Balance in critical equipment isn’t an optional goal for manufacturing facilities. It is a necessary part of keeping production running and preventing unplanned shutdowns. It’s particularly important for facilities with high demand for products, such as is the case for the Oman India Fertilizer Company S.A.O.C. (OMIFCO). OMIFCO is a joint venture business established to operate a state-of-the-art two train ammonia-urea fertilizer manufacturing facility in the Sur industrial estate in the Sultanate of Oman. The plant produces 1750 tons per day of anhydrous ammonia and 2530 tons per day of granular urea. Its products help meet the growing agricultural demand in India.
The company’s goal is to produce fertilizer 365 days a year. As a result, the company has focused extensively on ensuring reliability. Its strategy includes building in redundant equipment for all critical assets, performing predictive maintenance based on vibration, flow, pressure and temperature monitoring and completing routine preventive maintenance.
Each year, OMIFCO is able to meet its targets. The highest production values came in 2013 with 1.38 million tons of ammonia and 2.15 million tons of urea.
Choosing the right tool
In 2012, OMIFCO started using the Emerson portable analyzer to gather vibration data from heavy-duty boiler feedwater pumps, which produce steam used in processing ammonia and urea. The data was uploaded to AMS Suite where detailed analysis took place. Using PeakVue technology, OMIFCO technicians quickly identified a potential problem in a turbine thrust bearing. The impacting faults were readily visible in PeakVue waveform long before any significant increase in overall vibration was noticed. As a result, OMIFCO engineers began to carefully monitor that machine.
In February 2013, a sudden 50 percent increase in PeakVue spectrum and waveform was observed, followed a few days later by another large increase. At this time, a slight increase in turbine horizontal vibration velocity was evident for the first time. The machine was taken out of service to check the thrust bearing, which was found to be severely damaged with large pitting in the inner race and small pitting in the ball bearings. After the thrust bearing was replaced and the machine put back into service, all of the vibration readings returned to normal levels.
As experience with the portable analyzer increased, so did the ways it brought value. The maintenance inspection team began using the analyzer for in situ balancing of fans. With more than 12 uses of this application, the results have been fast and accurate. In situ balancing was performed for many fans, namely the granulator scrubber fan, the fluidization air fan, and the dedusting fan in the granulation unit. These fans were all large in size and driven by 1350 KW, 1600 KW, and 90 KW motors respectively.
A persistent problem with a motor led the maintenance inspection team to look at the portable analyzer for help. In each ammonia plant, there are three ammonia booster compressor drivers which pressurize ammonia. These compressors are powered by electric motors. To run the process, two out of the three motors are required to run at all times.
One particular motor had a history of high bearing temperature and high vibration. The motor was monitored closely, with data on vibration and temperature captured every two weeks. This particular motor also required frequent rotor balancing. Each time, the problem would stop for a short period and then it would start again.
After the third instance of high vibration and temperature, the motor was removed and brought to the vendor’s maintenance shop. The vendor found damage in the journal area. Using metallic spray and a lathe, the vendor repaired the issue. The part was returned to the motor and the balancing was done in the maintenance shop.
The motor was reinstalled but the analyzer indicated there was still high vibration. To determine the root cause, a number of tests were performed. The results of an impact test on the motor non-drive end and drive end vertical position indicated there was no sign of resonance. The team checked the cross phase on motor foundation, foot and casing, but they didn’t find any looseness. The phase difference between horizontal to horizontal was found equal +/- 20 degrees with vertical to vertical, within the normal range.
Safety threat
In short, the tests indicated that the only issue was with nonbalance. The vendor had already balanced the motor at its maintenance shop. So, that option had already been attempted. Yet risk was still high, as, if the rotor were not repaired, catastrophic damage could occur, resulting in a safety threat and loss of ammonia and urea production.
The management team was resigned to replacing the rotor at a $40,000 cost. But the internal maintenance team had an inkling that they could balance the motor in situ, using the portable analyzer.
The maintenance team had gained experiencing using the analyzer for in situ balancing of fans. The team had used the CSI 2130 Machinery Health Analyzer to aid balancing more than 12 times. Balancing a motor in situ had never been attempted. The perception was that it would not be easy. As there had been no previous cases where such a large motor balancing had been attempted on-site, it was difficult to select the weight planes considering the limitation of space.
Yet, even knowing the potential difficulties, the team was confident that the approach could work. Eventually, the management became convinced of the benefit letting them try.
Once they had the motor cage open, the maintenance team used fan as plane 1 and coupling as plane 2 and added trail weight calculated by the CSI 2130. After the startup of the machine, the CSI 2130 calculated the correction weight that had been applied at both the weight planes. Within four hours, team members were able to get the vibration to a normal level. The balancing data was entered into the AMS Suite predictive maintenance software, and the appropriate reports were generated. The entire balancing operation was wrapped up in less than a day. In comparison, removing the motor would have taken it out of commission for up to three days.
With the in situ balancing approach, OMIFCO didn’t have the cost of replacing the rotor, the cost in manpower of removing the equipment and reinstalling nor did they have to pay the vendor for a second round of balancing. In total, OMIFCO saved $250,000. Confidence in the technicians increased and the skeptics among the management team congratulated the team on its success.
(The author is an Instrument Engineer at OMIFCO.)
