Complete compressor drygas seal failure 1

[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

 

[flexibox]

It It is very unsual to have both primary and secondary seal fail simultanously. What indusry are you in? What is the application? This is not such a straght forward answer. There are many things to consider:
1 How long have the seals been in service?
2 How many stop / starts have you had?
3 What drives the compressor? Is slow roll part of the start up procedures?
4 When did the seals fail, during start up or normal operation.
5 What is the condition of the separation gas seals? Are they labyrinth seals?
6 Is there oil contamination in the secondary seal cavity?
7 What is the condition of the seal, has it shattered to bits ?
8 Do you have a positive flow of clean process gas to the seals at all times, not just during normal running but during start up/shut down and settle out conditions?
9 Who designed and supplied the gas panel, is it designed with a gas booster?
10 Most gas seal failures occur due to contamination, solids or liquids. Can you see what the seal faces and balance diameters look like. Are they clean or dirty?
11 Do you experience many plant trips?
12 What is the vibration history before the failure?

The list goes on but very difficult to conclude but hope this has shed some light for you

 

[ed16]

Flexibox, thank you a lot for yor reply.

We are running 8 compressors in an ethylene plant.
The risk analysis is made without any actual failure in mind.
We just want to be sure that all precautions are made in case of such an event....
Risk analysis asks for the probabiliy of events, so we need some figures.

1 How long have the seals been in service?
since last turnaround, 4 years.

2 How many stop / starts have you had?
approx. 2...10 depending on compressor.

3 What drives the compressor? Is slow roll part of the start up procedures?
Compressors are steam turbine driven, therefore each stop will result in slow roll for the seals.

4 When did the seals fail, during start up or normal operation.
Until now, we didnt face a complete seal failure.
We have had some failures of primary seal during first commissioning caused by process upsets / water.

5 What is the condition of the separation gas seals? Are they labyrinth seals?
They are lift off carbon rings. Maximum pressure is aprox. 10 bar before they will be destroyed.

6 Is there oil contamination in the secondary seal cavity?
No.

7 What is the condition of the seal, has it shattered to bits ?
No - still running. Its just a "what happened if..." question.

8 Do you have a positive flow of clean process gas to the seals at all times, not just during normal running but during start up/shut down and settle out conditions?
Yes, alternative clean gas source is available during pressurised stand still / slow roll / start conditions.


9 Who designed and supplied the gas panel, is it designed with a gas booster?
Gas Rack was designed by compressor supplier.
Booster is not required due to alternate cleangas supply (Ethylene tank / NP-Nitrogen). Design is in accordance with API614. Looks like good quality and design.

10 Most gas seal failures occur due to contamination, solids or liquids. Can you see what the seal faces and balance diameters look like. Are they clean or dirty?
We have had only sealfailures in the very beginning due to liquid contamination. We are lokking for "what if...."


11 Do you experience many plant trips?
Approx. once per year, mainly electrical power failure.

12 What is the vibration history before the failure?
Vibrations are all within Zone A of ISO.
No outstandings. Same with axial displacements.

Thank you for your support !!!
Ed

 

[flexibox]

you should be fine, looks like everything is covered.