JPH06158400A - Descaling method for steel product surface - Google Patents

Abstract

PURPOSE:To easily remove the scale on steel product surfaces without the need for making countermeasure for prevention of secondary environmental pollution by passing DC current under specific conditions with the steel products deposited with the scale as anode and a conductive metallic body as cathode in a neutral electrolyte soln. CONSTITUTION:The steel products stuck with the scale are connected as the anode to the positive electrode of a DC power source and the conductive metallic body is installed as the cathode to the counter electrode in the neutral electrolyte soln. and the DC current is passed between these two electrodes. The current density of the anode is specified to >=1A/m<2> and the energization quantity to >=50AH/m<2> at this time. As a result, the scale on the steel product surfaces is easily removed and the surface cleaning and activation are easily executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing scales on the surface of a steel material, and more particularly to a method for removing scales on the surface of a steel material which is capable of simple surface cleaning and activation and is particularly applied to a steel material laid in seawater.

[0002]

2. Description of the Related Art Conventionally, scales consisting of oxides and dirt formed or adhered to the surface of steel materials are removed by immersion in a mineral acid solution such as hydrochloric acid or sulfuric acid, or mechanical removal by cathodic electrolysis or blasting. Has been.

These methods are carried out as a pretreatment for applying a steel material surface treatment such as painting, plating, thermal spraying and adhesion to the steel material surface. Therefore, the surface treatment is performed before the steel material is placed in a practical environment. That is, the surface treatment is usually performed in a place different from the service environment.

For the surface treatment of the steel material, it is essential to clean and activate the surface of the steel material as a first step. Pretreatment such as degreasing, acid treatment or blasting greatly affects the performance of the surface-treated finished steel material.

When the pretreatment and surface treatment finishing can be carried out continuously in terms of time and process, surface cleaning and activation by pretreatment such as degreasing / acid treatment or blasting described above can be performed in a post process. Can be effectively applied to the surface treatment finish and performance of.

[0006] However, when the steel material surface is put to practical use in a clean and activated state, there may be a time lag and a process deviation before practical use. Especially for large area processing,
Not only is it difficult to carry out, but it is also difficult to avoid surface contamination again by the time of service even after cleaning and activation.

[0007] For example, in a steel plate-like anode used as a means for suppressing or preventing the settlement of marine organisms consisting of seaweeds that adhere and propagate in seawater-immersed parts such as water intake pipes and seaside structures that take in cooling seawater. Uses a large area of steel plate. This method of preventing marine organisms attaches steel plates to the wall surface of the target intake pipe or the surface of the marine structure that contacts seawater via an insulating material or cushioning material (which may also serve as insulation), The steel plate is connected to a positive electrode of a DC power source to serve as an anode, a counter electrode is installed via seawater, and the negative electrode of the DC power source is connected to serve as a cathode. The dissolution suppresses or prevents the growth of marine organisms on the surface of the steel (hereinafter referred to as an electric antifouling method).

The surface area of the structure which is the subject of this electric antifouling method ranges from several tens m ² to several 1000 m ² . For this reason, the area and the number of steel plates (anode materials) used also increase.

Since it is necessary to actively dissolve steel with a small anode current, the surface of the anode steel is required to be clean and have a uniform active surface at the start of energization. However, it is practically difficult to adopt the above-mentioned chemical / physical pretreatment before use. Even if the cleaning and activation treatments are performed in advance, it is inevitable that scales such as the formation of an oxide film and the adhesion of dirt are again formed on the surface of the anode steel in terms of the time until the electrode material is attached and the handling work.

In order for the surface of the anode steel to be as clean and uniform as possible at the start of energization, some kind of pretreatment is necessary.

[0011]

SUMMARY OF THE INVENTION The object of the present invention is to remove the scale of the surface easily and without the need for secondary environmental pollution prevention measures after the steel material has been installed on site, and it is possible to use special means especially in the field environment. An object of the present invention is to provide a simple method for removing scales on the surface of steel materials.

[0012]

[Means for Solving the Problems] The purpose is to elute the steel material by using the steel material as an anode in an electrolyte solution in a service environment and passing a current of about 5 times or more the practical anode current density in a short time. It is achieved by lifting the scale on the surface of the steel material and separating it from the steel material.

That is, according to the present invention, a scale-adhered steel material consisting of deposits such as oxides and dirt in a neutral electrolyte solution is connected to a positive electrode of a DC power source to serve as an anode, and a conductive metal body is used as a counter electrode. It is connected to a negative electrode of a power source to serve as a cathode, and current is passed between the both electrodes through the neutral electrolyte solution to float the scale on the surface of the anode steel material and remove it.

For example, in the case of applying the electric antifouling method to the above concrete intake channel, a steel material is put around the wall surface of the intake channel (a part where marine life adheres), and the steel materials facing each other are paired to form a positive electrode of a DC power source. When the present invention is carried out by connecting to the negative electrode and the negative electrode, the object is achieved by using a DC power source having a polarity converting function.

