Recently, a company that sought to temporarily shut down a papermaking machine consulted ExxonMobil because of an unusual situation. The papermaking machine was located next to a similar machine that would not be shut down.
To begin the process, filter elements were replaced on the subject units and 10% (by reservoir volume) of a solvent-free, oil-soluble cleaner was added to flush the systems over the next 48 hours at normal operation in order to clean up carbon, sludge, and other contaminants.
Once the system was shut down, while still warm, the oil was drained and the filter elements were replaced. Once the breathers were pipe plugged, paper machine oil was used to fill to the highest level possible without causing leakage.
The paper machine lubricating oil was then mixed with 10% (by reservoir volume) of Mobil Vaprotec Light, an ISO Viscosity Grade 32, turbine-quality circulation oil containing antioxidants and defoamants. It was then enhanced with a 3-phase inhibitor to protect surfaces lightly coated with oil, a liquid phase inhibitor to protect submerged surfaces with oil, and a vapor phase inhibitor to protect surfaces exposed to oil vapors. A red tag was placed on the units clearly showing that it had been properly mothballed and should be flushed, drained, and refilled with the correct lubricant prior to starting.
To address concerns that vibration would cause fretting corrosion in the load zone of the shutdown machine, it was determined that the mothballed machine should crawl periodically to prevent fretting corrosion. The steps listed in the main article were used to mothball standard equipment such as: gear reducers, turbine gear drives, vacuum and centrifugal pumps, for which vibration was not an issue. In this instance, due to vibration and the need to crawl the machine, paper machine oil was used to provide adequate oil viscosity to the bearing load zones while the Mobil Vaprotec Light provides the required 3-phase rust preventive. (In addition to crawling the machine, bearing inspections are also very important, since replacement of a failed bearing and the accompanying potential downtime can be very costly. Shown here, ExxonMobil engineers are inspecting paper machine bearings.)
After analyzing the situation, we developed a plan that would fit the paper mill''s equipment needs.
The procedure assumed that the machine''s oil system heating unit could heat the mothballing lubricant to the specified 150 deg operational level. In addition, we circulated oil throughout the system and crawled the equipment to rotate the bearings one-and-a-quarter turns, three times per week, to prevent costly fretting corrosion.
Following this procedure, the machine was successfully restarted after a six-month shutdown period.
During the process, this lubricant mothballing process touched more than 40 double spherical roller bearings. The cost of these bearings varies from $1,000 to over $5,000 to replace, not to mention the potential downtime costs associated with replacing a failed bearing.
As a result of successfully mothballing the paper machine, the customer potentially saved more than $100,000 by conducting this mothballing process. During the past three years since the equipment began operating again, no bearing failures have been caused by fretting corrosion or rust.
For more on mothballing, click here.