Even the best-maintained equipment can surprise plant operators with an unexpected breakdown, but as engineers at Braskem's PP4 polypropylene unit in São Paulo, Brazil, recently confirmed, if an incipient fault is detected early enough and monitored carefully, a potential catastrophic failure can be turned into a scheduled, routine repair. This week, at the 2013 Emerson Global Users Exchange in Grapevine, Texas, Braskem vibration specialist Julio Magalhães and Emerson engineer Fabio Chrispim described such a situation on a critical reactor pump.
On August 21, 2012, the plant's CSI 4500 online monitoring system showed an alarm due to sudden and excessive vibration in one of the reactor pump bearings. The vibration was verified in the field with a CSI 2130 measuring device, confirming the immediate need for intervention.
However, the reactor was scheduled be in production to fulfill a commitment to a customer. If the production system had to be shut down due to an unexpected failure, emergency repairs would have cost the company more than $400,000 in lost revenue.
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The source of the vibration was a radial bearing on the reactor pump shaft. This bearing had previously showed a rise in vibration due to excessive clearance and had been replaced along with its housing during a scheduled shutdown on April 25, 2012. At that time, the old bearing had shown no sign of damage, only normal wear.
Now, the sudden increase in vibration indicated a need for intervention. But thanks to the early detection provided by the CSI 4500 system, the need was not necessarily immediate. The customer's production run was scheduled to be completed in 10 days, and the decision was taken to continue to operate the equipment with close monitoring to avoid a catastrophic failure and the accompanying collateral damage.
Along with online monitoring to detect any abnormal change, the bearing was inspected daily with a portable CSI 1850. During the monitoring period, a spare bearing housing was assembled and made ready for replacement.
When the production was completed, the reactor was shut down, and the bearing and housing were replaced. It was found that the bearing failure was due to axial overloading when the bearing housing assembly was installed in April. The total repair time was 22 hours, for an estimated total cost savings of $250,000.