Cover leakage of centrifugal compressor

[lahcen]

Hi guys,
A centrifugal compressor (Thermodyn), there are two pipes (see the picture), I want to know the role of this pipes and if the pipe of the suction side is very hot that means there is a problem.

Thanks

 

[georgeverghese]

That means your HP compressor inboard (suction side) secondary shaft seal is leaking so much, it has significant backpressure buildup ( caused by the RO 961 -see lower right of the drawing), and some of this leak gas is breaking out of the inboard shaft seal cover. If you leave this unattended and leakage gets worse, it will set off the gas detectors in this area.

 

[lahcen]

Thanks georgeverghese,
I think these pipes are for leakage from the head flange (very hot suction pipe that means the Head flange's O-ring is damaged)? I want to confirm.
Because the parameters of the DGS are very good.
I want to confirm these pipes from the casing that meet with the primary vent of DGS and after to the flare, are for the leakage from the head flange or not and if one of them is hot that means that the O-ring of the head flange is damaged.

Thanks and sorry if my Thread was not very clear.

 

[LittleInch]

If I read this correctly the cover leakage sits at the pressure of the incoming purge gas supply which is??

If this pipe is getting hot then all you can say with any certainty is that there is a leak somewhere under the cover and you need to find it. Could be anything under there - we don't know and can't see what is contained within the "cover". The P&ID shows the cover covering the whole unit, but not sure if that's strictly correct.

What temperature is the cover itself?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[lahcen]

Thanks LittleInch,
I don't know how much the temperature of the cover, but I want to know what's the meaning of cover leakage (head flange leakage?), if any one is familiar with this pipe or Centrifugal compressor that has these pipe, or any one has a document about this.
I read that sometimes if the head flange has two o-rings; this pipe for the leakage between the two o-rings but I'm not sure.

Thanks

 

[LittleInch]

Errrr, it's your compressor, not ours.

All we know is what you tell us so it looks to me like there is a gas tight cover over all of the compressor components to catch any fugitive leaks from seals or gaskets or vents holes or whatever and pipe it away to the flare.

All you've told us is the make of the compressor and a seal P&ID drawing.

The people here are good, but we're not mind readers or have intimate knowledge of every compressor ever made.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

When you say "cover leakage", and at the same time you've got this hot vent line from the inboard seal, it seems obvious to me this is a failure of the secondary shaft seal on the inboard side. Not a leak from the O ring or gasket on the head flange.
Btw, this leakage from the shaft seal SHOULD'T be setting off your gas detectors, since the gas injected into the secondary seal of the DGS is usually inert gas or dry instrument air.
If the local DGS panel is saying all is still normal, I would check these settings for secondary seal buffer gas flow with the seal vendor or the compressor manufacturer data. What is your buffer gas, and is it adequately dry?

 

[lahcen]

Thanks georgeverghese,
our buffer gas is fuel gas and it is dry.
our DGS with two vents: a primary vent to flare and a secondary vent with another line ( not these lines from casing) to atmosphere, and with two injections: fuel gas and Nitrogen.
and we have an indicator if the secondary seal is damaged (Δp<5mbar at PDIT968&969)but the Δp is good).

Thanks

 

[georgeverghese]

The diagram shows another set of labyrinth seals downstream of the secondary labyrinth seal - it is this seal that may be damaged. Who is the shaft seal supplier? Do you know the model of the shaft seal assembly you have on this machine, and have you spoken to this supplier yet?

 

[lahcen]

Thanks georgeverghese,
I'll check with the supplier.