Various forms of oil pipes and their accessories are important components of the hydraulic system. According to statistics, about 50% to 60% of hydraulic system failures are caused by oil pipes and their accessories not meeting the requirements. Therefore, the oil pipes must be carefully inspected and cleaned before installation, and attention must be paid to cleaning and maintenance during the operation of the hydraulic system.
1. Importance of cleaning and maintenance
(1) Avoid serious contamination of hydraulic oil
If the oil pipe made on site is installed on the equipment without cleaning, when the oil pipe is filled with hydraulic oil, impurities such as welding slag and rust in the oil pipe will enter the hydraulic oil, thereby contaminating the hydraulic oil. In serious cases, the entire tank of hydraulic oil may be unusable.
(2) It can prevent the impurities remaining in the oil pipe from damaging the precision hydraulic components.
If the size of the impurity particles remaining in the oil pipe is equivalent to the clearance value of the valve components, the impurity particles will scratch the matching surface of the valve core and the valve body, thereby damaging the hydraulic components and causing the valve core to get stuck. In addition, it will also change the switching time and valve characteristics of the valve and increase the leakage in the system.
(3) Anti-corrosion treatment of the outer surface of the oil pipe
The outer surface of the oil pipe is easily corroded due to the influence of its surrounding environment. In severe cases, holes will appear in the oil pipe, causing a large amount of hydraulic oil to leak out, and the equipment is forced to shut down. Therefore, the outer surface of the oil pipe needs to be treated with anti-corrosion. Generally, after the oil pipe is cleaned, a layer of anti-rust paint should be applied on its outer surface. After the anti-rust paint is completely dry, a layer of topcoat with the same color as the equipment body should be applied. Practice has shown that the service life of the oil pipe is significantly extended after anti-corrosion treatment.
2. Technical treatment before cleaning
(1) Welding of oil pipe joints
Hydraulic oil circuits are connected through multiple straight pipes and bent pipes through pipe joints. Therefore, there will always be welding problems with pipe joints during the installation of oil pipes. When welding pipe joints, you need to first connect the joint to the oil pipe joint installed on the equipment, then connect the joint to the main oil pipe by spot welding, and then use an argon arc welder or a CO2 gas shielded welder to continuously weld the weld grooves reserved for the pipe joint and the main oil pipe, and ensure the strength of the weld. After the pipe joint and the main oil pipe are firmly connected by spot welding, the connecting bolts of the two pipe joints can be removed and the oil pipe can be removed. After welding the pipe joint using the above method, it can be ensured that the joint flange surfaces are tightly matched, and the sealing effect is excellent.
(2) Treatment of pipe joints
Generally, after the oil pipe joint is welded to the main oil pipe, there will be a small amount of residual welding slag at the weld on the inside of the pipe joint. To ensure the cleanliness of the inside of the oil pipe, the weld on the oil pipe joint needs to be cleaned. First, use a welding slag hammer to gently tap the weld on the outside of the pipe joint to shake off the residual welding slag on the weld on the inside of the pipe joint. Secondly, use a wire brush to extend into the weld inside the joint hole and brush the annular weld thoroughly to remove the welding slag that has not been shaken off.
3. Cleaning method
(1) Pickling
Generally, the inner and outer surfaces of steel pipes used as oil pipes will rust. If not cleaned, they will pollute the hydraulic oil after use and affect the normal operation of the hydraulic device. Therefore, it is necessary to remove the rust from the inner surface of the oil pipe by pickling. Pickling can also remove the rust on the outer surface of the oil pipe, which is conducive to applying anti-rust paint on the outer surface of the oil pipe and providing long-term anti-corrosion protection for the oil pipe. Pickling can generally be carried out with an acid solution with a percentage concentration of 10%~15%.
The specific method is as follows:
First, prepare sulfuric acid solution in a corrosion-resistant container according to the concentration requirements. Then, put the oil pipe into the sulfuric acid solution and make it completely below the liquid level of the sulfuric acid solution to ensure the pickling effect. During the pickling process, it is necessary to frequently check the surface of the oil pipe to confirm whether the rust has fallen off completely. The pickling time is based on the time when the rust on the surface of each part of the oil pipe has fallen off completely and the original color of the steel pipe is exposed.
(2) Washing and air drying
After the pickling reaches the required level, the oil pipe should be immediately placed in a container filled with 70~80℃ hot water for washing. During washing, the oil pipe should be constantly swung in the container so that the water exerts force on the inner and outer surfaces of the oil pipe, thereby washing away the sulfuric acid solution remaining on the inner and outer surfaces of the oil pipe.
After the first water washing, the water in the container should be drained and filled with hot water at 70~80℃ for the second water washing. The pH value of the water can be checked with PH test paper. When the pH value is about 7, the water washing can be stopped; otherwise, it should be washed again until the above requirements are met.
After the water washing, the inner and outer surfaces of the oil pipe should be blown with compressed air immediately to make the inner and outer surfaces of the oil pipe dry quickly to prevent the oil pipe from rusting again.
(3) Oil washing
After the oil pipe is washed and air-dried, it should be oil-washed to ensure that the inner surface of the oil pipe is clean.
First, a 600 L oil tank is made of stainless steel. Then, a hydraulic pump and oil filter for cleaning the inner surface of the oil pipe are installed on the oil tank. Next, the oil pipes that need to be oil-washed are connected in sequence from the outlet of the cleaning hydraulic pump, and finally connected to the oil return port of the oil tank.
After the above work is completed, add 510 L of hydraulic oil of the same brand as that used by the equipment into the oil tank, turn on the power of the cleaning oil supply hydraulic pump and the filter hydraulic pump, and start the cleaning hydraulic pump and the filter hydraulic pump to clean the oil pipe. At this time, on the one hand, the hydraulic oil in the oil tank enters the oil pipe through the cleaning hydraulic pump, flows through all the oil pipes and then flows back to the oil tank; the hydraulic oil continues to flow in the oil pipe, which can flush the impurities on the inner wall of the oil pipe. On the other hand, the filter hydraulic pump continuously circulates and filters the hydraulic oil in the oil tank and filters out the impurities flushed from the inner wall of the oil pipe through the inlet and outlet filters.
(4) Confirmation of oil washing results
The purpose of oil washing the oil pipe is to further remove impurities and contaminants on the inner wall of the oil pipe. After the oil washing starts, the impurities and contaminants in the hydraulic oil in the oil tank will gradually increase. As the oil washing cycle time increases, the impurities and contaminants in the hydraulic oil are gradually filtered out by the filter, and the contamination level of the hydraulic oil gradually decreases. When the contamination level drops to the same level as the contamination level required by the equipment hydraulic oil, the oil washing can be ended.
At present, there are 5 classification standards for hydraulic oil pollution levels. We generally use the NAS1638 standard to determine the pollution level of hydraulic oil. In the NAS1638 standard, the lower the pollution level, the fewer particles of pollutants contained in a certain volume of hydraulic oil. For hydraulic systems equipped with servo valves and proportional valves, the pollution level of the hydraulic oil should meet the requirements of NAS4~6 and NAS8~9 respectively.
At the equipment installation site, oil sampling is generally used to analyze the pollution level of the hydraulic oil in the oil tank. This method can quickly determine the oil pollution level in a short time, to draw a conclusion on whether the oil washing is qualified.
