FLUORO POLYMER LINED PIPELINES

General Specification

Fluoropolymers are used in the chemical processing industry principally for outstanding resistance to almost all chemicals their ability to withstand high temperatures also plays an important part in their functional role. The low mechanical Properties and high permeation rates of fluoropolymers at high temperature limit their use of linings to about 175 Degree Celsius, although they remain chemical inert up to 260 Degree Celsius.

Selection of polymers is an integral part of the overall material selection process. This implies that all the available material such as metals, ceramics and plastics are considered candidates for an application. The End user then considers these materials against established criteria such as required life, mean time between inspection, ease of fabrication, frequency of inspection ,extent of maintenance and capital cost.

More often than not it is the initial capital cost rather than life cycle cost of the equipment that affects the decision made during the material selection step. However the most important piece of data in the medium under consideration over the life of the equipment.

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PTFE/FEP/PFA Specifications

Liner type Specification Properties
Virgin PTFE paste extruded ASTM D4895 Minimum Tensile Strength : 20.7MPa
Minimum Elongation of break : 200 to 300 %
Specific Gravity : 2.14-2.18 (when tested to ASTM D792 or D1505)
Static dissipating PTFE Paste Extruded ASTM D4895 Minimum Tensile Strength : 20.7MPa
Minimum Elongation of break : 200 to 300 %
Specific Gravity : 2.14-2.18 (when tested to ASTM D792 or D1505)
Virgin FEP ASTM D 2116 Minimum Tensile Strength : 20.7 MPa
Minimum Elongation of break : 250%
Specific gravity : 2.18
Virgin PFA ASTM D3307 Minimum Tensile Strength : 26.2 MPa
Minimum Elongation of break : 300%
Specific Gravity : 2.12 – 2.17 (when tested to ASTM D792 or D1505)
Melt flow rate : 1-2.5 g/10mins ( when tested to ASTM D3307 at 3720 C)
Static Dissipating PFA ASTM D3307 Minimum Tensile Strength : 26.2 MPa
Minimum Elongation of break : 300%
Specific Gravity : 2.14-2.17 (when tested to ASTM D792 or D1505)
Melt flow rate : 1-2.5 g/10mins ( when tested to ASTM D3307 at 3720 C)

Technical Guideline

Permeation Through Fluoropolimers

Permeation is the transport of small molecules through the plastic liner. Permeation is a combination of absorption, solution, diffusion & desorption mechanisms. It is a function of several variables including the properties of the permeating species (i.e., molecular size, solubility parameters, concentration), properties of the plastic (i.e., crystallinity, density, thickness, thermal history), and operating parameters (i.e., temperature-pressure gradients and cycling). Permeation data published in most literature refers to thin coatings or films and should not be applied to plastic-lined products.

All products lined with fluoropolymers, such as PTFE, PFA, FEP, ETFE and ECTFE are subject to some permeation for certain fluids. Normally PTFE lined products in conjunction with the fluids having permeation in PTFE are substituted by PVDF to avoid permeation phenomenon.