JPH01254852A - Detection of corrosion - Google Patents

Abstract

PURPOSE:To enable the detection of the generation and progression of corrosion by continuous measurement even in both gaseous and liquid environments contg. a halogen element by determining the change in the speed of the increase in the concn. of the I3-Ions in the liquid drops in the gaseous phase and in the liquid phase with lapse of time from electrical conductivity measurement. CONSTITUTION:Gaseous halogen such as iodine entering a vessel 1 from an inlect part 1 thereof passes a liquid phase part 2 and emerges to a gaseous phase part 3. This gas is partly absorbed by the liquid phase part 2. Further, the gas emitted from the gaseous phase part 1 sticks partly to the inside wall of the vessel and is adsorbed to the liquid drops sticking to the inside wall of the vessel. The gas is simultaneously absorbed as well by a slight quantity of the liquid drops in a gaseous phase part-simulating liquid phase part vessel 4 for measurement made of the same material as the material of the above-mentioned vessel. Electrodes 6 are installed to the liquid in the liquid phase part 2 and the liquid drops 5 in the vessel 4. The conductivity of the liquid is measured by a conductivity meter 9 and is recorded 10. The change in the speed of the increase in the concn. of the halogen ions in the liquid drops in the gaseous phase part 3 and the liquid phase part 2 with lapse of time by the generation and progression of the corrosion in the metal corrosive environment in the atmosphere of the gaseous phase and liquid phase contg. the halogen element is determined from the measurement of the conductivity of the liquid contg. the halogen ions by a concn. meter 9. The generation and progression of the corrosion of the metal in the corrosive environment is thus detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting corrosion of metal materials, and particularly to a method for detecting corrosion suitable for determining corrosion caused by halogen elements in nuclear power plants.

[Conventional technology]

Nuclear fuel reprocessing plants release corrosive gases such as radioactive iodine If (approx. 10,100 ppm) and bromine Br (approx. 10 pp pm) in the spent fuel during the melting process in which spent fuel is dissolved with concentrated nitric acid. be done.

Conventionally, such off-gas is processed by a processing device shown in FIG. In FIG. 6, the off-gas from the melting tank 21 is introduced into the condenser 22, where the off-gas is cooled from about 90°C to about 40°C, and most of the water in the gas is condensed and removed.

The off-gas from the condenser 22 is supplied to the NOx absorption tower 24 , where it is absorbed by the absorption liquid (water) introduced from the top of the tower, becomes nitric acid, and is stored in the storage tank 23 .

The absorbed acid stored in the storage tank 23 contains iodine Iz and the like, and these iodine and the like are expelled into the gas in the iodine re-expulsion tower 25. Iodine and the like in the gas from the iodine re-expulsion tower 25 is adsorbed and removed in the iodine removal tower 26, and then NOx, iodine, etc. are released into the atmosphere from the exhaust stack 27 with concentrations below a specified level.

This radioactive iodine I2, bromine Br, and other halogen elements chlorine CI! It is a corrosive element like t, and at the same time has a very long half-life and remains in the reprocessing off-gas system for a long time, causing equipment leak accidents due to corrosion, especially in high humidity areas. . For this reason,
In off-gas treatment systems, it is necessary to detect the occurrence and progress of corrosion in equipment during operation, and conventionally the following detection methods have been used.

(]) A thin wire of the same quality as the device material is inserted into the device, and the amount of corrosion is detected by the increase in ohmic resistance due to the reduction in cross section due to corrosion. (Japanese Unexamined Patent Publication No. 51-30783) (2) Periodically take out the liquid in the device and analyze the amount of metal ions eluted therein. (Unexamined Japanese Patent Publication No. 60-4093
(3) Measure the change in polarization resistance of the sample metal. (Japanese Unexamined Patent Publication No. 56-24551) [Problem to be solved by the invention] Among the conventional detection methods (1) to (3), method (1) has the advantage of being able to measure the degree of corrosion in real time. but,
Only general corrosion can be detected as a form of corrosion, and it is difficult to predict the occurrence and progress of pitting corrosion, which is characteristic of halogen gas.

