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Common Failures and Maintenance of Reactor Mechanical Seals
The reactor is an integrated reaction vessel, and the pressure generated during the reaction process imposes extremely high demands on the container's sealing. The sealing effectiveness of the mechanical seal directly impacts the reactor's operation, with severe cases leading to incalculable losses such as production shutdowns, safety accidents, and environmental pollution.
Today, Jinzong Enterprise will explore the common failures of mechanical seals in chemical reactors and how to address them.
Sealing of Reactors
The sealing of reactors comprises two main categories: static seals and dynamic seals.
Static Seals:
In reactors, static seals are typically applied at leakage points such as the flanges between the head and the cylinder body, pipe flanges, manholes, handholes, thermometer connections, sight glasses, and pressure gauge connections. These are considered static because the sealing surfaces remain relatively stationary. Static seals are relatively straightforward to address and are generally implemented using various forms of static gaskets.
Dynamic Seals:
The leakage point at the gap between the agitator shaft and the reactor body requires a dynamic seal due to the relative motion between the rotating shaft and the stationary reactor body (upper head). The primary types of dynamic sealing devices are mechanical seals and packing seals.
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Packing Seals: These have a simple structure and allow for easy replacement of the packing. However, they possess inherent weaknesses that lead to a shorter service life and make them unsuitable for high-parameter conditions (such as high temperature, high pressure, high rotational speed, or high vacuum).
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Mechanical Seals: These are widely used in reactors. They can be custom-designed with specific structures, materials, and lubrication/cooling measures tailored to the reactor's operating conditions to meet process requirements.
Compared to soft packing seals, mechanical seals offer the following characteristics:
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They provide highly reliable sealing over long operational periods with minimal leakage rates—typically only about 1/100 of that of soft packing seals.
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They have a long service life, generally lasting 1 to 2 years or more in oil or water-based media, and often over half a year in chemical media.
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They consume less frictional power, only about 10% to 50% of that consumed by soft packing seals.
Reactor Mechanical Seal Failures and Treatment
1. Failures and Treatment of Mechanical Seal Components
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Causes and Phenomena:
During reactor operation, the sealing end faces frequently exhibit issues such as wear, thermal cracking, deformation, and damage. Over time, screws, threads, and springs can also loosen, fracture, or corrode. Auxiliary sealing rings may crack, twist, deform, or rupture. -
Treatment Methods:
If components of the mechanical seal fail, they need to be replaced, or the precision of their machining must be improved. Enhancing the machining accuracy of the mechanical seal itself, as well as that of other reactor components, is highly beneficial for the seal's performance.
To improve sealing effectiveness, the surface finish and flatness of the friction faces of the rotating and stationary rings must be high. The width of these friction faces is generally small, typically between 2 and 7 millimeters.
2. Causes and Treatment of Mechanical Seal Vibration and Overheating
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Causes and Phenomena:
During reactor operation, mechanical wear and chemical erosion can roughen the mating end faces of the rotating and stationary rings. If the clearance between these rings and the seal cavity is too small, vibration can occur due to impact caused by rotational swing. Sometimes, vibration and overheating can also result from inadequate temperature or corrosion resistance of the sealing end faces, insufficient cooling, or the presence of particulate contaminants trapped during installation. -
Treatment Methods:
If the clearance between the rotating/stationary rings and the seal cavity is too small, the inner diameter of the seal cavity must be increased, or the outer diameter of the rotating parts reduced, ensuring a minimum clearance of 0.75mm.
If the friction pair is mismatched, the materials of the rotating and stationary rings should be changed to ones resistant to temperature and corrosion. This will help reduce vibration and overheating of the mechanical seal.
3. Causes and Treatment of Mechanical Seal Leakage
Causes of Leakage During Static Pressure Testing of Mechanical Seals
Leakage during static pressure tests often stems from improper handling during installation. This includes damaging, deforming, or injuring the sealing faces; failing to clean surfaces thoroughly, leaving granular impurities; loose positioning screws; an inadequately tightened gland; or insufficient precision of the machine/equipment, preventing full contact of the sealing surfaces. If leakage occurs through the shaft sleeve, it is likely because the shaft sleeve sealing ring was not tightened sufficiently during assembly, had insufficient compression, or was damaged.
Causes of Periodic or Sporadic Leakage in Mechanical Seals
Periodic vibration of the rotor assembly or significant axial play can lead to leakage. The sealing faces of a mechanical seal require a specific specific pressure to function effectively. This is provided by the mechanical seal's spring having a certain amount of compression, which applies thrust to the sealing faces. When the reactor rotates, this creates the necessary specific pressure at the sealing interface.
To maintain this pressure, the shaft must not exhibit excessive axial play, typically limited to within 0.25mm. However, in practice, factors such as unreasonable design, manufacturing inaccuracies, and assembly errors often lead to significant shaft play, resulting in periodic or sporadic leakage.
Causes of Frequent Leakage in Mechanical Seals
Frequent leakage can arise from multiple sources:
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Defects in the sealing end faces.
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Issues with the auxiliary sealing rings.
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Imperfections in the spring.
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Other causes include leakage due to rotor vibration; leakage caused by poor quality or loosening of transmission, locking, and thrust components; leakage originating from the mechanical seal's auxiliary systems; and frequent leakage due to problems with the medium itself.
Methods to Reduce Mechanical Seal Leakage
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Ensure Clean and Smooth Assembly: Components, tools, lubricants, and wiping materials must be immaculately clean. Use soft gauze to wipe the sealing faces of the rotating and stationary rings.
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Smooth Edges and Radii: Chamfers on shafts and seal covers should be polished smooth. Relevant fillets on shafts and covers should be sanded and polished to a shine.
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Handle Auxiliary Seals Carefully: Rubber auxiliary sealing rings should not be washed with gasoline or kerosene, as these can cause swelling, deformation, and premature aging.
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Verify Assembly: After assembling the rotating and stationary rings, manually press the compensation ring to check if it moves into place smoothly and flexibly. Ensure the elastic snap ring is securely positioned. Once the rotating ring is installed, confirm it can move axially freely along the shaft.
4. Excessive Mechanical Seal Vibration and Treatment Methods
Causes and Phenomena
Excessive vibration in a mechanical seal will ultimately lead to seal failure. However, the root cause of significant vibration is not always the mechanical seal itself. Other components of the reactor can be the source, such as an improperly designed shaft, machining errors, insufficient bearing precision, poor parallelism of the coupling, or excessive radial forces.
Treatment Methods
Thoroughly clean the shaft, seal cavity, and the mechanical seal components during installation to prevent contaminants from entering the seal area. Design the axial force balancing device appropriately to ensure the axial play of the equipment rotor where the mechanical seal is installed is ≤ 0.3mm, thereby eliminating axial play.
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