Dear all,

Kindly please suggest me for Abnormal peaks vibration

My Fertilizer Plant has a Hydraulic Turbine (the HPRT) connected to a motor by a clutch, plays an important role in energy consumption reduction.

1.  HISTORICAL BACKGROUND

High vibration on the HPRT has been noticed since 2014. It was recorded abrupt increase, continuously and unstable high vibration on DE and NDE hydraulic turbine side in a certain period so we stop the HPRT for along time. 

Machine has been three-times modification of the suction piping system. The last overhaul after the third piping modification and commissioning in Nov 2018 was found the cracked shaft at turbine. Machine was run again sucessfully on 16 Apr 2019 after replaced new shaft at turbine.

2. In recent days, we found abnormal high peak vibration at dominant frequency is 1X, hamonic and 1X phase lag change 90 degrees. It is surprising to see NDE vibration reading tended increase up to 75 um while DE decrease. please look at attachment for detail.

 3. DISCUSSION

We suspected 1X phase lag change 90 degrees to be caused by readjusted/shifted clutch when turbine’s speed fluctuation. Do you have any opinions and suggestion for our action?

Thanks in Advance

Attachments

Files (1)
Original Post

The plot says 1491 rpm or 24.8 Hz, so the 1xSS is where you marked it. In spite of the low resolution of 800-lines, what you marked as harmonics appear to be correct. I am guessing the marker at 69 Hz is a lost cursor. I hate it when the cursor is not on something important. 

Walt

 

thi khuyen

Quote: "This is very normal spectrum for sleeve bearing monitoring. My problem is peaks and 1X phase change 90 degrees that is often appear."

Am I correct in thinking that you are saying, the phase and amplitude shifts/changes for no known apparent reasons?

No speed change involved? Only amplitude changes plus phase shift changes at the same time? Does the machine ever return to the original phase and amplitude for the same "no known apparent reasons"?

Thanks and Have a Great Day,

Ralph

Do any of these events with phase change happen to occur when you drop out the motor and later bring it back online?  With a SSS clutch, as you have shown, the phase will vary from engagement to engagement.  There are multiple positions of engagements, input relative to output, and in fact can be quite numerous.

Hi, thi khuyen

As a basic point when the clutch is engaged and transmitting torque there are no movements inside that can lead to a change in vibration amplitude or phase.

 On each engagement the clutch will engage in any of 44 angular positions depending upon the relative position of the turbine and the pump when the speeds of those synchronise.  In each position the clutch engages the residual unbalance effects from turbine and pump will add in different ways so vibration amplitude and angle will vary depending upon clutch engaging position but this is mainly the effect of the other machines unbalance and not a function of the clutch.  This is is normally a 1x vibration and again does not change once the clutch is engaged.

 I know that there can be many vibration effects caused from liquid flow effects within the Turbine and the Pump.  Unfortunately I am not knowledgeable about those details and ask you to discuss with the pump/turbine manufacturer or a process engineer is the best way you can solve it.

 

"We suspected 1X phase lag change 90 degrees to be caused by readjusted/shifted clutch when turbine’s speed fluctuation. Do you have any opinions and suggestion for our action?"

If the change in vibration (amplitude and phase) is coincident with clutch engagement and disengagement, then a full internal clutch inspection and possible overhaul should be considered for a scheduled outage.

Walt

I think that in this condition the turbine is always forcing the motor and therefore any speed variation is due to changes in the motor speed caused by changing pump load/electrical power etc and there is always positive torque in the clutch which will remain engaged.  If the clutch remains engaged it is acting like a flexible coupling with no internal movement and its speed is determined by the other machines and it will not affect vibration.

 Hope you understand

Walt Strong posted:

"We suspected 1X phase lag change 90 degrees to be caused by readjusted/shifted clutch when turbine’s speed fluctuation. Do you have any opinions and suggestion for our action?"

If the change in vibration (amplitude and phase) is coincident with clutch engagement and disengagement, then a full internal clutch inspection and possible overhaul should be considered for a scheduled outage.

Walt

Please know what the clutch is … a freewheel.  This is like a bicycle freewheel so it is impossible for the pedals to go faster than the wheel and the only way that the freewheel disengages is when pedals don’t go fast enough to drive the bike.

I think no chance for clutch engagement and disengagement meanwhile turbine is running

In other words, there is no failure inside the clutch that can cause a fully engaged clutch to allow the turbine to go faster than the motor. The issues may come from other sources such as process problem, internal clearances

I have been in the vibration industry for 50 years and in "hydro" most of the time. Your problem of :

  1. Cracked shaft and probably another one coming!
  2. Phase shift of 90 degrees
  3. Instant amplitude change

You most likely have a mechanical resonance. It all fits! Do a Bode or polar plot and you will most likely see a circle or half circle. If you continue to operate this machine you must have good vibration monitoring and inspections. Of course the proper thing to do is find out what is resonating. It should not be too difficult but it is very important! Convincing superiors that you have "resonance" is like trying to convince an apparently  healthy person they are really sick-- it is difficult but needs to be done

Let me know if you need more information. I have spent my life chasing esonances

Doug Franklin posted:

I have been in the vibration industry for 50 years and in "hydro" most of the time. Your problem of :

  1. Cracked shaft and probably another one coming!
  2. Phase shift of 90 degrees
  3. Instant amplitude change

You most likely have a mechanical resonance. It all fits! Do a Bode or polar plot and you will most likely see a circle or half circle. If you continue to operate this machine you must have good vibration monitoring and inspections. Of course the proper thing to do is find out what is resonating. It should not be too difficult but it is very important! Convincing superiors that you have "resonance" is like trying to convince an apparently  healthy person they are really sick-- it is difficult but needs to be done

Let me know if you need more information. I have spent my life chasing esonances

Dear Mr DOUG FRANKLIN,

Thank you very much for sharing your knowledge and It is an honor to discuss with a 50-year expert like you.

I would like to update data for this machine recently for more analysis. 

We had a plan to check bearing condition but with your useful analysis we will have to consider very carefully the upcoming action plan. 

Could you share more analysis about signal/symptom of rotor crack and solution for resonance case.

Attachments

Dear Thi Khuyen

Sorry about the late message,

The primary way to test for resonance is to operate the machine over a speed range while recording to amplitude and phase. You can do this using System 1. Start up the machine , take it to normal speed and then to overspeed by 10%. If the resonance is speed related it will show up. The alternative is that the resonance is the result of a softening/hardening spring system. This makes it much more difficult.

The primary vibration amplitude is at ~ 25 Hz. This is very, very close to operating speed. Do the speed rise test.

The turbine appears to be a bubble ended Francis style?

Do the speed rise test.

Regards, Doug Franklin

i want to see two things:

1. Any coincidence between changing speed of motor and vibration and phase change (trend to compare)

2. Waterfall which cover several times of amp and phase change.

By the way, which speed the clutch will be engaged, where is the keyphasor takes the reference at NDE side of HT or Pump.

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