To secure the reliability of critical company assets, parts and equipment must be protected from corrosion. During machine operation, oil is circulated or splashed to ensure additives are well dispersed throughout internal system surfaces. The movement of the fluid allows for proper protection, but once equipment is shut down and stored until a later date, standard lubricants often fail to protect unwetted surfaces from corrosion.
Several options are available to protect equipment during these idle stages. One is to introduce a corrosion inhibitor to the system. Corrosion inhibitors come in many forms with various functions to ensure the equipment is protected. The second is to supplement the system with a mist-lubrication or mist-circulating system. Mist-lubrication systems release a fresh rust-inhibiting lubricant supply to stationary equipment internal surfaces, which ensures a fresh dose of additive is always available.
This article focuses on corrosion inhibitors introduced by the equipment builder and/or users.
Corrosion inhibitors must be able to protect exposed surfaces, and this can be accomplished in many ways. Liquid-phase corrosion inhibitors ensure surfaces covered by the liquid will be protected by the strong additives in the fluid. Vapor-phase protection may be included with the liquid-phase protection or used in dry reservoirs. It works by filling the head space with a vapor that prevents corrosion. Surface coatings protect systems by adhering to the surface. Generally, surface coatings repel water from the surface and include an additive to reduce corrosion at the surface.
Intermittent operation is common in standby systems that are used only when the main system fails. For these systems, a corrosion inhibitor allowing intermittent operation is needed. Some of the liquid-based corrosion inhibitors will also function as a lubricant for intermittent operations.VAPOR-PHASE PROTECTION
These are often referred to as slushing compounds. They perform multiple tasks, but the coatings' two main functions are to prevent corrosion at the surface and to prevent moisture and oxygen from reaching the surface.
These coatings can be brushed on or sprayed on, or a part can be dipped into the corrosion inhibitor. They are normally formulated with a solvent that will flash off, leaving behind a more resilient product. Many surface coatings can be delivered in aerosol cans.REMOVAL
Assumed compatibility is a common problem. For example, slushing compounds used on new bearings are generally compatible with mineral oils, but are not always compatible with synthetic oils. Always make sure the corrosion inhibitors and lubricating fluid are compatible. Some corrosion inhibitors simply can be flushed with the operating fluid, while others must be removed with solvents or cleaners to strip the additives from the surfaces.SIDE EFFECTS
Side effects can also be created by the environment. In an article from Material EASE, a sidebar covered the topic of incompatible preservatives in aircraft hydraulics. The preservatives in the fluids were creating an organic plaque on the filters, causing premature clogging. It was determined that the hydraulic system's high-temperature operating conditions were incompatible with the preservative being used.
Numerous manufacturers and distributors offer preservatives and similar corrosion-inhibitor products. Consult them or Noria Corporation for answers to your specific questions.REFERENCES