Complete compressor drygas seal failure

[ed16]

Hello !

We are just performing a risc analysis for a complete drygas seal failure (inner and outer seal of a turbocompressor tandem seal).
In our company we didn-t face such an event until now,
so we are not able to determinate the probability of such an event.

I would appreciate any informations regarding complete seal failure at turbocompressors and the probability of such an event.

thanks in advance
Ed

 

[pmover]

provided that the buffer gas/air and seal gas remain clean and dry per the mfg recommendations (dirt, liquids, etc. are destructive to seals), provided the rotor is stable throughout the defined process conditions (i.e. avoid surge conditions, rotor unbalances, etc.), provided that other components in the seal gas system work as designed, dry gas seals should last a long time. there are many variables and components to consider in the risk analysis.

complete failure of dry gas seals are expensive and can be hazardous to equipment/personnel depending upon the gas being compressed - the compressed gas may leak to atmosphere.

hope this helps or this a start.

good luck!
-pmover

 

[DLite30]

One thing that our group has standardized on is a seal gas booster system, which boosts seal gas pressure on start-up and shutdown of the unit to ensure that there is always positive pressure at the seals such that gas is flowing into the compressor casing.

Generally your seal gas is supplied through a port on the discharge piping of the compressor and then regulated down to about 30 psig or so higher than suction pressure. During start-up/shutdown you don't have this differential pressure built up...so becomes the job of the seal gas booster.

Without this system, you cannot safely assume that you are keeping process gas/debris from the labrynth and/or the carbon seals.

 

[Rotator]

Complete failure can occur in destructive scenarios like severe surge, but can also occur if the outer secondary seal has failed but the failure has not been detected. A subsequent failure of the primary seal will then release gas to atmosphere. Secondary seal failure can be caused by oil contamination from the adjacent bearing, and is not uncommon. The risk mitigation is to have effective means of detecting failure of both primary and secondary seal.

 

[JoeySoap]

Look also for Nitrogen seal gas purity issues if the process gas contains H2S and you're using N2 seal/seperation/buffer gas. There have been failures from black powder formation in the seals due to impure N2 being used. HTH.

 

[CompSysNPD]

To best understand what your risks are you need to understand what kind of failure to expect. Typically if your are going to fail both seals at once, it is going to be some kind of major even that causes the issue.

If you have a stable rotor then seal contamination will likely be the number one killer of seals.

You have to ask yourself and the OEM what kind of failure modes the seal can undergo when it becomes contaminated. i.e. Will it fail slowly and simply stop providing the sealing performance required, or will the contamination cause the seal to hang up and basically self destruct sending debris throughout the rest of the seal system. I have seen both instances occur in the field.

Hope this causes you to think deeper and ask for the support from the compressor and seal vendor.

 

[jbattershell]

Seal failures are typically the result of contamination as indicated by the previous responders. it is the job of the seal support system to measure and detect when seals are not performing as designed. a good system will alert the operators of a problem with seal gas flow, excessive leakage, stoppage or shortage of N2 flow etc. It is the job of the seal support system to mitigate damage from seal damage. most times, the damage being caused to a seal can be sensed and the machine stopped before a catastrophic failure occurs. if the system is in adequate in this regard, then the seal will likely fail dramatically.

there was no report from original poster if there was a pre-warning of seal damage or if it just went south in a quick fashion. I can offer further help with some details of what happened prior to the total seal failure.