JP2719599B2 - How to clean piping - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an improved method of cleaning piping.

As used herein, the term “piping” refers to various hydraulic equipment piping, chemical plant pipelines, various heat exchangers and steam cans, various towers and tanks, and various pipes attached thereto. Generic name.

2. Description of the Related Art Conventionally, the following cleaning method has been generally adopted as a method for removing scale, rust, and the like generated over time in a pipe.

That is, the inside of the pipe to be treated is washed with an aqueous solution of an acid such as hydrochloric acid or phosphoric acid, and is subjected to a blow treatment using air or nitrogen gas. After neutralization, a method of performing rust prevention treatment is employed.

However, in such a washing method, rusting occurs if the blow treatment and the washing treatment after the acid washing are not sufficiently performed, so that the washing must be carried out with a large amount of washing water (usually, a plurality of washings). Rather, rusting occurs when the washing time becomes long, so high work efficiency is required, and it is extremely difficult to remove an acid solution remaining in a portion having a poor flow of water, for example, a gap between a high-pressure flange and a pipe. There is a high risk of rusting after washing with water.In addition, metals such as free iron generated by pickling change into salts in the treatment step with an alkaline aqueous solution, and precipitate and adhere to the inner wall of the pipe, causing rusting. (Particularly, the rusting rate is high in the gaps and the like).

DISCLOSURE OF THE INVENTION The present invention provides an improved method for cleaning piping, which simplifies work steps and saves cleaning water by omitting a water-washing step, and can effectively prevent rusting. It was done for.

Means for Solving the Problems That is, according to the present invention, the inside of the pipe to be treated is washed with an acid aqueous solution, blow-treated, treated with a chelating agent aqueous solution, and then washed with an ammonia aqueous solution. And then performing a rust prevention treatment.

The acids used in the present invention are those conventionally used,
For example, hydrochloric acid, phosphoric acid, sulfamic acid, sulfuric acid, etc. may be used as appropriate, and the concentration depends on the type of acid and the type of pipe to be treated, the degree of contamination, and the like, but is not particularly limited,
Usually about 5 to 15%.

After the pickling, the washing liquid is discharged out of the system, and then a blow treatment is performed using a gas such as air or nitrogen gas. in this case,
Blow treatment is incomplete, for example, about
Even if about 10% of the pickling solution remains, there is no problem because rusting is suppressed by the subsequent treatment using the chelating agent aqueous solution.

After performing the blow treatment, the treatment is performed using an aqueous solution of a chelating agent. In the conventional method, a metal such as iron generated by the pickling treatment is converted into a salt in a treatment step using an alkaline aqueous solution, and precipitates and adheres to the inner wall of the pipe, which is one cause of rusting. In, the metal is captured by the chelating agent, so that such a cause of rust is eliminated.

Examples of the chelating agent include citric acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, glycine, iminodiacetic acid, and salts thereof.

The concentration of the chelating agent aqueous solution depends on the type and concentration of the acid used for the above pickling treatment, the type of the pipe to be treated, the degree of contamination, and the like, and is not particularly limited.
It is 2 to 2% (from economic point of view 0.2 to 0.5%).

The above-mentioned chelating agent aqueous solution can be effectively suppressed from rusting by merely draining it once inside the pipe to be treated and then draining it.

After performing a rinsing treatment using an aqueous solution of a chelating agent, a neutralization treatment is performed by injecting an aqueous ammonia solution into a pipe without performing a blow treatment.

The concentration and the injection amount of the aqueous ammonia solution are not particularly limited, and depend on the type and concentration of the acid used in the pickling treatment, the amount of the acid remaining in the piping, and the like, but are usually limited to a commercially available 25% aqueous ammonia solution. Is appropriately diluted as required, and the injection amount is adjusted so that the pH of the treatment solution after the injection is about 9 to 9.
Assume the amount to be 10.

Ammonia has a higher neutralization efficiency and a higher permeability than the alkali used in the conventional neutralization treatment, so it is also used in areas where acids tend to remain, for example, in gaps between high pressure flanges and pipes. It effectively penetrates and effectively prevents rust.

