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We are facing a very interesting issue of high shaft vibration in one of the pinion shaft with operating speed of 69700 RPM for a IG compressor. The pinion shaft is a flexible rotor and has two critical speed within the operating speed, the OEM pinion shaft was of JIS standard (SNCM 420 material as per JIS G 4053-2016) and the newly manufactured pinion is as per EN10084 standard wherein the only variation is in the Chromium alloy % which is 1.5/1.8 % as per EN standrad and 0.4/0.6 % as per JIS standard.

The new pinion shaft is manufactured exactly a per the old one and has weight difference of 2%.

Both the pinion shaft are balanced to API standard and unbalance is not an issue.

The pinion vibrations are found increasing to trip limit only at a particular speed range which is near to operating speed (separation margin 5% or less).

Now, the question in front of us is, What is the effect of chemical composition and variation in alloying elements on the rotor stiffness which intern effects natural frequency.

Kindly, give some insight into the subject or share some of the litrature if you have come across.


Santosh S

Tags: API

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