JPH0445593B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for cleaning a hydraulic fluid piping system, and particularly to a method for cleaning piping having a small diameter, small internal volume, and complicated structure, such as hydraulic piping in steel plants. [Conventional technology] Hot rolling and cold rolling equipment in steel mills use hydraulic equipment, etc.
Many devices are used that operate using hydraulic fluids. Since these devices operate at high pressure, the hydraulic fluid piping system that supplies the hydraulic fluid is required to have a high degree of cleanliness. Hydraulic fluid piping systems are usually acid-cleaned before assembly and oil flushed after assembly, but in order to shorten the construction period, a method of sequentially performing acid cleaning and oil flushing after assembly is being considered. In this case, the neutralization rust prevention method after acid cleaning becomes a problem. Conventionally, as a method for neutralizing rust prevention on metal surfaces that have been cleaned by acid cleaning, the object to be cleaned is placed in a solution containing polyphosphate to prevent the formation of iron hydroxide after the pickling solution is discharged. There are two methods: washing with water and neutralizing at the same time by soaking and adding an alkali to the solution (for example, Japanese Patent Publication No. 42-24801), washing with an iron chelating agent, or adding an iron chelating agent to mineral acid, etc. A known method is to dissolve and remove scale, neutralize it by adding an alkaline agent, and further add a rust preventive agent to prevent rust (for example, Japanese Patent Publication No. 16401/1983). [Problems to be Solved by the Invention] However, in a hydraulic fluid piping system, it is difficult to discharge the fluid by gravity due to its structure, so the above method cannot be adopted. In other words, the liquid must be extruded under pressure using nitrogen gas, etc., so if iron is present in the final rust preventive liquid, it will not precipitate due to the added chelating agent, but when extruding with nitrogen gas, iron will not precipitate. There was a problem in that the wet residue and residual liquid evaporated, and the chelated iron became a solid substance and precipitated on the surface of the metal. The present invention is intended to solve these conventional problems, and it is an object of the present invention to provide a method for cleaning a hydraulic fluid piping system that can be cleaned using a simple process so that solid substances such as iron do not remain. The purpose is [Means for Solving the Problems] The present invention provides a method for cleaning a hydraulic fluid piping system that has a small diameter, a small internal volume, and a complicated structure, making it difficult to drain the fluid by gravity. After acid cleaning the liquid piping system, a rinsing liquid consisting of an alkaline aqueous solution containing an iron ion sequestering agent and a corrosion inhibitor is supplied from one end of the piping system, and the pickling liquid is pushed out from the other end. A method for cleaning a hydraulic fluid piping system, which comprises neutralizing and rinsing the wastewater until almost no iron can be detected, and then adding a rust preventive agent to the rinsing liquid in the system to perform rust prevention treatment. The hydraulic fluid piping system to be cleaned in the present invention is a piping system that supplies hydraulic fluid to hydraulic equipment, such as a hydraulic piping system in a steelworks. The piping system makes it difficult to drain the liquid. In such a hydraulic fluid piping system, the hydraulic pump, hydraulic equipment, etc. are usually separated and cleaned, but they may be cleaned at the same time. When cleaning only the piping system, install a temporary circulation pump to circulate the cleaning solution. The cleaning method is to first perform acid cleaning after assembling the piping system.
For acid cleaning, ordinary acid cleaning used for cleaning boilers etc. can be used, for example, inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, organic acids such as citric acid, gluconic acid, oxalic acid, or mixed acids of these. A pickling solution containing a pickling corrosion inhibitor is used. In acid cleaning, such a pickling solution is supplied and circulated within the working fluid piping system to dissolve and remove iron oxide scale within the piping system. After acid cleaning, a rinsing liquid is supplied from one end of the piping system, and the pickling liquid in the system is pushed out and discharged from the other end, thereby performing neutralization and water washing. At this time, an alkaline aqueous solution in which an iron ion sequestering agent and a corrosion inhibitor are dissolved is used as a rinsing liquid. Examples of iron ion sequestering agents include ethylenediaminetetraacetic acid,
