Fault analysis of leakage emergency shut-off valve

2022-09-22
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Failure analysis of the leakage emergency shut-off valve of liquefied gas tanker

the failure or improper operation of the leakage emergency shut-off valve of liquefied gas tanker will cause serious leakage and even explosion accidents. The causes of the failure are analyzed as follows:

1. The failure caused by the valve quality

(1) cut off before overflow. In the process of unloading, it often occurs that if the flow does not reach the rated value, we should first consider the phenomenon that the pull range of the demand test data is cut off, which leads to the interruption of unloading and prolongs the unloading time. The valve itself does not meet the index requirements specified in the factory certificate. This situation is more common, and users also have strong reactions

(2) the pilot rod is bent. The diameter of some tank car pilot rods is only 6m, so the machining accuracy is insufficient, and the cam surface in contact with them is also rough. The cam surface transition is not smooth, and the pressure process is very easy to bend the first conduit, resulting in poor switching and poor sealing

(3) break the cam. This part is usually made of nodular cast iron. When the force is too strong or the pilot rod has been bent, the cam will break, making the valve unable to continue to work

(4) overflow valve leaks. The main reason is that the processing accuracy of the sealing surface of the overflow valve is not enough In addition, sand and impurities in the medium wash the valve disc for a long time, making it rough, especially when the valve is closed, sand or impurities just stay on the sealing surface

(5) due to frequent rotation of camshaft, the sealing ring is damaged and the sealing is not tight, resulting in liquefied gas leakage

(6) failure of large and small springs

2. Fault caused by improper human operation

(1) overpressure operation. The design pressure of the hand oil pump is 4.0Mpa, and the pressure required to open the valve is 3.5 ~ 4.0Mpa, while there are many cases where the pressure is as high as 7.0 ~ 8.0MPa. Every year, about 30 vehicles' oil pumps are damaged due to overpressure, and 20% of them cannot be repaired and should be replaced

(2) valve opening procedure error. It violates the principle that the emergency shut-off valve must be opened when the ball valve is closed. The error of opening the ball valve first and then the emergency shut-off valve often occurs, which cannot make the upper and lower pressure of the overflow valve balance. Due to the pressure difference, the small spring cannot push the valve open. Desperately, the product is formaldehyde free, fire-proof and moisture-proof, and there are no pests. Increasing the pressure of the oil pump will not only fail to open the valve, but will damage the oil pump. This is caused by the low quality of personnel and their ignorance of the working principle

(3) the cylinder piston is rusted. Usually, when the hand oil pump leaks oil, the operator pressurizes and opens the emergency shut-off valve, and then closes the stop valve in front of the oil cylinder in order to maintain the pressure. After loading and unloading, forget to open the stop valve, only open the oil unloading handle of the oil pump, and return the pressure gauge to zero, mistakenly thinking that the shut-off valve has been closed, and the actual shut-off valve is still open. As the piston rod of the oil cylinder extends out and is exposed under the

frame at the bottom of the tank car, the piston rods of these domestic cars are not plated. In rainy days, the wet water vapor and sediment will soon erode the piston rod and make it rust. Especially in this state for a long time, it is easier to make the piston rod rust, so that the emergency shut-off valve cannot be closed and is in a normally open state. There are about 10 cars in this situation every year, which is extremely dangerous

(4) when the steel wire rope breaks or the oil pump fails, the user uses a hard object to hold the cam, and the emergency shut-off valve is open for a long time

what is the market pattern of global high-performance composites in the next six years? It is suggested that the departments engaged in valve design and manufacturing should investigate and analyze the various faults of the valve to further improve the quality of the emergency shut-off valve. Study and improve from the aspects of structure, material selection, processing, assembly and rust prevention. The most common faults such as cutting off before overcurrent, bending of pilot rod and cam breaking should be solved

the technical quality of escorts and relevant operators must be improved. We should not only understand the operation method, but also understand its principle, and master the technology of dealing with faults

before filling, the liquefied gas filling station and tank car users should check whether the action of the emergency shut-off valve is sensitive and reliable, and measures should be taken to ensure that the emergency shut-off valve is closed before the tank car leaves the station

the inspection unit must strictly implement the safety supervision regulations for liquefied gas tank cars. In particular, it is necessary to implement the technical indicators of valve disassembly inspection and assembly test. Clean, disassemble and check the valve body, pilot rod, spring, sealing surface, cam, etc. for damage, deformation, corrosion, rust, cracks and other defects; Check whether the oil pump, pipeline and fusible plug of the emergency cut-off loading and unloading control system are intact, and whether there is damage, looseness, leakage and other phenomena; Whether the cable control system is flexible, reliable and in place, and whether the cable is intact; The oil pressure or traction type emergency shut-off valve shall be fully opened under the working pressure, and the natural closure will be caused by continuous large-scale imprecision of 1/200000; We should really eliminate potential safety hazards

emergency measures for dealing with similar leakage accidents on site: move the car to a relatively open and ventilated place nearby, and it is strictly prohibited for sparks to cause a fire. Close the valve by extraordinary means, which can be disassembled without feeding the eccentric wheel and spring. Turn the square head with a wrench to force the emergency shut-off valve back to its seat. So as to close the leakage air source and control the expansion of the accident

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