Upon first glance, a gasket may appear to be an inconsequential part in a robust reactor system, but the job of this component is critical to the successful operation of your vessel. The role of a gasket is to create a tight seal between two components to prevent the unwanted emission of liquid or gas. Failure to do so can be catastrophic to your operation!
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
Glass-Lined-Steel Sealing Challenges
We’ve talked a lot in previous posts about the benefits of glass-lined steel (for those of you that aren’t familiar with this type of equipment can read our post entitled 5 Reasons your Process Could Benefit from Glass-Lined Steel Equipment or download our Introduction to Glass-Lined Steel Equipment eGuide). The composition and properties of glass-lined steel make it a desirable material of construction for processes that involve aggressive media that operate under severe conditions. These same harsh demands on this equipment can make it challenging to maintain a tight, lasting seal primarily due to limitations on gasket loads and fluctuations in the sealing surfaces. And these sealing challenges increase as flanged connections get larger in diameter. That is why it is important to make sure you are using the proper gasket for a given application. Failing to do so can lead to premature gasket failure, with consequences that range from problematic to catastrophic, including:
· Equipment damage
· Production downtime
· Risks to personnel safety
There are a number of different gasket solutions. Depending on the size of the flange and service conditions of the equipment, there might be a solution that is more effective for one scenario than another. In this post we’ll review the different types of PTFE gaskets available and their utilization.
Unfilled PTFE Gaskets
Gaskets made of 100% PTFE are referred to as unfilled PTFE. Unfilled PTFE gaskets are quite versatile and can be used in most general applications. Within this category are two classifications: Virgin grade PTFE is a soft, formable material that is made directly from the resin producer, giving it the highest physical properties and resistance to creep (the frequently used term that refers to compression under load). Mechanical grade PTFE is still 100% PTFE but it is made from reprocessed resin so it’s not suited for high-purity or food applications. Typically virgin grade can be recognized by its whiter color when compared with mechanical grade.
Filled PTFE Gaskets
Filled PTFE gaskets include additives whose material helps to expand the performance of the gasket, enhancing its physical and chemical properties. Due to the improved mechanical strength over virgin PTFE, filled PTFE gaskets are the most widely used for industrial applications. The three main types of filler that are used in this style are:
· Carbon: Ranging in amount from approximately 10-35%, carbon filler increases compressive strength and can improve conductivity while still providing good chemical resistance. Carbon additives also help to increase the hardness and can improve the wear properties of the gasket.
· Graphite: Beneficial in hydraulic/pneumatic compression type seals and rotary applications, the addition of graphite to a gasket (approximately 5-15%) reduces the coefficient of friction and increases strength when compared to unfilled PTFE models.
· Glass: The addition of fiberglass in increments of 5-40% effectively increases the compressive strength of the gasket, increasing wear and reducing creep. This type of gasket is useful in applications that require a reduction in cold flow, which can be an issue with PTFE. The addition of glass doesn’t negatively affect the chemical and electrical properties of virgin PTFE. Protection rings that are used on larger manway openings are usually made in this construction.