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Chemical flushing method for seamless hydraulic pipes

Date:2023-10-24View:787Tags:seamless hydraulic pipe
Chemical flushing method for seamless hydraulic pipes

The purpose of chemical flushing is to completely remove all pollutants in the seamless hydraulic tube, speed up the flushing oil flushing speed and make the hydraulic oil reach the corresponding cleanliness level standard, so as to ensure the safe and reliable operation of the production line. Online chemical flushing is divided into several steps such as water flushing, degreasing, pickling, rinsing, neutralization and passivation, manual inspection and nitrogen purging.

seamless hydraulic pipe

1. Rinse with water

The purpose of water flushing is to remove solid particles insoluble in the degreasing pickling solution such as welding slag, metal powder and sealing material fragments inside the hydraulic system, otherwise it will seriously affect the service life of system components and even cause serious accidents. During the water flushing process, the water flow rate should be controlled above 2m/s, a system is divided into several branches for flushing, and the turbidity of the water is tested every 20 minutes. When the outlet water turbidity is 0.0005% greater than the inlet water turbidity, the flushing ends.

2. Degreasing

The purpose of degreasing is to completely remove all kinds of organic matter such as engine oil, graphite and anti-rust oil in the system, and lay a good foundation for pickling and rust removal on the metal surface. The medicines used are NaOH, NaCO, Na. PO, Na2SiO. and defoamer, etc., the degreasing temperature is room temperature, and the time is 6-8 hours.

3. Pickling

Pickling is the use of pickling liquid to react chemically and electrochemically with pollutants and corrosion products to generate soluble substances to clean the inner surface of the pipeline. Pickling is a key step in the entire chemical flushing process. The chemicals used are hydrochloric acid, nitric acid and reducing agent, etc., the pickling temperature is normal temperature, and the time is 6-8 hours.

4. Rinse

Rinsing is to use low-concentration acid solution to react with iron ions remaining in the system to remove floating rust that may be generated during water rinsing and floating rust after pickling. The medicaments used are hydrofluoric acid and reducing agent, etc., the rinsing temperature is normal temperature, and the time is 1.5-2.0 hours.

5. Neutralization and passivation

The purpose of neutralization and passivation is to form a uniform and dense passivation film inside the system to prevent secondary floating rust. Use medicine for
Trisodium phosphate, sodium nitrite and ammonia water, etc., the pH value of the passivation solution is 9.510.5, the passivation temperature is 50-60°C, and the passivation time is 4-6hE.

6. Manual inspection

After washing with water, degreasing, pickling, rinsing, and neutralization and passivation, the system needs to be checked in detail, and some dead corners should be manually cleaned to remove the residual impurities that have not been brought out of the system after washing.

7. Nitrogen purge

The use of clean and dry nitrogen to blow out the residual liquid and fine particles in the hydraulic system is the premise and guarantee for flushing oil flushing, otherwise it will lead to difficulty in flushing oil flushing and prolonged flushing time, which will increase the number of filter element replacements and increase the cost. Intermittent purge is used at the beginning of purge. When the moisture and particle number at the outlet of the pipeline are small, continue to purge for about 24 hours to dry the system. The nitrogen pressure is 1.0-1.6MPa. If there is no nitrogen on site, it can be replaced by compressed air of the same pressure.

8.Flushing oil flushing

For flushing oil flushing, attention should be paid to the flow control, pressure control, temperature control, cleanliness control and flushing result judgment of flushing oil. Generally, flushing oil with lower viscosity is used for flushing.

Flush Oil Flow Control
The flushing pump is selected according to the flow velocity when the liquid flow in the larger pipe diameter in the flushing pipeline is in a turbulent state and the sum of the cross-sectional areas of the branch pipes when the pipelines are connected in parallel, and a high-pressure vane pump is generally used. The flow control of flushing oil includes two parts: bypass flow regulation and branch flow regulation. 1) Bypass flow regulation. Bypass setting The flow rate of the flushing pump actually selected is generally larger than the design flow rate, so a bypass must be used to divert the flow. When flushing, open the shut-off valve to the maximum and then start the flushing pump, and then gradually adjust the size of the shut-off valve switch to achieve the best flushing effect. 2) Branch flow regulation. When flushing, try to ensure that the liquid in each branch is in a turbulent state. There are stop valves before and after each branch to adjust the flow of flushing oil. If necessary, a flow meter can be installed on the main pipeline to confirm.

Flushing oil pressure control
The flushing oil pressure is controlled at 4-6MPa. For flushing circuits with long pipelines, thin pipe diameters, sudden changes in pipe diameters, or multiple bends, increase the number of branches to shorten the length of the flushing pipeline and reduce pressure loss. At the same time, adjust the size of the front and rear cut-off valve switches of each branch to realize the switching flushing of the branch.

Flush oil temperature control
Flushing oil temperature and temperature difference have an important impact on the flushing effect. In addition, when the size of the fine particles in the flushing oil is less than 0.005IJ,m, the temperature increase and the existence of the electric field can accelerate the transformation of small particles into large particles, making them easy to be filtered out. Therefore, the temperature of the flushing oil should be changed frequently during the flushing process, and the temperature of the flushing oil should be increased as much as possible without exceeding the dangerous temperature. Considering various factors, control the flushing oil temperature within 25-60cc.

Oil cleanliness control
Domestic filter elements are used in the initial stage of flushing, and imported filter elements are used in fine filtration to reduce costs. Determine the replacement time of the filter element according to the pollution degree of the pipeline and the results of online detection. At the same time, care should be taken to prevent the flushing oil from being shared with magnesium, lead, zinc and filter paper and lose its original hydraulic medium characteristics, and attention should be paid to replace the filter element when the pressure difference between the inlet and outlet of the oil filter is greater than 0.35MPa during flushing. Set a coarse filter before flushing the pump to prevent large particles of impurities from damaging the flushing pump. Set double filters before the flushing circuit to avoid contamination of the clean hydraulic system, especially for some hydraulic systems that only require flushing. Set a filter after the flushing circuit to prevent impurities in the flushing circuit from flowing into the oil tank.

Flush result judgment

There are two sampling methods for judging the flushing results: one is to take flushing oil samples from a specific sampling port (on the oil return line of the oil return filter) according to the specified time for instrument testing and inspection; the other is to select according to the type and characteristics of the system. A filter with a certain precision is placed at the oil return port of the flushing circuit to collect all the impurities flushed back, and check it every 2 to 4 hours. When the nature and shape of impurities do not affect the function of the system, the flushing is qualified.


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