JPH10318962A - Corrosion-monitoring method and polarization resistance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quantitatively monitor the corrosion status of a boiler steel material without stopping a boiler and without causing a personal difference. SOLUTION: The amount of flow from a branch pipe 1 is adjusted, the inside of a heating unit 2, a cell 4, and a buffer tank 10 is filled with blow water, and the blow water is stably overflowed from the overflow port of the buffer tank 10. A voltage is applied between a sample pole 7 and a reference pole 5 and a counter electrode and the polarization resistance of the sample 7 is measured. The obtained polarization resistance is checked against a calibration curve that has been obtained in advance, thus obtaining the change in the corrosion speed and hue (for example, a' value of L'a'b' color development system being defined in JIS Z 8729) of a material to be monitored in the boiler.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for monitoring the state of corrosion in a boiler can, and a polarization resistance measuring device used in the method.

[0002]

2. Description of the Related Art The state of corrosion of boiler steel can be checked periodically (once / year) by stopping and opening the boiler, and visually observing the state of corrosion of the surface of the steel (for example, the state of generation of oxides such as sabicob). Is being done.

[0003]

In this case, the internal corrosion state and color tone are important criteria for judging the water treatment effect of the boiler, but the expression is visually intuitive and individual differences are large. , Not quantitative.

[0004] Further, in the prior art, it was not possible to know the corrosion state of the steel material surface during the operation of the boiler. Therefore, it was not possible to recognize that the corrosion was progressing until the time of the open inspection, and troubles such as generation of rust on the steel material occurred.

Further, in the prior art, the effect of the boiler water treatment is unclear, and the results may differ depending on the inspector. It is difficult to compare the results with the results of the overhaul inspection of the previous year. There was a problem that it was difficult to compare the corrosion status between the two.

According to the present invention, it is possible to monitor (monitor or estimate) the corrosion state of boiler steel which will stop the boiler, and to perform this monitoring quantitatively without causing individual differences. It is an object to provide a monitoring method and a polarization resistance measuring device.

[0007]

SUMMARY OF THE INVENTION The corrosion monitoring method of the present invention comprises a counter electrode, a reference electrode, and a sample electrode made of the same material as the steel material of the boiler, which is arranged so as to come into contact with the boiler blow water. The monitor polarization resistance is measured, the calibration relationship between the polarization resistance of the heat transfer surface in the boiler can (hereinafter referred to as boiler polarization resistance) and the monitor polarization resistance, and the boiler determined in advance. The corrosion state in the boiler can is monitored from the calibration relationship between the corrosion rate and / or the color tone on the heat transfer surface in the can and the boiler polarization resistance value.

[0008] The polarization resistance measuring apparatus of the present invention comprises a cell having an inlet for introducing boiler blow water, a sample electrode, a reference electrode and a counter electrode installed in the cell, a heater for heating the blow water, A buffer tank provided in communication with the upper portion and having an overflow for discharging effluent from the cell.

In the present invention, the polarization resistance obtained by bringing the boiler blow water into contact with the above-mentioned counter electrode, reference electrode and sample electrode is determined, and a previously determined calibration curve (this calibration curve is represented by a graph. And may be stored in a computer memory) to monitor (monitor or estimate) the progress of corrosion in the actual boiler.

[0010] Such a calibration curve can be prepared, for example, using a simulation boiler. That is, the polarization resistance of the sample electrode corresponding to the boiler heat transfer surface is measured using a simulated boiler, or the sample electrode is taken out and the amount of corrosion and color tone are measured, and the polarization resistance, corrosion rate, and polarization resistance are measured. Understand the relationship between color and tone.

In the monitoring method of the present invention, the relationship between the polarization resistance value and the corrosion rate and the relationship between the polarization resistance value and the color tone are both viewed, so that the corrosion state can be grasped from different viewpoints and more accurate monitoring can be performed. It is preferred. However, the corrosion state can be ascertained by only one of them, so that only one of them may be used simply.

Further, by utilizing such a simulated boiler,
A polarization resistance measuring device (monitor) as described in claim 2 is connected to the blow water line of the simulated boiler, and a calibration relationship is created from the measurement results of the polarization resistance value by the monitor and the polarization resistance value of the simulated boiler. You can also.

By previously determining the above-described calibration relationship, the corrosion state of the actual boiler can be estimated by measuring the polarization resistance value by a monitor in the actual boiler.

The operating condition of the simulated boiler, for example,
The actual boiler can be monitored by changing the boiler temperature and the added anticorrosive, and grasping the calibration relationship assuming various operating conditions of the actual boiler.

When a polarization resistance measuring device (monitor) is attached to a boiler, it is preferable to branch a branch pipe having an adjusting valve from a blow pipe of the boiler and attach a monitor to the branch pipe. With this regulating valve, a predetermined flow rate of can water can be supplied to the monitor.

It is preferable that water is passed through the monitor cell at a substantially constant speed. By providing a buffer tank, it is easy to adjust the flow rate to a substantially constant speed. Further, the buffer tank can be provided with a water level gauge to prevent emptying.

