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kredegh
22-12-2016, 10:25 AM
hello every one,
I am working in Gas plant and our propane refrigeration package suffering from repeated mechanical seal damage at every compressor. we have 3 compression skids(A/B/C) at each gas train. two in operation and one auto stand by, by unfortunately , only one compressor AT THE MOMENT is ruining at each gas dew point train . other compressors are out of service due to mechanical seal damage and lube oil leak.
OUR PLANT is aged 12 years old.
Suction pressure 1st Stage:1280-mbar. /Suction pressure 2nd Stage:0.244-barg.
Suction temperature 2nd Stage:-19 C. /Oil separator temperature: 79.7C.
lube oil inlet temperature to mechanical seal:56.3C.
Export gas temperature: -16.5C.
we are using AgipDicrea S150 as Lube Oil for this compressor.

if any one had an experience with similar issue of mechanical seal damage please let me know your findings.
best regards,
Zuhear,

RANGER1
22-12-2016, 08:42 PM
Zuhear,
Can you explain what fails in seal once removed & inspected.
Is there anything obvious, like deteriorated "0" rings, or damaged seal faces?
The seals I have seen from these, if yours are the same, are very basic.
Sometimes a seal company would have a contract to look after a site like yours, is that the case at your plant?

A few pictures would be good.

The oil grade could be checked, as usually 68 grade would be used, not 150.


http://www.atlaskompresor.com/dosyalar/belgeler/Agip_Dicrea.pdf

mbc
23-12-2016, 07:14 AM
Hi
As you know coppling is very important to be come leaking
To repair that might only you need to change O ring and don't forget
Adjust agine coppling

kredegh
23-12-2016, 04:36 PM
Hello every body,
firstly I would like to thank you all for your kind replay with regards to shaft mechanical seal leaking issue. I am doing some investigation at the moment. I have found that the propane composition is out of specification, where there only 57% propane, and 42% (i-butane &n-butane), and 1% ethane, I dont know the impact of these impurities on the lube oil . specification, we tried to use Agip Dicrea S150 Lube Oil in gas train one , and we kept other trains with Toromont vendor lube oil 150. i have realized heavy foaming in the lube oil while taking the sample , is there any impact of all these issues on the mechanical seal?
I know that some hydrocarbons intends to dilute the oil and some could also react with oil additives.

heavy hydrocarbons dissolved in the lubricating oil could form sludge and some strange deposits can be the main reason behind the Hard agglomerate material that was found deposited on the sealing carbon rings which caused their failure to leak. Burned, deteriorated oil could be the origin of this substance.
****** is this correct? ***** many thanks in advance to you,
Zuhaer,

RANGER1
23-12-2016, 11:27 PM
http://www.slideshare.net/PremBaboo/fundamentals-of-mechanical-seals?next_slideshow=1

I think you should engage with shaft seal company like John Crane of similar to rectify problems.
There are to many things to give simple answers

kredegh
24-12-2016, 04:52 PM
thank you Ranger1,
in fact, our company has contacted john Crane , and John Crane has upgraded the face composition for the rotating face into hard face with new one “Silicon Carbide”.
John Crane has refurbished the failed seal on FOC basis as a trial, The refurbishment has included the change of the internal hardware (New faces, O rings, Springs, Set screws). this was installed only at one screw compressor as a pilot.
unfortunately , there was no improvement . lube oil still leaking throw mechanical seal.

mbc
24-12-2016, 05:34 PM
Hi
There is 2 pieces of 0 ring change it with 0.5 mm
big Dia ( if it is 4 mm go for 4.5 mm)
might you need more power to push seal to put in his place
Also Polish well where is O ring is setting there

Josip
24-12-2016, 08:19 PM
Hi, kredegh :)

welcome to RE forums ...


hello every one,
I am working in Gas plant and our propane refrigeration package suffering from repeated mechanical seal damage at every compressor. we have 3 compression skids(A/B/C) at each gas train. two in operation and one auto stand by, by unfortunately , only one compressor AT THE MOMENT is ruining at each gas dew point train . other compressors are out of service due to mechanical seal damage and lube oil leak.
OUR PLANT is aged 12 years old.
Suction pressure 1st Stage:1280-mbar. /Suction pressure 2nd Stage:0.244-barg.
Suction temperature 2nd Stage:-19 C. /Oil separator temperature: 79.7C.
lube oil inlet temperature to mechanical seal:56.3C.
Export gas temperature: -16.5C.
we are using AgipDicrea S150 as Lube Oil for this compressor.

if any one had an experience with similar issue of mechanical seal damage please let me know your findings.
best regards,
Zuhear,

Your plant is probably propane liquefaction plant, condensing boil off gas, chilling butane gas, etc ....

