JPH083715A - Structure for repairing cracking part of steel material - Google Patents

Abstract

PURPOSE:To easily repair the stress corrosion cracked part of a steel material developed by corrosive material mainly composed of nitric acid and to prevent the recurrence of the stress corrosion cracking from the repaired part. CONSTITUTION:After executing the ordinary seal welding to the stress corrosion cracked part 5 of the base steel material 1, a steel material 2 for repairing formed with a corrosion resistant metal layer 3 by Al thermal-spraying, and further, an acid-proof coating layer 4 composed of a heat resistant silicon on the metal layer 3, is weld-fixed to the recessed inside part of the steel material 2 for repairing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for repairing cracks generated when a corrosive substance comes into contact with a steel material, so-called stress corrosion cracking, and more specifically, NO generated in the combustion process of a blast furnace hot blast stove. _{The present invention} relates to the repair structure of the stress corrosion cracking part of the iron shell caused by _X.

[0002]

2. Description of the Related Art The iron shell of a blast furnace facility including a hot blast stove usually suffers from material deterioration due to exposure to high temperatures, thermal stress due to repeated heating / cooling of the facility or temperature difference between the inside and outside of the furnace. The environment is such that cracks are very likely to occur due to the occurrence of However, even if cracks occur during the operation of the blast furnace, it is extremely difficult to stop the operation. In order to reinforce this, welding of repair steel is carried out to prevent recurrence of cracks and repairs.

However, since the above-mentioned conventional method does not always prevent recurrence of the iron skin crack, many proposals have been made so far regarding the repairing method or the recurrence preventing method of the iron skin crack. For example, JP-A-51-112704, JP-A-51-112705, and JP-A-55-
Japanese Patent Laid-Open No. 34676 discloses a crack prevention method centered on welding that cancels the thermal stress concentration that causes the recurrence of cracks.
Japanese Patent Laid-Open Nos. 5-41958 and 4-9416 disclose methods for repairing an iron shell for the purpose of preventing recurrence of cracks, and Japanese Patent Laid-Open Nos. 49-94504 and 55-14855.
Japanese Patent Publication No. 5-52926 discloses a method for repairing a crack of a steel shell containing a fire wall protective material for a blast furnace, and Japanese Utility Model Laid-Open No. 5-54526 discloses the occurrence of a secondary crack in a hot-blast stove iron shell for a blast furnace considering relaxation of thermal stress. Preventive repair structures have been proposed.

[0004]

However, all of the conventional crack repairing methods and recurrence preventing methods for blast furnace equipment and the above-mentioned proposals use only the thermal stress as the cause of cracking, and the action of corrosive substances. There is no consideration of stress corrosion cracking including. However, it is said that nitrogen oxide NO _x is generated in the combustion process in the blast furnace, especially in the hot blast stove, and that nitric acid HNO ₃ is generated by the following reaction. N ₂ + O ₂ → 2NO NO + 1 / 2O ₂ → NO ₂ 2NO ₂ + H ₂ O → HNO ₂ + HNO ₃ 2NO ₂ + H ₂ O + 1 / 2O ₂ → 2HNO ₃ The inventors of the present invention keenly investigated cracks in the iron skin of the blast furnace hot blast furnace. Upon examination, the cause of cracking of the iron shell was not normal thermal stress, but stress corrosion cracking containing a corrosive substance whose main component was nitric acid generated in the combustion process.
It was found to be racking (hereinafter referred to as "SCC"). S due to corrosive substances such as nitric acid
In contrast to CC, the conventional repair methods and recurrence prevention methods have the drawback that secondary SCC recurs from the repaired point in any method, and the SCC
The reality is that there are few proposals regarding repair methods and recurrence prevention methods.

The present invention has been made in view of the above circumstances, and is a structure for repairing a crack portion of a steel material which is easy and excellent in recurrence prevention against SCC of a steel material generated by a corrosive substance containing nitric acid as a main component. The purpose is to provide.

[0006]

The feature of the repair structure of the present invention for achieving the above-mentioned object is to reinforce the cracks generated in the base steel material, for example, the iron skin of the hot-blast stove for blast furnace. A welding-fixed repair steel, a corrosion-resistant metal layer formed on the surface of the base steel of the repair steel, and a coating of an acid-resistant coating material formed between the corrosion-resistant metal layer and the base steel. A membrane layer and / or a filling layer.

