Discussion on the Causes of Oil Leakage in Hydraulic System Pipelines and Countermeasures

Discussion on the Causes of Oil Leakage in Hydraulic System Pipelines and Countermeasures

There are many types of pipelines used in the hydraulic system. According to the working pressure and installation position of the hydraulic system, steel pipes, copper pipes, rubber pipes, nylon pipes and plastic pipes are selected. Once these pipelines are damaged and leaking oil, it may pollute the environment and affect the normal function of the system, or endanger safety in severe cases. This article analyzes and summarizes the causes of oil leakage in hydraulic pipelines and the corresponding countermeasures taken.

1 Analysis of the cause of oil leakage

1.1 Poor quality of piping

When repairing or replacing hydraulic pipelines, if inferior pipelines are installed in the hydraulic system, oil leakage will occur due to their low pressure-bearing capacity and short service life. The poor quality of hard tubing is mainly manifested by the uneven thickness of the pipe wall, which reduces the load-bearing capacity; inferior hoses are mainly due to poor rubber quality, insufficient steel wire layer tension, and uneven weaving, resulting in insufficient load-bearing capacity. Under the impact of pressure oil, It is easy to cause pipeline damage and oil leakage.

1.2 The pipeline installation does not meet the requirements

1.2.1 Poor piping bend
In the process of assembling the hard pipe, the pipe should be bent according to the specified bending radius, otherwise the pipe will have different bending internal stresses and gradually leak under the action of oil pressure. If the bending radius of the rigid pipe is too small, the outer pipe wall of the pipe will become thinner, and the inner pipe wall will have wrinkles, which will cause the pipe to have a large internal stress at the bend, and the strength will be greatly reduced. Transverse cracks occur and oil leaks; if the bending part of the hard pipe has a large ellipse, longitudinal cracks and oil leakage are likely to occur when the oil pressure in the pipe fluctuates.
When the hose is installed, if the bending radius does not meet the requirements or the hose is twisted, it will cause damage to the hose and oil leakage.

1.2.2 The installation and fixation of the pipeline does not meet the requirements
Common improper installation and fixation：
(1) When installing the oil pipes, regardless of whether the length, angle, and thread of the pipe are suitable for assembly, the pipe is deformed and installation stress is generated. At the same time, it is easy to damage the pipe and cause its strength to decrease;
(2) When installing the oil pipe, do not pay attention to fixing it. When the bolts are tightened, the pipe will rotate together, causing the pipe to twist or collide with other parts and cause friction, which shortens the service life of the pipe;
（3）Sometimes the pipe clamps are too loose, which increases the friction and vibration between the pipe and the clamp; sometimes they are too tight, which causes the pipe surface (especially aluminum pipe) to be clamped and deformed; these conditions will damage the pipe and cause oil leakage;
（4）The tightening torque of the pipe joint is severely exceeded, causing the bell mouth of the joint to be broken, the thread is strained, and the tripping leads to a serious oil leakage accident.

１．３ Fatigue damage or aging of hydraulic pipeline

The observation and analysis of a large number of hard hydraulic pipeline fractures show that the rupture of the hard pipeline is a kind of fatigue failure, so there must be an alternating load on the pipeline. When the hydraulic system is working, the hydraulic pipeline has to withstand higher pressure, coupled with the combined effect of alternating stress caused by unstable pressure, vibration stress caused by equipment vibration, assembly stress, etc., so that the hard tube is in the material defect. , Stress concentration occurs at the corrosion point or damage, and the pipeline is fatigued and fractured and oil leaks. As for the rubber pipeline, it will be aged, hardened and cracked from the place where the high temperature, high pressure, bend and distortion are serious, and the oil pipe will burst and leak oil.

