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Choosing a Safe Lubricant When Using Reactive Chemicals

Mon, 05/05/2008 - 6:30am
PLANT SAFETY
By Greg Bell
It is well-known that oxygen rich atmospheres are potentially dangerous environments. And within the chemical industry in particular, oxygen is not the only hazardous chemical commonly used. Other reactive chemicals such as chlorine, fluorine, and bromine can and are often used in a wide variety of processing equipment including compressors, vacuum pumps, and cryogenic pumps. While the operators of this equipment are often fully knowledgeable on the properties and risks inherent in reactive gases and chemicals, the introduction of other chemicals used for equipment maintenance may change the rules of the game. Most notably, lubricants in processing equipment are critical for proper maintenance and operation but when used incorrectly can have disastrous consequences.


Lubricants and Reactive Gases

Proper lubrication selection is critical to maximizing performance, uptime, and productivity of operating equipment. The viscosity of the lubricant must be adequate to carry the load, and the additives in the grease must be capable of preventing wear and rusting. It's a delicate balance.

Lubricants which are used in the maintenance of processing equipment are often overlooked as a potential source of fuel. Equipment failure, friction between parts, or even something as seemingly benign as static electricity can serve as the ignition point. Reactive gases and chemicals add another layer of complexity. Though most lubricating oils won't burn well if you put a match to them, they can become explosive in the presence of pure oxygen or reactive gases. In addition to safety in the presence of reactive gases, lubricants also need to perform over the wide range of temperatures present in operating conditions.

Take the example of cryogenic pumps, which sit in a liquid that drastically drops the temperature in the environment. Accordingly, the lubricant that is used to grease the pump needs to be able to withstand freezing temperatures. However, as the cryogenic pump turns, heat is generated and the extremely cold temperature adjusts to a higher operating temperature. For the period of time that the pump runs at a high temperature, the wrong lubricant (which was effective at freezing temperatures) could now fail to operate at the other end of the spectrum. Most lubricants are effective at one temperature setting or another, but rarely are they effective across the board.

There are many different kinds of lubricants that are used in the chemical industry today. While they range widely in terms of lubricity, flammability, and price, there are four that are commonly used - some safer than others when used in the presence of reactive gases and chemicals. Let's review these below.
Hydrocarbons

Hydrocarbons, the most common lubricant, are everywhere - in the engine of your car and as the base oil of most greases. However, in an environment where oxygen and other reactive chemicals are present, all it takes is an ignition source for hydrocarbons to combust. In addition, chemically contaminated hydrocarbons, which need to be disposed of in a special incinerator, can pose an environmental hazard. Luckily, the hazards and costs of using hydrocarbons with reactive gases and chemicals are fairly well-known. However, because hydrocarbons are less expensive than other lubricants, decision-makers in organizations can sometimes make the mistake of focusing solely on price and fail to consider safety hazards and environmental costs.
Phosphate Esters

Phosphate esters are often considered safe because they are advertised as having low flammability. However, the ads often fail to mention that phosphate esters offer low flammability only under specific conditions. When pure oxygen is introduced, for example, phosphate esters will burn vigorously and can be very dangerous. With hydraulic systems, in particular, there is tremendous potential for disaster. If a pinhole leak in a pipe or hose occurs in a hydraulic system, phosphate ester fluid can spray out under pressure and form a mist that can create the conditions for a potential explosion.
CTFEs

Overall, polychlorotrifluorethylenes (PCTFE, CTFE) are effective, nonflammable lubricants. They are one of the few lubricants that contain fluorine, which replaces hydrogen and makes the lubricant nonflammable and non-reactive when used with oxygen and reactive chemicals. While CTFEs are commonly used in the chlorine industry, they are more of a niche player and are not considered a universal lubricant. Two disadvantages with CTFEs are their lack of thermal stability and their potential for reactivity with some substances such as sealing materials.
PFPEs

Whereas conventional lubrication technologies that use mineral oils or synthetics react with oxygen and other reactive gases, perfluoropolyethers (PFPEs) have been independently tested by organizations such as BOC, Air Liquide, BAM, NASA, General Dynamics, and Praxair and proven acceptable for oxygen and other reactive chemical compatibility. PFPE lubricants are safe for use in chlorine, fluorine, bromine, and oxygen as well as common acids and bases such as sulfuric acid, nitric acid, and caustic. These high-value lubricants are also compatible with polymers used in seals, O-rings, and valves. This chemical resistance delivers nonflammability and helps reduce lubricant deterioration and the chances of equipment failure. In addition, the fluorine has replaced all of the hydrogen, creating a saturated molecule that is completely non-reactive.

