JPH07318528A - Method and apparatus for measuring corrosion resistance - Google Patents

Abstract

PURPOSE:To facilitate the measurement of the corrosion resistance in a specified region of a submerged member by employing a double cylindrical body and discharging an electrolytic solution from the space between inner and outer tubes so that an apparatus is attracted to a member being measured through pressure reduction thereby bringing the electrolytic solution only in the inner tube into contact with the member being measured. CONSTITUTION:Within a vessel 13 filled with electrolytic solution 15, a corrosion resistance measuring apparatus 1 is set for a member 14 to be measured and a vacuum pump 17 is operated to discharge the solution from the space between the outer tube 3 and the inner tube 4 of a double tubular cell body 2 so that the apparatus 1 is attracted to the member 14 through pressure reduction. The pump 17 is operated continuously to dry the surface of the member 14 between the outer tube 3 and the inner tube 4. Under that state, signals are delivered on lead wires 6, 11 from a probe 7 and the member 14 to a measuring unit 12 where true corrosion resistance Rc per unit area is determined for the member 14. This apparatus can determine the true corrosion resistance Rc of submerged environmental member, e.g. ocean structure, tank or piping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the corrosion resistance of members in a submerged environment such as marine structures, tanks and pipes, and a method for measuring the corrosion resistance using the apparatus.

[0002]

2. Description of the Related Art When evaluating the corrosion state of structural members, only the corrosion state can be evaluated by visual observation, but it is necessary to measure the corrosion rate for diagnosing deterioration or remaining life of structural members. . In recent years, an electrochemical method has been widely used as a method for measuring the corrosion rate of metal materials and coating materials (painted or lining steel materials). These measures the corrosion resistance Rc of a metal in an electrolyte solution and evaluate the corrosion rate, and the principle will be briefly described. Corrosion resistance Rc and electric double layer capacity C at the interface between metal and solution
d is present, and the electrical equivalent circuit of the corrosion system is as shown in FIG. The relationship of the equation (1) is established between the corrosion resistance Rc and the corrosion rate W (where k is a proportional constant). W = k / Rc (1) From this, the corrosion rate can be known by measuring the corrosion resistance Rc.

The following methods are available for measuring the corrosion resistance Rc. AC impedance method A method of determining corrosion resistance by applying a broadband sinusoidal AC voltage to a corrosion system and analyzing the frequency response characteristics of the potential and current obtained at this time. Since this method requires a long time (1 to 3 hours) for measurement, a method of simultaneously applying an alternating current of two frequencies of a high frequency and a low frequency to obtain the corrosion resistance Rc is also used. Constant current step method A method of obtaining the corrosion resistance Rc from the transient phenomenon of the potential obtained when a stepwise current i is applied to the corrosion system. Coulostat method A method in which a corrosion resistance Rc is determined by measuring a process in which a minute electric charge is instantaneously applied to a corrosion system by using an external power source for charging, and the potential returned by the shift returns to the original potential as a potential-time curve.

[0004]

When electrochemically evaluating corrosion, the most important thing is to determine the corrosion resistance per unit area (Ω-cm ² ). For this,
It is necessary to limit the measurement area to the measurement. Since the size of the resistance is inversely proportional to the area, the resistance obtained when the measurement area is large becomes small, and the resistance obtained when the measurement area is small becomes large. Therefore, if you measure without limiting the measurement area,
The value of the corrosion resistance Rc changes the range of the current flowing into the member to be measured (current reach). Fig. 6 shows an example of plotting the relationship between the current intensity (f (I)) and the reaching distance (f (L)) when seawater is used as the electrolyte solution, using the corrosion resistance Rc as a parameter. The current intensity is the current density (A / cm ² ) flowing into the member to be measured, and the graph of FIG. 6 shows the attenuation of the current density with the distance from the probe (horizontal axis) with 100% immediately below the probe. . It can be seen from FIG. 6 that when the corrosion resistance is small, the current reaching distance is short (the current flowing area to the member to be measured is small), and when the corrosion resistance is large, the reaching distance is long (the current flowing area is wide). That is, since the measured resistance is inversely proportional to the current inflow area, it becomes constant regardless of the corrosion resistance (true corrosion resistance) of the measured member, and the corrosion rate cannot be evaluated. For these reasons, in order to evaluate the corrosion rate of a member in a submerged environment, it is required to fix the measurement area and perform the measurement. In the laboratory test, the measurement area is limited by sealing the unnecessary surface of the member to be measured with an insulating material, but in the actual machine it is impossible to measure by sealing the unnecessary surface. Therefore, conventionally, the corrosion rate was not measured in an actual machine, and only the appearance was inspected. The object of the present invention is to solve the above-mentioned problems in the prior art, and to measure the corrosion resistance in a specified region of a member under a submerged environment, that is, a device suitable for measuring the corrosion resistance per unit area. And a method of measuring corrosion resistance using the same.

