JP2794772B2 - Prediction method of corrosion of water-based metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for predicting corrosion of water-based metal, and in particular, to prevent accidents caused by water-based corrosion in which deposits and deposits containing microorganisms are formed on metal surfaces. The present invention relates to a method for predicting the occurrence of corrosion of a metal material in a lower part of the deposit or the deposit in order to prevent the deposit.

[Prior Art] Suspended substances containing microorganisms are generated in an aqueous system such as a cooling water system of various plants and tend to increase with time. Plant members such as pipes used for such water systems are usually made of metal materials such as copper and steel.If suspended substances containing microorganisms are present in the system, they adhere to and deposit on the metal materials, Local corrosion occurs in the lower part. The local corrosion contributes to water leakage and process leak.

[Problems to be Solved by the Invention] Conventionally, there has been provided a method for strictly predicting the occurrence of corrosion of a metallic material in a lower layer of a deposit or a sediment containing microorganisms (hereinafter collectively referred to as “sediment”). Therefore, it is desired to establish a corrosion prediction method from the viewpoint of safe operation of the process.

The present invention has been made in view of the above-described conventional circumstances, and has as its object to provide a method for reliably and accurately predicting the occurrence of corrosion of water-based metal.

[MEANS FOR SOLVING THE PROBLEMS] The method for predicting corrosion of a water-based metal according to claim (1) is a method for predicting corrosion of a water-based metal in which a deposit containing microorganisms is formed on a metal surface, the method comprising: Metal corrosion is predicted based on the difference between the state quantity in the lower layer and the state quantity in water.

The method for predicting corrosion of a water-based metal according to claim (2) is characterized in that, in the method of claim (1), the state quantity is pH, dissolved oxygen amount or natural potential.

[Action] When dirt (suspension substance) containing microorganisms adheres and accumulates on the surface of the metal material, the lower layer of the sediment becomes anaerobic, the amount of dissolved oxygen decreases, and the natural potential of the metal decreases due to the decrease in oxygen concentration. . When the lower part of the sediment becomes anaerobic, anaerobic decay occurs and an organic acid such as acetic acid is generated, so that the pH of the lower part of the sediment decreases. Therefore, when the pH, dissolved oxygen concentration, or natural potential of the metal material in the lower layer of the deposit tends to decrease, it can be estimated that the metal material surface has a tendency to corrode.

 Hereinafter, the present invention will be described in detail.

As a sensor for measuring the state quantity in the lower part of the deposit, for example, a pH sensor, a dissolved oxygen concentration sensor, a natural potential sensor, or the like can be used. From these detected state quantities, for example, corrosion can be predicted as follows.

A pH meter is installed in the lower part of the sediment and in the target water system to measure the pH, and the occurrence of corrosion of the target metal is predicted from the difference between the pH in the lower part of the sediment and the pH in the target water system.

Dissolved oxygen concentration measurement equipment is installed in the lower part of the sediment and in the target water system to measure the dissolved oxygen concentration.Corrosion of the target metal occurs from the difference between the dissolved oxygen concentration in the lower part of the sediment and the dissolved oxygen concentration in the target water system Predict.

An electrode made of the target metal or platinum is installed in the lower layer of the sediment and the target water system, and the occurrence of corrosion of the target metal is predicted from the difference in the natural potential between the two. In the above method,
When predicting the occurrence of metal corrosion, the difference between the pH, dissolved oxygen concentration, or natural potential between the lower layer of the sediment and the target water system, which serves as a criterion, is determined by the type of the target water system, the type of metal material, and the operating conditions. Normally, the difference in pH is 0.2 or more, the difference in dissolved oxygen concentration is 1 ppm or more, and the potential difference is 50 m.
When it becomes V or more, it can be determined that corrosion starts to occur soon.

In carrying out the present invention, the state quantity of the lower layer of the sediment may be measured directly by installing an appropriate sensor on the surface of the metal member for which corrosion is to be predicted. Environmental conditions similar to the components (flow velocity, temperature, etc.)
May be provided, and the state quantity of the lower layer of the deposit deposited on the sensor in the monitoring device may be measured.

In an actual water system, when corrosion of a metal is predicted by such a method of the present invention, the sediment is peeled off. As a treatment for removing the sediment, physical means such as pulsation in the water system, ball washing, hydrogen peroxide,
Chemical means for injecting a detergent such as a surfactant, an acid, and hydrazine may be used. Further, the separation can be performed by changing the flow rate of the cooling water.

Such a peeling process may be performed manually or automatically. In order to perform the operation automatically, for example, a difference between a detection signal from a sensor in the lower part of the sediment and a detection signal from a sensor in the water system is calculated, and if the difference is equal to or more than a predetermined value, the operation is stopped. Without
A control device for outputting a signal for operating the peeling processing means is provided. This makes it possible to automatically and efficiently predict and strip metal corrosion, prevent metal corrosion, and prevent accidents due to corrosion.

The method for predicting corrosion of a water-based metal of the present invention is an industrial water system,
Steel in water systems where the generation of microorganisms such as cooling water systems, heat storage water systems, wastewater systems, etc. that are expected to be from rivers and lakes,
It is extremely effective in predicting the occurrence of corrosion of metallic materials such as copper, stainless steel, and aluminum, and particularly in a cooling water system with a flow velocity of 1 m / s or less.