Method (2) allows predicting the degree of corrosion occurrence and progress through periodic sampling of the liquid and chemical analysis thereof, but the analysis requires a long time. On the other hand, method (3) is easy to handle and allows for continuous measurement, but since the applicable environment is only in liquid, it is less corrosive than in liquid for halogen elements such as iodine gas. It is difficult to detect the occurrence and progress of corrosion in a gas phase environment where corrosion products are attached which are not seen in liquids.

An object of the present invention is to solve the problems of the prior art described above, and to provide a corrosion detection method that can perform continuous measurement in both gas and liquid environments containing halogen elements and can detect the occurrence and progress of corrosion. .

[Means to solve the problem]

In an environment containing a halogen element such as iodine, the present invention can be applied to liquid droplets in the gas phase and 1. - Corrosion occurs when ions, etc. reach a certain value, and as the corrosion progresses, the I in the liquid, -
This was achieved by focusing on the self-propagation of ions, and the change over time in the concentration rate of I, - ions in droplets in the gas phase and in the liquid phase was determined by measuring the conductivity of the liquid. It is designed to detect the occurrence and progress of metal corrosion in the environment.

[Effect]

The corrosion loss of metals in the wet gas phase and liquid phase containing halogen elements such as iodine is shown in Figure 2 for material 5US3 at 60°C.
As can be seen from the example of 04L stainless steel, it begins to increase rapidly over time.

On the other hand, as shown in FIG. 3, when corrosion starts, the concentration of I3- ions in the droplets in the gas phase and in the liquid phase begins to accelerate with the passage of time.

This concentration of I, - ions is explained by the following equation.

I ff” +M (metal)→M!” +31-
・−・・−・(1) 31− +31z−+ Is −
+21s-...(2) Equation (1) is the oxidation of corrosion.
It is a reduction reaction, and I, - ions oxidize metal M at the anode, and M2' ions are formed in the liquid phase. 8, and itself is reduced to 3 moles of I- ion. -Ions have no oxidizing power and cannot elute metals any further. (2) - ions are complex ions in which 12 molecules of iodine and I- ions are combined, and the 12 parts corrode metals.

Equation (2) is 1 where 3 moles of ■-ions are constantly replenished.
This reaction formula combines two molecules to form 3 moles of 13-ion, and the equilibrium constant is very large at about 700.
2) The reaction in equation 2) instantly proceeds to the right. The 3 moles on the right side of equation (2)! , - ions, 1 mole of 1. -Ions are used in the reaction of equation (1) as corrosion progresses continuously, but the remaining 2 moles of I,'' ions remain in the system as the corrosion cycle progresses and participate in the corrosion reaction. This results in accelerated corrosion loss and increase in I3 concentration.

On the other hand, the concentration of I, - ions concentrated in the liquid is detected in real time by measuring the conductivity according to the following equation.

Here, k is conductivity (Ω/Cl11), α is ionization degree, λ
, and λ- are the ionic conductivities of cations and anions at infinite dilution (CT1/Ω·mol), and C is the ionic concentration (
mole/2).

α, λ. and λ- are constant in a small range of ion concentration C once the ion species is determined, so the conductivity includes I, -
Proportional to ion concentration. Therefore, with the passage of time, the conductivity also changes to 1. - The concentration will increase at an accelerated rate.

An example is shown in FIG.

As mentioned above, corrosion loss over time can in principle be detected by measuring conductivity values, but other ion pairs may be included in the actual machine from the beginning, so
The shape of the conductivity vs. time diagram does not change, but the absolute value level may increase.

This problem can be solved by using the temporal gradient of conductivity as shown in FIG. 5 to detect the amount of corrosion. This is because conductivity increases at an accelerating rate with corrosion, and its slope does not become a constant value, but instead shows a simple increasing curve over time.

Also, the measured conductivity value includes metal ions eluted due to corrosion, but since there is a proportional relationship between the concentration and the amount of eluted metal ions, Figure 4 is corrected. It can be used by doing the following.