To measure the polarization resistance, a constant potential is applied between the reference electrode and the sample electrode, and the amount of current at the counter electrode is measured. The electrical signals from the sample electrode, counter electrode, and reference electrode are input to the measurement circuit of the measuring instrument, compared with the calibration relationship by a calculator, and output in any format.

In order to quantitatively measure the above color tone, the hue of the reflected light from the sample piece is detected. In order to accurately measure the hue, it is preferable to irradiate only the light from a specific light source to the surface of the steel material, receive the reflected light with a spectrophotometer, and obtain the hue of the reflected light.

The hue is, for example, JIS Z 8
729 can be represented by the a ^* and / or b ^* values of the L ^* a ^* b ^* color system. Obviously, L ^* may be added.

[0020] In addition, L ^* a ^* b ^* other than the color system L ^* C ^*
h color system, Hunter Lab color system, Munsell color system (J
ISZ 8721), or a color system such as the XYZ (Yxy) color system.

It is preferable to measure the hue using a spectrophotometer. For example, a sensor having high sensitivity in the red wavelength range, a sensor having high sensitivity in the green wavelength range, and a high sensitivity in the blue wavelength range. , And may quantify the respective sensitivities, or a plurality (for example, 40
) May be used to measure the reflectance for each wavelength by splitting the reflected light.

[0022]

Embodiments of the present invention will be described below.

I. First, a polarization resistance measuring apparatus according to an embodiment will be described with reference to FIG.

FIG. 1 is a side view of the polarization resistance measuring apparatus. A branch pipe 1 branched from a blow pipe of a boiler is connected to a blow water inlet 2 a of a blow water heating unit 2.
An electric heater 3 is provided in the heating unit 2. A cell 4 for measuring polarization resistance is connected to the blow water outlet 2b of the heating unit 2.

The cell 4 has a cylindrical shape with the cylinder axis extending vertically, and has a reference electrode 5, a counter electrode 6, and a sample electrode 7 from the side.
And a thermometer 8 is inserted.

As the reference electrode 5 and the counter electrode 6, for example, those made of stainless steel are used. As the sample electrode 7, a round bar made of mild steel made of the same material as that in contact with boiler water in the boiler is used. A heating element (resistance heating element) is attached to the sample electrode 7, and the element is heated to the same temperature as the surface of the monitoring target material in the actual boiler.

A buffer tank 10 is provided above the cell 4, and the inside of the buffer tank 10 communicates with the inside of the cell 4. An overflow port 11 is provided on a side surface of the buffer tank 10. A liquid level gauge 12 is inserted from above the buffer tank 10. The liquid level sensor 12 is connected to the heater controller 1 via a lead wire 12a.
In order to prevent empty heating, the heater 3 is energized only when the liquid level sensor 12 detects the liquid level.

The reference electrode 5, the counter electrode 6, the sample electrode 7, and the thermometer 8 are connected to a polarization resistance measuring instrument 20 by lead wires 5a, 6a, 7a, 8a. As this measuring instrument 20, a commercially available potentiostat / galvanostat can be used.

The procedure for measuring the polarization resistance using the apparatus shown in FIG. 1 is as follows.

The amount of inflow from the branch pipe 1 is adjusted so that the heating unit 2, the cells 4 and the buffer tank 10 are filled with blow water, and the blow water stably overflows from the overflow port of the buffer tank 10. To do. The amount of electricity supplied to the heater 3 is adjusted so that the temperature detected by the thermometer 8 becomes constant (for example, 90 ± 5 ° C.). Leave in this state for about a week. This is because it takes enough time for the blow water to contact the surface of the sample electrode 7 to form an anticorrosion film. After a lapse of one week, a voltage is applied between the sample electrode 7 and the reference electrode 5 and the counter electrode 6, and the polarization resistance of the sample electrode 7 is measured. By applying the obtained polarization resistance value to a previously determined calibration curve as shown in FIG. 3, the corrosion rate and hue (a ^* value indicating redness) of the monitoring target material in the boiler are determined. The method for obtaining the calibration curve will be described later. The degree of corrosion is determined from the determined corrosion rate and hue. Generally, the larger the polarization resistance value, the more corrosion-resistant the boiler steel material, the lower the corrosion rate and the more hue the color becomes.

II Next, a method for preparing a calibration curve of the polarization resistance value of the sample electrode and the corrosion rate of the sample electrode will be described with reference to FIG.

FIG. 2 is a side view of a simulation boiler for preparing the calibration curve.

The pressure gauge 30 for water / water separation has a liquid level gauge 31,
A thermometer 32, a steam extraction pipe 33, a water supply pipe 34, and a blow pipe 35 are connected.

A heating pressure-resistant case 40 made of SUS316L is provided on the side of the case 30. The lower part and the upper part of the case 30 and the case 40 are connected by circulation pipes 41 and 42.

A SUS tube (313) was used as the resistance heating element.
(mm × 41.5 mmφ) 43 a is inserted into the case 40. This heater 4
The third tube 43a is a counter electrode. The heat transfer amount of the heater is 98900 kcal / h · m ² .