[0007]

The function of the repair structure of the present invention is that the cause of cracks in the hot blast stove for blast furnace is SC generated by the interaction between thermal stress and corrosion.
It is considered to be C, and there is a focus on corrosive substances. Therefore, in the conventional structure focusing only on the action of thermal stress,
It is unavoidable that the corrosive substance acts on the welded portion of the repair steel and / or the repair steel itself, and the risk of SCC occurring again is extremely high.

That is, in order to effectively prevent recurrence of SCC, it is important to easily and effectively cut off the contact between the corrosive substance and the welded portion of the repair steel and / or the repair steel itself. .

Usually, when the SCC portion of the base steel material is subjected to seal welding or gouging overlay welding, the stress corrosion cracking portion 5 is projected as shown in FIG. 2, so that the inside of the repair steel material 2 is made into a concave shape. It is generally performed by working to improve the adhesion with the base steel material 1. The first constitution of the present invention is this repair steel material 2
As shown in FIG. 1, the inside of the above is formed with the corrosion resistant metal layer 3 by, for example, a thermal spraying method or a plating method. It goes without saying that this is to block the contact between the repair steel material 2 and the corrosive substance. The type of corrosion-resistant metal is not particularly limited, but Al and Al are used due to cost and availability.
Alternatively, a Ni-Cr alloy is preferable. Among these, as Ni-Cr to be subjected to the thermal spraying method, the one having a component of Ni50% -Cr50% is the most common, and this is sufficient. In the case of the thermal spraying method, the thickness of the metal layer is preferably about 200 to 500 μm, and if it is thinner than this, the durability is insufficient to block the contact with the corrosive substance. Although it seems to be effective, the effect for the purpose of the present invention is not substantially changed and the cost is increased, which is not preferable.

However, in the case of the thermal spraying method, the formed corrosion-resistant metal layer 3 is usually porous, and if it is left as it is, the corrosive substance gradually permeates through the pores into the interface between the repairing steel material and its welded portion and is sprayed. The corrosion-resistant metal layer 3 may be peeled off, or SCC may be recurred in the repair steel material 2 or the welded portion 11.

Therefore, in the second aspect of the present invention, as shown in FIGS. 1 and 3, the acid-resistant coating film layer 4 and / or the acid-resistant coating film layer 4 of the coating material having acid resistance is further provided on the corrosion-resistant metal layer 3.
Alternatively, the acid-resistant filling layer 7 is formed. By applying this, since it is possible to block the above-mentioned pores and suppress the penetration of corrosive substances, it is necessary to completely block the contact between the repairing steel material 2 or its weld 11 and the corrosive substances. You can The coating layer and the filling layer are applied not only to the corrosion-resistant metal layer formed by the thermal spraying method but also to the metal layer formed by another method such as the plating method, especially for the SCC of the welded portion of the repair steel material. It is effective in preventing recurrence.

This coating material is formed by applying the corrosion resistant metal layer and then forming it as an acid resistant coating layer 4 and welded to the stress corrosion cracking portion 5 of the base steel material 1 as shown in FIG. It may be fixed, or as shown in FIG. 3, after the repair steel material 2 having the corrosion resistant metal layer formed thereon is fixed by welding, it is injected and filled from an injection hole 6 provided in the repair steel material to form an acid resistant filling layer 7. You may form as. Alternatively, the acid resistant coating layer 4
It is even more effective if the acid-resistant filling layer 7 is used together.

As the coating material, when the operating temperature of the repair section is room temperature or a temperature close to room temperature, it only needs to have acid resistance, but when it is at a high temperature, for example, in the case of a blast furnace hot blast stove, it is normal. 50 to 8 as the outermost surface temperature in the operating state
Epoxy resin or acrylic resin that can withstand 0 ° C., or heat-resistant silicone resin that can withstand up to about 300 ° C. is preferable in consideration of abnormal cases such as damage to the refractory inside. Further, when the temperature is high, the Cr / Ni ratio is 1 instead of forming the corrosion resistant metal on the repair steel material.
8/8 stainless steel, eg SUS304 or 31
It is also possible to use those obtained by lining 6 or the like, but since these are not always sufficient for the acid resistance of the present purpose, it is preferable to lining a high Ni corrosion resistant steel with a Ni content of 42% or more. Good to use. Also, FIG.
The inert gas of a pressure slightly higher than the operating pressure in the furnace, for example, nitrogen gas, is injected into the gap between the repair steel material 2 and the weld repair portion of the stress corrosion cracking portion 5 as shown in FIG. Although a method of suppressing the permeation of the corrosive substance can be considered, this requires a pipe, a gas source, etc., and is costly and not practical for this purpose.

