Failure causes and countermeasures analysis for a large-scale reciprocating compressor vibration

The crankshaft with 6 crank reciprocating compressors often cracks and the 1st and 2nd crank bearing often scuffs due to torsional vibration. Such problems are handled by connecting the 2nd and 3rd shaft by means of interference hot assembling two plate flanges. Using ANSYS software, finite element analysis model is set up for pre-and-aft modification of crankshaft. Modal analysis and dynamic response calculation of crankshaft under different modification plans are performed and results show that the frequency ratio r between sevenfold rotating speed of initial crankshaft and the first order torsional vibration natural frequency is 1.016, which makes the initial crankshaft resonates. With the rotating inertia-mass of modified crankshaft enlarged, the frequency ratio increases to 1.064, and resonance is eliminated. The rotating vibration displacement of initial crankshaft at the first crank pin is far bigger than that of the 6th, which is the main reason of crank bearing scuff. The inertia-mass of initial crankshaft results in additional stress at resonance, which is the main reason of crank cracking.