Paper No. 110
By Dong-Ju Lee, Dr. Jae-Yeol Park and Troy Feese
Torsional Vibration Symposium 2022 – Salzburg, Austria
Two new hydrogen reciprocating compressor systems were equipped with stepless capacity control. Initial problems after commissioning included high crosshead guide vibration, failures of the shaft-driven mechanical oil pump (MOP) and a motor cooling fan. It was later observed by personnel at the plant that elevated vibration and speed fluctuation of the system generally occurred while operating at medium compressor load. The manufacturers performed torsional vibration analyses (TVAs) in the design stage, which predicted adequate separation margins from significant compressor harmonics. Therefore, any concerns of torsional vibration were initially dismissed. Field testing with a strain gage telemetry system found that the first torsional natural frequency (TNF) was coincident with 8× running speed. This resulted in amplifying alternating torque up to 800% of full load torque (FLT) and the system being very sensitive to compressor loading due to the torsional resonance. The compressor crankshaft and motor shaft later experienced fatigue failures and had to be replaced after a relatively short time of operation. Spiral cracks occurring at a 45-degree angle to the shaft axis were consistent with failure due to high torsional vibration. As a short-term solution, the compressor was operated at a load condition that minimized the alternating torque. The TVA was then normalized to match the field data. The long-term solution involved detuning the TNFs by adding inertia to the flywheel and to the motor external cooling fan. The modified systems were retested to verify satisfactory operation over the entire compressor load range.