JPH06346261A - Method for dissolving scale - Google Patents

Abstract

PURPOSE:To remove metal oxide-contg. scale from the surface of a metal. CONSTITUTION:When metal oxide-contg. scale sticking to the surface of a metal is removed by using a detergent based on phosphonic acid and/or its salt in a neutral region (pH 5-9), powder or granules of a metal such as iron are dispersed in a washing liq. and the scale is dissolved and removed. Scale dissolving ability is enhanced and washing time is considerably shortened.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for removing scales containing oxides of metals from the surface of metals.

[0002]

2. Description of the Related Art Conventional general scale remover is hydrochloric acid,
It can be roughly classified into inorganic acids such as sulfuric acid and organic acids such as citric acid and hydroxyacetic acid. Both inorganic and organic acids are formed by adding various auxiliaries in order to suppress the corrosion of the metal substrate or to accelerate the dissolution of oxides. Generally speaking, the cost of inorganic acid is low, and the dissolving power of iron oxide etc. is large, but on the other hand, depending on the type of metal material to be cleaned, there is a risk of hydrogen embrittlement and overpickling, making the neutralization process difficult. However, since it is strongly acidic, it has problems such as handling hazards and pollution of the environment due to the generation of gas and mist. In order to avoid these problems, cleaning with an organic acid is performed. However, since it has a low dissolving power for iron oxide and the like in the normal temperature range, it needs to be heated to 70 ° C. or higher, and has the disadvantages of high cost, but it has a gradual action on the constituent metal material to be washed, It has features such as easy neutralization process. Among them, the feature that phosphonic acid or a salt thereof dissolves iron oxide in a weakly acidic and neutral range is noted as an extremely safe scale removing agent, and some proposals regarding this have been made in the past. For example, JP-B-55-5400 discloses that by adding a ferrous salt to phosphonic acid, the cleaning time can be significantly shortened at a temperature lower than the conventional organic acid cleaning temperature. US Pat. No. 4,810,405. In addition, it is possible to obtain effective rust removal and a passivated surface by adding a reducing agent, a corrosion inhibitor, and a surfactant to phosphonic acid. Japanese Patent Publication No. 56-34637 discloses phosphonic acid and a carbonate solution. It has been proposed to dissolve iron oxide, and then make the solution alkaline to dissolve metallic copper.

[0003]

As in the conventional method, a detergent containing phosphonic acid and / or phosphonate as a main component is used in a neutral region (pH: 5 to 9) to remove metal from the surface of the metal. In the case of removing the scale containing oxides of the above, the dissolution of the scales is promoted by the cleaning liquid coming into direct contact with the metal surface substrate through the scale containing oxides of the metal. Therefore, in a system in which the cleaning liquid and the metal surface substrate are completely blocked by the scale, the dissolution rate of the scale containing a metal oxide such as iron is extremely reduced, which is not practical.

In view of the above-mentioned state of the art, the present invention is to provide a scale removing method which can solve the problems of the scale dissolving method using a detergent containing phosphonic acid and / or phosphonate as a main component.

[0005]

The present invention provides a detergent containing phosphonic acid and / or phosphonate as a main component in a neutral region (p
H: 5-9), in a method for removing a scale containing a metal oxide attached to a metal surface, a metal powder or metal particles such as iron are dispersed and mixed in a cleaning liquid. It is a dissolution method.

The phosphonic acid used in the present invention is, for example, 1
-Organophosphonic acids such as hydroxyethylidene-1,1-diphosphonic acid, ethylenediamine-3-phosphonic acid and triaminomethylphosphonic acid and / or water-soluble salts thereof such as sodium, potassium and ammonium.

[0007]

When a detergent containing phosphonic acid and / or phosphonate as a main component is used in a neutral range (pH: 5 to 9) to remove the scale containing metal oxide from the surface of the metal, It is considered that the surface substrate plays a very important role, but its mechanism of action is not clear. In any case, in order to obtain a good cleaning effect, an environment in which the cleaning liquid and the metal surface base material are in direct contact is necessary. Therefore, it is necessary to form an environment in which the cleaning liquid and the metal surface substrate are in direct contact with each other by dispersing and mixing metal powder or metal particles such as iron in the cleaning liquid (cleaning system). Also, when the cleaning system is put into a fluidized state using a circulation pump or the like, the metal powder or metal particles such as iron physically destroys the scale on the metal surface, forming a portion where the cleaning liquid and the metal surface substrate are in direct contact. Is a particularly preferred method.

[0008]

[Example] Outer diameter: 50 mm of a straight pipe part of a water pipe (with rust bumps and thick scale adhered on the inner surface)
Using a scale dissolution test apparatus (flow rate: 1 m / s, normal temperature) shown in FIG. 1, a test tube cut into a length of 00 mm was subjected to a dissolution test for about 10 hours with various test solutions. In FIG. 1, 1 is a circulation tank, 2 is a circulation pump, 3 is a test tube, and 4 is a plastic pipe.

Test liquid (1-hydroxyethylidene-1,
The composition of 1-diphosphonic acid) and the test results are summarized in Table 1 below. In both of the cases where iron powder was used in combination, the pipe inner surface scale could be completely removed, but in the case where iron powder was not used together, the pipe inner surface scale was Almost could not be removed.

[0010]

[Table 1]

[0011]

According to the present invention, a detergent containing phosphonic acid and / or phosphonate as a main component is added to a neutral range (pH: 5 to 5).
When used in 9) and removing scales containing metal oxides from the surface of metal, the scale dissolving power is improved by dispersing and mixing metal powder or metal particles such as iron in the cleaning system, and the cleaning time is greatly increased. Can be shortened to

[Brief description of drawings]

FIG. 1 is an explanatory view of a scale dissolution test apparatus for demonstrating the effect of the method of the present invention.

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

Claims (1)

[Claims] 1. A method for removing scales containing a metal oxide attached to a metal surface by using a detergent containing phosphonic acid and / or phosphonate as a main component in a neutral region,
A method for dissolving a scale, characterized in that metal powder or metal particles are dispersed and mixed in a cleaning liquid.