A sample electrode 45 and a reference electrode 46 are inserted into the case 40. The sample electrode 45 is a 13 mm × 2 mm mild steel flat plate. A resistance heating element (not shown) is in close contact with the sample electrode 45, and power is supplied so that the sample electrode 45 has the same temperature (for example, 230 ° C.) as the tube 43 a of the heater 43.

A pressure-balanced external reference electrode is used as a reference electrode.

The procedure for creating a calibration curve using the simulation boiler shown in FIG. 2 is as follows.

(1) The same boiler water as that supplied to the actual boiler is introduced from the water supply pipe 34 so that the insides of the cases 30 and 40 are filled with the boiler water. The blow water is caused to flow out from the blow pipe 35 so as to be at the upper part of the blow pipe 30. Total water volume is 4L
And the flow velocity in the case 40 is 8 to 12 cm / sec. (2) The heater 43 and the sample electrode resistance heating element are energized so that the temperature of the tube 43a of the heater 43 and the sample electrode 45 becomes 230 ° C. The pressure in the cases 30 and 40 was 1.0 MPa. After a lapse of three days, the polarization resistance is measured, the sample electrode 45 is taken out and weighed, and the corrosion rate is measured. Further, the surface of the sample electrode 45 taken out is measured by color, and an a ^* value indicating redness is obtained. (3) The above-mentioned experiments (1) and (2) are performed using a plurality of types of boiler water having different water qualities, and the corrosion rate and a ^* value of the polarization resistance sample electrode 45 are obtained. (4) A calibration curve between the polarization resistance value and the corrosion rate and a calibration curve between the polarization resistance value and the a ^* value are prepared by writing the results of the above (1) to (3) on a graph. The obtained calibration curve is as shown in FIG.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The specifications of the polarization resistance measuring apparatus shown in FIG. 1 were as follows. Blow water heating unit 2 capacity 80 mL Blow water heating unit 2 heater 3 capacity 200 W Cell 4 capacity 30 mL Reference electrode 5 and counter electrode 6 Stainless steel (dimensions 6 mmφ × 80 mm) Sample electrode 7 Mild steel (dimensions 6 mmφ × 80 mm) Sample Target temperature of electrode 7 90 ± 5 ° C. Target temperature of thermometer 8 90 ± 5 ° C. Capacity of buffer tank 10 300 mL Blow water flow 10 mL / min The mild steel of sample electrode 7 is composed of the members constituting the heat transfer surface of the actual boiler. It is of the same material. FIG. 4 is a graph showing the relationship between the measured values of the polarization resistance measuring device and the measured values of a ^* obtained by opening the actual boiler. As shown in FIG. 4, according to the present invention, it was found that the degree of corrosion of the actual machine could be monitored with high accuracy.

Further, the blow water from the blow pipe 42 of the simulated boiler of FIG. 2 is supplied to the apparatus of FIG. 1 to measure the polarization resistance of the sample electrode 45 and the sample electrode 7 of FIG. 1 in the simulated boiler of FIG. I tried to. The result is shown in FIG.

FIG. 5 shows that the sample electrode 45 of the simulated boiler of FIG.
It is recognized that the polarization resistance of the sample electrode 7 of FIG. 1 corresponds to the polarization resistance of the sample electrode 7 with high accuracy.

[0043]

As described above, according to the present invention, the state of corrosion of boiler steel can be measured during operation without stopping the boiler. Further, according to the present invention, the corrosion rate of the boiler steel can be quantitatively determined. Further, the color tone of the boiler steel can be quantitatively determined. From these, the processing effect of the boiler water can be determined without stopping the boiler.

[Brief description of the drawings]

FIG. 1 is a side view of a polarization resistance measuring device according to an embodiment.

FIG. 2 is a side view of a simulation boiler.

FIG. 3 is a graph showing calibration values.

FIG. 4 is a graph showing a correspondence between a monitoring value and an actually measured value.

FIG. 5 is a graph showing a correspondence relationship between polarization resistance values in a simulated boiler and a polarization resistance measurement device.

[Explanation of symbols]

 2 Heating unit 3 Heater 4 Cell 5, 46 Reference electrode 6 Counter electrode 7, 45 Sample electrode 10 Buffer tank

Claims (2)

[Claims] 1. A monitor polarization resistance value of a sample electrode is measured with a sample electrode made of the same material as a counter electrode, a reference electrode, and a boiler steel material, which is disposed so as to be brought into contact with blow water of a boiler, and is determined in advance. Calibration relationship between the polarization resistance of the heat transfer surface in the boiler can (hereinafter, referred to as boiler polarization resistance) and the monitor polarization resistance, and the corrosion rate and / or the heat transfer surface in the boiler can determined in advance. A corrosion monitoring method that monitors the corrosion state in boiler cans based on the calibration relationship between color tone and boiler polarization resistance. 2. A cell having an inlet for introducing boiler blow water, a sample electrode, a reference electrode, and a counter electrode installed in the cell, a heater for heating blow water, and provided in communication with an upper part of the cell. And a buffer tank having an overflow for discharging effluent from the cell.