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Permeation can be defined as the passage of gases and liquids through a second material such as a solid. It is a significant consideration in the selection of plastic material for the construction of chemical processing equipment’s because process fluids may travel across the thickness of the polymer by permeation.

Permeated species in sufficient quantity could cause Corrosion, Contamination or Unacceptable Environmental Emission, Singly or in combination.

Several factors affect the permeation rate of the polymer. Temperature increase raises the permeation rate for two reasons. First, solubility of the permeate increase in the polymer at higher temperature. Second polymer chain movements are more abundant which allows easier diffusion of permeate. The permeation rate decreases at higher thickness.

Molecular structure is important. A polar chemical will normally have a lower permeation rate in a nonpolar polymer than a non-polar species would or vice versa. Amore condensed chemical will also be more effective in swelling the polymer, resulting in higher rates of permeation.

Environmental Stress Cracking:

A weakness of many polymers in their tendency to fail at fairly low stress level due to the impact of some hostile environments, this phenomenon is known as Environmental Stress Cracking. Cracking occurs when the polymers is stressed for a long time under loads that are relatively small compared to the yield point of the material.

The environmental stress cracking effect of chemicals on polymers can be measured by exposing the polymer to the chemical under the desired conditions. Tensile Properties of the exposed samples can then be measured. Any significant loss of Elongation and Tensile Strength would indicate Environmental Stress Cracking.

Processing of fluoro polymers plays an important role in minimising the tendency to undergo stress cracking. Reducing crystallinity as much as possible and minimizing residual stresses lowers tendency of a part to experience environmental stress cracking.


All lined products system must have vent hole drilled into the body. This is for two reasons, primary it allows air to be evacuated from within and around the fabrication for permeate gases through liner over a period of time to the atmosphere.

Secondly if the inside liner get damages from any reason then leakage will take place through the vent hole to prevent Hazards.

We should be very careful that these vent holes are in open conditions while network building process.