The anode current density required to float and peel off the scale on the surface of the anode steel material is 1 A / m ² or more and the energization amount is 50 AH / m ² or more. Preferably 1.5A
/ M ² or more and 80 AH / m ² or more.

The steel electrode plate used for the electric antifouling method is intended to prevent the aquatic organisms from growing in seawater, brackish water, or fresh water containing an electrolyte.
Consumption of a large amount of electricity is not preferable for uniform activation of the electrode surface. An energization amount of 100 to 150 AH / m ² / m ² is appropriate.

The removing method of the present invention can be carried out as a pretreatment of the above-mentioned electric antifouling method. In this case, after the scale is removed at an anode current density of 1 A / m ² or more for a predetermined time, the anode current density may be reduced to ⅕ or less and the electrical antifouling method may be performed as it is.

[0018]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 Hot rolled steel sheet (SS400) 1.6 mm ^T and 4.5 mm ^T
And cold-rolled steel plate (SPCC) 1.6 mm ^T anodically electrolyzed in seawater.

All the steel sheets have a size of 100 ^W × 200 ^L mm. SS400 had a black skin, and the surface was a residual material used for other purposes, and slime such as oil was remarkable. SP
Although CC is a polished steel plate, its surface was cleaned with a solvent before use.

As the test steel plates, steel plates of the same kind as cathodes were set on both sides of the plate so that the front and back sides were anode surfaces. The test steel plate was connected to the positive electrode of the constant current power source, the counter electrode negative electrode steel plate was connected to the negative electrode of the power source, and a current was passed between both electrodes.

The applied current has an anode current density of 0.2 to 3.
A non-energized test steel plate was added for comparison with 9 stages of 0 A / m ² . The electrolyte used was natural seawater and was not stirred. Water temperature is 19 ~ 21 ℃. The energizing time is 48 hours,
After 24 hours and 48 hours, the peeling state of dirt and deposits such as mill scale was observed, and after 48 hours, the pulling weight reduction was determined.

The observation result is 0.8
When the anode current density was A / m ² or less, neither lifting nor peeling of the scale was observed. If it exceeds 1 A / m ² , the scale will be lifted, and if it exceeds 1.5 A / m ² , it will be noticeable, and if it exceeds 2 A / m ² , peeling and falling will be observed, but it will not reach the full drop. After 48 hours, 1A / m ² or more in most of the scale is peeled off and loss, in 1.8A / m ² or more was exhibited beautiful steel surface regardless of the thickness of the steel sheet.

Table 1 shows a black leather plate 1.6 mm ^T , 4.5 m
m ^T and 1.6 mm ^T of polished steel plate are shown the wear rate (wear rate) and erosion rate of the steel plate for each anode current density after 48 hours of energization. Table 2 shows the difference in the degree of wear calculated based on the data in Table 1 (corresponding to the consumption rate of black leather steel sheet-the consumption rate of polished steel sheet = the scale consumption rate), the difference from the theoretical consumption rate, and the estimated scale thickness. In Table 2, the estimated peeling scale thickness was calculated from the difference in consumption rate (consumption degree) between the black leather plate and the polished steel plate. However, the density of the scale was 5.21 g / cm ³ .

[0025]

[Table 1]

[0026]

[Table 2]

FIGS. 1 and 2 show Tables 1 and 2 in relation to the anode current density.

Among the consumption rates (g / m ² · h) shown in FIG. 1, the polished steel plate is a steel plate with no stain such as scale, and naturally, it linearly increases as the anode current density increases. It is close to the theoretical consumption rate. The black leather steel plate also changes almost linearly, but it is 0.5 to 1 g compared to the polished steel plate.
/ M ² · h is higher.

Looking at the difference between the black leather plate and the polished steel plate, that is, the difference in the degree of wear, as shown in the figure (broken line), there is a bending point at the anode current density of 1.0 to 1.2 A / m ^2. The gradient is steep below the current density, and is slow and almost constant above the current density. This constant value is the steel plate thickness of 1.6 m
It is presumed that 4.5 mm is higher than m and corresponds to the thickness of stains such as scale on the surface of the steel sheet.

When the thickness is estimated by considering the stains such as scales as the black scale (mill scale) formed on the surface of the steel sheet, as shown in Table 2 and FIG.
It becomes 8 to 10 μm at m and 4.5 mmt. The estimated black skin thickness is 5 μm at the published value of 1.6 mmt.
As described above, it is extremely close to the value of 10 μm or more at 7 mmt, and the almost constant value of the difference in the degree of wear is due to the peeling of the scale of the steel sheet.
It can be regarded as the dropout amount.

According to the above-mentioned observation result of 48-hour energization,
Most of the scale peeled off and fell off at a current density of 0 A / m ² or more, which corresponds to the current density at the bending point in FIGS. 1 and 2.

Further, it is desirable that a current of ^{2 A} / m ² or more is used for peeling off of the scale when energized for 24 hours. Ie 2
A / m ² × 24H = 48 AH / m ² or more is required.