[0005]

The present invention comprises (1) a main body composed of a double cylindrical cell which is made of an insulating material and has one end closed, and an outer cylinder and an inner cylinder on the open side of the main body. A packing attached to the end, a probe for measuring corrosion resistance connected to the lead wire attached to the inside of the cylinder and pulled out from the bottom of the inner cylinder, and a liquid for discharging the liquid in the outer cylinder attached to the outer cylinder wall. A corrosion resistance measuring device characterized by having a discharge port; and (2) a main body composed of a double cylindrical cell made of an insulating material and having one end closed, and a body on the open side of the main body. Packing attached to the ends of the outer and inner cylinders, a corrosion resistance measurement probe connected to the lead wires that are attached to the inside of the cylinder and pulled out from the bottom of the inner cylinder, and the inside of the outer cylinder attached to the outer cylinder wall. Corrosion resistance, which has an outlet for discharging the liquid. Using a measuring device, the surface of the member to be measured immersed in the electrolyte solution, the ends of the outer cylinder and the inner cylinder to which the packing is attached are brought into contact, and between the outer cylinder and the inner cylinder from the outlet. By discharging the electrolyte solution with a vacuum pump and reducing the pressure inside the outer cylinder, the corrosion resistance measuring device is brought into close contact with the member to be measured, and a measurement area of an area equivalent to the cross-sectional area of the inner cylinder is set and corrosion in that area is set. It is a corrosion resistance measuring method characterized by measuring resistance.

[0006]

In the corrosion resistance measuring device according to the present invention, the main body is a double cylinder type, and the electrolyte solution between the inner cylinder and the outer cylinder is discharged by the vacuum pump, so that the device is vacuum-adsorbed on the member to be measured. Since the electrolyte solution in the inner cylinder can be brought into contact with the member to be measured, the measurement area can be limited and the measurement site can be specified. Further, since it has a double-sealed shape and the space between the inner cylinder and the outer cylinder can be in a dry state, leakage of current to the periphery of the measuring device can be completely prevented.

The apparatus of the present invention and the method of measuring corrosion resistance using the apparatus will be described below with reference to the drawings showing the embodiments. FIG. 1 shows a corrosion resistance measuring device 1 according to the present invention.
FIG. 2 is a schematic cross-sectional view showing an embodiment, and FIG. 2 is a schematic perspective view showing an appearance of the device of FIG. 1. The main body 2 of the corrosion resistance measuring device 1 composed of a double cylindrical cell is made of an insulating material and has an outer cylinder 3 and an inner cylinder 4 which are closed at one end and open at the other end. As the insulating material, an insulating synthetic resin such as acrylic resin or vinyl chloride resin is suitable. Outer cylinder 3 and inner cylinder 4
A packing 5 is attached to the open end of the to form a contact portion with the member to be measured. As the packing material, nitrile rubber, silicone rubber, fluororubber, or the like is used. A step 9 is provided in a portion of the outer cylinder 3 and the inner cylinder 4 where the packing 5 is attached so as to prevent the packing from being sucked out when the pressure between the outer cylinder and the inner cylinder is reduced. A probe 7 for measuring corrosion resistance is attached near the center of the closed end of the main body 1, and a lead wire 6 for connecting to a separately provided measuring instrument is connected to the probe 7. There is. The probe 7 comprises a reference electrode such as saturated calomel and a counter electrode such as platinum-plated titanium. Also,
The outer cylinder 3 is provided with a discharge port 8 for discharging the electrolyte solution between the outer cylinder and the inner cylinder, reducing the pressure inside, and drying.

FIG. 3 is a schematic explanatory view showing one embodiment of a corrosion resistance measuring method using the apparatus of FIG. In FIG. 3, 6 and 11 are the probe 7 and the member to be measured 1, respectively.
4 is a lead wire for guiding a signal from the measuring instrument 12 to the measuring instrument 12, both of which are sufficiently insulated and sealed in the electrolyte solution 15. Reference numeral 13 denotes a container for accommodating the corrosion resistance measuring device 1, the electrolyte solution 15 and the member to be measured 14, which is used in a laboratory so that the measurement can be performed in a submerged environment. 10
Is a discharge pipe for discharging the electrolyte solution between the outer cylinder and the inner cylinder, is made of a flexible pressure resistant material such as a vacuum rubber tube, and is connected to the vacuum pump 17 via the trap 16. . The trap 16 is for accumulating the electrolyte solution to be discharged, and a drain valve 18 for discharging is provided at the bottom thereof. Reference numeral 19 denotes a cock for returning the portion between the outer cylinder and the inner cylinder to the atmospheric pressure after the measurement is completed, which is in a closed state at the time of measurement, and is opened after the measurement is completed to allow air to flow thereinto. Measuring instrument 1
Reference numeral 2 is a device that receives signals from the probe 7 and the member to be measured 14 sent via the lead wire and displays the corrosion resistance. The measuring means is the above-mentioned AC impedance method,
Any method such as the constant current step method or the coulostat method may be adopted.

