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Typical seal failures that occur in actual production and countermeasures

January 12, 2022

 

  During the operation of the machine, the mechanical seal suddenly leaked, the medium was gasoline, and the temperature reached 200

 

degrees Celsius. During the seal disassembly and inspection, it was found that the seal face was excessively worn, and the seal was a single-

 

face bellows mechanical seal.


The following situations were found:

 

1. The moving ring is separated from the moving ring seat, and the moving ring is broken;

 

2. The seal is severely worn both dynamically and statically;

 

3. There are obvious narrow wear marks on the end face of the broken moving ring;


Cause analysis of seal failure:


1. The moving ring and the moving ring seat: they are hot-loaded, and the linear expansion coefficient of the selected base material is different. Under the condition of high temperature, there may be improper interference fit, resulting in the separation of the moving ring and the moving ring seat;


2. There are obvious wear scars on the end face of the moving ring and the color of the wear scars is darker, indicating that there is excessive heat generation, dry friction on the sealing end face and thermal deformation of the sealing end face. If the seal compression is too large, it will aggravate the wear of the sealing end face , The particulate matter enters the sealing end face, resulting in serious wear of the sealing end face;


3. Due to the harsh operating environment of the seal, the large thermal stress leads to radial thermal cracks on the end face of the moving ring. When the pump is started and stopped, the change of the axial force of the pump and the vibration of the pump body cause the moving ring to be completely broken;

 

Actions to take in case of failure:

 

1. Add sealed cooling water to improve the sealed operating environment, and the cooling water is demineralized water;


2. Properly adjust the amount of seal compression, and it should not be too large;


3. Before replacing the seal, check the sealing parts to avoid the problem of the quality of the seals;


In the reforming device, almost every dismantling and inspection can find the wear of the seal end face, the phenomenon of cavitation, the blockage of the cooling inlet and outlet of the cooling chamber of the seal chamber, and the blockage of the seal flushing liquid cooler;

 

Reason analysis: The pump medium is hot water higher than 100 degrees Celsius, and the cooling medium of the seal flushing cooler is circulating water, which is easy to scale, which makes the water chamber of the sealed cavity block, and the self-flushing cooler has poor scaling and circulation, causing the inside of the sealed cavity The medium is vaporized, and the seal end face is cavitated due to dry wear of the end face, etc., which makes the seal fail;

 

Corresponding measures:

 

1. Replace the heat exchanger with a larger heat exchange area to avoid leakage of seals due to insufficient heat exchange;


2. It is recommended to change the circulating water for cooling to softened water to seal the sealing leakage caused by the blockage of the cooling system structure;