Seal with Compression: Power of Graphite (Part A)

In the realm of industrial applications, sealing materials play a pivotal role in ensuring the integrity and efficiency of various systems. Among the options available, expanded graphite is considered the most versatile and effective sealing material, finding widespread use across diverse industries.

Upon the ban on Carcinogenic Asbestos Fiber based Sealing Materials, Expanded Graphite was the natural replacement for majority of all high temperature applications. This article will attempt to delve into the properties, benefits, and applications of expanded graphite in high temperature applications.

Understanding Expanded Graphite and how it seals.

As per our earlier articles, we have explained that Sealing is achieved based on the relationship of two mechanical properties: Compression and Recovery.

Every Sealing material has a different relationship between Compression & Recovery. For eg, Elastomers have very good compression and excellent recovery. Hence initial thickness (pre-compressed) selected for elastomer is nearly similar to the available height or space available or groove provided in the joint.

Expanded graphite, also known as graphite intercalation compound (GIC), is derived from natural graphite through a process of intercalation and expansion. This involves expanding the Graphite flakes into highly expanded particles that allow compression.

Hence due to this expanded nature, the Graphite material offers excellent compression but poor recovery. Hence the initial (pre-installed) thickness required to affectively seal is usually higher or more than the height or space available or groove machined.

Since compression is the primary parameter for Expanded Graphite sealing components, the available bolt load and at what surface stress, the designed seal achieves the desired compression is critical to achieve low permeability sealing. Various inserts such as jacketed wires, Tang Sheets, Foils etc are introduced into this material to improve recovery and offer a mechanical compression stop.

Properties of Expanded Graphite:

High Temperature Resistance: One of the most significant advantages of expanded graphite is its exceptional resistance to high temperatures. Based on the purity (>98%) of the Expanded Graphite material used, the performance of the Seal would be between 450 Deg C to 600 Deg C.

Chemical Inertness: Expanded graphite exhibits excellent chemical inertness, making it resistant to a wide range of corrosive substances. This property is particularly valuable in sealing applications where exposure to harsh chemicals is common, such as in chemical processing plants and petrochemical refineries.

Low Permeability: The structure of expanded graphite consists of numerous interconnecting pores, which impart low permeability to gases and liquids. This makes it an effective sealing material for preventing leakage in various systems, including valves, pumps, and flanges. Other factors such as density of Graphite (> 1 g/cc), purity and manufacturing consistency is also important to achieve low permeability.

Conformability: Expanded graphite possesses a high degree of conformability, allowing it to deform and conform to irregular mating surfaces. This property ensures a tight and reliable seal, even in applications with uneven or rough surfaces.

Thermal Conductivity: Despite its excellent thermal resistance, expanded graphite also exhibits good thermal conductivity. This property enables efficient heat transfer across sealed interfaces, making it suitable for heat exchangers and thermal management systems. This primarily means the material will dissipate the heat from the Seal but also the Metal contact surfaces around it.

Each different insert or construction is primarily to improve the "Recovery" parameter of Expanded Graphite and achieve sealing at a lower surface stress.

Applications of Expanded Graphite as a Sealing Material:

Gaskets and Seals: Expanded graphite gaskets and seals are widely used in various industries, including automotive, aerospace, oil and gas, and manufacturing. They provide reliable sealing solutions for flanges, pipe joints, and other connections, effectively preventing leakage of fluids and gases. With the advent of EV Batteries, the usage of Graphite based Seals and its Fire Safe properties will only increase its applications even more.

Packing and Packing Rings: In applications where dynamic sealing is required, such as pumps and compressors, expanded graphite packing and packing rings are employed. These components effectively seal rotating or reciprocating shafts, maintaining fluid containment and preventing leakage.

Heat Exchanger Gaskets: In heat exchangers and other thermal management systems, expanded graphite gaskets are utilized to seal the interfaces between heat exchange plates. This facilitates efficient heat transfer while preventing cross-contamination between the fluid streams.

Conclusion:

Expanded graphite stands out as a highly versatile and effective sealing material, offering a unique combination of properties that make it suitable for a wide range of applications. The Material is available in different constructions, forms and various grades such in Sheets, Tapes, Forms. Its high temperature resistance, chemical inertness, low permeability, conformability, and thermal conductivity make it an ideal choice for demanding sealing requirements across various industries.

In Part B we will look into detail on how to select the right "Grade" of Expanded Graphite for your Sealing application.

W: www.pilotgaskets.com | www.pgeindia.com E: info@pgeindia.com