In the process configured as shown in FIG.
First, set the corrosion resistance measuring device 1 on the member to be measured 14,
The vacuum pump 17 is operated. As a result, the electrolyte solution 15 is discharged from the portion between the outer cylinder 3 and the inner cylinder 4 of the main body 2 in the form of a double cylindrical cell, and the corrosion resistance measuring device 1 is the member to be measured 1
Adsorb to 4 under reduced pressure. By subsequently operating the vacuum pump 17, the surface of the portion of the measured member 14 between the outer cylinder and the inner cylinder is dried. By measuring the corrosion resistance Rc with the measuring device 12 in such a state, the measured member 14 is measured.
The true corrosion resistance Rc per unit area can be calculated.

FIG. 4 shows that the corrosion resistance measuring apparatus 1 of the present invention is set on an acrylic plate which is an insulating material instead of the member to be measured 14, and is adsorbed under reduced pressure, and the electrolyte solution outside the main body 2 of the corrosion resistance measuring apparatus 1 is set. 6 is a graph showing the seal resistance of the main body 2, which is the result of measuring the resistance between the metal material and the probe 4 by immersing a bare metal material in (using seawater). As shown in Fig. 4, the seal resistance is 10 ⁹ Ω-cm when the pressure is reduced for 10 minutes
It turns out to be extremely high as ² . Since the corrosion resistance Rc of the metal under seawater environment is at most about 10 ⁷ Ω-cm ² , the sealing property is sufficiently maintained.

[0011]

Example According to the process of FIG. 3, the corrosion resistance of the coated steel sheet was measured in seawater. The measurement was performed by the AC impedance method. FIG. 7 shows the state of changes in the measured resistance value with respect to the elapsed measurement time (elapsed time from the start of discharge of seawater between the inner cylinder and the outer cylinder). It can be seen that when the seawater between the inner cylinder and the outer cylinder is discharged and the portion between them is dried, the resistance rapidly increases and becomes steady. The resistance after the steady state is the true corrosion resistance of the coated steel sheet measured.

[0012]

According to the corrosion resistance measuring apparatus and the measuring method of the present invention, it is possible to easily measure the corrosion resistance within the specified region of the member under the submerged environment, and the corrosion resistance per unit area Can be asked. That is, it is possible to determine the true corrosion resistance Rc of submerged environment members such as marine structures, tanks, and pipes, and the corrosion resistance measuring apparatus and measuring method of the present invention are extremely useful for diagnosing deterioration of these members. It is useful.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one embodiment of a corrosion resistance measuring device of the present invention.

FIG. 2 is a schematic perspective view showing the appearance of the apparatus shown in FIG.

FIG. 3 is a schematic explanatory view showing one embodiment of a corrosion resistance measuring method using the apparatus of FIG.

FIG. 4 is a graph showing an example of the relationship between the pressure reduction time and the seal resistance in the device of the present invention.

FIG. 5 is an explanatory diagram showing an electrically equivalent circuit of a corrosion system.

FIG. 6 is an explanatory diagram showing the relationship between the current intensity and the reach distance when the measurement area is not limited.

FIG. 7 is a graph showing how the resistance value measured in the example changes with the elapsed measurement time.

Claims (2)

[Claims] 1. A body made of an insulating material, which is composed of a double-cylindrical cell whose one end is closed, packings attached to the ends of the outer cylinder and the inner cylinder on the open side of the main body, and a cylinder. A probe for corrosion resistance connected to a lead wire attached inside and drawn out from the bottom of the inner cylinder, and an outlet for discharging the liquid in the outer cylinder attached to the outer cylinder wall. Characteristic corrosion resistance measuring device. 2. A body made of a double cylindrical cell which is made of an insulating material and has one end closed, a packing attached to the ends of the outer cylinder and the inner cylinder on the open side of the main body, and a cylinder. Corrosion resistance that has a corrosion resistance measurement probe connected to the lead wire that is attached inside and pulled out from the bottom of the inner cylinder, and a discharge port that discharges the liquid inside the outer cylinder that is attached to the outer cylinder wall Using a measuring device, the surface of the member to be measured immersed in the electrolyte solution, the ends of the outer cylinder and the inner cylinder to which the packing is attached are brought into contact, and between the outer cylinder and the inner cylinder from the outlet. By discharging the electrolyte solution with a vacuum pump and reducing the pressure inside the outer cylinder, the corrosion resistance measuring device is brought into close contact with the member to be measured, and a measurement area of an area equivalent to the cross-sectional area of the inner cylinder is set and corrosion in that area is set. Corrosion characterized by measuring resistance Resistance measurement method.