The probability of equipment failure is relatively high following the commissioning of equipment, whether for initial operation or after completing rebuild activities. Machines often sit idle at a new industrial site for months while construction progress slows down. It is not unusual for projects to be canceled with no thought given to equipment preservation.
Unless the buyer clearly specifies storage measures in the contract, it is likely that machines will be shipped without provisions for storage. On-site storage protection needed for 3 to 12 months at a construction site requires a preventive maintenance (PM) program. At best-in-class performers, on-site storage preservation with oil mist is standard practice, and its cost is included in the initial budget for projects.
This article is based on a chapter in the author’s book
“Optimized Equipment Lubrication, 2nd Edition, 2021;”
De Gruyter, Berlin/Boston, (ISBN 978-3-11-074934-2).
Additional chapters will be highlighted on this website in the future.
Only in dire circumstances would best-in-class performers revert to the conventional ways of temporary storage protection. This section highlights those circumstances. The strategies and recommendations refer strictly to short-term preservation using conventional, old, non-optimized protection methods. These plans and methods are described here for plants located in northern, dry climates.
♦ SHAFT-ROTATION REQUIREMENTS (short-term storage only)
Rotate all equipment, such as motors, turbines, gears, and compressors, at a minimum once per month, but optimally every 2 weeks. Keep in mind that for rolling element bearings, a single turn of the shaft means the bearing cage would have made only a half-turn. Therefore, rotate the shafts a minimum of two-and-a-half turns.
For gears, refer to the upcoming Gears section below for the required number of shaft turns. On gears with teeth dipping in oil, you want to have each tooth dipped in the oil sump at least once per month. The number of recommended shaft rotations (i.e., turns) differs for gear-speed increasers versus gear-speed reducers.
Gear units where oil is pumped into bearings and sprayed into gear teeth must have their breathers plugged and their shaft protrusions caulked with silicone caulk and then taped. The void space above the oil level must be filled with oil mist or blanketed with nitrogen. No periodic turning of shafts is needed.
A tag explaining the protection and preservation method must be affixed to the gear unit, machine, compressor, or whatever the equipment may be.
♦ VISUAL INSPECTION (short-term storage only)
When rotating exposed machine surfaces, check the shafts and couplings to verify a protective coating of product C has been applied and that neither this protective coating nor the tape has been removed. Reapply both, if needed.
Check all lubricating lines to make sure no tubing, piping, tank, or sump covers have been accidently removed. Retape all ends and covers. If flanges are open on the machinery, notify the pipefitter, first-line supervisors, or other designated personnel.
♦ DRAINING OF CONDENSATE (short-term storage only)
Drain the condensation from all bearing housings, sumps, and oil reservoirs on a once-per-month schedule. If an excessive amount of condensation is found, recheck once a week or at 2-week intervals, depending on the amount of condensate present.
♦ BEARINGS (short-term storage only)
Fill all bearing housings that are oil lubricated (and not force-fed) with rust preven- tion concentrate, bringing the oil level up to the bottom of the shaft. For force-fed bearings, the upper bearing cap and bearing must be removed. A coat of heavy, inhibited oil can be applied to the journal and bearing surfaces. This should be reapplied as needed.
♦ ELECTRIC MOTORS (short-term storage only)
Electric motors with greased bearings should not be lubricated. If a grease fitting is supplied with the motor, it should be removed and the opening plugged or capped.
♦ STEAM TURBINES (short-term storage only)
Spot-check turbines by removing the upper half of the turbine case and visually inspect. Plan to open a sampling of these turbines, selecting from the first preserved and those in the worst condition. This should be done on a 3-month schedule. Other turbines may be inspected by the manufacturer’s field-service engineer during monthly visits. This inspection is done through the opening in the top case while the rotor is being rotated/turned,
♦ GEARS (short-term storage only)
Fog the interior of the housings with rust prevention concentrate. Coat all tooth contact points with an inhibited grease or heavy, tacky oil (such as product C). Remove the inspection plates and visually inspect the interior on a 3-month schedule. If storage will not extend beyond 3 months, shaft rotation will not be needed.
♦ COMPRESSORS (short-term storage only)
Applying atomized lube oil from fog nozzles is occasionally done. It is considered a less effective substitute for oil mist, but some equipment manufacturers recommend fogging “because we’ve always done it this way.” It can be inferred that short-term storage preservation by conventional means often involves the compressor manufacturer. The manufacturer’s representative should inspect the compressor(s) during monthly visits. Furthermore, to protect warranty provisions, any needed preservatives must be applied under the supervision of the manufacturer’s representative.
Apply oil fog to centrifugal compressors’ internals and consider placing desiccant bags in these machines. Ideally, inspect these compressors once a month or at least on a 2-month schedule. Inspect high-speed air compressors on a 3-month schedule. Inspect and fog axial compressors on a 3-month schedule.
REGARDING OIL MIST IN SHORT-TERM STORAGE
Oil mist is ideal for storage preservation mainly for its simple operating principles and excellent reliability. Benefits of this method in short-term equipment preservation include, among other things:
♦ straightforward lubricant application
♦ competitive costs if new consoles are chosen
♦ reduced costs if oil-mist-generator equipment is purchased on the used-equipment market
♦ few man-hours typically required for oil-mist maintenance or surveillance
♦ oil-mist lubrication and oil-mist preservation are identical except for oil consumption
(e.g., oil-mist for standstill equipment preservation consumes only 10% of the amount
consumed for oil-mist lubrication).
♦ OTHER CONSIDERATIONS FOR SHORT-TERM STORAGE
In a warm, high precipitation climate, it is best to look for optimized solutions for field storage during construction and prior to start-up. If oil-mist lubrication is not already part of the original design, it should be seriously considered because, in the overwhelming majority of cases, it will provide the best protection against contaminant ingress.
Oil mist will reach all spaces and voids. Other methods may not reach oil galleys and condensation hanging in droplet form from casing covers and other parts.
When looking at the cost outlays for routine maintenance and the related activities needed with conventional equipment storage preservation, many are surprised that these can greatly exceed the outlays for oil mist preservation.
Next week, Part 2 of this article will discuss a number of additional equipment-storage-preservation issues, starting with the topic of storage protection in the context of industry standards.TRR
ABOUT THE AUTHOR
Heinz Bloch’s long professional career included assignments as Exxon Chemical’s Regional Machinery Specialist for the United States. A recognized subject-matter-expert on plant equipment and failure avoidance, he is the author of numerous books and articles, and continues to present at technical conferences around the world. Bloch holds B.S. and M.S. degrees in Mechanical Engineering and is an ASME Life Fellow. These days, he’s based near Houston, TX.
Tags: reliability, availability, maintenance, RAM, electric motors, bearings, compressors, steam turbines, gears, gearboxes, lubrication, lubricants, oil mist