JPH093670A - Method for removing scale containing metal oxide - Google Patents

Abstract

PURPOSE: To provide a method by which scale is removed from the surface of iron base metal on which the scale containg metal oxide is stuck on the surface of an ion base metal and also, the resulting surface can be subjected to rustproof treatment. CONSTITUTION: An ion base metal on the surface of which scale contg. metal oxide is stuck is immersed in a cleaning solution that is prepared by dissolving at least one sulfonic acid compound in water and adjusting the pH of the resulting solution to a value within the range of 5.5 to 7.5, to dissolve and remove the scale contg. metal oxide. Then, pH of the cleaning solution is adjusted to a value within the range of 8.0 to 9.5 to perform rustproof treatment of the surface of the iron base metal. Thus, this method has the advantages of enabling the use of a solution that has a nearly neutral pH as the cleaning solution, a high safty scale-removing operation at ordinary temp., operations of both the cleaning and the rustproof treatment in the same vessel, etc.

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 containing metal oxides, and more specifically to removing scales from the surface of an iron-based metal to which scales containing metal oxides are attached, as well as performing anticorrosion treatment. The present invention relates to a method for removing a scale containing a metal oxide that can be used.

[0002]

2. Description of the Related Art As a conventional general method for removing scale from a metal surface, there is a method of cleaning with an inorganic acid or an organic acid. In these methods, an acid as shown in Table 1 is used as a cleaning agent, and the type and concentration of the chemical agent are determined according to the type and situation of the object to be cleaned. In addition,
In terms of steps, in any method, a washing step at a pH of 4 or less, a water washing step, a neutralizing step, a rinsing step, a rust-preventing treatment step using hydrazine, sodium nitrite, etc. are performed.

[0003]

[Table 1]

[0004]

The conventional cleaning methods using inorganic acids and organic acids have the following problems. (1) The acidity of the cleaning liquid is high (pH 4 or less), and there is a concern of over-pickling. (2) There is a risk of hydrogen embrittlement. (3) In addition to acid cleaning, a rust prevention process is required, and the work process is complicated. (4) Handling the acid cleaning solution is dangerous. (5) Construction sites are limited because there is a risk of polluting the environment due to generation of acid gas or leakage of acid liquid. The present invention provides a method for removing a scale containing a metal oxide, which does not have the above problems.

[0005]

Means for Solving the Problems The present invention provides (1) one or two types of scale-containing iron-based metal containing a metal oxide.
One or more phosphonic acid compounds are dissolved in water to adjust the pH to 5.5.
The scale containing the metal oxide is dissolved and removed by immersing in a cleaning solution adjusted to a range of 7.5, and then the pH of the cleaning solution is adjusted to 8.
A method for removing scale containing metal oxides, characterized in that the surface of an iron-based metal is rust-proofed by adjusting it in the range of 0 to 9.5, and (2) the pH of the cleaning solution after rust-proofing is performed again. The method for removing a scale containing a metal oxide according to the above (1) is characterized in that it is adjusted to a range of 5.5 to 7.5 and reused.

As the phosphonic acid compound used in the present invention, aminotrimethylenephosphonic acid, aminotrimethylenephosphonic acid pentasodium salt, 1-hydroxyethylidene-1,1-diphosphonic acid, 1-hydroxyethylidene-1,1- Diphosphonic acid trisodium salt, 1-hydroxyethylidene-1,1-diphosphonic acid tetrasodium salt,
Ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid 7 sodium and the like can be used. In the method of the present invention, one or more kinds of these phosphonic acid compounds are dissolved in water to form a cleaning liquid. The concentration of the phosphonic acid compound in the cleaning solution is 0.1% by weight
If it is more than the above, it is preferably 0.5 to 50% by weight,
More preferably, it is 1 to 20% by weight.

The pH of this cleaning solution is adjusted to a range of 5.5 to 7.5, and the scale containing metal oxide is dissolved and removed by immersing the iron-based metal to which the scale containing metal oxide is attached. You can If the pH is less than 5.5, the acidity is too strong to cause the same problem as in the conventional pickling, and if it exceeds 7.5, the ability to dissolve metal oxides is lowered, which is not preferable. The temperature during washing is in the range of 0 to 100 ° C. Since the scale containing the metal oxide adhered to the surface of the iron-based metal is dissolved and removed by this cleaning treatment, it may be lifted as it is and washed with water. However, in the method of the present invention, the pH of this cleaning solution is further adjusted to 8.0-9. The anticorrosion treatment can be performed by adjusting the range to 0.5 and immersing the metal after the scale removal in this. Anticorrosion treatment temperature is 0-100 ℃
It is preferable to set it in the range. The dissolution removal of the scale and the rustproofing treatment may be performed in separate treatment tanks, but normally the pH may be adjusted as it is after the dissolution removal of the scale is completed. The pH of the cleaning liquid after the anticorrosion treatment is 5.5 to 7.
By adjusting to the range of 5, it can be reused as a cleaning solution for scale dissolution.