１．４ Hydraulic oil pollution and pipeline surface pollution

When the hydraulic oil is contaminated, it will cause the oil pipe to be worn and corroded, which will accelerate the rupture of the pipe and cause the oil to leak. Moreover, this kind of damage is not easy to be found, and the damage is more serious.
Since the hydraulic system is easily contaminated, the hydraulic oil containing solid contaminants is similar to the abrasive used to grind the metal processing surface, increasing the friction between the oil and the inner wall of the pipeline. Moreover, the hardness of solid contaminant particles is usually much higher than the hardness of the inner wall material of the catheter, which accelerates the wear of the inner wall of the catheter, and even scratches the inner wall. Especially when the flow rate of the liquid is high and unstable (fast flow rate and large pressure pulsation), the material on the inner wall of the catheter will be impacted and peeled off.
When the hydraulic oil contains water, it will promote the hydraulic oil to form an emulsion, reduce the lubrication and anti-corrosion effect of the hydraulic oil, and accelerate the wear and corrosion of the inner wall of the pipeline. When the hydraulic oil contains a lot of air bubbles, the air bubbles in the high-pressure pipeline are compressed, and the surrounding oil flows at a high speed to the space originally occupied by the air bubbles, causing a strong hydraulic shock. Under the impact of the high-pressure liquid mixture, the inner wall of the pipeline is affected. Corroded and peeled off. These conditions will eventually rupture the pipeline and cause oil leakage. (Tianyang Steel Pipe)
In addition, the outer surface of the pipeline is often stained with moisture, sludge and dust. If the protective layer is damaged, it is easy to corrode, resulting in a decrease in strength, until blasting oil occurs from high temperature, high pressure, bending, and serious distortion.

2 Countermeasure

Although the hydraulic pipeline bears high pressure and the working environment is harsh, oil leakage can be prevented and avoided. The following preventive measures should be taken during use and maintenance.

２．１ Check the quality of the pipeline carefully, and strictly prohibit the use of unqualified pipelines

When repairing, the newly replaced pipeline should be carefully checked by the manufacturer, date, batch number, specified service life, and whether there are any defects. The pipeline that does not meet the requirements must not be used. When in use, always check the pipeline for wear and corrosion; if the rubber hose is found to be severely cracked, hardened or bubbling during use, it should be replaced immediately.

２．２ Install the pipeline correctly, and it is strictly forbidden to assemble in violation of regulations

2.2.1 Correct assembly of hose lines
When installing the hose to tighten the threads, be careful not to twist the hose, you can draw a colored line on the hose for observation; when the hose is installed in a straight line, there should be about 30% of the length allowance to meet the needs of oil temperature, tension and vibration ; The bending radius of the hose bend should be greater than 9 times the outer diameter of the hose, and the distance from the bend to the pipe joint should be at least 6 times the outer diameter of the hose; do not use the rubber hose in an environment with high temperature and corrosive gas; if the system is soft There are many pipes, and pipe clamps should be installed to fix them or separate them with rubber plates.

2.2.2 Correct installation of hard pipe piping （www.steeltube-cn)
The installation of rigid pipes should be horizontal and vertical to minimize turns and avoid crossing; the radius of the turns should be greater than 3 to 5 times the outer diameter of the tubing; long pipes should be fixed firmly with standard pipe clamps to prevent vibration and collision; The distance between the clamps should meet the regulations. For pipelines with high vibration, the clamps should be equipped with vibration damping pads; when connecting the pipelines to the mechanical parts, first fix the auxiliary parts joints, and then fix the pipelines to prevent the pipelines from being affected. Twist, must not be forced to install.

２．３ Properly use and maintain, it is strictly prohibited to pollute the hydraulic system

In daily maintenance work, it is not allowed to step on, pull or press the pipeline at will, and it is not allowed to hit the pipeline with metal tools to prevent mechanical damage; hydraulic machinery or hydraulic equipment parked in the open should be covered with cloth to prevent damage. Dust, rain and snow work, water removal, drying and rust removal should be carried out in time after rain and snow; oil and dust on the surface of the pipeline should be frequently wiped to prevent pipeline corrosion; when adding oil and disassembling parts, be careful Pollution gates to prevent debris and moisture from being brought into the system. In addition, be sure to prevent harmful solvents and liquids from being spilled on the catheter.

２．４ other

For pipelines with large changes in oil temperature and ambient temperature on the equipment, thermal expansion compensation should be considered during installation to reduce the impact of thermal stress; in order to ensure the safe operation of the pipeline and extend the service life, The rubber tube should be insulated and cooled, such as wrapping the insulation layer and introducing heat dissipation air, etc. are effective measures; on the premise of meeting the system performance requirements, it should be considered to install a suitable accumulator in a place that is prone to hydraulic shock. Or vibration absorber, and try to use hydraulic components with buffer devices to reduce hydraulic pulsation and prevent hydraulic shock.

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