CASE STUDY Equipment & Location: Steam Condensate Pump-A Dates of Checking’s: January to July 2006 Instruments used: Vibration Data Collector/Analyser, Model Easy-Viber Abstract of Case: This pump had been experiencing high vibration levels after few months’ operation since commissioning. The maintenance personnel had seen the wear of pump parts and centralizer bearings. The clearances of the bearings were increased by the personnel in anticipation rubbing of shaft due to less clearance. On the contrary vibration levels continued to show the same pattern of characteristics and did not yield any fruitful results. Thus the pump was required to be checked every after 3~4 months operation and the wear pattern appeared to be of similar nature. However, the other similar pump “B” had not shown this kind of problem. While studying further on this recurring problem, it was observed that normally both the pumps were put in operation due to generation on more quantity of steam condensate than the designed/rated estimates. In such situation, the suction of this pump was near the baffle plate in the shell and tube type steam condenser, was found leading to the starvation, cavitations, inadequate dynamic suction head resulting in erratic behavior of the vibration levels. Ultimately, recirculation of steam condensate was recommended to keep the minimum level in the condenser, so that the dynamic suction head on this pump remains more or less constant and to remove the effect of transient vibrations caused by the hydraulic effects. Thus the frequent repair/overhaul, replacement of spares, production loss due to non-availability of this pump was resolved permanently, saving maintenance efforts, time and money.
Transcript
CASE STUDY Equipment & Location: Steam Condensate Pump-A Dates of Checking’s: January to July 2006 Instruments used: Vibration Data Collector/Analyser, Model Easy-Viber Abstract of Case: This pump had been experiencing high vibration levels after few months’ operation
since commissioning. The maintenance personnel had seen the wear of pump parts and centralizer bearings. The clearances of the bearings were increased by the personnel in anticipation rubbing of shaft due to less clearance. On the contrary vibration levels continued to show the same pattern of characteristics and did not yield any fruitful results. Thus the pump was required to be checked every after 3~4 months operation and the wear pattern appeared to be of similar nature. However, the other similar pump “B” had not shown this kind of problem. While studying further on this recurring problem, it was observed that normally both the pumps were put in operation due to generation on more quantity of steam condensate than the designed/rated estimates. In such situation, the suction of this pump was near the baffle plate in the shell and tube type steam condenser, was found leading to the starvation, cavitations, inadequate dynamic suction head resulting in erratic behavior of the vibration levels.
Ultimately, recirculation of steam condensate was recommended to keep the minimum level in the condenser, so that the dynamic suction head on this pump remains more or less constant and to remove the effect of transient vibrations caused by the hydraulic effects. Thus the frequent repair/overhaul, replacement of spares, production loss due to non-availability of this pump was resolved permanently, saving maintenance efforts, time and money.
Equipment Specifications: Motor - ABB Type M2BK280SMA2. Coupling: Metastream Type TSKS 0033. Pump: Vertical Centrifugal Pit Type, Two Stages, Rated Power 22.2 KW, Flow Rate
79.7 M3/Hour, Suction Pressure 0.107 bar, Discharge Pressure 6.7 bar, Speed 2,940 rpm. Mechanical Seal Make Burgmann, Seal Type H75K/70.
Vibration Data: Observed Trend of Vibration Levels during the Operations is given below.
Actual Dates Point No. & Direction
Velocity mm/sec
BC Value
Displ. Microns Accln. G pk
4th Feb 2006 1-Axial 0.5708 0.00 ------ ------ 7th Feb 2006 1-Axial 0.6663 0.01 ------ ------
Background History: The pump had undergone repairs/overhaul works during first week of February 2006. The parts of pump like shaft, bearings, guide bushes, wear rings etc. were replaced by during the repairs/overhaul works. The vibration level had decreased considerably after carrying out the repairs/overhaul works, which were all well within the acceptable limit.
Operational Variations: According to the original operational philosophy considered during design stage was to
operate only single pump and other pump shall be in standby duty. But, in fact, the operator had to operate both the pumps in parallel operation for handling the excess generation of steam condensate than the anticipated during the design stage. This resulted in to operational requirement of both the pumps in normal operation, causing depletion of standby one. This was a serious problem in operating the entire plant in a reliable manner. However the OEM and Designing Agency had been informed time to time on this typical problem, who had never come forward with any viable solutions in studying the root cause or for suggesting the necessary changes in operations.
Vibration Analysis: This pump had been experiencing high vibration levels after few months’ operation
since commissioning. The maintenance personnel had seen the wear of pump parts and centralizer bearings. The clearances of the bearings were increased by the personnel in anticipation rubbing of shaft due to less clearance. On the contrary vibration levels continued to show the same pattern of characteristics and did not yield any fruitful results. Thus the pump was required to be checked every after 3~4 months operation and the wear pattern appeared to be of similar nature. However, the other operating pump “B” had not shown this kind of problem. While studying further on this recurring problem, it was observed that normally both the pumps were put in operation due to generation on more quantity of steam condensate than the designed/rated estimates. In such situation, the suction of this pump was near the baffle plate in shell and tube type steam condenser, was found starving, leading to cavitations, inadequate dynamic suction head resulting in the erratic behavior of vibrations. Ultimately, recirculation of flow of the steam condensate was recommended to keep the minimum level in the condenser, so that the Dynamic Suction Head is maintained constant for reducing transient vibrations caused by hydraulic effects. Thus frequent repair/ overhaul, replacement of spares, production loss due to non-availability of this pump could be resolved permanently, saving maintenance efforts, time and money. Otherwise, Operational Staff had been insisting to install one more additional pump installed as a ready standby unit as the generation of steam condensate had been showing increasing trend and they had no confidence in operation of these pumps.
Conclusion: The Design and Installation of Machinery can have some differences in comparison to
similar models machines, exhibiting a quite different characteristics and operational problems due to the variations existing in the associated/auxiliary components. Some times past experience of similar kind of machinery may not be of much help or useful due to the inherent design or operational variations. Also, some times, designer or original equipment manufacturer may not be of any help due to lacking of their own experience on the operations of their products in a typical operational situation. Hence, the end user must carry out a comprehensive/detailed study looking in to integration of all available operating parameters and experiences, which can give a better idea and viable solution to such engineering problems.
