Reasons for the failure of mechanical seals

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In a mechanical seal, within the mean time between planned maintenance intervals specified in its design (MTBPM), if its leakage rate exceeds the limits permitted by production or environmental conditions, it is considered to have failed. Mechanical sealing may occur before or after MTBPM. The failure of mechanical seals is the main cause of failure and shutdown in the mechanical equipment they are part of. According to statistics, among mechanical equipment, about 50% of the total number of equipment that comes to a stop due to failures in mechanical seals account for such incidents. There are many factors that can cause mechanical seal failure, including defects in the design and manufacturing of the seals, improper selection of materials or incorrect installation, as well as issues with the equipment itself. However, a large number of cases of mechanical seal failure are due to operational reasons; for pumps, operational factors account for 40% of the causes of seal failure. Studies show that many failures stem from incorrect use and maintenance of the equipment, such as pump seals operating in a dry condition, operation with the outlet valve closed, operation outside the design parameters, and excessive vibration, especially in high-flow pumps. For more information on seals, please follow the WeChat official account cxzhongde. Additionally, proper operation of the support systems is also a necessary condition to ensure that the seals function as designed. Furthermore, mechanical seal structures are usually quite complex, featuring moving sealing surfaces as well as numerous auxiliary components and secondary seals, each of which can lead to failure. Leakage is the main manifestation of mechanical seal failure. In a typical internal double-faced mechanical seal, the sealing fluid can leak outward through four channels, namely: 1. Between the end faces of the sealing pair ； 2. At the auxiliary sealing ring of the moving ring ； 3. At the auxiliary sealing ring of one static ring ； 4. At the interface between the machine body and the gland sealing surface. Here, when there is a shaft sleeve, there is also a leakage path between the shaft sleeve and the shaft. Reasons for mechanical seal failure: There are many factors that contribute to the failure of mechanical seals. Generally speaking, there are mainly the following reasons: 1. Improper sealing design or selection of materials; the materials do not meet the specified requirements and are unable to cope with the conditions related to temperature, pressure, speed, and the type of fluid involved ； 2. The seal was already damaged before or during installation, such as cracked sealing surfaces, scratches, dents, or dirt, as well as damaged O-rings ； 3. Incorrect installation, such as improper fixing of the spring, loose set screws, or the sleeve not being in the correct position ； 4. Incorrect startup procedure, dry operation of the seal, or failure of the support system ； 5. Poor lubrication of the sealing surface ； 6. Product curing between the sealing surfaces, accumulation of solid matter around the seal, etc ； 7. The sealing fluid contains abrasive particles or corrosion products ； 8. During dry operation, the introduction of coolant causes thermal shock; the sudden change in pressure overloads the sealing pair ； 9. Shaft runout, deflection, vibration, or excessive bearing wear ； 10. Mechanical failures such as shafts or bearings. Therefore, mechanical seal failure is much more complex than bolted flange joint failure, but similarly, mechanical seal failure is related to the time it occurs. Failure can occur during boosting or startup, a few hours or days after startup or after restart, or it may happen suddenly during normal operation. To analyze the failure of mechanical seals, it is necessary to conduct a thorough investigation not only of the seal itself but also of the equipment’s hardware, the sealing fluid, and operating conditions. This includes examining the accident site and relevant documentation in order to gain a detailed understanding of the symptoms and patterns of seal failure. By analyzing these factors, the causes of failure can be identified, and measures such as improvements to seal design, material selection, installation and operation procedures, as well as environmental controls, can be proposed. This helps to enhance the reliability of mechanical equipment and extend its actual service life