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ELECTROSTATIC DISCHARGE IN PTFE HOSES
Most applications of PTFE hose do not require the use of a conductive inner tube. Under certain applications, the potential for Static Discharge must be considered and that there is an awareness that static electricity can be a hazard. Under those conditions where static discharge can occur, the use of conductive PTFE is recommended. The following should serve to increase your knowledge and understanding of this phenomenon and how to avoid its occurrence. When two different materials are in contact, electrons from one material can move across its boundary and associate with the other. These electrons align themselves with the material contacted. If the two materials are good conductors of electricity, the positive and negative electrons will flow back and forth between them, keeping them in balance. If one or both of them are insulators, this flow will not occur. A charge will build up on the surface of one of the materials. When the charge exceeds the dielectric strength of the material, dielectric breakdown occurs.

In the application of hose of PTFE, we must consider fluids and gasses which are poor conductors of electricity and the flow rates of those fluids and gasses. A liquid or gas to be a poor conductor of electricity will usually satisfy one or more of the following conditions:
1. Be non-polar-that is, an imbalance exists between protons and electrons, and or
2. Contain an immiscible component or a suspended solid, i.e., water in kerosene.
Therefore, when a liquid comes in contact with a PTFE tube that is not a good conductor (white innercore of PTFE) phase separation occurs and the electric charge starts to build. The rate of static charge build up now becomes a function of the fluid flow rate. When the dielectric strength of the PTFE tube is exceeded, the electric charge will puncture the tube wall and ground itself on the braid.

In hydraulics, high pressures usually mean high velocities. Historically fluids were filtered upstream using metallic filter elements. The metallic element helped to ground the charge. Today, however, most filtration is accomplished with paper type and glass-fiber filter elements that have a tendency to put an electrostatic charge in the fluid they are filtering.

There are two specific material areas of concern; fuels and steam.

Fuels are generally "non-conductive" liquids and have a resistivity greater than 108 ohm, i.e., gasoline and white spirits, hydrazine, benzene, diesel oils, etc. Generally these fluids are transferred at fairly low velocities but the potential does still exist for an electrostatic discharge due to external environmental factors such as humidity and to some extent temperature. All of these factors should be taken into account even at fluid velocities at or below 1 meter/second.

When it comes to the use of PTFE hose, the potential for electrostatic discharge can be overcome by use of a conductive PTFE inner tube. Carbon is added to the PTFE inner tube wall during the manufacturing process. The carbon black allows for the electrostatic charge to be conducted down the inner diameter of the hose to the metal end fittings, there by preventing the charge from building up on the inner tube wall, exceeding the dielectric strength of the PTFE and discharging through to the outermetallic braid causing static pinholing or burn through.

Cyclohexane
Lacquers Decalin
Lacquer Solvents
Diacetone
Naphtha
Dibutyl Ether
Naphthalene
Dibutyl Phthalate
n-Octane
Dibutyl Sebacate
Paint
Dimethyl Phthalate
Petroleum
Dioctyl Phthalate
Pinene
Dipentene
Silicone Oils
Fuel Oil
Skydrol 500 & 700
Gasoline
Steam
Hexane
Toluene
Hezene
Transformer Oil
Hydrazine
Turpentine
Kerosene
Varnish
Versilube
Following is a list of some of the chemicals which meet at least one of the criteria necessary to create electrostatic discharge:

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