Example 2 A steel plate with black skin (SS400) was attached to a portion of the side wall of a box culvert type intake channel of a thermal power plant to which marine organisms were attached, and the effects of those with and without the removal method of the present invention were tested. did.

The steel plate is 1.6 ^T × 918 ^W × 1829 ^L mm
6 sheets were used, and a steel plate having an insulating material and a cushion material bonded to the back surface of the steel plate was attached to both side wall surfaces of the water channel. Three sets of two steel plates with opposite wall surfaces facing each other were set as one set. Independent steel materials were installed on the bottom of the waterway for each set. Each of the three sets was connected to an independent positive electrode of a DC constant current power source, and the shaped steel material installed on the bottom was connected to the negative electrode of the DC power source.

A steel material for suppressing the growth of marine life on the surface of the anode steel material by actively dissolving the steel material as an anode in seawater. The constant current is 0.2 A / m ²
It is a degree. Of the 3 sets of steel plate anodes, 2 sets are steel plates with black skin,
The remaining one set is a polished steel plate.

Each steel plate was attached to the side wall surface of the intake channel for each set. About one week after installation, seawater was poured into the waterway. Immediately, the other set of black steel plate and black steel plate except for one set of black steel plate passed an anode current of 0.2 A / m ^{2 which} was a steady current. One set of steel plates with black skin was subjected to electrolytic treatment in seawater for 50 hours at an anode current density of 2 A / m ² which was 10 times the constant current.
After 50 hours, the black skin (mil scale) of the electrolytically treated steel sheet was completely peeled off and exhibited a silver-white surface. Then, like the other sets, the anode current density was reduced to 0.2 A / m ² and constant current energization was performed.

In the middle of March, constant current energization was performed from early spring to autumn when the attached marine life is most active. The electrolytically treated steel plate was entirely covered with colloidal hydroxide of iron, but there was almost no adhesion of shell algae and the quantity was 0.3 kg / m ^2.
Can be virtually ignored.

The milled steel sheet was exposed to the atmosphere in the waterway before pouring and energizing seawater, and during this time, steady energization was performed in the state where natural red rust was generated. Although no noticeable adhesion of marine organisms was observed, almost all surfaces were covered with colloidal iron hydroxide, similar to the electrolytically treated steel sheet, and the natural oxidation generated during exposure to the atmosphere in the waterway was observed. Adhesion of protozoa and algae was found in some of the areas that were thought to have remained. 0.7k in quantity
It is g / m ² , which is not a problem in practical use.

In the steel sheet with black skin that is not subjected to electrolytic treatment, most of the black skin is peeled off and dropped, and the adhesion of marine organisms is suppressed in that part.
Although blocked, barnacles and small amounts of protozoa were found to be attached to the uncut areas of the black skin. It is considered that due to the formation of black scale (mill scale) on the surface of the steel sheet, the thickness and the close contact with the steel material, or the difference in the electric potential, there are some areas that cannot be cut off sufficiently with a small steady current. The outflow current flows out intensively from the defective parts and active parts of the black skin of the steel plate, and as the peeling and falling of the black skin progresses due to the energization, the active surface expands and the black skin part firmly adhered to the steel plate until the end. As a result, the outflow current from the remaining part is suppressed, and as a result, the adherence of slime and organic matter is assumed to be followed by the growth of marine life. In fact, it was a small organism at the early stage of growth compared to the adhesion of marine organisms on the surrounding concrete wall. As a result, it was found that the removing method of the present invention is an extremely effective means.

[0040]

As described above, according to the scale removing method of the present invention, the conventional mineral acid treatment is carried out in the neutral solution of the environment in which it is anodically electrolyzed at a current of at least 5 times the normal current for a short period of time. The scale on the steel surface can be removed without using a separate process such as blasting or blasting, and without considering the troublesomeness of environmental pollution. Furthermore, after carrying out the removal method of the present invention, an electric antifouling method for preventing the growth of marine organisms can be carried out simply by reducing the current to a normal value, so that the process and construction can be shortened and performance can be improved. Stabilization can be achieved. Therefore, it is a method having great industrial and economic value.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of consumption of steel sheet and the current density in Example 1.

FIG. 2 is a graph showing the estimated black skin thickness calculated from the amount of wear in FIG. 1 in relation to the anode current density.

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[Procedure amendment]

[Submission date] January 21, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

[0026]

[Table 2]

Claims (3)

[Claims] 1. A scale-attached steel material is connected to a positive electrode of a DC power source as a positive electrode in a neutral electrolyte solution, a conductive metal body is installed on a counter electrode and connected to a negative electrode of the DC power source, and between both electrodes. A method for removing scale from a steel surface, which comprises applying an electric current. 2. The current density of the anode is 1 A / m ² or more,
The method for removing scale from a steel surface according to claim 1, wherein the amount of electricity applied is 50 AH / m ² or more. 3. The method for removing scales from the surface of a steel product according to claim 1, which is carried out as a pretreatment for preventing marine organisms from growing on the steel product.