The extreme temperatures and pressures under which glass-lined vessels often operate make it imperative that you select the right kind of gasket to withstand the specifications of your process.
Since compression is required to maintain the seal, gaskets are typically made with a malleable material, such as PTFE (polytetrafluoroethylene). A supple material like this is able to more effectively create a seal between the harder surfaces of the components it is placed between than a gasket made from rigid material, such as stainless steel.
PTFE is the most commonly used fluoropolymer for gasket construction. Its inertness and superior chemical resistance make it a choice material throughout a variety of industries. The rigorous operating conditions of glass-lined equipment make PTFE an ideal gasket selection due to its chemical properties, low coefficient of friction, and outstanding temperature resistance.
There are a number of different gasket solutions, but for glass-lined equipment PTFE envelope gaskets are most commonly used. Envelope gaskets feature virgin PTFE enclosures that offer protection to insert rings, which are made of a highly compressible, liquid-resistant material. These asbestos-free gaskets include a corrugated metal ring made of stainless steel, for long life in most services (a special benefit in corrosive atmospheres). Alternative materials of construction are available, such as monel and hastelloy. Additional features like grounding tabs for antistatic use or retaining clips to assist in retaining gaskets on manways and handholes. Different design options are also available, including:
· Single Envelope Gaskets: Designed for both small and larger nozzles, the virgin PTFE slit envelope is constructed of formed tape with a smooth, butt-welded junction (especially important for high-vacuum service). This envelope is used to protect the compressible inserts from the process environment. There are a lot of different envelope gaskets available, so it is important to make sure you are purchasing one that is appropriate to use with glass-lined equipment.
· Double Envelope Gaskets: This is similar to the single-envelope, except that a second envelope is used to “enclose” the entire gasket. The inner envelope protects the process side while the outer envelope protects from any atmospheric contaminants. A virgin PTFE slit type or butt-welded type envelopes are used to fully encapsulate the gasket from both the process side and the atmospheric side of the joint. Again, it is critical to ensure you are using a design suitable for glass-lined equipment.
· U-cut Gaskets: A multi-purpose U-channel gasket is an exceptionally high quality gasket for normal service applications on all glass-lined and alloy process equipment where PTFE is compatible with the product and process operating conditions. Instead of a butt-welded envelope, this design incorporates an envelope that is machined from a solid piece of PTFE, eliminating the need for any welds in the fabrication. The U-cut design combines a unique convex geometry to allow the gasket to conform more uniformly to the compressive forces when the nozzle bolts are torqued, making it highly attractive for food and pharmaceutical applications where product build-up is not acceptable and CIP is required.
For even more information, download a copy of our Gasket Portfolio, that contains specs and part numbers for our most popular envelope gasket designs.
Expanded PTFE is created by rapidly stretching PTFE under the right conditions to create a very strong, microporous material. The resulting material, known ePTFE, exhibits the array of properties found in virgin PTFE, such as strength, chemical inertness, and high thermal resistance.
ePTFE is much softer and more flexible than regular PTFE, giving it the ability to be manufactured into tape that can be fitted and installed onto a flange with an end product similar to how a traditional gasket would function. The added benefits of ePTFE tape are ease of compression, minimal creep and cold flow, and the ability for on-site customization (which eliminates the long lead times and complicated logistics that are brought about by offsite shipping, handling and installation).