JPS602390B2 - Chemical cleaning method for steel parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chemical cleaning method for descaling and rust-proofing steel members including steel equipment using a single solution.

Traditionally, it has been used to prevent corrosion due to scale and rust in systems through which water or steam passes through, such as steam generation plants and chemical plants, or to improve thermal conductivity for boilers and other steel equipment in thermal power plants after operation. For the purpose of
After acid cleaning, thoroughly drain the acid solution by washing with water,
Finally, an anti-mirror treatment protects the cleaned surface, which has been cleaned by pickling, from rust.

Specifically, there are methods such as 'a' and {b- shown in Table 1 as chemical cleaning methods from acid cleaning to rust prevention treatment, but all of them have the following drawbacks. .

{1} The chemical cleaning process consists of four steps: acid cleaning → water washing → citric acid rinsing → neutralization rust prevention, so it is not only complicated due to the large number of steps, but also the processing from water washing to neutralization rust prevention. It takes dozens of hours, often all night, and requires a great deal of labor and expense.

[21 The amount of waste liquid from chemical cleaning, from acid cleaning to neutralization and anti-corrosion treatment, is approximately four to five times the amount of water held by the equipment being cleaned due to the complicated process. It takes.

Table 1 In addition, after adding an oxyacid of dibasic acid or more to a mineral acid and acid washing, without discharging the acid solution, add an alkali to the acid solution to neutralize it, and then add a rust preventive agent. An acid cleaning method for preventing rust is known from Japanese Patent Publication No. 46-16401.

In this method, scale is removed using key acid, and the eluted iron ions are sequestered using the above-mentioned oxyacid. However, if key acid remains after washing with water after rust prevention treatment, CI caused by this mineral acid -, S- not only becomes a corrosion factor for steel materials during boiler operation, but if sodium carbonate, sodium hydroxide, alkaline sodium phosphate, etc. of the alkali added as a neutralizing agent remain, it will cause damage to high-temperature and high-pressure boilers. In this case, there are disadvantages such as condensation in the high-temperature part of the boiler evaporation tube during operation, which can cause alkali corrosion. It is necessary to completely remove these factors.

The present invention has been made in view of the above points, and the chemical cleaning process of steel members is made into two steps: a mirror removal/descaling process and a rust prevention treatment process, and these two steps are combined with the above-mentioned known method. The purpose of the present invention is to provide a chemical cleaning method that can be carried out rapidly and easily using substantially one liquid, and is free from the disadvantages described above.

That is, the present invention provides p
After descaling with a solution of at least one organic acid selected from citric acid, malic acid, glyconic acid, and glycolic acid with H adjusted to 3.0 to 3.5, polyphosphate and ultra phosphate are added to the same solution. Rust prevention by adding at least one type of Doai phosphate from acid salts and metaphosphates and at least one pH adjuster from aqueous ammonia, ethanolamine, and hydrazine to adjust the pH to 5 or higher. The present invention relates to a method for cleaning steel members, which is characterized by a method of cleaning steel members.

The effects of each chemical used in the method of the present invention will be explained below.

○}Organic acid: In the present invention, sulfamic acid, tartaric acid, citric acid, malic acid, glyconic acid, and glycolic acid can be used, and the latter four are adjusted to pH 3.0 to 3.5 by adding aqueous ammonia. I'll keep it.

The main purpose of the organic acid of the present invention is to dissolve iron scale and descale it. It has low dissolving power and cannot completely descale when used as is.

However, as a result of research by the present inventors, it has been found that if these are adjusted to an axis of 3.0 to 3.5 with aqueous ammonia, the ability to dissolve iron scale increases significantly. It is based on this knowledge that ammonia water is added to the latter four to adjust the feed. In addition to descaling steel equipment, the purpose of these organic acids is to prevent precipitation of eluted iron during rust prevention treatment after adding a pH adjuster, so the optimum concentration of organic acids to be used depends on the amount of iron scale. It is preferable to decide.

By the way, in the case of a boiler of a thermal power plant to which the method of the present invention is applied, the amount of iron eluted by acid cleaning is usually within the range of 3000 to 800Q, so the organic acid concentration for dissolving iron scale is 2 to 100%. However, in the method of the present invention, after scale removal, spot-adjusting new and old skin dori phosphate is directly added to the acid solution to adjust the pH to 5 or more, preferably 6 to 8, and perform rust prevention treatment, so that the iron ions eluted at that time are The organic acid concentration must be high enough to prevent precipitation.

The sequestering power of organic acids against iron ions differs depending on the type of rust preventive vessel, the higher the pH, the lower the sequestering power, and it also varies depending on the type of organic acid.

Therefore, when chemically cleaning equipment with a large amount of iron scale, it is necessary to use organic acids with high sequestering power.When the concentration of each organic acid is the same, citric acid>glyconic acid>
The order is malic acid > sulfamic acid > glycolic acid > tartaric acid. If the organic acid concentration is insufficient relative to the amount of eluted ions, the sealing power will be lost during rust prevention treatment and iron hydroxide will precipitate, which will not only contaminate the cleaning surface but also have a negative effect on the chemical formation of the rust prevention film. It is necessary to select organic acids and spots during rust prevention treatment depending on the amount of iron scale in steel equipment.
Note that the organic acid can also be used in combination with an acid corrosion inhibitor, and conventionally known ones can be used as the acid corrosion inhibitor.

