Resolving High Vibration On a Vertical Pump

Abstract

There is a single stage vertical pump installed in Acetic Acid area in a petrochemical plant. The unit is vertical high pressure (HP) reactor feed pump (High speed single stage, 230 kW, 12338 rpm & 3.444 gear ratio) driven by induction motor through a flexible shim pack coupling. High vibration levels were observed on the motor, pump and structure for more than 2 years with 1X dominant vibration (1X motor dominant frequency). Assuming that the issue is completely structural as this motor was running well in the past, there were some structural modifications have been carried out at site with inadequate engineering calculations. The modifications were welding a total mass of 100 kg onto the structure and the installation of braces to the structure which did not yield any positive results. A systematic structural measurement along with the Operating Deflection Shape carried out at site with the help of experts did not reveal a significant issue with the structure itself except for the structural natural frequency being slightly closer to the running frequency of the motor. The timely right decision by the experts to carry out an onsite balancing on the motor, which was intended to remove the excitation force, yielded good results which exposed a mistake in the balancing activities carried out by a local vendor at work shop. This case study is designed to outline how the high vibration issue was successfully diagnosed using various tests on site including the operating deflection shape, the root cause for the high vibration and finally how it was mitigated.