In part one and part two of this three-part post, we discussed how shutdowns could negatively affect lubricant film and increase contamination risks. For part three, we’ll reveal the oil health can decline in shutdown equipment.
Declining Oil Health During Periods of Shutdown
While you may think that the life of the oil is not being affected if the machine isn’t running, in fact it often is. Additives and byproducts of oil degradation are soluble in the oil, meaning they stay in solution during normal operation. But just like salt dissolved in water, the solubility of additives, and in particular degradation byproducts, are temperature dependent meaning they can come out of solution when the oil cools during shutdown. The result is the formation of sludge and varnish which can cause deposits to form, coating surfaces and negatively impacting oil flow when the machine is started back up.
With aged oils or heavily additized oils, some larger additives such as viscosity index improvers and foam inhibitors can come out of solution under low ambient temperature conditions. Once they settle, it’s next to impossible to resuspend these additives resulting in problems when the machine is restarted. This is one of the reasons why your personal vehicle owner’s manual recommends changing oil based on the number of miles driven, or every 3 months, whichever comes first.
Sludge and varnish formation and additive precipitation are in part caused by contamination. Water acts as a catalyst to drive oil oxidation, while particles can either catalyze oxidation or serve as nucleation sites for deposit formation. Because of their impact on oil health, protecting stop/start assets through proper control of particles and moisture is a vital component of maximizing oil life.
One simple way to prevent water and particulate ingression is to install a desiccant breather on the oil sump. Properly selected desiccant breathers not only remove moisture when a machine is actively breathing, but with the right type of breather the silica gel is actually in contact with the headspace within the oil sump. Just like the small sachet of silica gel contained inside a new shoebox or consumer electronics that’s designed to keep the product dry during storage and transportation, a desiccant breather will keep the inside of the oil sump dry, helping to limit the impact of moisture ingression during shutdowns.