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When creative, dedicated minds come together to provide the right product for every customer, it’s no surprise Equistar Chemicals turned to oil analysis to improve plant operations so it could produce better products.
This $6 billion company ranks among the world’s leading producers of ethylene and propylene with an annual ethylene capacity of more than 11 billion pounds (5 billion kg) and more than 6 billion pounds (3 billion kg) of polyethylene. Equistar is 5,000 employees strong with 16 manufacturing facilities along the Gulf Coast and in the Midwest.
Figure 1. Ethylene Plant Quench Water Turbine
The following case histories are examples over the past few years where maintenance costs and production downtime have been reduced or avoided through the use of an oil analysis program at the Morris Plant in Morris, Illinois.
Oil analysis at Equistar is performed to monitor the condition of in-service lubricants, to identify the presence of contamination and to determine the condition of machinery components. Oil analysis and vibration analysis technologies are integrated and complement each other to diagnose equipment problems.
At the Morris Plant, results from both technologies are trended together in the same database. This gives the plant the advantage of diagnosing both the vibration levels and the oil sample trends concurrently. In some instances, Equistar has seen an increase in the wear particles on the oil sample trends before increases in the vibration level trends are visible.
Figure 2. Line 2 Extruder Gyrol
One January, the oil sample results indicated an increase in the concentration of ferrous wear particles in the oil from the Ethylene Plant Quench Water Turbine and Gearbox (Figure 1).
The turbine and gearbox have a common reservoir, which complicated diagnosing the source of the ferrous particles in the oil. The Reliability Group requested full analytical ferrography of the sample. It revealed the majority of the particles were babbitt. In addition, the particles were discolored (exposed to high temperature) and were formed from cutting/shearing action.
It was suspected that either the gearbox’s large babbitted thrust bearing or radial bearing was failing. A work order was written, the spare gears were balanced, spare bearings were inspected and planning for the gearbox inspection/repairs were made.
During this time, the vibration levels, which had remained low, showed an increase in the axial (thrust) direction. Shortly thereafter, the gearbox was shut down. Gearbox inspection revealed that the thrust bearing was failing and would have been operational for only a short time longer before failing completely. A complete failure of the bearing would have resulted in damaging the gear set.
This opportunity to shut down the gearbox before it completely failed significantly reduced the maintenance costs and equipment downtime. A complete failure of the gearbox potentially could have resulted in the trip of the Ethylene Charge-Gas Machine.
In January, the oil analysis sample from the Line 2 extruder gyrol indicated an increase in iron. Samples on the aluminum clutch assembly only indicated a presence of iron in the oil. Vibration readings taken on this unit indicated an increase in vibration amplitude levels (Table 1).
The vibration spectrum indicated a bearing defect on the inner race. The unit was shutdown and a visual inspection revealed that the bearing race had spalled but there was no damage to the aluminum clutch assembly. The assembly was rebuilt in-house without replacing the shaft or clutch.
Maintenance costs and production downtime were minimized by catching this bearing. A total bearing failure would have potentially damaged the clutch assembly itself. Maintenance cost savings were estimated between $15,000 and $20,000.
Figure 3. Propylene Reactor Gearbox
In February, oil sample results from the Propylene Reactor Gearbox indicated an increase in iron from 19.9 ppm to 54.3 ppm (Table 2). Analytical ferrography revealed the particles originated from gear wear.
The gearbox was inspected and the oil spray nozzle for the intermediate bevel gear set was found plugged. The gear was beginning to show minimal wear, the oil nozzle was cleaned, reinstalled and the gearbox restarted.
This was a simple repair, thanks to the oil sampling program. The early detection of this problem avoided the complete failure of these gears. Several days of downtime were avoided along with the maintenance costs associated with changing out the gearbox.
Figure 4. Line 2 Extruder Gyrol
In early September, maintenance personnel saw a large increase in the concentration of ferrous wear particles in the oil sample from a satellite extruder gearbox (Table 3). The filters were checked and found to be collecting metals.
Inspection for proper flow of the oil spray nozzles in the gearbox was recommended as well as the inspection of the gear and bearing. The inspection revealed that the spray nozzles had become partially plugged, reducing oil flow. The nozzles were removed and cleaned.
The gears and bearings were further inspected for wear and found to be in good condition. The unit was reinstated after only a couple hours of downtime. The estimate of gearbox maintenance repair cost savings is $20,000 to $25,000 plus several days of avoided production downtime.
In October of that same year, a large increase in copper in the oil sample of the Polyethylene hyper compressor crankcase was observed (Table 4). PPM recommended an inspection of the crankshaft thrust bearing. Ferrographic analysis indicated that particles were from bearing wear with some particles as large as 35 microns.
The compressor was shutdown and an inspection of the thrust bearing (shoes) revealed that it was heavily worn and that the crankshaft had moved to the south. The oil filters had been contaminated by the presence of copper in the oil system.
Further inspection lead to the motor pedestal bearing which had a cracked inner race and allowed the compressor crankshaft to move to the south. This wiped the thrust bearing. The thrust bearing and pedestal bearings were changed out and the unit was brought back online. The dollar savings to both maintenance costs and production downtime due to the early detection of this failure were estimated in the hundreds of thousands
The Acid Number (AN) of the oil from one of the cycle gas compressors started trending upward, indicating the oil was becoming corrosive. The AN had increased over the past couple months from 0.9 to 4.67 (Table 5).
Since shutting down the process was to be avoided while changing the oil, the Reliability Group drained a few drums of oil at a time and added new makeup oil until 440 gallons had been changed out. The AN was reduced to 1.6. Again, oil analysis alerted the team of a problem that may not have become known until the machinery was already damaged.
These case histories have proven the value of a total oil analysis program, such as the one Morris Plant has in place. Sample points are labeled and the samples are collected from the same location, ensuring that representative samples are collected every time. The lab forwards the results the same day the tests are completed.
Oil analysis and vibration data are diagnosed and a recommendation is made to correct or repair the equipment problem. The oil analysis program has proven to be a valuable condition-monitoring tool which enables the Reliability Group at the Morris Plant to substantially reduce equipment problems and maintenance costs.