JPS602391B2 - 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 machinery using a single solution.

For the purpose of preventing 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 the thermal conductivity of boilers and other steel equipment in thermal power plants after operation. After the scale and rust are completely removed by acid cleaning, the acid solution is thoroughly drained by washing with water, and finally the cleaned surface is protected from mirrors by anti-corrosion treatment.

Specific chemical cleaning methods from acid cleaning to rust prevention treatment include methods such as {a} and 'b) shown in Table 1, 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 and rust prevention, so it is not only complicated due to the large number of steps, but also the process from water washing to neutralization and rust prevention. Processing takes dozens of hours, often overnight, and requires a great deal of labor and expense.

[21 The amount of waste liquid from Ihigaku cleaning, from acid cleaning to neutralization and anti-bell treatment, is 4 to 5 times the amount of water held by the equipment being cleaned due to the complicated process, and it takes a lot of effort and money to process the waste liquid. It takes.

Table 1 Also, after adding an oxyacid of dibasic acid or more to potic acid and washing with acid, add an alkali to the brewing liquid to neutralize it without discharging the acid solution, and apply a rust preventive to Zara. An acid cleaning method in which rust prevention is carried out by adding oxidants is known from Japanese Patent Publication No. 46-16401.

In this method, scale is removed using key acid, and iron ions eluted are sequestered using the above-mentioned oxyacid. However, if ferrous acid remains after washing with water after the rust prevention treatment, CI due to this stannic acid is removed. -, S042- not only becomes a corrosion factor for steel materials during boiler operation, but also when sodium carbonate, sodium hydroxide, alkaline sodium phosphate, etc. of the alkali added as a neutralizing agent remain, in the case of high temperature and high pressure boilers. There are disadvantages such as condensation in the high-temperature parts of the boiler evaporation tube during operation, which causes alkali corrosion. Needs to be completely removed.

The present invention has been made in view of the above points, and the chemical cleaning process for steel manufacturing is made into two processes: a rust removal/descaling process and a rust prevention treatment process, and these two processes are combined with the above-mentioned known method. The object of the present invention is to provide a chemical cleaning method that can be carried out rapidly and easily using substantially one solution without the above-mentioned drawbacks. That is, the present invention provides citric acid, malic acid, glyconic acid, and glycolic acid whose pH is adjusted to 3.0 to 3.5 by adding at least one of sulfamic acid and tartaric acid and/or aqueous ammonia. After descaling with at least one organic acid solution, add ammonia water,
At least one bait conditioner selected from ethanolamine and hydrazine and at least one type of phosphate and nitrite selected from polyphosphates, ultraphosphates, and metaphosphates are added to adjust the pH. This invention relates to a scientific cleaning method for steel members, which is characterized by carrying out anti-corrosion treatment with a corrosion resistance of 5 to 9.

The effects of each chemical used in the method of the present invention will be explained below. {1'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 can be adjusted to PN3.0 to 3.5 by adding aqueous ammonia. Adjust 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 conducted by the present inventors, it has been found that when these are adjusted to pH 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 prepare the base. In addition, the purpose of these organic acids is to descale iron and steel equipment as well as to precipitate and block eluted iron during rust prevention treatment, so the optimum concentration of organic acids to be used is determined by the amount of iron in the scale. preferable.

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 iron eluted by acid washing is usually in the range of 3000 to 800 ml, so the organic acid concentration for dissolving iron scale may be 2 to 3 wt%. However, in the method of the present invention, after scale removal, a pH adjuster, Doai phosphate, and nitrite are directly added to the acid solution to adjust the pH to a range of 5 to 9 and perform rust prevention treatment, so that the eluted iron ions 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 an organic acid with a high sequestering power.The superiority of these acids is determined by the following formula: <Etic acid > Glyconic acid > Apple acid The order is acid>sulfamic acid>glycolic acid>tartaric acid. If the organic acid concentration is insufficient for eluted iron ion particles, 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. Therefore, it is necessary to select an organic acid and a material 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,
Hibilon K-150 (manufactured by Sugimura Chemical Industry ■, trade name), Vivit 3M (manufactured by Sumitomo Chemical Industry ■, trade name), etc. can be used. [2' Gear phosphates and nitrites Gear phosphates and nitrites act as rust preventive agents during rust prevention treatment.
Salt [general formula MM2PnQn10, M: monovalent cation,
Oxide molar ratio M20/P205co1-2], Na, K salt of ultraphosphoric acid [general formula (vs. M20) P2Q, M:1
valent cation, 0<x<1], Na, K salt of metaphosphoric acid [general formula Mn (P03).

M: monovalent intestinal ion, oxide molar ratio M20/P205=
1] etc. are effective, and Na and K salts are effective as nitrites. The concentration of polymerized phosphate added is around 0.1 wt%, and the concentration of nitrite added is 0.02 to 0.1 wt%.
It may be about 1 wt%.

