In our first article, we discussed what rust is and why it become so important over the last year. In this article, we will discuss ways to prevent rust and how to rust preventatives work. The first principle of corrosion protection is to coat internal and external metal surfaces with a protective barrier. Parts that are painted are already protected, but bare metal needs an extra coating of rust preventive. There are several choices, depending upon application.
Let’s say you are needing to mothball a pump that is mostly painted, but the drive shaft is not. The pump sits out in the open, exposed to rain, snow, sleet and hail. If the pump is not operating, the shaft will certainly rust. Good external rust preventives for this application are a waxy-type corrosion inhibitor. These come in various forms to make them easy to apply. Some require heating, and some are dissolved in a solvent that make them fluid enough to apply with a brush. The solvent evaporates, leaving behind a tenacious film. It only takes a few minutes and a brush, and you’ve saved a lot of grief when there is demand for the equipment again. This activity needs to three or six months to maintain the proper film.
Internal surfaces are a bit trickier. Ideally, a corrosion inhibitor should have the following characteristics:
1) protects all surfaces inside the equipment
2) easy to apply
3) relatively inexpensive
4) easy to remove when the equipment is put back into service
5) needs to be compatible with paint, elastomers and seals, and with the lubricant currently in use
Fortunately, such a thing exists. It is generically called a vapor space rust inhibitor. It is formulated with an additive that sublimates, which means to change from a solid to a gas without going through a liquid phase (think of dry ice as another example of something that does this).
The rust inhibitor in a volatile rust inhibitor is attached to a substance that sublimates. It is dissolved in the carrier. When the liquid is added to the equipment the additive sublimates out as a vapor, hits the metal surfaces above the level of the oil, then condenses back onto the surface as a solid to hold the rust inhibitor in place.
This type of rust inhibitor can be added to the oil that is already in the sump at about 10%. Alternately, drain out all the oil and add an inch or two of rust inhibitor to the bottom of the sump. The additive will protect all the surfaces that the oil touches, all the surfaces that it touched when circulating, and all the surfaces above the level of the oil. For this reason, it is often called a 3-phase rust inhibitor. Three phase corrosion inhibitors are usually good for a year or more, but it depends on how well the equipment is sealed.
What if you’re having to mothball larger, specialty equipment like a natural gas engine or diesel engine used for either power generation or gas compression? These types of equipment require special procedures and will be a little more complicated. For example, mothballing procedures done in the oil and gas industry for gas engines can take up to seventeen steps.
While a process like this sounds complicated, it is worth the effort to avoid costly replacements in the future and the personnel exposure that occurs to replace rusted equipment. Taking the time to mothball the engine properly preserves its value and ensures that it can be started again when needed.
To find out what could happen without a robust rust prevention program, stay tuned for the last article in the series, “What can happen without a strong rust prevention program.” To learn more about how to properly mothball and preserve your equipment, check out our Contamination Control Study and/or reach out to your local Mobil Rep for more information. Do you have Rust Prevention Program? If so, please share your results in the comments!
Thank you Cody for the article which explains a new method of rust prevention.