I need some help to analysis abnormal vibration trend.
This machine is centrifugal compressor and has 5 impellers. And it is driven by steam turbine. This machine is compressing propylene from -35'C to 70'C.
At normal state, compressor drive side radial vibration was increased gradually from 20 micron to 30 micron. After load change this vibration have cyclic pattern from 20 micron to 30 micron.
We did some action to do reduce vibration level and to find root cause. (Base bolt tightening, proximitor replacement) But We can not find root cause for this abnormal phenomenon. please review attachment and give some advice.