Introduction to Perfluoroelastomers - Part 2

Gallagher recently released our Introduction to Perfluoroelastomers White Paper, available for download on our site.  This was written by Russell Schnell, a current contracted employee of Gallagher Fluid Seals, and more importantly, a former Senior Application Engineer with the Kalrez® perfluoroelastomer parts business at DuPont.  The following is the second excerpt from the White Paper, discussing the common industries in which perfluoroelastomer seals are used, and why.

Common Industries in Which Perfluoroelastomer Seals are Used and Why
In general, perfluoroelastomers are the most expensive elastomer seals specified in the marketplace; however they also provide the highest performance sealing service. As with any product, the selection of these products should be the result of a cost-benefit analysis.

Oil Processing Industry
One of the earliest uses of perfluoroelastomer seals was in the oil industry (down-hole).  Seals used in down-hole oil applications required resistance to high temperatures and aggressive chemicals. Sour oil and gas, resulting from H2S, often caused swift degradation of fluoroelastomer seals. The ability of perfluoroelastomer seals to resist H2S was a major reason for their selection and use. Over time, as wells became deeper and deeper, the application temperatures increased. As a result, in addition to aggressive chemicals, better high temperature resistance was needed and FFKM seals provided that benefit. Finally, seals used in these applications must have an “acceptable” service life. Oil wells are expected to last for many years and a seal failure, especially during initial exploration results in lost time and great expense when down-hole equipment must be retrieved to repair a seal. So the important points for this industry are resistance to aggressive chemicals, high temperatures, and reduced chance of seal failure which can result in tremendous expense.

Chemical Process Industry
As chemical processes have increased in temperature to improve yield and chemical reaction speed, the need for products with high service temperatures and long life has increased. The cost of the seals is not the major issue in such applications, but rather the downtime and lost production associated with seal failure.

Elastomer seals are often used in mechanical seals. Mechanical seals are the critical components to prevent product leakage at pumps. Elastomer seals, in a mechanical seal, replaced packing as the preferred shaft seals in pumps for longer life and lower leakage. Mechanical seals on pumps and agitator shafts are critical components in many chemical operations, and failure of these components can shut down an operation. Mechanical seals in pumps or on agitator shafts may be in locations that don’t allow for easy access. For example, agitator shaft seals can be extremely large, and if a mechanical seal fails, a crane may be required to assist in seal replacement. This results in longer downtime, lost production and increased operating expense. The goal when choosing an elastomer seal is typically to maximize MTBR (mean time between repairs).

There are many other types of sealing applications at chemical plants including: valves, piping connections, instrumentation, lab equipment for testing product, and hoses. This equipment may need to handle numerous products. That is, a pump or valve may have different chemicals running through it depending on the production needs of the plant. A fluoroelastomer may handle one product stream, but ethylene propylene elastomer may be required for a different product stream. In this case a perfluoroelastomer seal would be used to handle both product streams and avoid down time to change out seals between production runs. Perfluoroelastomer seals are also used in applications where a product stream can vary in composition and differing trace chemicals might attack a lower performance seal. Finally, perfluoroelastomers may be used to reduce replacement part inventory. An alternative to stocking four of the same replacement valves, each containing a different elastomer for a specific process stream, is to stock one valve with FFKM seals which can be used in any of the applications.

Semiconductor Industry
The semiconductor market continues to expand as the use of integrated circuits (“chips”) becomes more common in everyday life. The ability to make chips quickly, efficiently, and with few defects is the goal of manufacturers. The major equipment manufacturing companies today continue to search for better seals to allow their equipment to run longer between cleaning and repair cycles. Longer runtimes generate greater production efficiency and profit. Downtime and lost chip production are very costly for this industry.

This industry continues to push the high temperature envelope in order to improve processing efficiency. Temperatures above 200°C are becoming more common and the only products that can withstand these temperatures long term are perfluoroelastomers. In addition, new plasma gases are being developed to improve manufacturing performance. Oxygen plasmas, NF3, etc. can cause serious issues with non-perfluoroelastomers. Note that even FFKM materials will eventually break down in these extremely aggressive environments.

Another benefit of perfluoroelastomers to this industry is their low outgassing performance. Although not the case with every FFKM, there are specific formulations that are designed for low outgassing at elevated temperatures. Since chip manufacturing equipment is typically run at high vacuum and high temperatures, low outgassing is the key to avoiding product contamination.

Aerospace Industry
The aerospace industry is another area where the use of perfluoroelastomer seals provides significant benefit. Seals are critical for use in gas turbine engine systems, and the seals need to withstand high temperatures and aggressive chemicals. However, the major concern is high temperatures. During standard engine operation, seals are typically exposed to temperatures that standard fluoroelastomers could handle. Problems occur when aircraft engines are shut down soon after use and engine oils are not circulated, resulting in high soak-back temperatures.  In that case, some engine locations, and seals, can see temperatures well over 225°C. The result is that fluoroelastomer seals will harden over time, due to the elevated temperature, and become ineffective as a seal. FFKM seals can withstand these elevated temperatures and continue to function without leakage. This greatly increases “time on wing”. The result is longer aircraft utilization between engines teardowns, which means lower cost of operation.

Pharmaceutical and Biotech Industry
These two industries are similar, but have different requirements regarding elastomer performance. In general, the pharmaceutical industry is similar to the chemical process industry and may require perfluoroelastomer seals, when aggressive chemicals are used. Typical applications would include:  mechanical seals, valves and instrumentation.

The biotech industry is unique with applications that are typically batch processes and often require involve an equipment cleanout between batches. If the operation is clean-out-of-place (COP), the equipment is broken down, cleaned and the seals are replaced.  For this service, the seals may only have to last a few days to a few weeks before being replaced and lower performance seals may be adequate. However, the equipment may be designed for clean-in-place (CIP). CIP usually involves cleaning the process tanks and piping with aggressive chemicals, steam sterilization and then drying with nitrogen. In this service, the batch process chemistry may not be an issue, but the aggressive chemicals used for cleaning and the steam may attack lower performing elastomers. If that is case, perfluoroelastomer seals can provide the chemical and steam resistance required for long term service. Finally, FFKM seals often have very low extractables (low contamination potential), a very important performance requirement for this industry.

If you have any questions on how perfluoroelastomer seals can implemented in your product or process, please contact the Gallagher Engineering Department for more information.

About the Author
Russell Schnell spent more than 37 years as an engineer with DuPont, the last 26 years  as a Senior Application Engineer with the Kalrez® perfluoroelastomer parts business. Recognized for his expertise in elastomer applications, seal design and failure analysis, he provided technical support for a wide range of industries including: chemical processing, aerospace, oil and gas, pharmaceutical and semi-con. He created and conducted hundreds of training seminars and workshops in this field and was solely responsible for the development of the Kalrez® Application Guide software tool.

Russ received a Bachelor of Science in Chemical Engineering from Columbia University in New York and MBA from the University of Delaware.