Subsequently, the inside of the pipe is subjected to a rust preventive treatment without discharging the neutralization treatment liquid to the outside of the system. The rust preventive treatment is usually performed by injecting an aqueous solution of a known rust preventive.

Examples of this kind of rust inhibitor include phosphate, nitrite, hydrazine and the like.

After discharging the rust inhibitor aqueous solution out of the system, a blowing treatment may be performed using a gas such as air or nitrogen gas, if desired.

 Hereinafter, the present invention will be further described with reference to examples.

Example 1 Hydraulic device hydraulic pipeline (material: STPT 42 STPG3
8. After cleaning the inside of inner diameter: 20-50A, length 3640m) using phosphoric acid aqueous solution (concentration: 10%), draining, and performing blow processing with air (all contents of pipeline) About 10% of the product remains), citric acid aqueous solution (concentration: 1%)
, Followed by an aqueous ammonia solution (concentration:
0.25%).

Further, without discharging the aqueous ammonia solution from the pipeline, rust prevention treatment is performed by injecting an aqueous solution (concentration: 0.5%) of Neos CM306 (main component: sodium nitrite), and then the aqueous rust inhibitor solution is discharged. Was.

All of the above processing steps were performed at ambient temperature.

The cleaning effect of the inside of the pipeline subjected to the above-mentioned cleaning treatment is good, and the operation time is reduced by half and the waste liquid is reduced by two-thirds as compared with the conventional cleaning method. No rust was observed.

Example 2 A heat exchanger (7.5 m ³ ) according to the washing line shown in FIG.
The washing of (1) was performed.

Using a treatment liquid preparation pump (6), an acid aqueous solution (containing 5 to 10% of hydrochloric acid and 0.05 to 1% of a nonionic activator) was prepared in the treatment liquid preparation tank (2), and this was kept at room temperature to 55 ° C.
After being transferred into the treatment liquid circulation tank (4) at a temperature of, the mixture is circulated in the heat exchanger (1) for about 6 to 10 hours using the circulation pump (3), and then the heat exchanger (1) and the pipe Was discharged into the waste liquid tank (5) using N ₂ gas.

Next, a 1% aqueous citric acid solution is prepared in the same manner as in the case of the aqueous acid solution, and after circulating it for 2 to 3 cycles in the heat exchanger (1), a 0.25% aqueous ammonia solution is injected into the heat exchanger. Then, a neutralization treatment was carried out, and an aqueous solution of a rust inhibitor was injected into the heat exchanger and circulated for 2 to 3 cycles.

Finally, waste liquid tank of rust inhibitor aqueous solution using N ₂ gas (5)
It was discharged inside.

According to the above-mentioned cleaning method, the cleaning time was about half as compared with the conventional method, the amount of waste liquid was reduced to about 60%, the cleaning effect was good, and there was no inferiority to the conventional method.

Example 3 Instead of a heat exchanger, a water pipe of a boiler (water volume: 8.1 m ³ ) composed of a water drum and a steam drum was used as an object to be treated, and a 7.5% phosphoric acid aqueous solution was used as an acid aqueous solution. The same processing operation as in Example 1 was performed except that the inside of the tube was circulated for 4 to 6 hours.

Also in this case, the cleaning time was about half as compared with the conventional method, the waste liquid amount was reduced by about 60%, the cleaning effect was good, and there was no inferiority to the conventional method.

Effects of the Invention According to the method of the present invention, a washing step using a large amount of washing water, which is an essential step in the conventional method, can be omitted, so that the working process can be simplified and washing water can be saved. In addition, rusting can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a cleaning line for carrying out the present invention. (1) is a heat exchanger, (2) is a treatment liquid adjusting tank, (3) is a circulation pump, (4) is a treatment liquid circulation tank, (5) is a drain tank,
(6) shows a processing liquid adjusting pump.

Claims (2)

(57) [Claims] 1. The inside of a pipe to be treated is washed with an acid aqueous solution, subjected to a blow treatment, treated with a chelating agent aqueous solution, then washed with an ammonia aqueous solution, and then subjected to rust prevention treatment. A method of cleaning piping characterized by performing: 2. The method according to claim 1, wherein the aqueous solution of the chelating agent is an aqueous solution of citric acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, glycine, iminodiacetic acid or a salt thereof.