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"What should be considered in preservation lubricants? We are in the construction phase, and we have a lot of equipment in preservation. The people responsible for preservation are filling the equipment with any lubricant and say it is not important because we are going to flush before the startup. I don't think that is best practice, but what can I do to preserve the machinery in the best possible condition?"
The first consideration should be the type of seals in place. If the seals being used are lip seals, then the machinery in question can be completely filled with lubricant to coat all parts inside with a film. If the machine has labyrinth-style seals, then it can only be filled to the bottom of the shaft, which in some cases can leave a large volume of headspace above the oil unsubmerged.
Preservative fluids come in a variety of different types. Preferably, you would use the same lubricant in the machine as you would if it were operational. Even though this fluid will be drained before it goes into service, there can still be incompatibility issues between any residual fluid and additives that may not have been drained out entirely.
Best practice would dictate that all machines be flushed after being stored for a period of time. This ensures that all the fluid and additives are removed and greatly diminishes the chances of incompatibility.
Once you have decided the best course of action regarding the amount of oil that the equipment will be stored with (completely full or normal levels), you may need to find a preservation additive known as a vapor-phase rust inhibitor. This additive evaporates, enabling the rust inhibitor additives to then attach themselves to any machine parts that are exposed above the oil level. This helps ensure that the exposed parts won't rust if any moisture gets into the machine. Several of these additives are available on the market and can be blended with the lubricant that is in the machine for storage.
If the machinery is critical, you may want to explore the option of using a mist system to constantly purge the stored equipment. A mist system adds positive pressure to the machine and brings in small oil droplets that effectively fog the inside components with additives to keep corrosion to a minimum. Plus, with the positive pressure, there is virtually no way to ingress moisture and contaminants through a breathing process.
One aspect of stored equipment that should not be overlooked is the rotation of shafts and bearings. By rotating the shafts once a month, you can help distribute the oil to all bearings and prevent corrosion and false brinelling. Also, always remember to visually inspect the insides of equipment during installation to identify any possible root causes of failure due to improper storage.