When Is a Spare Not a Spare?

You are driving down the highway in your car when a tire suddenly goes flat. You pull over and prepare to change the tire when, to your dismay, you discover that the spare has no air—and the jack is missing. Every day, a similar scenario plays out somewhere in the pump industry. A pump breaks down; you immediately go to the spare storage area for parts or a replacement pump only to find that the pump, part or spare rotor is rusted and the bearings are locked up. Turns out your spare is really not a spare. At this point, the plant is no longer facing an inconvenient shutdown; the breakdown has become an emergency situation. What can prevent this problem in the future? Proper preservation and storage procedures, as well as the discipline and cooperative company culture required to incorporate these procedures, are critical to prevent unnecessary downtime. Many end users disregard the original equipment manufacturer (OEM) instruction manual guidelines and industry best practices, but it is best to heed them.

Short- or Long-term Storage

How long the spare unit or part will be in storage affects how it should be stored. If you do not know how long the component will be in storage, be conservative. Typically, less than six months is considered short-term storage. Regardless of the storage period, a proper procedure and good records are critical. At a minimum, environmental controls should include temperature, humidity, airborne pollution and mitigation of vibration. If antifriction bearings are involved, periodic rotation of the rotor is imperative to prevent false brinelling. Ideally, the rotor should be rotated (by hand) every four to six weeks. Each rotation evolution should be a different and odd (or fractional) quantity of turns to prevent the rotor bearings from ending back in the original position. Bearings that are not installed should be kept in their OEM package and stored flat. Do not store sealed (grease) bearings for more than five years. Bearings other than antifriction types can present their own set of storage problems, so be sure to check with the manufacturer. Is the pump used or new? The biggest issue with a used pump or part is that usually the pumped product’s complete removal is necessary before the preservation procedure can begin. Many people disregard this step or make a 50 percent action that renders the unit 100 percent unusable. Is the used pump being stored in place or in a storage area? In most cases, the pumped product will need to be removed and the metal surfaces sprayed or fogged with a preservative oil. Coat all exposed machined surfaces. Where and how the items will be stored is one of the most important factors to consider. In a perfect world, the storage space would be indoors and climate-controlled, where the humidity is kept less than 50 percent and the temperature under 95 degrees F. Temperature swings should be limited to less than 10 degrees, especially if the humidity is not well-controlled. Consistency is imperative for successful storage because it reduces condensation that will lead to corrosion. Many pump rotors, especially multistage models, should be stored vertically. For long-term storage, rotors with the bearings already installed—even small rotors—should be vertically stored. This is more to address the bearing concerns than to prevent bows in the rotor. Rotors stored horizontally should have the couplings removed and the shafts rotated to preclude bowing. In many cases, a pump can be stored with bolted flange covers (with gaskets on the covers), an adequate fog of some preservative oil or a vapor phase oil in the bearing housings. An adequate amount of desiccant and/or vapor phase inhibitor should be placed inside the casing. Preservation items placed in the pump must be conspicuously tagged and documented so they can be removed before the pump is placed in service. The amount of desiccant to use is a function of the pump volume. Moisture indicators are inexpensive, and each pump or container could benefit from having a few. Some long-term storage procedures require placing the rotor in an enclosed airtight case, or the pump itself is made airtight at the flanges and penetrations. A vacuum pump is used to pull the air out, and the vacuum is “broken” with bone-dry nitrogen. It is a standard practice to “break” the vacuum with an inert gas, commonly nitrogen. A simple gauge monitors the nitrogen pressure at a few pounds above ambient.

Unintended Consequences

Some mechanics use lubricants to assist in pump reassembly. This practice is not incorrect, but the wrong lubricant can attack certain materials. For example, residue from a lubricant designed to be used on O-rings can accelerate corrosion on the machined surfaces of metal parts. When ball bearings are heated to facilitate installation on the shaft, the OEM’s preservative oil is at least partially removed. The preservative oil coating must be reestablished. Check with the OEM or the bearing manufacturer for the proper product. In most cases, the product should be compatible with the oil that will be used when the pump is finally put in service. For outdoor storage, the pump will need to be protected from the elements. I have seen people with good intentions simply wrap the pump in plastic only to later find the unit rusted and rodent-infested. Another challenge of outdoor storage is freezing weather, especially for used pumps stored in place. Every year during the first deep freeze of the season, I encounter dozens of freeze-cracked pump casings. This issue is common on self-priming pumps that store water in the casing for the priming evolution.

Storing the Wrong Part

Another concern is if the part or component is the correct one in the first place. I have seen many parts stocked incorrectly, so when the spares are pulled from storage, they are the wrong material or size. This problem is common with impellers and casings of similar sizes. Another challenge is missing parts. I have witnessed numerous incidents where a box of smaller but critical parts for the main unit is set aside for safe keeping and then lost or trashed.

Mechanical Seals

Mechanical seals require a chapter of their own. The best place to store mechanical seals is in the package provided by the OEM in a cool, dry place away from UV light. If the seal is already in the pump, it is usually acceptable for it to remain there for up to 24 months. A best practice is to remove the seal, but if this is not possible, ensure that the pumped product is drained and the seal is dried with dry air or an inert gas such as nitrogen. Make sure that any pump and seal chamber penetrations are plugged and all sources of vibrations are eliminated. Pumps stored near large operating equipment, highways, gantry/overhead cranes and railroads are subject to low-frequency vibration. Refer to the OEM or the Fluid Sealing Association for more details. Cartridge seals should be kept with the shipping clips tightened and centered and the collar set screws loosened. This is known as the “sleep mode.” Cartridge seal faces that have been stored for more than 18 months should be checked for flatness before being used. After some time, if there is any residual internal stress, the face will warp and no longer be the required flatness. Seals with monolithic faces can be stored for up to five years in most cases. Check with your supplier for more details.

Conclusion

A properly preserved pump is only possible through a joint effort by the end user and the manufacturer. A responsible pump OEM must take proactive steps to preserve the pump while remaining aware that each end user is unique. Whatever the situation, be advised that pumps and parts from OEMs are not prepared to be stored long-term (more than six months) unless requested by the end user. References Pump Users Handbook: Life Extension Heinz P. Bloch Mechanical Seal Handbook FSA (Fluid Sealing Association)