The method of the present invention is not limited to the cracking of the skin of the hot-blast stove for a blast furnace, and is extremely effective for repairing SCC by a corrosive substance containing an acidic substance such as nitric acid as a main component. .

[0015]

EXAMPLES Examples of the present invention will be shown below. Example 1 After repairing the SCC part of the hot-blast stove for a blast furnace by seal welding, Al spraying and Ni-Cr spraying were both performed on the surface of the repaired steel material 2 processed into a concave shape based on FIG. 1
After applying a thickness of 00 μm to form the corrosion resistant metal layer 3, a heat resistant silicone resin was further applied thereon to form the acid resistant coating layer 4. This was welded and fixed to the repair part. In addition, as a comparative example, a conventional repair steel material in which neither the metal layer nor the coating layer was formed was also prepared, and this was also welded and fixed to the repair portion. As a result, in the repair structure of the present invention in which the metal layer and the coating layer are formed, no change is observed even after 24 months have passed, whereas in the conventional repair structure, 12 months after the repair. After the lapse of time, S is again applied from the welded portion of the repair steel material.
Occurrence of CC was observed. Example 2 After repairing the SCC portion of the hot-blast stove for a blast furnace by seal welding, Al spraying and Ni-Cr spraying were both performed on the surface of the repaired steel material 2 processed into a concave shape based on FIG. 1
After applying a thickness of 00 μm to form the corrosion-resistant metal layer 3, this was welded and fixed to the repaired portion. After that, a heat-resistant silicone resin was press-fitted through an injection hole 6 provided in the repair steel material to form an acid-resistant filling layer. Then, the nozzle of the injection hole 6 was cut from the root of the repair steel material 2 to smooth the surface of the repair steel material 2. In this case as well, as a comparative example, a conventional repair steel material in which neither the metal layer nor the filling layer was formed was prepared, and this was also welded and fixed to the repair portion. As a result, in the repair structure of the present invention in which the metal layer and the filling layer are formed, no change is observed even after 24 months have passed, whereas in the conventional repair structure, 12 months have passed since the repair. After that, generation of SCC was again seen from the welded portion of the repair steel material.

[0016]

As described in detail above, in the repair structure of the present invention, the cause of cracks in the hot blast stove for blast furnace is considered to be SCC generated by the interaction between thermal stress and corrosion, and attention is paid to corrosive substances. Is constructed so as to block the contact between the welded portion of the repair steel and / or the repair steel itself, so that SCC generated by a corrosive substance containing an acidic substance such as nitric acid as a main component is removed. It can be easily repaired, and recurrence of SCC from the repaired part can be effectively prevented.

[Brief description of drawings]

FIG. 1 is a view showing a repair structure including a corrosion resistant metal layer and an acid resistant coating layer according to the present invention.

FIG. 2 is a view showing a repair structure composed of conventional seal welding and repair steel material.

FIG. 3 is a view showing a repair structure including a corrosion resistant metal layer and an acid resistant filling layer according to the present invention.

FIG. 4 is a conceptual diagram of a method of suppressing the permeation of corrosive substances from the inside by injecting an inert gas having a pressure slightly higher than the operating pressure in the furnace.

[Explanation of symbols]

1. Mother steel, 2. Steel for repair, 3. 3. Corrosion resistant metal layer, 4.
Acid resistant coating layer, 5. Stress corrosion cracking part, 6. Injection hole, 7.
Acid-resistant packed bed, 8. Gas injection tube, 9. Inert gas mains,
10. Monitoring pressure gauge, 11. welded part

Claims (2)

[Claims] 1. A repair steel material fixed by welding to reinforce cracks generated in the base steel material, a corrosion resistant metal layer formed on the surface of the repair steel material on the base steel material side, a corrosion resistant metal layer and a base steel material. And a coating layer and / or a filling layer of a coating material having acid resistance formed between the coating material and the coating layer, and a repair structure for a crack portion of a steel material. 2. The repair structure for a cracked portion of a steel material according to claim 1, wherein the base steel material is an iron shell of a hot blast stove for a blast furnace.