Analysis for Fatigue Failure Causes on a Large-scale Reciprocating Compressor Vibration by Torsional Vibration

The crankshaft of a large-scale reciprocating compressor frequently cracks because of the fatigue failure and the 1st and 2nd crank bearings often are scuffed due to torsional vibration. Such problems are handled by connecting the 2nd and 3rd shaft with two plate flanges in the form of interference fit assembling. Using numerical simulation, models are built for the two crankshafts with modification. Modal analysis and dynamic response calculation of crankshaft system under different modification projects are performed. The results show that the frequency ratio r between sevenfold rotating speed of the initial crankshaft and the first order torsional vibration natural frequency is 1.016, which makes the initial crankshaft to resonate. With the enlarged rotating inertia-mass on modified crankshaft, the frequency ratio r increases to 1.064, and the resonance is eliminated. The rotating vibration displacement of the initial crankshaft at the 1st crank pin is far larger than that of the 6th, which is the primary cause of crank bearing scuffing. The inertia-mass of initial crankshaft results to additional stress with resonance, which is the primary cause of crank cracking for fatigue failure.