Q&A: PTFE Sealing Solutions

Dec. 12, 2005

Rick Freer, W.L. Gore Rick Freer is an associate with the Sealant Technologies business unit of W.L. Gore & Associates. He has been with Gore in progressively responsible leadership

Rick Freer, W.L. Gore

Rick Freer is an associate with the Sealant Technologies business unit of W.L. Gore & Associates. He has been with Gore in progressively responsible leadership positions since 1992. During his time with Gore, Mr. Freer has worked with a variety of industrial users to engineer sealing solutions to meet the requirements of a wide range of applications. He earned a bachelor’s degree in Mechanical Engineering from Purdue University and an MBA from the University of Houston. Mr. Freer can be reached at [email protected] or 410 392-3200.

Q: For what type of applications is polytetrafluoroethylene (PTFE) a particularly good fit?

A: PTFE is primarily known for its chemical resistance, so PTFE is a sensible choice for virtually any aggressive media where other materials would be attacked, particularly for applications involving chemical substances such as acids, bases, and chlorinated organics.

Expanded PTFE (ePTFE), a Gore invention, is a mechanically strengthened PTFE structure that combines the properties of chemical resistance with enhanced creep resistance. It’s a very good choice for almost all piping systems, from fragile flanges (FRP and PVC) to lined pipe, glass, and metals.

ePTFE gaskets can also be used to standardize on flanges, because their chemical compatibility and versatility reduces the likelihood of process incompatibility. For some plants, this can help realize significant savings on maintenance and inventory control.

Q: For what type of applications is PTFE not a particularly good fit?

A: Generally, PTFE gaskets are selected because of the aggressive media involved. Applications that require fire safety and higher temperatures (above 600 F, such as steam lines) are generally not appropriate applications for PTFE gaskets. Also, in benign systems such as plant air and water, elastomers perform well and thus these applications do not require the performance advantages of PTFE.

Q: How has Gore’s PTFE compound been improved over the past five to 10 years?

A: Gore’s expanded PTFE (ePTFE) products have continually undergone innovations. Within the last five years, there have been groundbreaking improvements in the realm of creep performance (improved creep resistance and lower stress-to-seal technology), and leakage performance under low-load conditions.

Because of these developments, Gore now produces ePTFE gaskets that maintain bolt loads in service far beyond what other PTFE gaskets can deliver — even at high temperatures with high load conditions. Also, combined with new barrier layers, the newest ePTFE gaskets can also perform exceptionally well under lower load conditions, such as in plastic or glass-lined flanges. For this reason, plants have a realistic option to standardize on one gasket choice across all flange material types.

Q: What is the difference between sheet-and-cut and form-in-place gasketing? Isn’t the common perception that a form-in-place is a "quick fix," whereas sheet-and-cut is the more permanent solution?

A: The term "form-in-place" is often used to describe a category of ePTFE gaskets invented by Gore wherein long lengths (or "ropes") of gasketing material are used to customize flange seals. The most widely popular product in this category is called Joint Sealant. While fully "mainstream" today, Joint Sealant was quite a novelty in the 1970s when it was first introduced. Some maintenance people viewed it primarily as an "emergency" gasket. Over the years, users have come to realize that Joint Sealant is also incredibly tight-sealing — thus a very reliable long-term solution instead of a "quick fix."

Sheet-and-cut gaskets are pre-manufactured, then made to fit a specific sealing surface. The specific dimensions are cut from a large sheet of gasket material — normally patterned after an existing gasket, a blueprint, or published standardized flange dimensions.

The installation working space available may determine what form of product is easiest or most efficient to install. Form-in-place products can be real maintenance time-savers when replacing a gasket on vessels where a mixer would previously require disassembly, or in the case of heat exchangers where complete removal of the tube sheet may be needed. On the other hand, sheet-and-cut gaskets sometimes require less working space to install — particularly in pipe flanges.
With more flexibility of use, form-in-place products can be a way to save on inventory expenses, because one spool of product can be used to fit all types of shapes and flange sizes.

Q: What are the most common reasons for PTFE gasket failure? What are some best practices users can employ to limit the risk of failure?

A: The most common reasons for PTFE gasket failure come from not following proper installation practices. Best practices include: cleaning the flange surface; properly torquing bolts to 50-80 percent of yield strength; using star pattern torquing procedures with a minimum of three passes; lubricating the bolts, nuts, and washers; sizing the gasket thickness to accommodate the flange deviations, and creating the stress required to seal.

Q: How can PTFE gasketing be improved going forward? What technology improvements can users look forward to seeing over the next five to 10 years?

A: Today is a very exciting time for expanded PTFE technology developments. The most recent innovations have greatly raised the performance bar of what was previously believed possible for PTFE-based gaskets. Looking forward, there will be more and better opportunities for users to standardize and simplify their gasketing practices and systems. Continuing advancements in creep resistance and form-in-place products will allow for more inventory consolidation than industry has ever experienced.


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