Graphite – A Little Background
Graphite was first discovered in Cumbria, North England at the beginning of the sixteenth century.
From it’s discovery – graphite has been useful. First it was used to mark sheepskins by shepherds wanting to distinctly “mark” their property . Latter it was used in the moldings for cannon ball production. Then it became popular as a material used by artists.
The first documented use of graphite as a pencil occurred in 1565. The use of graphite as an art material became popular, sold by Flemish merchants throughout Europe. At first, pencils consisted of rough pieces of graphite wrapped in sheepskin. The Italians first began using pencils that consisted of pieces of graphite embedded in wood. (University of Waterloo Earth Science Article)
Graphite is a mineral composed exclusively of carbon. Interestingly enough, graphite has the same chemical makeup as diamonds, which is also carbon, but the molecular structure of Graphite and Diamonds is entirely different. This causes opposite characteristics in their physical properties. And it’s in these differences that make flexible graphite a superior performing packing and gasket material.
Flexible graphite is the first fluid sealing material made exclusively from natural graphite flake. Graphite flake is exfoliated or expanded (by various methods either chemically or through rapidly heating the graphite flake) making it flexible and soft. Ideal for gasket material.
5 Characteristics of Flexible Graphite.
1.Flexible Graphite is a Natural Lubricant:
Graphite has a natural greasy, slippery characteristic that makes it a good lubricant. For example, flexible graphite yarn is very popular for use in compression packing around pump shafts. The lubrication it provides minimizes shaft wear and can be used on higher speed rotating equipment.
2.Flexible Graphite is Heat Resistance:
Graphite has three notable thermal properties that make it unique. First, graphite has a high melting point. Which makes it a good gasket material in higher temps (continuous service up to 700F in inert atmospheres) Second, graphite has remarkable heat transfer properties, dissipating heat away from critical, heat sensitive components. And Third, graphite has low thermal expansion. In heated environments, graphite doesn’t expand all that much relative to other materials.
3.Flexible Graphite is Chemically Resistance:
Graphite is insoluble. It cannot be dissolved in a liquid, especially water. And graphite is infusible. Making it one of the most chemically resistance gasket materials. However at operating temperatures at or above 842 degress F, it is advisable to contact your local provider for additional information. Graphite chemical resistant charts are available upon request.
4.Flexible Graphite Has the ability to Compress and Conform:
Because flexible graphite can be compressed it conforms to flange surfaces and “flows” into irregularities in flange faces under a wide range of compressive loads. Once in place, flexible graphite’s low creep relaxation characteristics maintains stability, enhancing sealability.
5.Flexible Graphite Can Oxidized Under Certain Conditions
One of the more typical concerns when using flexible graphite is thermal oxidation. Thermal oxidation is a function of time and temperature. The longer flexible graphite is at high temperatures (850F and above) where oxygen is present within the process fluid oxidation (the breakdown of the graphite to carbon monoxide and carbon dioxide) occurs. This conversion creates microscopic voids and weight loss in the material, which can reduce compressive load on the gasket and begin to leak. Other factors to consider:
- Oxidation of a flexible graphite gasket occurs most often at the edges of the gasket. Where the gasket comes into contact with an oxidizing environment.
- Oxidation of a flexible graphite gasket can be reduce by adding a oxidation inhibitor such as a phosphate. Your typical flexible graphite material already comes with an oxidation inhibitor added.
- Oxidation of a flexible graphite gasket can be reduce by ensuring the gasket is properly crushed as the then denser material is less permeable.
- Oxidation of a flexible graphite gasket can be reduced with a change in the design of the gasket. Such as including a high temp barrier material.
Flexible Graphite Gasket Applications
Over the years we’ve seen flexible graphite gaskets, and compression packing, used effectively in many industrial applications with great success. Here’s a few application examples:
- Compressor engine exhaust stack piping flanges.
- Fire tube gaskets on separators and dehydrators.
- As a filler material in spiral wound gaskets. Widely used in standard piping flanges.
- As a facing material on double jacketed, camprofile or corragated gaskets for industrial processing vessels.
- Pump and valve compression packing.
- Oval manway tank gaskets that are normally hard to seal due to uneven flange surface finish and irregularities.
- Flanges that have irregularities where other materials cannot flow and fill those imperfections.
- Some styles of flexible graphite have a stainless steel substrate that improves the mechanical strength and rigidity of the material.
If you have questions or need assistant with a gasket application, please feel free to contact any of our personnel here at Four States Gasket and Rubber.