In order to adjust the pH of the cleaning liquid, sulfuric acid, hydrochloric acid, sodium hydroxide, potassium hydroxide or the like inorganic acid or inorganic alkali agent or gluconic acid, oxalic acid, acetic acid, alkanolamine, ammonia or the like organic acid or organic alkali agent Can be used. If the pH at the time of rust prevention exceeds 9.5, handling the liquid is dangerous and it takes time to neutralize the drainage, which is not suitable. Further, in order to promote the cleaning effect of the cleaning liquid, an oxidizing ion such as Cl ⁻ can be added and used.

[0009]

The mechanism of scale removal and rust prevention in the method of the present invention is not clear, but the phosphonic acid compound used in the present invention is strong against metal oxides even in the pH range of 5.5 to 7.5. Has the ability to dissolve,
At a pH of 8.0 or higher, it has almost no dissolving ability and is considered to have a rust preventive effect.

[0010]

EXAMPLES The method of the present invention will be described more specifically with reference to the following examples. Example 1 A test piece (structural steel: JIS-G-3101, JIS-G-3101, 2) in which 300 ml of each of the 12 kinds of phosphonic acid compound solutions shown in Table 2 was placed in a 500 ml beaker, was forced. Seed, size 40 x 75 x 4 mm, exposed to the atmosphere for 3 weeks after blasting) were used for 2 minutes each and a dipping test (room temperature, standing state) for 30 minutes was performed, and the test piece was removed after the dipping test. The scale situation was observed. In addition, in order to confirm the rusting condition after the treatment for those that could be completely descaled, the test piece taken out of the solution as it was after descaling and left for 1 hour in the atmosphere, and the pH of the solution were 8.5.
The rusting conditions of the test pieces that were taken out and left in the atmosphere for 1 hour after the adjustment was compared. The descaling status and rusting status in each test example are as shown in Table 3. In addition, hydrochloric acid or sodium hydroxide was used for pH adjustment of each solution.

[0011]

[Table 2]

[0012]

[Table 3] [Remarks] (1) Evaluation criteria for descaling status: Completely descaled: ○ Not descaled: × (2) Evaluation criteria for rusting status: No rusting: ○ Rusted There are: ×

[0013]

The method for removing metal oxide scale of the present invention has the following advantages. (1) Since the descaling effect is exhibited even in the vicinity of neutrality (pH 5.5 to 7.5), the treatment operation is easy. (2) Since the pH of the cleaning liquid is around neutral and it can be applied at room temperature, it is highly safe. (3) There is no risk of causing hydrogen embrittlement. (4) It has sufficient descaling performance even at room temperature and does not necessarily require a heating operation. (5) Since there is no generation of pickling gas or leakage of strongly acidic liquid, the environment is not polluted and the construction site is not limited. (6) Cleaning and anticorrosion treatment can be continuously performed in the same tank, and the work process is simple.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Watanabe 5-717-1 Fukahori-cho, Nagasaki-shi, Nagasaki Sanryo Heavy Industries Ltd. Nagasaki Research Institute (72) Inventor Akihiro Sakanishi 5-717, Fukahori-cho, Nagasaki-shi, Nagasaki Prefecture No. 1 Sanryo Heavy Industries Co., Ltd. Nagasaki Research Institute (72) Inventor Shuji Makiura 1-1, Atsunoura-machi, Nagasaki, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (72) Inventor Shigenori Fukuoka Nishikujo, Nara, Nara Prefecture 5-2-2, Kyoeisha Chemical Co., Ltd. Nara Research Institute (72) Hideki Tezuka 5-2-5, Nishikujo-cho, Nara City, Nara Kyoeisha Chemical Co., Ltd. Nara Research Center

Claims (2)

[Claims] 1. A cleaning liquid in which a scale-containing iron-based metal containing a metal oxide is dissolved in water to adjust the pH to a range of 5.5 to 7.5 by dissolving one or more phosphonic acid compounds in water. Metal oxide characterized by carrying out rust-prevention treatment on the surface of iron-based metals by immersing and removing scales containing metal oxides, and then adjusting the pH of the cleaning liquid in the range of 8.0 to 9.5. A method for removing scales containing matter. 2. The pH of the cleaning liquid after the anticorrosion treatment is adjusted to 5.5 again.
The method for removing a scale containing a metal oxide according to claim 1, wherein the method is adjusted to a range of to 7.5 and reused.