In this way, through the measurement of conductivity over time for the materials of various component devices, the 1. - It is possible to determine the corrosion loss due to a liquid containing an iso-λ halogen element in real time, and to predict and warn the occurrence and progress of corrosion.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a system diagram of an apparatus for carrying out the corrosion detection method of the present invention. Halogen gas such as iodine that enters from the inlet of the container 1 passes through the liquid phase section 2 and exits into the gas phase section 3, but some of the gas is absorbed by the liquid phase section 2. Furthermore, part of the gas released into the gas phase part 3 is adsorbed by droplets attached to the inner wall of the container, and at the same time, about It is also absorbed by minute droplets 5 of 2 cc or less. Most of the other halogen gas flows out to the next system through the container outlet. Electrodes 6 are installed on each of the liquid in the liquid phase section 2 and the droplet 5 in the vapor phase simulated liquid phase container 4 in the gas phase section 3, and the conductivity of the liquid is measured through a changeover switch 7 and a conductivity meter 9. and recorded by the recorder 10. Further, the conductivity measurement circuit is driven by an alternating constant voltage generator 8.

Furthermore, the conductivity meter 9 has a relay 11 for disconnecting the valve.
is connected, and this relay 11 opens and closes valves 12 and 13 according to commands from conductivity meter 9. Valve 13
There are 1. A halogen gas bypass pipe 14 such as gas is connected.

In the liquid in the liquid phase part 2 and in the droplet in the gas phase simulated liquid phase container 4 in the gas phase part 3? The concentration of halogen ions such as I and -, which have been a1iI, is determined by the conductivity meter 9 alternately using the changeover switch 7.
When the time gradient of conductivity exceeds a preset limit value, the switching relay 11 connected to the conductivity meter 9 is activated to switch the valve 12 on. The valve 13 is closed and the valve 13 is opened to allow the iodine ring/% halogen gas to escape to other systems via the halogen gas bypass piping 14, thereby cutting off the flow of halogen gas into the container and preventing the progress of corrosion of the container.

With the above detection method, it is possible to detect the occurrence of pitting corrosion as a form of corrosion, and the occurrence and progress of corrosion can be determined extremely easily and in a short time based on the conductivity of the liquid. Corrosion in the environment can be detected.

In addition, as with iodine, it can also be applied to the determination of corrosion of metals in the gas phase and liquid phase of gases containing other halogen elements, as long as they have properties similar to those shown in Figures 2 to 5. Needless to say, it can be done.

〔Effect of the invention〕

According to the present invention, the corrosion loss of metal in a wet gas phase and liquid phase containing a halogen element such as iodine can be adjusted to increase the growth rate of the concentration of halogen ions in the liquid, such as Since changes over time can be determined from conductivity measurements, the occurrence and progress of corrosion in the above environment can be detected.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an apparatus for carrying out the corrosion detection method of the present invention, Fig. 2 is a diagram showing the relationship between corrosion weight loss and test time, and Fig. 3 is a diagram showing the relationship between I, -ion concentration and test time. Figure 4 is a diagram showing the time dependence of conductivity due to corrosion, Figure 5 is a diagram showing the rate of change of conductivity over time, and Figure 6 is a system diagram of the reprocessing off-gas treatment equipment. It is. 2...liquid phase part, 3...gas phase part, 4...
... Gas phase simulated liquid phase container, 5 ... Liquid droplet, 6
... Electrode, 7... Changeover switch,
8... Alternating constant voltage generator, 9... Conductivity meter, 10... Recorder, 14... Halogen gas bypass pipe. Agent Patent Attorney Masaru Nishimoto - Figure 4 Figure 5 Karougiginma t fhrl IX Karuginmon t
fhr) Figure 6

Claims (1)

[Claims] In a metal corrosive environment in a gas phase and liquid phase atmosphere containing halogen elements, the halogen ion concentration increases over time in droplets in the gas phase and in the liquid phase due to the occurrence and progress of corrosion. 1. A corrosion detection method characterized by measuring the change in velocity over time through the conductivity of a liquid containing halogen ions, and detecting the occurrence and progress of metal corrosion in the corrosive environment.