These include citric acid, malic acid, and tartaric acid. Alkaline agents include, for example, sodium hydroxide, ammonia, hydrazine, and alkylamines, which may be dissolved in water together with iron ion sequestering agents, and ethylenediaminetetraacetic acid, citric acid, etc., which are used as iron ion sequestering agents. It may also be added to water in salt form. Furthermore, a corrosion inhibitor is added to this aqueous solution to prepare a rinsing liquid. The concentration of the iron ion sequestering agent to be added is determined depending on the iron ion concentration in the system, and an amount that can chelate most of the iron ions is required. The appropriate pH of the rinse solution is 8 or higher, preferably about 9 to 10. In the method of neutralization and water washing, the above-mentioned rinsing liquid is pressurized into the piping system after acid washing, thereby pushing out the pickling liquid, and at the same time, neutralization and water washing are performed. The rinsing liquid is supplied until almost no iron is detected in the liquid discharged from the piping system. By extrusion water washing with this rinsing liquid, the residual pickling liquid in the system is discharged, and dissolved iron ions are also discharged. In this case, if the pipe is simply washed with water, the dissolved iron becomes a hydroxide solution and remains attached to the pipe wall, but due to the action of the iron ion sequestering agent, it is discharged as dissolved and does not remain on the wall surface. Acids are also immediately neutralized by the alkaline components of the rinse solution. Due to the rinsing effect of such additive chemicals, pickling waste liquid can be easily and quickly discharged from the system, and the amount of rinsing liquid used is approximately 1.5 to 1.5 times the amount of pickling liquid.
With a relatively small amount (3 times the amount), water can be washed until no iron ions are detected in the waste water. After washing with water, a rust preventive agent is added to the rinsing liquid in the system to perform rust prevention treatment. As the rust preventive agent, it is sufficient that it forms a rust preventive film on the metal surface, and sodium nitrite, ammonium nitrite, etc. can be used. The rust preventive agent is usually added in an amount of about 0.1 to 1% by weight, and the solution is heated to 60℃ or the boiling point and circulated.
Anti-corrosion treatment is performed by contacting for a period of time. Heating may be done by blowing steam or by using a heating device such as an electric heater. After anti-rust treatment, drain the liquid in the system. Exhaust is performed by blowing gas such as air or nitrogen. Thereafter, hydraulic fluid or other fluid is supplied to the piping system to perform oil flushing, and then new hydraulic fluid is supplied to operate the equipment. [Examples] Examples of the present invention will be described below. In the examples, % is by weight. Example 1, Comparative Example 1 Hydraulic piping used in the hydraulic piping system of a steelworks was used as the object to be cleaned, and the acid cleaner Cliffresh 111 (registered trademark, manufactured by Kurita Engineering Co., Ltd.) containing hydrochloric acid as the main component was used. Acid cleaning was performed by circulating a pickling solution containing 10%. Antilas F-3 (registered trademark, manufactured by Kurita Engineering Co., Ltd.), a rinsing agent containing citric acid and a corrosion inhibitor for hydraulic piping after acid cleaning
A 1% solution of (PH9.5) was supplied as a rinsing liquid from one end of the piping system, and the pickling liquid was pushed out from the other end, and the iron concentration of the discharged liquid was washed with water until the iron concentration became 5 mg/. The amount of rinsing liquid at this time was equivalent to 2 volumes of hydraulic piping. Next, 0.5% of antirust F-2, a rust preventive agent containing sodium nitrite as a main component, was added to the rinse solution, and the mixture was circulated at 80°C for 2 hours and brought into contact with it. After that, nitrogen gas was blown into the system. The liquid inside was drained. The results are shown in Table 1. Comparative Example 1 also shows the results of neutralizing and rust-preventing hydraulic piping after acid cleaning under conventional conditions.

〔Effect of the invention〕

According to the present invention, since the pickling liquid is extruded by the rinsing liquid to prevent rust, cleaning can be performed through a simple process without leaving any solid matter such as iron, and clean hydraulic piping can be achieved. system can be obtained.

Claims (1)

[Scope of Claims] 1. In a method for cleaning a hydraulic fluid piping system that has a small diameter, small internal volume, and complex structure and is difficult to drain by gravity, the assembled hydraulic fluid piping system is cleaned with acid. After that, a rinsing solution consisting of an alkaline aqueous solution containing an iron sequestering agent and a corrosion inhibitor is supplied from one end of the piping system, and the pickling solution is pushed out from the other end. A method for cleaning a hydraulic fluid piping system, which comprises neutralizing and rinsing with water until the rinsing liquid disappears, and then adding a rust preventive agent to the rinsing liquid in the system to perform rust prevention treatment. 2. The method for cleaning a hydraulic fluid piping system according to claim 1, wherein the hydraulic fluid piping system is a hydraulic piping system.