High Vibration Problem Resolution in Centrifugal Pump through Design Change

Abstract

Case Study 4: The case study is about single stage API BB2 pump. Pump operates at the temperature of 355 degree C (671 degree F), rated for pumping 442 m3/hr of Hydro-treated VGO (Vacuum Gas Oil) and is driven by a steam turbine. Pump bearing housing at Drive End (DE) side started exhibiting intermittent high vibrations during commissioning phase. This resulted in repeated failure of DE bearing and damage to bearing housing. Root cause was analyzed as uneven expansion of pump casing during pump warm-up, which misaligns the DE side floating bearing within bearing housing and restrict its axial displacement (bearing used is of deep groove design). As a consequence, thermal growth of pump shaft was restricted and it was rotating in deflected shape, rubbing within throat bushes. Problem was resolved by replacing the bearing design with NU type Cylindrical roller bearing, which allows higher amount of axial displacement. This case highlights a balanced approach towards the site investigations, root cause analysis and corrective actions implementation. It also provides hints to address thermal growths issues when equipment operates at very high temperature.