It is well known that an oxygen-rich atmosphere is a potentially dangerous environment. Other reactive chemicals, such as chlorine and fluorine, are often used in a wide variety of processing equipment. While the operators of the equipment are often fully knowledgeable of the properties and risks associated with reactive gases and chemicals, the introduction of new lubricants for equipment maintenance may create new challenges.
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 corrosion. Lubricants that are used in the maintenance of processing equipment are often overlooked as a potential source of fuel. Though most lubricating oils won’t burn well if a flame is applied to them, these oils can become explosive in the presence of pure oxygen or reactive gases.
There are many different types of lubricants used today. While there is a broad range in terms of lubricity, flammability and price, there are four that are commonly used – some safer than others – in the presence of reactive gases and chemicals.
Hydrocarbon-based lubricants are the most common types used today, and they are 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. Fortunately, the hazards and costs of using hydrocarbons with reactive gases and chemicals are well known; however, because hydrocarbon-based lubricants are less expensive than other lubricants, decision makers in organizations can sometimes make the mistake of focusing solely on price, failing to consider the safety hazards.
Phosphate esters are often considered safe because they are advertised as having low flammability. However, these ads often fail to mention that phosphate esters offer low flammability only under specific conditions. When pure oxygen is introduced, for example, phosphate esters can burn vigorously.
In general, polychlorotrifluorethylene (PCTFE, CTFE) are effective, nonflammable lubricants. They are among the few lubricants that contain fluorine, which replaces hydrogen and makes the lubricant nonflammable and non-reactive when used with oxygen and reactive chemicals. CTFEs are commonly used in the chlorine industry. Disadvantages of CTFEs include their lack of thermal stability and potential for reactivity with some substances, such as sealing materials.
Perfluoropolyethers (PFPEs) have been independently tested 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 acids and bases such as sulfuric acid, nitric acid and caustic. These lubricants are also compatible with polymers used in seals, O-rings and valves. This chemical resistance delivers nonflammability and helps reduce lubricant deterioration and chances of equipment failure. In addition, fluorine has replaced all of the hydrogen, thereby creating a molecule that is highly stable towards the reactive chemical environment.
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 nonoxidizing nature of the oils makes the greases last longer.
In summary, working with reactive gases and chemicals adds another layer of complexity to the decision of which lubricant to use – a decision that should be an informed one. Conventional lubrication technologies that use mineral oils or common synthetics react with oxygen and chemicals such as chlorine and fluorine, increasing the potential for explosion, fire and deterioration. Reactive gas applications require lubricants that help provide safe operations.
Thomas J. Blunt is a Technical Services Consultant at Dupont Performance Lubricants. You can find his contact information in our membership directory.
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