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 Carbon steel (STB-3) was used using the water flow test device shown in FIG.
Water was continuously passed around the outer periphery of the tube 1 made of 5) to predict corrosion of the tube.

In FIG. 1, the tube 1 is inserted into a glass tube 2. Both ends of the glass tube 2 are sealed by rubber stoppers 3 and 4. Both ends of the tube 1 penetrate the rubber stoppers 3 and 4 and protrude to the outside. In addition, in the tube 1,
O-rings 5 are mounted at predetermined intervals.

A water inlet 2a and a water outlet 2b are provided at both ends of the glass tube 2, and water in the circulating water tank 6 is introduced through a pipe 10 having a pump 7, a valve 8 and a flow meter 9. . Water from the outlet 2b is returned to the water tank 6 via the pipe 11. A commercially available plate-type pH meter (“CARDY” manufactured by Dig Seisakusho) is installed in piping 11
A transparent polyvinyl chloride tube is attached to the tube, and the tube is processed so that the circulating water flows along the pH sensor surface of the pH meter under the same conditions as the tube surface when the circulating water of piping 11 is passed through the tube. An apparatus 12 is provided, and the circulating water tank 6 is provided with a pH meter 13 for measuring the pH of the stored water therein.

In FIG. 1, reference numeral 14 denotes a pipe for makeup water, and reference numeral 15 denotes a pipe for overflow. The pipe 14 is provided with a pump 16.

As the circulating water, pure water was used as a base, and synthetic water to which dirt collected from the actual cooling water system was added as turbidity was used.
Table 1 shows the water quality. Water temperature is 30 ℃, flow rate is 0.1m
/ s, and the water flow test period was 15 days.

When water flow was continued, dirt adhered to the pH sensor of the pH measuring device 12, and the temporal change of pH in the lower layer of the sediment could be followed. FIG. 2 shows a temporal change of the pH of the lower layer of the sediment detected by the pH measuring device 12 and a temporal change of the pH of the circulating water detected by the pH meter 13.

As shown in FIG. 2, while the pH of the circulating water hardly changed, the pH of the lower part of the sediment decreased over time.

On the other hand, the same degree of contamination as the pH measuring device adhered to the surface of the tube 1 made of carbon steel, and the occurrence of corrosion was recognized. As shown in FIG. 2, the occurrence of corrosion on the surface of the tube 1 substantially coincides with the time when the pH of the lower layer of the sediment was detected by the pH measuring device, and this pH decreased by about 0.5. The occurrence of rust was observed at the time of the rusting, and the progress of rust was observed at the time of a decrease of about 0.8.

In such a water flow test, when the pH of the lower layer of the sediment detected by the pH measuring device started to decrease, the sediment was peeled off and the water flow was continued. The peeling treatment was performed by injecting 50 ppm of hydrogen peroxide without stopping the flow of water to wash the inside of the system. As a result, the second
As shown in the table, the progress of the corrosion of the tube was greatly suppressed as compared with the case where the deposit was peeled off and the peeling treatment was not performed.

From the above results, it is clear that the occurrence of corrosion of the metal material can be predicted from the change in pH in the lower part of the sediment, and that this enables effective sediment peeling treatment and suppresses the progress of corrosion.

Example 2 Dissolved oxygen (DO) in Example 1 instead of the pH measurement device
The operation was performed under the same conditions except that a meter was attached. That is, commercially available
The DO measurement surface of the DO meter was inserted into a transparent vinyl chloride tube provided with an opening, and the DO meter was attached so that circulating water flowed smoothly inside the tube.

 The results are shown in FIG.

As is clear from this, the DO reduction at the bottom of the sediment
Occurs earlier than the decline. Therefore, it is clear that more preferable results can be obtained by performing the peeling treatment when the difference between the readings of the DO meter becomes 1 ppm or more.

[Effects of the Invention] As described above in detail, according to the method for predicting corrosion of a water-based metal of the present invention, the occurrence of corrosion of a metal material in a lower part of a sediment can be easily and appropriately determined during operation of a target plant. It can be predicted for sure.

Therefore, effective anticorrosion treatment can be efficiently performed based on the prediction result, and safe and stable operation of the plant and extension of the life of the metal device member can be achieved. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a water flow test apparatus used in Example 1, and FIG. 2 is a graph showing the results of Examples 1 and 2. 1 ... test tube, 6 ... circulating water tank, 12 ... pH measuring device, 13 ... pH meter.

Continuation of the front page (56) References JP-A-57-33348 (JP, A) JP-A-60-233539 (JP, A) JP-A-2-242146 (JP, A) Corrosion protection '89, B-308 (1989, May 1) Hirano SP. 189-192 (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/26 G01N 27/416 G01N 17/02

Claims (2)

(57) [Claims] 1. A method for predicting corrosion of an aqueous metal in which a deposit containing microorganisms is formed on a metal surface, comprising comparing a state quantity in a lower layer of the deposit with a state quantity in water, and A method for predicting corrosion of a water-based metal, comprising predicting the corrosion of a metal based on the difference between the two. 2. The method for predicting corrosion of a water-based metal according to claim 1, wherein the state quantity is pH, dissolved oxygen amount or natural potential.