If the concentration of nitrite is too high, the pH during rust prevention treatment should be adjusted to 5.
In the case of 6 to 6, the corrosion of the steel surface will increase and the rust preventive film will lack granularity, reducing the rust preventive effect, so in such cases, about 0.02 to 0.05 wt% is sufficient. Yes, P
In the case of H7-9, it may be 0.02-0.1 wt%. The rust prevention mechanism during the rust prevention treatment of the present invention is not clear, but by adding the two types of Atsumi phosphate and nitrite together, the rust prevention is more effective than using Doai phosphate or nitrite alone. The effect increases by 1.5 to 2 times, and the surface condition of the chemical conversion coating is very fine and exhibits a glossy interference color. Therefore, in a suitable axial solution, polymerized phosphate reacts with the steel surface. When a passivation film of unrelated iron phosphate (FeHP04) and iron tertiary phosphate (Fe3(P04)2) is formed on the steel surface and crystallized, nitrite is responsible for the formation of the conversion film. This is thought to be because it acts as a promoter. '3} PH adjuster The pH adjuster added during the above rust prevention treatment is at least one of aqueous ammonia, monoethanolamine, digital/alamine, triethanolamine, and hydrazine.

These can be descaled with an organic acid and then added to the same solution simultaneously or sequentially with phosphate and nitrite to adjust the bait of the rust prevention treatment solution to 5 to 9, preferably 6 to 8. .

If the amount of bait used in the rust prevention treatment is less than 5, corrosion of the steel material increases, the rust prevention film lacks granularity, and the rust prevention effect decreases, which is not preferable. Moreover, if the pH exceeds 9, the amount of chemical conversion of the anti-mirror film will be small and the rust-preventing effect will be poor. Hereinafter, the method of the present invention will be explained in further detail by giving examples.

The acid corrosion inhibitor Hibiron K-4 (Sugimura Chemical Co., Ltd. product name) is 0. A poira tube (outer diameter 31.80 mm, inner diameter 200 mm) with scales mainly composed of triiron tetroxide (Fe304) attached to the solution containing [%] was added to the tube. (from which the external scale was removed) was soaked and held at 85 to 90°C for 6 hours.

Next, a crucian carp conditioner, a seaweed phosphate, and a nitrite were added to the same acid solution, and the mixture was adjusted as shown in Table 2, followed by antirust treatment at 80 to 8yo for 2 hours. After the anti-rust treatment, the test pieces were rinsed with water, allowed to dry naturally, and subjected to an antworm test on the rooftop to evaluate the anti-rust effect with the naked eye. The results are shown in Table 2, although scale removal is complete with any organic acid, the effective pH during antirust treatment is in the range of 5 to 9, with a range of 6 to 8 being particularly preferred. It is also understood that if iron precipitates are formed during rust prevention treatment, iron hydroxide precipitates adhere to the steel surface even within the appropriate pH range, impairing the rust prevention effect. Precipitate formation affects the organic acid concentration and pH, and if the amount of iron ions eluted by acid washing exceeds 600, citric acid,
For glycolic acid and tartaric acid other than malic acid, sulfamic acid, and glyconic acid, by lowering the feed to 6 during rust prevention treatment, iron precipitate formation is eliminated, the organic acid concentration is reduced, and the rust prevention effect is improved. Recognize. 33←←← Age Tachibana gomi female; Miko female ◎○× Ink pseudotitle loss As detailed above, the present invention is applicable to thermal power generation at the time of new installation and after operation. It is ideal as a chemical cleaning method for boilers, heat exchangers, and other steel parts in plants, chemical plants, etc. {1} It is a two-step chemical cleaning method that does not require water washing after pickling, so chemical cleaning is not required. The time required is reduced to about 1/2 compared to the conventional method, resulting in significant savings in labor and personnel costs.

■ By adding a pH adjuster, Doai phosphate, and nitrite together to the acid solution after descaling, it is possible to combine the pH adjuster and Doai phosphate, or the mother adjuster and nitrite. Its rust-preventing effect increases by 1.5 to 2 times.

'3} Since the method of the present invention is a two-step, 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. 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 '11 key acid at all, but even if it remains as a pH adjuster during rust prevention treatment, it Because we use materials that decompose into harmless substances,
Washing with water can be simple, and the amount of water used and the washing time can be small. In the method of the present invention, it is used as a so-called mirror protection promoter, and a concentration of 0.02 to 0.1 wt% is sufficient compared to 0.1 to 1 wt% in the known method.

{31 The rust prevention effect of the known method depends on what is generally called a nitrite film, but in the method of the present invention, the reaction between the car phosphate and the steel surface is promoted by the nitrite, and an insoluble I-based film is formed on the steel surface. This is due to the chemical formation of a delicate passivation film of secondary and tertiary iron phosphates, and the rust prevention effect is about 2 to 2 times higher than that of known methods.
It has the effect of increasing the amount of energy by as much as three times.

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%, aqueous ammonia, ethanolamine,
At least one pH adjuster such as hydrazine and at least one polymeric phosphate and nitrite selected from polyphosphates, ultraphosphates, and metaphosphates are added to adjust the pH to 5 to 9. A chemical cleaning method for steel parts, which is characterized by anti-corrosion treatment.