the switch SW1 is now on the (a) side, the output (3) of the differential amplifier DA of the potentiostat is zero, and only the magnitude of the voltmeter ■ is input to the input (1) of this PO. ing. That is, only the natural electrode potential (versus the reference electrode R) Erst of the metal W is measured. Then, the magnitude of this potential difference, that is, Er5t, is manually input to the calculation means CL as the output of the voltmeter ■, and the reciprocal of this magnitude is adjusted by the servo motor M with the power supply for varying the applied voltage, and the magnitude of this power supply is ( −E,j). Next, when the switch SWI is set to the (b) side, the potential difference between the input of the differential amplifier, that is, terminals 1 and 2, is
Er5t Er5t ' becomes 0, output of DA (3)
becomes almost atmosphere, and the output of the ammeter (2) also becomes almost zero (that is, electrolysis occurs near the natural electrode potential of W). Then,
Switch SW2 to the (d) side and pulse application means E
ll) and apply a pulse voltage (rectangular wave) for a short time. That is, this pulse voltage is applied between inputs (1) and (2) 7 of D, and at the same time the pulse voltage is applied between C and W, the voltmeter ■ and ammeter ■ show the values shown in Figure 4. Change will appear. Then, this change can be expressed by formula (2)
According to (8), Rr and Rr are calculated by the calculating means CL. Furthermore, by setting an arbitrary overvoltage in the overvoltage setting means H, the applied voltage applied to the coated metal W can be calculated, and this applied voltage is applied to the applied voltage variable power supply via the servo motor M. Set the magnitude of the applied voltage E. Then, the above method may be repeated at certain time intervals. Note that the above calculation means are analog/
A so-called microcomputer calculates the results digitally via a digital converter.
The servo motor M may be automatically controlled via an analog converter.

Note that the timing of applying a voltage pulse, measuring the magnitudes of Rr and Rf, and correcting the overvoltage η is determined by Rr or Rf.
The more f or both Rr and R4 are susceptible to change, the faster the so-called deterioration, the more frequently it is necessary. Conversely, the smaller the change, the longer the time interval for measuring Rr and Rr(7) by applying a pulse voltage may be longer. Further, if the rate of decrease in R4 is higher than the rate of decrease in Rf, the applied voltage increases over time, and conversely, if the rate of decrease in Rr is lower than the rate of decrease in J, the applied voltage decreases over time.

"Effects of the Invention" It is possible to maintain overvoltage at a predetermined value and cause the coating metal to deteriorate. Therefore, prediction of the life of the coated metal becomes more reliable.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of the deterioration device. FIG. 2 is a model circuit during electrolysis in the deterioration device. FIG. 3 is a diagram of an example of an electrical equivalent circuit of coated metal. FIG. 4 is a graph showing the response to application of a potential pulse to the coated metal. FIG. 5 is a conceptual diagram of a voltage curve during sweep polarization of a coated metal. FIG. 6 is a block diagram of an example of a deterioration device. W...Covered metal, C...Counter electrode, R...Reference electrode, L...
・・Corrosive liquid, PO・Botenyostat, El)・
...Pulse application means, Ev...Applied voltage variable means, G...Overvoltage setting means, CL...Calculation means, RFC...
・Display means.

Claims (4)

[Claims] (1) In a coated metal deterioration method, the coated metal coated with paint or lining material and a counter electrode are immersed in a corrosive liquid, and a voltage is applied between the coated metal and the counter electrode to deteriorate the coated metal. Among the resistances of the electric circuit between the coated metal and the counter electrode, measure the polarization resistance to which overvoltage is applied and the resistance other than the above polarization resistance, and adjust the overvoltage to a predetermined level based on the measurement results. A method for degrading a coated metal, characterized by controlling the voltage described above. (2) A coated metal deterioration method as set forth in claim 1, wherein the measurement and control described above are performed at predetermined intervals. (3) The coated metal deterioration method described in claim 1, characterized in that the above-mentioned resistance measurement is performed by a pulse polarization method in a state where almost no current flows between the coated metal and the counter electrode. Coated metal deterioration method. (4) A sample electrode made of coated metal coated with paint or lining material, a counter electrode for the sample electrode, a reference electrode for the sample electrode, and a variable voltage electrolysis that applies a set voltage between the sample electrode and the counter electrode. means, a pulse voltage applying means for setting a voltage so as to apply a pulse voltage to the variable voltage electrolytic means, and a voltage for setting the voltage to the variable voltage electrolytic means so that almost no current flows between the coated metal and the counter electrode. 1. A coated metal deterioration device comprising applied voltage setting means for setting a voltage value at which a predetermined overvoltage can be applied, which is measured by a pulse polarization method and calculated from the measurement results, to a voltage variable electrolysis means.