Session: 27-02: Damping, Stability, Swirl-Induced Effects & Seal Dynamics.

Submission Number: 176262

Destructive Axial Vibrations on IGC Thrust Collars: RCA 

Axial vibrations in centrifugal compressors are rarely mentioned in technical literature. Furthermore, unlike lateral and torsional vibrations, traditionally API 617 does not require specific design checks for this phenomenon, nor does the installation of dedicated instruments to monitor it (only the last revision of the above code requires to monitor axial vibrations during MRT in order to save dry face seals).

Here, we present a case report of such a phenomenon that caused the destruction of the first-stage rotor of a three-stage centrifugal compressor with integrated gears, used as a MAC, a few months after installation in an ASU system. The twin compressor installed on the same plant was also inspected, and the incipient phenomenon was also observed there, consisting of a series of indentations with variable radial extension due to direct metal-to-metal rubbing between a collar generator and the impeller.

Root cause analysis identified the origin of the problem as an inadequate thrust collar design for such a unique application, which featured only a large, cantilevered impeller on one end of the pinion, while the other end was free. The geometry of the gear teeth and the collar coupled with radial synchronous vibration due to imbalance with axial vibration. The high axial thrusts generated by the large impeller excited the natural frequency of the axial system, which was too low due to the significant mass of the pinion and the insufficient rigidity of the collar. The oil film, capable of providing the hydrodynamic support necessary for the collar's proper operation, requires a very precise geometry, compromised by excessive deformations.

An axial vibration probe, installed on the free end of the pinion, confirmed the presence of axial vibrations with a harmonic spectrum.

Several options were considered to address the problem in the field, taking into account environmental constraints: the decisive intervention selected consisted of replacing the thrust collar with a thrust bearing.

Presenting Author: Andrea Fusi Compression Service Technology srl

Presenting Author Biography: Andrea Fusi graduated in Mechanical Engineering at “la Sapienza” Rome Engineering University.
After a short cooperation with Energetic Department of Florence University for development of simulation software of thermo-dynamical systems, in 1984 he joined Nuovo Pignone spa working as Project Engineer for Reciprocating Compressors and then as Design Responsible for Integrally Geared Compressor.
In 2003 he moved to Compression Service Technology where he now leads the R&D department. In this position he created innovative software for machines and systems analysis and taught and managed advanced training courses on Reciprocating and Centrifugal Compressors.

Authors:

Andrea Fusi Compression Service Technology srl
Andrea Betti Compression Service Technology srl
Giovanni Karahoxha Compression Service Technology srl