Not sure, but if 510 is related to screw diameter that would be Howden compressor 510 with 4 pole motor ... i.e. running at 1500-1800 rpm, but I can be wrong ;) either... smaller screws are running normally at 3000-3600 rpm depending on power network frequency...

Important thing is to have a very good alignment (motor-compressor) otherwise a lot of problems with shaft seal. Alignment should be checked once a year ...

When did you last time replace your shaft seal/s ... i.e. how many working hours you can run with new shaft seal?

How many working hours you have with your compressors?

From your description of working pressure 1st and 2nd stage I am little bit confused ...

Do you have 3 skids each with first and second stage compressor, condenser or some other design?

First stage is always one operating at lower suction pressure ... in your case that would be one with suction pressure of 0.244 bar - what is discharge pressure and discharge temp?

1280 mbar is 1,28 bar and that would be discharge pressure of the first stage and suction pressure of the second stage ... what is discharge pressure and temperature of the second stage?

What is export gas temperature !?! (


The best is to use the same units (bar) in Absolute/Relative scale (to avoid any confusion)...


I believe on compressor you have double seal arrangement ... normal wet seal and dry seal with seal pot...

I am curious where exactly you have oil leak ... some photo?

To not lost the time discussing possible "wrong presumptions" ... can you, please, upload schematic diagram of your plant where we can see all ... at least PFD ...Process Flow Diagram. Technical stuff is much better to discuss with drawings, hope you agree with me.

Oil viscosity should be OK ... probably it is by design documentation and recommended by compressor manufacturer.

Best regards, Josip :)

kredegh
25-12-2016, 11:14 AM
14467

kindly see attached picture of damaged mechanical seal for screw compressor

kredegh
25-12-2016, 11:20 AM
14468
kindly find some other pictures.

RANGER1
26-12-2016, 12:02 AM
Zuhaer,
Maybe you should contact Howden to see what they suggest.
If you do not have ask for service manual with tilted pad & main bearing clearances.

Do you think they have worked OK in the past, or never?

I would ask is it a balanced type shaft seal.

Also if drive rotor moves in or out, can seal faces be held together with spring tension, or even have enough or to much spring tension, which comes back to thrust bearing end play.


https://www.howden.com/Resources/Product%20Brochures/Shaft%20Seal%20Bulletin.pdf.

Howden always seem to have to many "0' rings, so not a big fan, as well as cost.
But this is specialised piece of equipment.

Mechanical checks should also be carried out, as this size machine would have tilted pad thrust bearings.

- coupling alignment as MBC mentions
- drive rotor end float (using a lever & dial indicator (push & pull) to measure bearing clearance
- main bearing wear, using dial indicator measure clearance of bearing by lifting upwards.
- determine oil flow in & out of seal housing chamber for lubrication, cooling. Oil can flow in, but can it flow out a vent & where too.
- make sure oil is propane free by having oil temperature above saturated refrigerant temperature.

kredegh
14-01-2017, 02:42 PM
hello every one,

I would like to ask , what is the acceptable water content in the screw compressor lube oil ?

because in our lube oil we we found 0.93 ppm.

RANGER1
14-01-2017, 10:26 PM
kredegh,
From this it says it's OK
Maybe test new oil as base guideline.
Do you have filter/drier in system as used in standard refrigeration system?

http://us.kaeser.com/images/basics%20of%20rotary%20screw%20compressor%20lubricants-tcm9-319606.pdf

http://www.machinerylubrication.com/Read/192/water-contaminant-oil