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Maintaining the operating integrity of idled equipment presents unique challenges. Equipment in service receives routine maintenance and continuous lubrication of internal components. All components of idled equipment are at static rest and receive no lubricant replenishment. More importantly, the internal cavities of the equipment can collect water from condensation caused by the normal ingress and egress of air due to daily temperature fluctuations. Under these conditions, extensive rusting of bearings and other critical components can render the equipment inoperable in a surprisingly short period of time.
There are many reasons why equipment may be idled for extended periods of time. Cyclical market downturns or labor actions can cause individual operating units within plants to shut down. Start-up delays on new projects can result in new equipment being stored for extended periods of time. Even new machinery subjected to salt air in transoceanic shipments can accumulate rust on internal components before arriving at its destination. Regardless of why equipment is idled, vapor phase corrosion inhibitors (VPIs) provide a simple and inexpensive means to protect the internal components of idled equipment against damaging rust and corrosion.
VPIs protect metal surfaces against rust in gearboxes, engines and other closed systems. The VPI fills the closed spaces with a vapor that forms a monomolecular protective layer on all metal surfaces. This layer pacifies metal surfaces to prevent rust and corrosion. Because the system is sealed, the protective layer is constantly maintained. The length of time the protection continues depends on how well the system is sealed, but protection for one year or longer is attainable.
Although the name “vapor phase corrosion inhibitors” seems to indicate the inhibitor is in the form of a gas, VPIs actually have surprisingly low vapor pressures and are solids or liquids at room temperature. The most common form of VPI is a salt of an amine and a weak acid. An example is the carbonate salt of dicyclohexylamine. Research has shown that the VPI disassociates to the amine and the acid and the two volatile components recombine on metal surfaces.
When oil containing a VPI is used to “mothball” a piece of equipment, it is best to fill the equipment to normal oil levels and run it for a short time. This distributes the oil to all surfaces normally wet by oil and helps to saturate the air inside the equipment with the VPI components. The oil can then be drained back into the original container, leaving a small puddle of the preservative in the equipment. The drained corrosion inhibitor can then be reused on another piece of equipment and then another, etc. The equipment should then be sealed by whatever means available such as tape or shrink wrap or exchanging breather fittings for plugs to keep the VPI in and humidity out.
A desiccant breather can be used if large temperature and/or pressure changes are anticipated. In addition to proper application of VPI products, other OEM-recommended procedures for storage, such as shaft rotation frequencies, should be observed. When returning the stored equipment into service, it is normally unnecessary to flush the residual vapor phase inhibitor from the equipment before it is filled with new oil. However, it is a good practice to consult the lubricant manufacturer regarding compatibility of the two products.
VPIs are offered by a number of oil suppliers. Royal Purple offers a VPI product called VP Preservative Oil 10. Properly used, vapor phase corrosion inhibitors are an economical and effective way to protect new or idled equipment against rust and corrosion. Manufacturers of blowers, gearboxes, etc. have had excellent results using them to protect new equipment from rusting in transit to customers. The adage that an ounce of prevention is worth a pound of cure certainly applies to the case for using VPIs.