(20 min.) Investigating high vibrations on newly commissioned vertical centrifugal can type pumps

Ghulam Jillani , Lead Engineer Rotating Equipment , Dubai Natural Gas Company Limited


Five vertical can type centrifugal pumps were commissioned as a part of new project. Three were handed over to operations after commissioning and trial runs whereas two pumps (working and standby) on similar process duty experienced high vibrations. As these pumps were under manufacturer’s warranty; it was agreed to involve pump vendor to support us. Pump vendor witnessed field testing of both pumps. These pumps were on liquid butane (specific gravity 0.6) transfer application, running at 2965 rpm. All three vibration values as measured on motor NDE, DE mounting flange and on pump bearing housing were out of acceptable limits. Increased vibration observed at 22 Hz (1320 CPM) frequency, which is approximately 0.45 X the operating speed. Bump tests were carried out on above ground structure of pump (motor support bracket and mounting flange) and structural resonance observed close to 22 Hz. Pump vendor did FEA (Finite Element Analysis) of above ground structure and results resembled field bump tests. Increasing and decreasing stiffness of bearing bracket did work for reducing the vibrations levels to acceptable limits. It seemed that excitation most likely was shaft vibration due to “oil whirl”. The effect is created by lubricant whirl in the bearing clearance, rotating with 40-48% of running speed. Pump vendor performed lateral analysis of shaft train using FEA techniques and no harmful natural modes were found. It was recommended to reduce the number of shafts and subsequently the couplings to have better balanced shaft train. Carbon bearing bushings with one spiral groove were replaced with “Vespel” bearing bushings with straight grooves. Straight grooves would stabilize the shaft better than one spiral groove and disrupt the oil whirl movement. Bearing gap was also reduced to increase the bearing load to eliminate the occurrence of oil whirl. All recommended modifications had been carried out on pump “B”. Field testing proved elimination of high vibrations due to oil whirl. Same modifications were done on pump “A” and both were handed over to operations.


A highly motivated, enthusiastic individual, who is confident in his approach, driven by the need to succeed and achieve a competitive market place. Enjoys working in a challenging environment that demands teamwork, initiative, creativity and sound analytical skills when making effective decisions and finding solution to problems. 18 years of experience in Engineering & EPC environment comprising of Feasibility Studies, FEED, Open Book Development, Detailed Engineering, Engineering & Procurement, PMC, Reimbursable, EPC projects specializing in rotating equipment design engineering, techno commercial evaluations, on site operational & maintenance support, commissioning, site completion activities, HSE, maintenance activities & their planning, quality assurance & control

Core Competencies

• Strong analytical and practical field engineering skills along with dynamic leadership qualities for effective contributions at a higher level for interaction with client, vendor and company management.

• Hands on work experience for detailed engineering of all rotating equipment i.e.; all pump types, steam turbines, fans & blowers, gas turbine, process centrifugal compressors, reciprocating compressors, utilities packages, refrigeration systems etc.

• Hands on experience in centrifugal compressors installation, start up, and commissioning activities.