PFPE lubricants also exhibit stability in high temperatures, allowing for extended lubrication intervals and longer equipment life. The superior film-forming capability of PFPEs provides a thick oil layer that reduces friction and wear, extending equipment life in severe duty applications. The non-oxidizing nature of the oils makes the greases last longer.

Unlike other lubricants, PFPE has the ability to be regenerated, in which the oil can be cleaned up and reused, saving money and helping the environment in the long run. In addition, fluorinated lubricants are such high-performance lubricants that they can extend the life of the components, resulting in reduced maintenance costs.
Selecting a Lubricant

Safety issues. Environmental issues. Disposal costs. Increased equipment performance. Reduced maintenance costs. Extended equipment life. There are numerous considerations when selecting the best lubricant for processing equipment. Here are a few additional tips to keep in mind:

1. Be wary of manufacturer guidelines and advertising claims.

Equipment manufacturers will provide guidelines for the proper lubricant; however, the manufacturer often has no idea how the equipment will be used by the customer. If a compressor is purchased, for example, the manufacturer may not know if it will be used to compress air, oxygen, or other reactive gases each of which may require a different lubricant. Advertising claims can pose another problem. While most are accurate, there are some exaggerated claims made by companies in regions where governments do not have tight regulations concerning advertisements. For example, one recent ad stated that a particular advertised grease would work in conditions of up to 1,500°F. However, under closer examination, it was found that the hydrocarbon grease contained only 1 percent of an additive that would still be present at 1,500°F, long after the grease had turned to smoke.

Choose a supplier that has more than one product or is focused on more than one industry. Large suppliers will often have a wide variety of base oils and thickeners and will not be motivated to push a particular product based on their own need rather than yours. In addition, these suppliers often have technical resources, such as an 800 number, for customers to use for guidance.

3. Use information readily found on the Internet.

When properly filtered, the Internet has a wealth of information available on lubricants. NASA, in particular, has conducted thorough research on conditions with reactive gases and has a mountain of readily available data such as safety manuals that detail which products should be used in high-oxygen atmospheres.

4. Consider the additives used in lubricants.

Look at all the ingredients in the lubricant, not just the base oil. Many lubricants have anywhere from five to eight additives including antioxidants, anti-corrosion agents, and tackifiers. You can have a good base oil and a safe thickener, but the reactive gas or chemical could react with the additives and result in negative consequences. For example, if a lubricant with an antioxidant is used in a high-oxygen atmosphere, the antioxidant will be consumed, which can make the lubricant fail much faster. Unfortunately, most lubricants fail to advertise what additives, if any, are included. Fact sheets often state no hazardous components or synthetic hydrocarbon, but they won't tell you what various additives are included, which could be present at 1 percent to 15 percent. Speak directly to a technical contact at the supplier for information on the additives included and their reactivity with the specific chemicals.

In summary, working with reactive gases and chemicals adds another layer of complexity to the decision of which lubricant to use - a decision not to be made uninformed. Conventional lubrication technologies that use mineral oils or common synthetics react with oxygen and chemicals such as chlorine, fluorine, and bromine, increasing the potential for explosion, fire, and deterioration. Reactive gas applications require lubricants that help provide safe operations.
Greg Bell joined DuPont in 1974 with a bachelor of engineering degree in mechanical engineering from Youngstown State University. For more than 15 years, he has been responsible for technical service and product development for Krytox performance lubricants. Bell is a member of the National Lubricating Grease Institute, the Society of Tribologists and Lubricating Engineers, and the American Society of Mechanical Engineers. He has patents for grease thickeners and improved oils and was a consultant for the History Channel presentation titled Modern Marvels Lube Job. More information is available by contacting DuPont Performance Lubricants, Barley Mill Plaza, Bldg. 23, Box 80023, Wilmington, DE 19880, at 800-424-7502 or by visiting www.lubricants.dupont.com.'When pure oxygen is introduced, for example, phosphate esters will burn vigorously'
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