Precision Lubrication Applies To Spares
EP Editorial Staff | March 1, 2021
How you lubricate and store critical spares determines whether you’ll realize maximum service life.
By Mark Barnes, PhD, CMRP, Des-Case Corp.
Having an inventory of spare parts and consumables is critical to success for asset-intensive industries. From pipes to valves, hoses, and fittings, most storerooms are packed with commonly used components. For larger rotating and reciprocating assets that are critical for success, but may only require replacement parts once or twice a year, how we store and handle those components and assemblies can have a profound effect on their performance and longevity, once put into service. While not exhaustive, here are some considerations when storing spare parts that are lubricated with grease or oil.
Ambient Storage Conditions
The effects of the ambient environment should always be considered. Ideally, all spares should be stored in an environment with a relative humidity less than 60%, at a temperature between 60 F and 90 F. While the exact temperature is less important, maintaining a temperature that varies no more than 10 deg. is critical since any change in temperature will cause air exchange and the possibility of contamination ingress through thermal syphoning.
All spare parts should be stored away from production areas where vibration can cause false brinelling of bearings and other components. If this is not possible, efforts should be made to dampen or isolate the component from the vibration source.
Storing lubricants, cleaners, fuel, solvents, or other chemicals in the same location as spare parts is not recommended since these can volatilize, creating caustic or acidic conditions that can corrode metals and seals.
Pumps, Gearboxes, Wet Sumps
Most plants carry an inventory of commonly used or hard-to-source pumps and gearboxes. For smaller units, the best practice is to plug openings to isolate the interior parts from the outside environment. Also, fill any sumps with a mineral oil containing a 5% to 10% vapor-phase corrosion inhibitor (VPCI). Shaft extensions should be coated with a corrosion inhibitor or oiled impregnated tape and rotated monthly to prevent fretting corrosion and false brinelling. Often, the shaft keyway makes a good reference point: rotating the shaft through 10 to 15 revolutions, before aligning the keyway at the 3, 6, 9, or 12 o’clock location, distributes the lubricant and dissipates the shaft load (weight).
If the gearbox or pump is equipped with lip seals, packing grease around the outside of the seal can help prevent seal degradation. For components equipped with labyrinth seals, normal oil levels should be maintained with the addition of a VPCI.
While not always practical in all situations, larger or more costly pumps and gearboxes can and should be protected with a dedicated oil-mist system to ensure adequate lubrication and prevent corrosion.
Electric motors, equipped with grease-lubricated antifriction bearings, should be stored in a clean, dry, low-humidity environment. Protect the shafts of motors stored for less than 12 months with a corrosion inhibitor and rotate them monthly. Bearings in motors stored longer than 12 months should be re-greased annually and rotated monthly.
Shafts in vertical motors equipped with oil-lubricated hydrodynamic bearings do not need to be rotated but the oil should be changed annually if stored longer than 12 months. Oil levels should be filled to the correct operating level and the vent or fill port protected with a desiccant breather to maintain a low relative humidity in the headspace.
Bearings should be stored horizontally, away from any source of vibration. Most bearings come with appropriate packaging to prevent rust and corrosion and should be left in their original packaging prior to use. Bearings should be stored to promote first-in-first-out (FIFO) inventory rotation. For bearings that are going to be installed in circulating-lube oil systems, it’s a good idea to check compatibility with the corrosion inhibitor used for storage and the operating lubricant. Stored properly, most bearings have a shelf life of 5 to 10 years. Sealed-for-life bearings that use an elastomeric seal or double-shielded bearings with no-connect metallic shields should be used in 2 to 3 years, making FIFO practices even more important.
Hydraulic-fluid contamination is the leading cause of hydraulic-component failure. When storing hydraulic components, isolate the system from particles and moisture. Valves and other fittings should be stored with appropriate plugs or caps to prevent contaminant ingress. Hoses should likewise be capped and shielded from direct sunlight. UV rays degrade hose materials. Similarly, hoses can also be affected by ozone emitted by strong electromagnetic fields.
Cylinder eyes, clevis bushings, and bearings should be protected with a thin layer of grease to prevent rust and corrosion. Like centrifugal pumps and gearboxes, hydraulic pumps and motors can be stored filled with clean, dry hydraulic fluids.
Cylinders can also be filled with clean fluid. However, extreme caution should be paid to possible temperature fluctuations, which can result in a buildup of pressure due to fluid expansion. Make sure that port plugs, blanking plates, and other components are rated for the possible increased pressure, tagged with a caution, and that there is a safe means of relieving pressure before use.
Modifications to Critical Spares
In my article “Mods Enhance Lube Practices”, I discussed the importance of modifying critical assets to enable precision lubrication. Modifications include adding visual clues such as oil-level gauges and 3-D bullseyes; quick-connect ports to permit filling, draining, and offline filtration; sample ports to take proper oil samples; and desiccant breathers to protect the oil from particle and moisture ingression. Often, when equipment is replaced, mechanics or millwrights who remove the old component do not understand the importance of upgrading the soon-to-be installed replacement component with these same modifications. While removing the original modification components and installing them on the new asset is obviously feasible, it’s often simpler to ensure that critical spares held in storage are kitted with the requisite hardware so that it can be added during installation.
Even with the best maintenance practices, components wear out and need periodic replacement. The simple act of replacing a worn component should not, in itself, become a new failure mode. By employing just a few common-sense steps, spare parts can be safely and reliably stored. EP
Mark Barnes, PhD, CMRP, is Senior Vice President at Des-Case Corp., Goodlettsville, TN (descase.com). He has 21 years of experience in lubrication management, oil analysis, and contamination control.