Relationship between secondary failure of dry gas seals and shaft displacement fluctuations
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During the startup of our company’s unit, the secondary dry gas seal on the non-driven side of the compressor’s low-pressure cylinder failed. The cause was identified as sticking of the secondary static ring. While the secondary seal fails, the shaft displacement fluctuates within the range of 7 um. Is there a relationship between the two? What is the cause of the shaft displacement fluctuations in this situation?
In my memory, the shaft displacement range for dry gas seals is relatively large; as long as the compressor’s shaft displacement remains within the alarm limits, the dry gas seal should not be damaged
An axis displacement of 7 um should not be the cause of the jamming in the secondary static ring
What does it mean for the static ring to get stuck? The static ring is supposed to remain fixed; so how can there be any issue of getting stuck? The stationary and rotating rings of a dry gas seal do not come into contact with each other; a rigid air film keeps them apart, so there is no risk of jamming. During operation, if the stationary and rotating rings were to make contact, the dynamic pressure grooves would be worn out, resulting in the failure of the seal. Before starting up, was the secondary seal air turned on? Is the pressure and flow normal? It could also be that the shaft displacement caused damage to the seal; the cause and effect have been reversed! As for why the shaft displacement fluctuates, could it be due to fluctuations in the amount of air intake and exhaust, issues such as surge, which cause imbalance in the rotor? Also, was this compressor started after maintenance, or was it started without any maintenance?
The stationary ring remains fixed; only the moving ring can move slightly axially on the shaft sleeve. Have you got it wrong?
What I mean is whether a slight displacement of the dynamic ring on the sleeve could cause fluctuations in the shaft’s displacement
Axial displacement refers to axial movement, which can cause the dry gas seal to open and close; however, movement on a scale of 7 micrometers requires further investigation to understand the specific situation.
The sealing gas didn’t get injected, or the sealing gas contained liquid
This post was last edited by tanxjzm on 2018-9-12 21:22. Generally, for rotors equipped with dry gas seals, the design takes into account the impact of these seals on axial thrust. Under normal circumstances, it will point in a relatively stable direction. After the dry gas seal fails, due to the effect of the combined thrust oil film, if the actual axial force is too low, it is possible for the rotor’s operation to become unstable, resulting in fluctuations in axial displacement.
I’d like to ask how the oil film functions What is the typical thickness of the thrust side oil film?