Adre measuring: Oilwhirl

Observation: 

An engine driven compressor (integrated gears) trips during shutdown procedures. 

Unburden the machine slowly. During this procedure the machine tripped on vibrations. 


The figure below shows this in trend: 


ADRE surge oilwhirlADRE meting oilwhirl

The increase is most visible on stage 5.

When we look at the shaft centerline, we see the following images: 



ADRE surge oilwhirl

On stage 5 we see a decline of the bearing shaft of 50┬Ám when pressure on the machine is released. 

During the run out period there is a further decline. We may assume that the shaft runs high in his bearings during normal procedures. When the shaft declines, it comes towards the middle, where is more freedom of movement, which results in higher vibrations. 


Looking at the orbitals during the event we get this image: 

ADRE surge oilwhirl

There is an unstable behavior of the axis, which can be related to the process or oilwig.

In the spectra we see this image: 


ADRE surge oilwhirl

There is a clear formation of sub-synchronous peaks. 

In the waterfall plot below the formation of these peaks is visible. 



ADRE surge oilwhirl

The blue spectra are those from before the shut down. The red spectra are derived from the fall out. In the green circle the formation of sub-synchronous peaks is visible. 

Conclusion: 

The cause of the alarm on high vibrations is located in stage 5. 

An unstable behavior appears, likely we are dealing with an unstable oilwhirl.