maximum vibration limit of process gas compression??

[mmmumuw]

Dear All,

i have a question regarding to our decission to install a unit of oxygen compressor.
we have 2 candidate of compressor vendor which all have design :
vertical, dry running - oil free type, comply to API 618 4th edition
its service with output pressure up to 40 BarG and shaft power 350 kW, driven by electric motor w/ speed 720 rpm.

all the specification of compressor vendor meet with our requirement.
only one the diffrence, its the vibration velocity.

The first vendor gurantee of vibration velocity 11 mm/s (RMS)
The second vendor only gurantee 17 mm/s (RMS)

the second vendor said that 17 mm/s (RMS) are acceptable for servicing the above condition.

could you passing the information regarding above??
any article to support above information??
how about the compressor live and effect to maintenance??

Best Regards,
Ng Tjan - bcu

 

[sms]

I consider both 11 and 17 mm/s RMS a bit high for a 618 compressor but the question is where are they measuring? Recip compressors have a wide variation in vibration levels depending on where the measurement is made.

-The future's so bright I gotta wear shades!

 

[BigInch]

Just to give you something else to think about, 720 is very bad rpm for compressor foundations on concrete foundations.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

what's so special 720 rpm (710 actual?)? I would rarely even use concrete under 500 HP compressor. Just have the skid concrete filled. If this is in criticle service, the foundation is still very minimal and would only be grouted with a cement-sand grout.

 

[pmover]

with regards to vibration, one needs to understand the sources of vibration for a recip unit. there are vibrations related to the motion of the oscillating components and vibrations related to the pressure pulsations created by each cylinder. each should be addressed and resolved prior to purchase so as to clarify responsibility & measurement (quantifying actual values & location).
good luck and have fun!
-pmover

 

[BigInch]

Its in a common range of natural resonance frequencies of machine-foundation systems. Companies that value their equipment would always put some concrete under a skid (or check the dynamics of a supporting structure) for a 500 HP recip. Centrifugal - optional, but reaching the serious consideration point. Many company standards require a full dynamic design proof of the compressor and the foundation design at 500, recip or not.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[sms]

In our design standards we would not allow for a 720 rpm machine in this kind of service. About 500 is as fast as we would go.

-The future's so bright I gotta wear shades!

 

[BigInch]

!

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

OK, the rpm is a function of two things, stroke and at some point gas velocity limits through valves. Most compressors have speeds where S * RPM < 7000 (S= stroke in inches) A more conservative is S * RPM < 6000. If the gas has a high molecular weight, the typical cylinders won't have a high enough valve capacity and the volumetric effiency drops and the internal ratios increase. To compensate, the speed is reduced to S * RPM <4000 for propane.

 

[mmmumuw]

Dear All,
sorry for given uncomplete data.

the first vendor guarantee a maximum effective vibration velocity of 11 mm/s (rms) measured at the cylinder edge with requirement : highly adjusted, rigid foundation with rigidly fixed pipes.
the effective vibration velocity of the foundation inferior to 1.5 mm/s (rms)

the second vendor only guarantee the effective vibration velocity of 17 mm/s (rms) mesured on the cylinder edge. they do not stated the effective viobration velocity of the foundation.

so, kindly give me the advice regarding of above two option.

do you all have ISO 10816 - 6 publication??

BR,
Ng Tjan - bcu

 

[PulseMaster]

These levels (17,11) are not that high. I've seen higher speed machines, of a much larger class, with 25+ mm/s with no incidence of failure.

Keep in mind that you can't believe what the vendor (any vendor) tells you. A system like this is dependant upon many variables that the vendor has no control of. If you need an extremely reliable machine, you should have independant vibration and pulsation studies done that take into account many of these variables, like the piping, the skid, your specific operating conditions, etc. Or request a reference from the vendor, for the quoted machine, in the same service, and get the details of the installation.