For example, Hibilon K-4, which is an amine-based pickling anticorrosive,
Hibiron K-150 (manufactured by Sugimura Chemical Industries, Ltd., trade name), Ebitsu 3M rudder (manufactured by Sumitomo Chemical Industries, Ltd., trade name), etc. can be used. '2' Doai phosphate Polyphosphoric acid salt is Na, K salt of polyphosphoric acid [general formula MM2Pn○kiju, M: monovalent cation, oxide molar ratio M20/P205=1-2 ], ultra phosphate Na
, K salt [general formula (xM20) P205, M: monovalent cation, 0 x <1], Na, K salt of metaphosphoric acid [general formula Mn (P03) nM: monovalent intestinal ion, oxidation molar ratio M
20/P205=1] is effective.

The concentration of addition is 0.05-0. A concentration of about 100 t% is sufficient; too high a concentration is not preferable because the rust preventive film lacks granularity and the rust preventive effect decreases. The rust prevention mechanism during the rust prevention treatment of the present invention is not clear, but since the chemical formation state of the rust prevention film differs depending on the base, in a solution with an appropriate pH, the rust phosphate will dissociate moderately and react with the steel surface. Insoluble ferric phosphate [FeHP04] and tertiary iron phosphate [Fe3(P04)]
This is thought to be due to the formation and crystallization of passive suppuration on the steel surface.

The polymerized phosphate salt may be used from the beginning by being added to the organic acid separately from the spot-controlling agent. [31 Spot Control Agent The spot control agent added during the above-mentioned rust prevention treatment is at least one of aqueous ammonia, monoethylamine, jetteramine, triethylamine, and hydrazine.

After these are descaled with an organic acid, they may be added to the solution simultaneously or sequentially with Doai phosphate to adjust the bait of the antirust treatment solution to 5 or more, preferably 6 to 8.

If the number of spots is less than 5, the rust preventive film lacks granularity and the rust preventive effect is reduced, which is not preferable. Moreover, when the degree of mottling exceeds 9, the amount of formation of the rust-preventing film is small and the rust-preventing effect is poor. Hereinafter, the method of the present invention will be explained in further detail by giving examples.

Example Table 2 Acid solution (citric acid, malic acid, glyconic acid, glycolic acid were adjusted in advance to feed 3 with ammonia water) 120 yen and sour food suppressant Hypi.

K-4 (manufactured by Sugimura Chemical Industry ■, product name) at 0.0%
A boiler tube (outer diameter 31.8◇, inner diameter 2
00 was cut into 5-arc lengths, the outer surface of the tube was cut to remove the scale), and the tube was immersed to give 85 to 90
It was kept at ℃ for 6 hours. Next, Doai phosphate and a spot control agent were added to the same acid solution to adjust it as shown in Table 2, and anti-corrosion treatment was carried out at 80 qo for 2 hours. After the anti-rust treatment, the test pieces were rinsed with water and air-dried, and an explosion test was conducted on the rooftop to evaluate the anti-rust effect with the naked eye. As shown in Table 2, scale removal is complete with any organic acid, but the effective scale during rust prevention treatment is in the range of 5 to 9, as is clear from the mirror-proofing effect; is particularly preferred.

It can also be seen that if iron precipitates are formed during rust prevention treatment, the rust prevention effect is lost even within the appropriate bait range. Precipitate formation affects organic acid concentration and feed, and if the iron ions eluted by acid washing exceeds 600 ml, citric acid,
Glycolic acid and tartaric acid, excluding malic acid, sulfamic acid, and glyconic acid, reduce the pH during rust prevention treatment to 6 to 8, which eliminates the formation of iron precipitates, reduces the concentration of organic acids, and improves the rust prevention effect. I understand. 2nd table 甭电子calculated by Mina {Kashiya Zōsō sōgān sanfū komei mother of the above-mentioned building hi〃 1
As detailed above, the present invention is most suitable as a chemical cleaning method for boilers, heat exchangers, and other steel members of thermal power plants, chemical plants, etc. when newly installed and after operation. Since it is a two-step IG cleaning method that does not require water rinsing after cleaning, the time required for chemical cleaning can be shortened to approximately 1'2 compared to conventional methods, resulting in significant savings in labor and labor costs. '2} Since the method of the present invention is a two-step, essentially one-component method, the amount of waste liquid generated by chemical cleaning is reduced to about 1/2 compared to the conventional method, and the cost required for processing the waste liquid is also reduced by almost half. do.

This has an extremely remarkable effect industrially.

Furthermore, compared to the method of Japanese Patent Publication No. 46-16401, the method of the present invention not only does not use mineral acids at all, but also does not use mineral acids at all in the high-temperature liquid even if they remain as pH adjusters during rust prevention treatment. Because we use materials that decompose into harmless substances,
Washing with water is simple, and the amount of water used and washing time may be small. ■ The antirust effect of known methods is based on what is generally called a nitrite film, but the method of the present invention uses passivation of iron phosphate. It is based on a film, and the rust prevention effect is about 1. This has the effect of increasing the needle sound.

Claims (1)

[Claims] 1 Add at least one of sulfamic acid, tartaric acid, and/or aqueous ammonia to adjust the pH to 3.0 to 3.
．． After descaling with a solution of at least one organic acid selected from citric acid, malic acid, glyconic acid, and glycolic acid adjusted to 5%, polyphosphate, ultraphosphate,
At least one kind of polymerized phosphate among metaphosphates and at least one kind of pH adjuster among aqueous ammonia, ethanolamine, and hydrazine are added to adjust the pH to 5 or higher for rust prevention treatment. Characteristic chemical cleaning method for steel parts.